JP2014068173A - Base station device, radio communication method, and radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform spatial multiplexed transmission with a plurality of terminal devices without impairing an efficiency of a MAC layer.SOLUTION: A base station device 400 comprises: a weight calculation section for calculating and storing a weight for in-phase combining signal received at a plurality of antenna elements 401-1 to 401-K on the basis of training signal transmitted from terminal devices for each combination of terminal devices and antenna elements; a radio processing section provided to each of antenna elements and for dividing signal received at antenna elements for every frequency component; a weight multiplication section provided to each of terminal devices and for multiplying weights of each frequency component corresponding to each terminal device by signal for each frequency component and divided by each radio processing section to additively combine multiplication results for every frequency component; and a reception processing section provided to each of terminal devices and for determining presence/absence of signal from a corresponding to the terminal device on the basis of the additively combine result by the weight multiplication section corresponding to the terminal device, and for performing a reception processing for the additively combine result when the signal from the terminal device is present.

Description

  The present invention relates to a base station apparatus, a radio communication method, and a radio communication system.

  With the spread of the Internet in recent years, lines using optical fibers are already available in 90% of all households. In this way, the trend toward broadband has certainly progressed, but in reality there are areas where profitability is not expected due to the laying of optical lines, so how to eliminate the broadband zero area? There is currently no way to find a way to solve the problem. Such an area where profitability is not expected by laying an optical line is called an unprofitable area (conditionally disadvantaged area).

  As a countermeasure in such unprofitable areas, it is advantageous to use a wireless line. For example, a service using a wireless standard called WiMAX (Worldwide interoperability for microwave access) (registered trademark, the same shall apply hereinafter) is used. For this reason, a measure called “Region WiMAX” has been implemented, in which 10 [MHz] is reserved for the frequency channel for this purpose, and the WiMAX service using this frequency channel is applied mainly to conditionally disadvantaged areas. In WiMAX used for this measure, for example, the base station device transmits signals with a large transmission power of about 10 [W], and as a result, an area with a radius of about 3 km can be covered by one station. Yes.

In general, in an environment where the line of sight is clear, the received signal strength is inversely proportional to the square of the distance due to propagation between the transmitting station and the receiving station. In the case of out of line of sight, the received signal strength is inversely proportional to the 3rd to 4th power of the distance, which places more severe restrictions on the circuit design. Even if a line of sight is assumed, in order to extend the transmission distance by a factor of 2, it is necessary to increase the transmission power to 2 ² = 4 times, and a transmission amplifier with higher linearity is required. However, such a transmission amplifier is expensive, and when such a transmission amplifier is used, the power efficiency is remarkably lowered, so that the power consumption increases rapidly.

  In recent years, environmental problems have attracted particular attention, and low power consumption of infrastructure including radio is required, and inefficient communication using a high-output transmission amplifier is not preferable. As a method for solving such a problem, for example, as described in Non-Patent Document 1, coherent transmission with a plurality of relay stations interposed is effective. In Non-Patent Document 1, non-regenerative relay is assumed for relay, but the point of this coherent transmission depends on whether the form of relay is “non-regenerative relay” or “regenerative relay”. However, the transmission is performed so that the signals are combined in the same phase on the receiving side. As another form when performing such coherent transmission, there is a distributed antenna system as described in Non-Patent Document 2, for example.

A distributed antenna system is a radio module or remote base station in which a plurality of antennas installed in a distributed manner in one control station (strictly speaking, an antenna is combined with a device that performs optical / electrical conversion, signal amplification, etc.) ), And the control station and each antenna are connected by an optical fiber or the like.
Further, as another form, a configuration (wireless relay system) in which a plurality of relay stations are wirelessly connected to one base station can be taken. In this case, the base station serves as a control station, and the relay station serves as an antenna or a radio module, which constitutes a distributed antenna system as a whole, but differs in that the base station and the relay station are connected by radio. is there.
In any case, coherent transmission is performed in which a plurality of antennas (relay stations) transmit on the receiving terminal side so that the signals are combined in the same phase. The detailed description will be given below.

[Outline of coherent transmission system in the prior art]
(Wireless relay system)
FIG. 2 is a diagram showing an outline of a wireless relay system in the prior art.
As shown in the figure, the wireless relay system includes a transmission station 901, N ₁ relay stations 902-1 to 902 -N _1, and a reception station 903. The transmitting station 901, once transmitted to the relay station _{902-1~902-N 1} radio packets destined receiving station 903. The relay stations 902-1 to 902-N ₁ perform various reception signal processing on the signal received from the transmission station 901, and reproduce (restore) the wireless packet transmitted by the transmission station 901. Then, each relay station _{902-1~902-N 1} transmits to the receiving station 903 the same radio packet reproduced at the same time. In this case, each relay station _{902-1~902-N 1,} as the signal, each transmitted are received by the same phase at the receiving station 903 adjusts the phase of the transmission signal. In the receiving station 903, all signals transmitted from the relay station _{902-1~902-N 1} is received is synthesized on the transmission path. At this time, the signal transmitted from the relay station 902-1~902-N ₁ is, if the received at comparable received power at the receiving station 903, the signal after synthesis, is synthesized the N ₁ times the amplitude with respect to the previous signal. Further, the received power is proportional to the square of the amplitude _(N ¹⁾ is ^doubled.

Here, a comparison is made between the case where the number of relay stations 902 in the wireless relay system is one and the case of N ₁ stations. In order to make the evaluation condition fair, a single relay station 902 transmits the transmission power as P when relaying by _one station, and relay stations 902-1 to 902-N when relaying by N1 station. ₁ is compared with the transmission power of P / N ₁ (the condition that the total transmission power is constant). When transmitted from the relay station _{902-1~902-N 1} of N ₁ station, signals transmitted from the relay station _{902-1~902-N 1} is synthesized in the transmission path, the relay station 902-1～902- Compared with the received signal from any _one of N ₁ stations, the amplitude of the received signal at the receiving station 903 is N ₁ times, and as a result, the total received power is (N ₁ ) ² times. However, when transmission is performed at N ₁ station, the transmission power per relay station 902 is 1 / N ₁ when transmission is performed at a single relay station 902. Therefore, the received power is (1 / N ₁ ) × (N ₁ ) ² = N ₁ times.
That is, although the total transmission power of the relay stations 902-1 to 902-N ₁ is constant, the reception power at the reception station 903 is N ₁ times as compared with the case of relaying at one station, and the line gain is It is possible to earn 10 × Log ₁₀ N ₁ [dB].

(Distributed antenna system)
FIG. 3 is a diagram showing an overview of a distributed antenna system in the prior art.
As shown in the figure, the distributed antenna system includes remote base stations 912-1 to 912-3 that form three cells 911-1 to 911-3 that perform cooperative communication, and a plurality of terminal devices 913-1. 913-6 and a control station 914 connected to each of the remote base stations 912-1 to 912-3 via an optical fiber 915. The optical fiber 915 connecting each remote base station 912-1 to 912-3 and the control station 914 may be a coaxial cable or the like. Further, here, the description will be made assuming three cells 911-1 to 911-3 and three remote base stations 911-1 to 912-3, but in general, the number may be other than three.

Each remote base station 912-1 to 912-3 communicates with each terminal device 913-1 to 913-6 located in the cell formed by each using the same frequency channel. The control station 914 controls the remote base stations 912-1 to 912-3 via the optical fiber 915. In order to perform communication using the same frequency channel, each terminal device 913-1 to 913-6 can simultaneously receive signals transmitted from a plurality of remote base stations 912-1 to 912-3. For example, the terminal device 913-4 can receive signals from all the remote base stations 912-1 to 912-3.
Here, if the channel information between each of the remote base stations 912-1 to 912-3 and the terminal device 913-4 is known, each of the remote base stations 912-1 to 912-3 has the terminal device 913-3. 4, transmission weight multiplication can be performed so that signals transmitted from the remote base stations 912-1 to 912-3 have the same phase in the terminal device 913-4. In this case, since the signal received by the terminal device 913-4 is synthesized in phase, the received power increases. As a result, the communication characteristics in the terminal device 913-4 are improved. Such control of signal processing for performing in-phase synthesis is all performed by the control station 914, and the remote base stations 912-1 to 912-3 operate according to instructions from the control station 914.

  In the distributed antenna system, the control station 914 and each remote base station 912-1 to 912-3 are connected by an optical fiber 915, and a signal transferred on the optical fiber 915 is transmitted to each remote base station 912-2. In 1 to 912-3, an electrical signal to be transmitted on the wireless line is generated by performing optical / electrical conversion, and this is transmitted from the antenna after processing such as signal amplification. By utilizing such control, the signal processing functions for in-phase synthesis on the receiving side are aggregated in the control station 914 that has grasped all channel information, and as a result, each remote base station 912-1- It is possible to improve the communication quality while avoiding the uncertainty of the phase control in 912-3.

  In the strict sense of the distributed antenna system, each of the remote base stations 912-1 to 912-3 simultaneously performs multi-user MIMO (Multiple MIMO) that performs spatial multiplexing on the same frequency as a plurality of terminal devices 913-1 to 913-6. It is possible to further improve the characteristics by using (Input Multiple Output) technology. The control when using the multi-user MIMO technology is performed by using multiple transmission antennas, so that in-phase synthesis of desired signals in the terminal device 913 and null control for removing interference signals between different terminal devices 913, Is basically control based on coherent transmission.

[Overview of channel feedback in coherent transmission]
In order to perform coherent transmission, it is necessary to grasp the channel state between the transmitting and receiving stations. In order to ensure that signals transmitted from a plurality of transmitting stations or relay stations reach the receiving station in the same phase, the transmitting station and the relay station grasp the state of the channel between the receiving station and the channel. This is because a signal is transmitted using a transmission weight according to the state.

  FIG. 4 is a flowchart showing channel feedback processing in the prior art. There are roughly two types of channel feedback methods in the prior art. Here, “(A) a direct method” for directly acquiring the channel estimation result of the forward link and “(B) an indirect method” for performing conversion estimation using information on the backward link will be described.

In general, the channel information of the forward link and the backward link in the reverse direction do not match. This is because the combination of the high-power amplifier on the transmission side and low-noise amplifier on the reception side used in the forward link is different from the combination of the high-power amplifier on transmission side and the low-noise amplifier on the reception side used in the backward link. This is because the complex phase and amplitude differ between the information and the channel information of the backward link.
However, by performing a conversion process (calibration process), which will be described later, it is possible to estimate conversion of the forward link information from the backward link channel information. In the following description, when the “remote base station” and the “relay station” in the above description are not distinguished, they are referred to as “wireless modules”.

FIG. 4A is a flowchart showing the processing of the direct method. As shown in the figure, in the direct method, when channel information estimation is started (step S901), a radio packet including a channel estimation preamble signal and the like is transmitted from each radio module to the terminal device (step S902). ).
The terminal apparatus receives the wireless packet transmitted from each wireless module, and performs channel estimation using a preamble signal or the like included in the received wireless packet (step S903). In the terminal device, this channel estimation result is accommodated in a “radio packet for accommodating control information” and transmitted to the radio module (step S904).
The wireless module receives the “radio packet for accommodating control information” transmitted from the terminal device, and acquires channel information (step S905). Further, the wireless module stores the received channel information in a memory, constructs a database related to the channel information (step S906), and ends the process (step S907).

FIG. 4B is a flowchart showing processing of an indirect method. As shown in the figure, in the indirect method, when channel information estimation is started (step S908), a radio packet including a preamble signal for channel estimation is transmitted from the terminal device to the radio module (step S909). .
The wireless module receives a wireless packet transmitted from the terminal device, and performs channel estimation using a preamble signal included in the wireless packet (step S910). The wireless module performs conversion processing on the estimation result of the channel information in the backward link, and acquires the channel information on the forward link side (step S911).

The conversion process for calculating the channel information in the forward link from the channel information in the backward link can be performed by using a coefficient that corrects the difference between the high power amplifier in the forward link and the low noise amplifier in the backward link. is there. Specifically, the conversion process in step S911 can be performed by multiplying the channel information in the backward link by a coefficient for correcting the difference between the high power amplifier and the low noise amplifier.
Further, the radio module stores the channel information in the backward link received from the terminal device and the channel information in the forward link obtained by the conversion process in a memory, and constructs a database for storing the channel information (step S912). The process is terminated (step S913).

  In this way, the channel information is acquired in advance, and generally the transmission weight is calculated based on this channel information when actually communicating. In addition, since channel information changes with time, it is common to update periodically according to a situation, for example. Further, in the above, the channel information may be stored as a database in a control station other than the wireless module.

  Taking a distributed antenna system as an example, this transmission weight calculation processing is generally not performed individually by each wireless module, but is collectively performed by a control station in a centralized manner. In particular, when communication is performed on the same frequency channel simultaneously with a plurality of terminal devices by multiuser MIMO, the transmission weight cannot be calculated unless all channel information is used. However, if the transmission is limited to one-to-one communication with one terminal device instead of multi-user MIMO, a transmission weight that cancels the rotation of the complex phase on the transmission path obtained from the channel information (that is, Since the complex phase becomes a constant when the channel information and the transmission weight are multiplied in all the wireless modules, it is possible to perform processing individually in the wireless modules.

  Here, an explanation will be given taking as an example the case of using an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme and an SC-FDE (Single Carrier Frequency Domain Equalization) scheme. In the OFDMA (Orthogonal Frequency Division Multiple Access) method, processing in the physical layer basically uses the OFDM modulation method, and therefore the following description treats OFDM and OFDMA as equivalent methods. I will decide.

[Phased array antenna technology]
As a technique similar to coherent transmission, there is a phased array antenna technique using many antenna elements (for example, Non-Patent Document 3).
FIG. 5 is a diagram showing the principle of the phased array antenna. The figure shows a phased array antenna in which five antenna elements 961-1 to 961-5 are linearly arranged with a distance d therebetween. In the phased array antenna, when the directivity in the angle θ direction is formed with respect to the arrangement direction of the antenna elements 961-1 to 961-5, there is a difference in path length for each antenna element 961-1 to 961-5 with respect to the direction. In consideration of dCosθ, adjustment may be made to each of the signals transmitted and received using each of the antenna elements 961-1 to 961-5 so as to perform in-phase synthesis.

Here, when the wavelength of a signal to be transmitted / received is λ, a signal whose phase is shifted by ((2πdCosθ) / λ) between adjacent antenna elements 961-1 to 961-5 is output in the direction of the angle θ. A directivity can be formed. This phase difference ((2πdCosθ) / λ) may be given to a signal to be transmitted / received in an analog manner using a phase shifter or may be given in digital signal processing.
In the phased array antenna, the antenna gain with respect to a predetermined angular direction can be obtained in this way. In general, since a sublobe showing a fine wave of undulation is generated around the main lobe direction in which the directivity gain is maximized, in order to reduce the influence and stably operate the main lobe, the antenna element 961- The interval d between 1 and 961-5 is set to λ / 2 or less.

  However, as the distance between the antenna elements 961-1 to 961-5 is shortened with respect to the wavelength λ, the antenna elements 961-1 to 961-5 are coupled to each other and various factors, compared with the case of simple in-phase synthesis. The gain is greatly reduced. In this case, the signals transmitted and received from the individual antenna elements 961-1 to 961-5 are different from the waves that can simply add the amplitudes as independent waves at the transmission and reception points, as if many antenna elements 961-1 to 961-5. As a whole, one virtual antenna element is configured, and one signal (wave) is transmitted from the virtual antenna element. In this respect, it can be regarded as a phenomenon different from coherent transmission in which simple in-phase synthesis is realized.

[About multi-user MIMO technology]
(Outline of multi-user MIMO)
Coherent transmission and phased array antenna technology are basically technologies that improve channel gain, and in order to increase the channel capacity when covering a wide service area with one base station device, another wireless communication Technology is required. On the other hand, since frequency resources are limited, here, for example, a multi-user MIMO technique studied in Non-Patent Document 4 will be described as a technique for using limited resources with high frequency utilization efficiency.

  FIG. 6 is a schematic diagram illustrating a configuration example of a multi-user MIMO system. As shown in the figure, the multi-user MIMO system includes a base station device 801 and terminal devices 802-1, 802-2, and 802-3 (terminal devices # 1 to # 3). There are actually a large number of terminal devices 802 accommodated in one base station device 801, but several of these are selected (terminal devices 802-1 to 802-3 in the figure) to perform communication. Each terminal device 802 generally has a smaller number of transmission / reception antennas than the base station device 801. For example, a case where communication (downlink) from the base station apparatus 801 to the terminal apparatus 802 will be described.

  Base station apparatus 801 forms a plurality of directional beams using a large number of antenna elements. For example, consider a case where three MIMO channels are allocated to each of the terminal devices 802-1 to 803 and nine signal sequences are transmitted as a whole. At that time, the signal transmitted to the terminal device 802-1 is adjusted so that the directivity gain becomes extremely low in the direction of the terminal device 802-2 and the terminal device 802-3. As a result, the terminal device 802 2 and the terminal device 802-3. Similarly, the signal transmitted to the terminal device 802-2 is adjusted so that the directivity gain becomes extremely low in the direction of the terminal device 802-1 and the terminal device 802-3. The same processing is performed on the terminal device 802-3. The reason for performing the directivity control in this way is that, for example, in the terminal device 802-1, there is no way of knowing information of signals received by the terminal device 802-2 and the terminal device 802-3. A cooperative reception process is not possible. That is, in the reception process of only the terminal device 802-1 having only three, it is very strict to separate all nine signal sequences. Therefore, interference separation is performed in advance on the transmission side so that each terminal device 802-1 to 802-3 does not receive signals from other terminal devices 802.

The above is the outline of the existing multi-user MIMO system. Next, a method for forming a directional beam will be described below. Here, a case will be described in which base station apparatus 801 includes nine antenna elements, and each terminal apparatus 802-1 to 802-3 includes three antenna elements. For example, in FIG. 6, channel information between the j-th (j = 1,..., 9) antenna element of the base station apparatus 801 and the first antenna element of the terminal apparatus 802-1 is denoted as h _1j . . Each antenna element of the base station apparatus 801 (j = 1, ..., 9) and, the first row vectors _{h 1} using the channel information of the antenna element _{(h 11} of the terminal apparatus _{802-1, h} 12, h ₁₃ ,..., H ₁₈ , h ₁₉ ). Similarly, channel information between the j-th antenna element of the base station apparatus 801 and the second antenna element and the third antenna element of the terminal apparatus 802-1 is denoted as h _2j and h _3j and corresponds. The row vectors h ₂ and h ₃ are denoted as (h ₂₁ , h ₂₂ , h ₂₃ ,..., H ₂₈ , h ₂₉ ) and (h ₃₁ , h ₃₂ , h ₃₃ ,..., H ₃₈ , h ₃₉ ). Pretend similar serial number to the antenna elements of the terminal apparatus 802-2 and the terminal device 802-3, the row vector _{h 4 ~h 9 (h 41,} h 42, h 43, ..., h 48, h 49) To (h ₉₁ , h ₉₂ , h ₉₃ ,..., H ₉₈ , h ₉₉ ).

In addition, nine systems of signals transmitted by the base station apparatus 801 are expressed as t ₁ to t ₉ , and a column vector having these components as T x ^[all] = (t ₁ , t ₂ , t ₃ ,..., T ₈ , t ₉ ) ^T Here, the letter T on the right shoulder indicates transposition of a vector or a matrix. Similarly, received signals at the nine antenna elements of the terminal devices 802-1 to 80-3 are denoted as r ₁ to r ₉ , and a column vector having these components as components Rx ^[all] = (r ₁ , r ₂ , r ₃ ,..., r ₈ , r ₉ ) ^T Finally, a matrix having the row vectors h _{1 to} h ₉ as the first to ninth row components is denoted as an overall channel information matrix H ^[all] . In addition, noise is expressed as n.
In this case, the relationship of the following formula (1) is established for the entire multiuser MIMO system.

  On the other hand, in order to perform transmission directivity control, a transmission weight matrix W of 9 rows and 9 columns is introduced, and the equation (1) is rewritten as the following equation (2).

Furthermore, the transmission weight matrix W is decomposed into column vectors _{w 1 ~w 9, W = (} w 1, w 2, w 3, ..., w 8, w 9) If the denoted ^"H in the formula (2) ^{[ all]} · W ”can be expressed as the following equation (3).

Here, for example, the multiplication of the six row vectors h _{4 to} h ₉ and the three column vectors w _{1 to} w ₃ (the sum of the multiplication of each component, which is different from the inner product in the case of a complex vector) is all zero. Consider that the values of w ₁ to w ₃ are selected. At the same time, the multiplication of the row vector _h 1 to h ₃ and _h 7 to h ₉ column vector _w 4 to w _6, multiplication becomes all zero row vector _h 1 to h ₆ column vector _w 7 to w ₉ Thus, the values of w ₄ to w ₉ are selected.
Then, the 9 × 9 matrix H ^[all] · W shown in Equation (3) can be expressed as the following Equation (4) using a 3 × 3 partial matrix.

In Equation (4), H ^[1] , H ^[2] , and H ^[3] are 3-by-3 matrices, and “0” is a 3-by-3 matrix with all components zero. By selecting a transformation matrix that satisfies such conditions as the transmission weight matrix W, the equation (4) can be decomposed into three relational expressions represented by the following equations (5-1) to (5-3).

^{_{Here, Tx [1] = (t}} 1, t 2, t 3) T, Tx [2] = (t 4, t 5, t 6) T, Tx [3] = (t 7, t 8, t ^{_{9) T, Rx [1]}} = (r 1, r 2, r 3) T, Rx [2] = (r 4, r 5, r 6) T, Rx [3] = (r 7, r 8, r ₉ ) ^T In this way, it can be considered that one base station apparatus performs MIMO communication on a one-to-one basis, that is, so-called single-user MIMO communication is communicating in three systems simultaneously in parallel.

Next, an example of a method for determining the transmission weight vectors w _{1 to} w ₉ will be described below. As a procedure, transmission weight vectors w _{1 to} w ₃ for the terminal device 802-1 are determined, and transmission weight vectors w _{4 to} w _{6 for} the terminal device 802-2 and transmission weight vectors w ₇ for the terminal device 802-3 are sequentially set. to determine the ~w _9.
First, as a first step, six basis vectors e _{4 to} e ₉ in a six-dimensional subspace spanned by six row vectors h _{4 to} h ₉ for the terminal devices 802-2 and 802-3 are obtained. There are various methods other than the Gram Schmidt orthogonalization method. The Gram Schmidt orthogonalization method will be described as an example here.
First, paying attention to one row vector h ₄ , a vector having an absolute value of 1 in this direction is set as a base vector e ₄ . The basis vector e ₄ is expressed as the following equation (6).

( ^H ₄ h ₄ ^H ) in Equation (6) is a scalar quantity that means the square of the absolute value of the same vector, and division by the square root of this value means normalization of the row vector h ₄ . “H ₄ ^H ” is a Hermitian conjugate vector for the row vector h ₄ , and is a vector obtained by transposing the row and column and taking the complex conjugate of each component.
Next, focusing on the row vector h _5, after obtaining the row vector h _{5 'canceling} the basis vectors e ₄ direction component from among the row vectors further normalized. The row vector h ₅ ′ and the basis vector e ₅ are expressed by the following expressions (7-1) and (7-2).

( ^H ₅ e ₄ ^H ) in Equation (7-1) means the projection of the row vector h _{5 in} the direction of the base vector e ₄ . The same processing is performed as in the following equation (8-1) and the following equation (8-2).

Here, the range of the summation of Σ in the equation (8-1) is the summation for the integer i of 4 ≦ i ≦ (j−1) (j is an integer of 5 to 9). That is, it means that the component in the defined vector direction that has already been determined is canceled. In this way, six basis vectors e _{4 to} e ₉ can be obtained.
Next, as a second step, transmission weight vectors w _{1 to} w ₃ for the terminal device 802-1 are obtained. First, the components of the 6-dimensional subspace spanned by the base vectors e _{4 to} e ₉ are canceled from the row vectors h _{1 to} h ₃ . Specifically, it is represented by the following formula (9).

Here, j in the formula (9) is an integer of 1 to 3, and the range of the sum of Σ is the sum for the integer i of 4 ≦ i ≦ 9. The three-dimensional space spanned by the three vectors of the row vectors h ₁ ′ to h ₃ ′ thus obtained is orthogonal to any of the above-described row vectors h _{4 to} h ₉ . If three vectors in this three-dimensional space (not necessarily an orthogonal vector) are selected and the complex conjugate vector of the vector is set as transmission weight vectors w _{1 to} w ₃ , another terminal device 802-2, Interference with 802-3 can be suppressed.
Note that any method may be used for selecting the three vectors. For example, if three orthogonal vectors that form a unitary matrix obtained by performing singular value decomposition are used, the sub-spaces that do not interfere with other terminal devices 802 are used. The eigenmode transmission limited to 1 is possible, and efficient transmission becomes possible.

Finally, as a third step, if the same processing is performed for the terminal device 802-2 and the terminal device 802-3, finally the entire transmission weight vectors w _{1 to} w ₉ can be obtained. .
The above is how to obtain the transmission weight matrix W.

FIG. 7 is a flowchart showing a procedure for calculating the transmission weight matrix W in the multiuser MIMO system. First, in calculating the transmission weight matrix W, channel information matrices H for all the terminal devices 802 are acquired (step S801). When a serial number is assigned to the destination terminal device 802 and the variable indicating the serial number is k, k is first initialized (step S802). Further, k is counted up (step S803), and partial channel information (herein expressed as H ^main for convenience) corresponding to the terminal device 802 (# 1) corresponding to the current value indicated by k is extracted (step S804). ), And a partial channel information matrix (indicated here as H ^sub for convenience) for the other terminal device 802 is extracted (step S805).

Further, an orthogonal basis vector of a subspace spanned by each row vector of the partial channel matrix H ^sub is calculated, and this is set as a basis vector {e _j } (step S806). Next, as processing corresponding to Equation (9), the component related to the basis vector {e _j } obtained in step S806 from the partial channel information matrix H ^main for the terminal device 802 (# 1) of interest is canceled, Is a matrix to H ^main (step S807). Here, in step S807, H with “˜ (tilde)” added thereto is denoted as “˜H”. Hereinafter, similarly, in a mathematical expression or the like, when a character such as “^ (hat)” is written on the character, the symbol is written before the character.

Further, an arbitrary orthogonal basis vector of the subspace spanned by the row vectors of the matrix to H ^main is calculated, and this is set as the basis vector {e _i } (step S808). Here, as the arbitrary base vector, for example, a vector constituting the right singular matrix when the matrix ~ H ^main is subjected to singular value decomposition may be selected. Thereafter, a transmission weight vector {w _j } relating to the signal of terminal apparatus 802 (# 1) is determined as a Hermitian conjugate vector (column vector obtained by transposing a complex conjugate vector) of each vector of basis vectors {e _i } (step S809). ).

Here, it is determined whether or not the transmission weight vectors of all destination terminal devices 802 have been determined (step S810), and if there are remaining terminal devices 802, the processing from step S803 to step S809 is repeated. If the transmission weight vectors of all the terminal devices 802 have been determined, the transmission weight matrix W is determined as a matrix having the transmission weight vector {w _j } as each column vector (step S811), and the process ends.
Since channel information generally differs for each frequency component, if a wideband signal, for example, a signal using the OFDM modulation method, a similar transmission weight is calculated for each frequency component, that is, for each subcarrier. Become. In addition, here, the case where each of the terminal devices 802-1 to 802-3 includes three antennas has been described as an example, and in step S808, the orthogonal basis vectors of the subspace spanned by each row vector of ~ H ^main are obtained. In the case where the terminal device includes only one antenna, the step S808 simply corresponds to normalizing a row vector corresponding to ~ H ^main .

(Multi-user MIMO device configuration example)
FIG. 8 is a schematic block diagram showing an example of the configuration of the base station apparatus 80 in the multiuser MIMO system. As shown in the figure, the base station apparatus 80 includes a transmission unit 81, a reception unit 85, an interface circuit 87, a MAC layer processing circuit 88, and a communication control circuit 820. The MAC layer processing circuit 88 has a scheduling processing circuit 881.
The base station apparatus 80 inputs / outputs data to / from an external device or network via the interface circuit 87. The interface circuit 87 detects data to be transferred on the wireless line among the input data, and outputs the detected data to the MAC layer processing circuit 88. The MAC layer processing circuit 88 performs processing related to the MAC layer in accordance with an instruction from the communication control circuit 820 that performs management control of the operation of the entire base station apparatus 80. Here, the processing related to the MAC layer includes conversion of data input / output by the interface circuit 87 and data transmitted / received on the wireless line, addition of header information of the MAC layer, and the like. In this process, the scheduling processing circuit 881 performs various scheduling processes including a combination of terminal devices that simultaneously perform spatial multiplexing in multiuser MIMO transmission. The scheduling processing circuit 881 outputs the scheduling result to the communication control circuit 820.
In multi-user MIMO, signals are transmitted to a plurality of terminal devices at a time, so that a plurality of signal sequences are output from the MAC layer processing circuit 88 to the transmission unit 81.

FIG. 9 is a schematic block diagram illustrating an example of the configuration of the transmission unit 81 in the base station apparatus 80 in the multiuser MIMO system. As shown in the figure, the transmission unit 81 includes transmission signal processing circuits 811-1 to 811-L (L is an integer of 2 or more) and addition synthesis circuits 812-1 to 812-K (K is an integer of 2 or more). ), IFFT (Inverse Fast Fourier Transform) & GI (Guard Interval) assigning circuits 813-1 to 813 -K, and D / A (digital / analog) converters 814-1 to 814- K, local oscillator 815, mixers 816-1 to 816-K, filters 817-1 to 817-K, high power amplifiers (HPA) 818-1 to 818-K, and antenna elements 819-1 to 819. -K and a transmission weight processing unit 830. The transmission signal processing circuits 811-1 to 811-L and the transmission weight processing unit 830 are connected to the communication control circuit 820 shown in FIG.
The transmission weight processing unit 830 includes a channel information acquisition circuit 831, a channel information storage circuit 832, and a multiuser MIMO (MU-MIMO) transmission weight calculation circuit 833.
Here, the subscript L of the transmission signal processing circuits 811-1 to 811-L in FIG. The subscript K of the circuits from the adder / synthesizer circuit 812-1 to 812-K to the antenna elements 819-1 to 819-K represents the number of antenna systems provided in the base station apparatus 80.

  In multi-user MIMO, in order to transmit signals to a plurality of terminal devices at a time, a plurality of signal sequences are input from the MAC layer processing circuit 88 to the transmission unit 81, and the input plurality of signal sequences are transmitted signal processing. Input to the circuits 811-1 to 811-L. The transmission signal processing circuits 811-1 to 811-L, when data to be transmitted to each destination terminal device (data input # 1 to #L) are input from the MAC layer processing circuit 88, wireless transmission is performed via a wireless line. A packet is generated and modulated. Here, for example, if the OFDM modulation method is used, the signal of each signal series is subjected to modulation processing for each frequency component. Further, the baseband signal subjected to modulation processing is multiplied by a transmission weight for each frequency component. The signal multiplied by the transmission weight corresponding to each of the antenna elements 819-1 to 819 -K is subjected to the remaining signal processing as necessary, and is added and synthesized as a sampling signal of the transmission signal in the baseband 812-1. 812-K.

  The signals input to the adder / synthesizers 812-1 to 812-K are synthesized for each frequency component. The synthesized signal is converted from a signal on the frequency axis into a signal on the time axis by IFFT & GI adding circuits 83-1 to 813-K, and further, a guard interval is inserted or between OFDM symbols (block for SC-FDE). (Between transmission blocks) is processed, and for each antenna element 819-1 to 819-K, a D / A converter 814-1 to 814-K converts a digital sampling data into a baseband analog signal. Is converted to Further, each analog signal is multiplied by the local oscillation signal input from the local oscillator 815 by the mixers 816-1 to 816-K and up-converted to a radio frequency signal. Here, since the signal is included in the frequency component outside the band of the channel to be transmitted in the up-converted signal, the frequency component outside the band is removed by the filters 817-1 to 817-K, and the electrical signal to be transmitted is transmitted. A typical signal. The generated signals are amplified by the high power amplifiers 818-1 to 818 -K and transmitted from the antenna elements 819-1 to 819 -K.

In FIG. 9, after adding and synthesizing the signals of the respective frequency components by the adding and synthesizing circuits 812-1 to 812-K, processing such as IFFT processing, insertion of guard intervals, waveform shaping, and the like is performed. The signal processing circuits 811-1 to 811-L may perform these processes, and the IFFT & GI giving circuits 83-1 to 813-K may be omitted. In this case, the remaining signal processing as necessary after transmission weight multiplication in the transmission signal processing circuits 811-1 to 811-L refers to IFFT processing, insertion of guard intervals, waveform shaping, and the like.
Note that the transmission weights multiplied by the transmission signal processing circuits 811-1 to 811 -L are acquired from the multiuser MIMO transmission weight calculation circuit 833 provided in the transmission weight processing unit 830 during signal transmission processing. In the transmission weight processing unit 830, channel information is separately acquired by the channel information acquisition circuit 831 and stored in the channel information storage circuit 832 while being updated sequentially. At the time of signal transmission, the multiuser MIMO transmission weight calculation circuit 833 reads channel information corresponding to the destination station from the channel information storage circuit 832 and calculates a transmission weight based on the read channel information. Multi-user MIMO transmission weight calculation circuit 833 outputs the calculated transmission weight to transmission signal processing circuits 811-1 to 811-L.
Further, the communication control circuit 820 manages control related to the entire communication such as management of the destination station and overall timing control. The communication control circuit 820 outputs information indicating the destination station and the like to the transmission weight processing unit 830 that performs signal processing related to the calculation of the transmission weight described above.

FIG. 10 is a schematic block diagram illustrating an example of the configuration of the reception unit 85 in the base station apparatus 80 in the multiuser MIMO system. As shown in the figure, the base station apparatus 80 includes antenna elements 851-1 to 851-K, low noise amplifiers (LNA) 852-1 to 852-K, a local oscillator 853, and mixers 854-1 to 854-. K, filters 855-1 to 855-K, A / D (analog / digital) converters 856-1 to 856-K, and FFT (Fast Fourier Transform) circuits 857-1 to 857-K. And reception signal processing circuits 858-1 to 858 -L and a reception weight processing unit 860. Reception signal processing circuits 858-1 to 858 -L and reception weight processing unit 860 are connected to communication control circuit 820 shown in FIG. 8.
Reception weight processing section 860 includes channel information estimation circuit 861 and multiuser MIMO (MU-MIMO) reception weight calculation circuit 862.

  Signals received by the antenna elements 851-1 to 851-K are amplified by the low noise amplifiers 852-1 to 852-K. The amplified signal and the local oscillation signal output from the local oscillator 853 are multiplied by mixers 854-1 to 854-K, and the amplified signal is down-converted from a radio frequency signal to a baseband signal. Since the down-converted signal includes frequency components outside the frequency band to be received, the out-of-band components are removed by the filters 855-1 to 855-K. The signal from which the out-of-band component is removed is converted into a digital baseband signal by the A / D converters 856-1 to 856-K. All digital baseband signals are input to FFT circuits 857-1 to 857 -K, and signals on the time axis are converted into signals on the frequency axis (separated into signals of each frequency component) at a predetermined symbol timing. The signals separated into the frequency components are input to the reception signal processing circuits 858-1 to 858 -L and also input to the channel information estimation circuit 861.

  In the channel information estimation circuit 861, the antenna element of each terminal device and the base station device 80 based on a known signal for channel estimation separated into each frequency component (such as a preamble signal added to the head of the radio packet). Channel information between each of the antenna elements 851-1 to 851-K is estimated for each frequency component, and the estimation result is output to the multiuser MIMO reception weight calculation circuit 862. Multi-user MIMO reception weight calculation circuit 862 calculates reception weights to be multiplied for each frequency component based on the input channel information. At this time, reception weights for synthesizing signals received by the antenna elements 851-1 to 851-K are different for each signal series, and reception signal processing circuits 858-1 to 858-L corresponding to the signal series to be extracted. Input to each.

In the reception signal processing circuits 858-1 to 858 -L, the signal for each frequency component input from the FFT circuits 857-1 to 847 -K is multiplied by the reception weight input from the multiuser MIMO reception weight calculation circuit 862. Then, the signals received by the antenna elements 851-1 to 851-K are added and synthesized for each frequency component. The reception signal processing circuits 858-1 to 858 -L perform demodulation processing on the added and combined signals and output the reproduced data to the MAC layer processing circuit 88.
Here, different received signal processing circuits 858-1 to 858 -L perform signal processing of different signal sequences. The MAC layer processing circuit 88 performs processing related to the MAC layer (for example, conversion between data input / output to / from the interface circuit 87 and data transmitted / received on the wireless line, termination of header information of the MAC layer, etc.). Do. In this process, the scheduling processing circuit 811 performs various scheduling processes including a combination of terminal apparatuses that simultaneously perform spatial multiplexing in multiuser MIMO transmission, and outputs a scheduling result to the communication control circuit 820. The received data processed by the MAC layer processing circuit 88 is output to an external device or network via the interface circuit 87.
In addition, the communication control circuit 820 manages control related to overall communication such as management of a transmission source terminal device and overall timing control. In addition, information indicating a transmission source terminal device or the like is input from the communication control circuit 820 to the reception weight processing unit 860 that performs signal processing related to the calculation of the reception weight described above.

  As for signal reception, as in the case of transmission, in the wideband system using the OFDM modulation scheme or SC-FDE scheme, the above-described reception weight multiplication is performed for each frequency component. That is, the signals output from the A / D converters 856-1 to 856-K are subjected to FFT in the FFT circuits 857-1 to 857-K and separated into frequency components, and channel information is obtained for each separated frequency component. The signal processing in the estimation circuit 861 and the reception signal processing in the reception signal processing circuits 858-1 to 858 -L are performed.

(Multi-user MIMO transmission processing)
FIG. 11 is a flowchart showing a transmission process of the base station apparatus 80 in multiuser MIMO. In multi-user MIMO, feedback of downlink channel information, which is performed separately from data transmission, is periodically performed. When the channel information acquisition circuit 831 acquires channel information in the downlink (step S831), the channel information storage circuit 832 stores the channel information of each frequency component for each terminal device (step S832). Steps S831 and S832 are performed sequentially.

When signal transmission processing from the base station apparatus 80 is started (step S821), the multiuser MIMO transmission weight calculation circuit 833 obtains channel information of each frequency component corresponding to the terminal apparatus that is the destination from the channel information storage circuit 832. Read (step S822).
Based on the read channel information, the multiuser MIMO transmission weight calculation circuit 833 calculates a transmission weight for multiuser MIMO for each frequency component by the processing described above (step S823). Separately from the processing of step S822 and step S823, the transmission signal processing circuits 811-1 to 811-L perform each frequency for each destination station by performing transmission signal processing such as various modulation processing on the data to be transmitted for each destination. A component transmission signal is generated (step S824).

  The transmission signal processing circuits 811-1 to 811-L multiply the generated transmission signal by the transmission weight calculated by the multiuser MIMO transmission weight calculation circuit 833 in step S823 (step S825). The transmission signal processing circuits 811-1 to 811-L perform a series of signal processing, and the adder / synthesizing circuits 812-1 to 812-L each terminal device of each frequency component for each of the antenna elements 819-1 to 819-L. Addition synthesis is performed on the transmission signal addressed to the signal, and the IFFT & GI adding circuits 83-1 to 813-K convert the signal on the frequency axis to the signal on the time axis, and further insert a guard interval or between OFDM symbols (SC- If it is FDE, it performs processing such as waveform shaping between the blocks in the block transmission) and outputs it to the D / A converters 814-1 to 814-K (steps S826-1 to S826-K). The signals output from the IFFT & GI adding circuits 813-1 to 813 -K are subjected to signal processing in the high power amplifiers 818-1 to 818 -K from the D / A converters 814-1 to 814 -K, and the antenna element 819. -1 to 819-K (steps S827-1 to S827-K), and the process ends (steps S828-1 to S828-K).

  Note that the processing in steps S827-1 to S827-K includes up-conversion processing from a baseband signal to a radio frequency, removal of frequency components of a band by a filter, signal amplification by a high power amplifier, and the like.

(Multi-user MIMO reception processing)
FIG. 12 is a flowchart showing reception processing of the base station apparatus 80 in multiuser MIMO. First, when reception processing is started (step S840), signals are received by the first to Kth antenna elements 851-1 to 851-K (steps S841-1 to S841-K). Here, reception includes processing for performing analog / digital conversion on a received signal or a signal obtained by down-converting the received signal. Subsequent signal processing means processing on a digitized received signal.
Subsequently, the received signals corresponding to the antenna elements 851-1 to 851-K are subjected to signal processing such as separation into frequency components by the FFT circuits 857-1 to 857-K (steps S842-1 to S842). -K). Furthermore, the channel information estimation circuit 861 performs channel estimation of each frequency component based on the reception state of the preamble signal having a known pattern attached to the wireless packet (steps S843-1 to S843-K). Here, the attenuation of the signal on the propagation path and the rotation state of the complex phase are grasped. In the channel estimation performed in steps S843-1 to S843-K, channel estimation is individually performed for each spatially multiplexed signal sequence, as shown in steps S843-1, S843-2,. Need to do. This individual channel estimation needs to be performed in a state in which the signals transmitted from the respective transmission source terminal devices can be separated. Taking the OFDM modulation method as an example, generally, a preamble signal for channel estimation having the same number of symbols as the number of spatial multiplexing is required. Each terminal apparatus performs signal transmission with the same number of symbols as the number of spatial multiplexing (or more) and assigns a different pattern of preamble signals, and the base station apparatus 80 uses the difference in pattern to perform step transmission. Individual channel estimation is performed in S843-1 to S843-K.

The multiuser MIMO reception weight calculation circuit 862 uses the channel information estimated by the channel information estimation circuit 861 to calculate individual appropriate reception weights for each spatially multiplexed signal sequence and each frequency component (step S844). Further, the reception signal processing circuits 858-1 to 858 -L multiply the reception signal calculated for each signal series and each frequency component by the reception signal of each antenna element separated for each frequency component (step S <b> 845-). 1-S845-K).
Here, since reception weights are prepared for each spatially multiplexed signal sequence, the multiplication results in steps S845-1 to S845-L are different results for each spatially multiplexed signal sequence. The signals of the respective signal sequences are obtained by adding and synthesizing the signals of the antenna elements 851-1 to 851-K for each frequency component (steps S846-1 to S846-L). Processing from signal sequence signal processing (step S847-1) to signal processing of the Lth signal sequence (step S847-L) is performed, and the processing ends (steps S848-1 to S848-L).

  Here, for the sake of simplicity, an example in which a linear reception weight is used is shown, but in general, nonlinear signal processing such as MLD (Maximum Likelihood Detection) may be performed for MIMO. In this case, the processes in steps S845-1 to S845-L, steps S846-1 to S846-L, and steps S847-1 to S847-L are integrally performed with nonlinear signal detection processing. Further, the linear reception weight can be calculated by a method similar to the transmission weight calculation process shown in FIG. In addition, it is also possible to use a reception weight using a pseudo inverse matrix or an MMSE weight. Here, the number of spatially multiplexed signal sequences is described as L for the number K of antenna elements 851-1 to 851-K used for reception, but in general, K and L need to match. If the value of L is equal to or less than the value of K, a number of signal series signals can be spatially multiplexed.

  As described above, a typical feature of multi-user MIMO is that, in the reception processing in the base station apparatus 80 in the uplink, the reception weight is set for each reception based on the channel information between the transmission side and the reception side. And the latest channel information in the downlink transmission process is read (step S822), and the transmission weight is calculated based on the read channel information (step S823). In other words, the transmission weight and the reception weight are calculated every time transmission or reception is performed. This is due to channel time variation, and in order to obtain good channel estimation accuracy, it is necessary to periodically perform feedback processing of channel information. As the channel feedback period is set shorter, transmission / reception of control information for channel feedback becomes necessary and the overhead increases. Furthermore, when the base station apparatus 80 receives a spatially multiplexed signal, it is necessary to individually perform channel estimation for a plurality of terminal apparatuses, and thus a desired number of orthogonal preambles are required. In general, it is preferable that the preamble signal patterns themselves are orthogonal, but if such a pattern cannot be set, overhead of the same number of symbols as the number of spatial multiplexing is required, and the number of spatial multiplexing increases. Accordingly, the overhead also increases.

[Requirements for actual system]
In the coherent transmission and distributed antenna system described above, the channel information needs to be known on the transmission side. Therefore, in an actual system, it is necessary to clear the following requirements.

(Requirement 1)
For example, consider a case where a line gain of 20 [dB] is gained using a radio module of 100 stations. In communication, since a circuit such as a wireless communication device is designed on the assumption that the line gain is improved by 20 [dB], when performing channel estimation between one wireless module and a terminal device, 20 [ dB] Channel estimation must be performed in a degraded environment. For example, if the required SNR in actual communication is 10 [dB], channel estimation must be performed in a noise-dominated environment with an SNR of −10 [dB]. However, in such an environment where noise is dominant, even if the transmission weight is obtained from the estimated extremely uncertain channel information, in-phase synthesis cannot be realized.

  Note that the distributed antenna system is assumed to be a terminal device that exists in a region where a plurality of cells overlap as shown in FIG. That is, only a few remote base stations that are involved in transmission / reception in a distributed antenna system are geographically relatively close to the terminal device. As a result, the SNR does not become low, and the above-mentioned channel estimation accuracy problem occurs in the first place. It wasn't. Further, in Non-Patent Document 1 in which coherent transmission using a plurality of relay stations is described, as described in the chapter “Summary”, various control achievement methods including channel information estimation methods are described. In this document, it is clearly stated that “don't mention it”. In other words, the author recognizes that it is difficult to realize coherent transmission at present, and Non-Patent Document 1 makes a claim that there is a possibility that a beneficial effect can be obtained if these various problems can be solved. It is inferred that Thus, in the prior art, a method for performing feedback of channel information in an ultra-low SNR region necessary for coherent transmission has not been established. Therefore, it is required that these technologies be established in an actual system.

(Requirement 2)
Assuming an environment where there is no constant traffic such as in urban areas, the channel conditions change over time. Even if the channel estimation accuracy is at a desired level and channel feedback is possible, the channel feedback period should be set relatively long, considering the decrease in transmission efficiency due to the overhead required for channel feedback. As a result, a transmission / reception weight based on channel information past the actual transmission / reception time is used. However, since the optimum transmission / reception weight changes due to channel fluctuations, the expected line gain may not be obtained, and communication may become unstable. Therefore, in an actual system, establishment of a countermeasure technique for this channel time variation is required.

  As described above, in order to perform coherent transmission via a plurality of wireless modules or a plurality of antenna elements, the above-mentioned “measures for reducing accuracy of channel information in an environment where reception power is low” (requirement condition 1 ), “Technique for countermeasures against communication destabilization due to channel fluctuation” (Requirement 2) so that signals are synthesized in the same phase in the terminal device as the receiving side Therefore, a new technique for adjusting a signal transmitted from each wireless module or each antenna element is required. Similar to the transmission side, there are exactly the same requirements in the received signal processing for signals received by each wireless module or each antenna element.

(Requirement 3)
Even if the above requirements can be cleared, if a high line gain such as 20 [dB] can be obtained, a very wide area can be collectively set as a service area. Therefore, frequency resources must be shared by many terminal devices located in a wide area. As the area becomes wider and the number of terminal devices sharing frequency resources increases, the throughput per terminal device decreases as a result. In order to increase the throughput per terminal device to a predetermined value or more, it is necessary to increase the throughput of the entire system. However, since frequency resources are limited, the frequency band used for communication cannot be expanded. In other words, it is necessary to improve the throughput per terminal device by increasing the frequency utilization efficiency. In other words, it is necessary to establish a technology for increasing the capacity of a system for use in such an environment.

For the above (Requirement 3), the multi-user MIMO technique is effective, but it is necessary to increase the number of spatial multiplexing in order to significantly increase the throughput. Newly occurs.
For example, in multi-user MIMO transmission using an extremely large number (for example, 100) of antenna elements, a matrix of “total number of transmission antenna elements” × “total number of reception antenna elements” is used in calculation of transmission weights and reception weights. In other words, the influence on the calculation of the transmission weight and the reception weight required for each data transmission / reception increases as the matrix size increases. In general, the amount of calculation processing such as inverse matrix calculation and singular value decomposition (specifically, because the circuit scale of a multiplication circuit is larger than that of an addition circuit when it is configured as a circuit, evaluation is based on the number of multiplications or divisions. Is said to increase in proportion to the cube of the matrix size. When the number of antenna elements that are one digit or more larger than the number of antenna elements generally used for multi-user MIMO is used, the required calculation amount is 1000 times or more. Further, in an environment where the channel fluctuates over time, it is necessary to calculate a transmission weight or a reception weight every time data is transmitted / received. That is, there is a problem in that it takes a long time to calculate the transmission weight and the reception weight, and it is difficult to efficiently perform spatial multiplexing.

  Further, when a very large number of signals are spatially multiplexed by multi-user MIMO transmission, it is necessary to separate the spatially multiplexed signals at least in the uplink and then perform channel estimation of individual paths on the receiving side. In order to perform such channel estimation, at least spatially multiplexed number of orthogonal preamble signals are required. In general, it is preferable that the preamble signal patterns themselves are orthogonal, but if such a pattern cannot be set, an overhead of the same number of symbols as the number of spatial multiplexing is required. This lowers the efficiency of the MAC layer and lowers the frequency utilization efficiency. That is, the conventional countermeasure technique for (Requirement 3) creates a new problem. Therefore, in an actual system, it is possible to suppress a decrease in the efficiency of the MAC layer due to a realistic calculation load and overhead including channel feedback, a preamble for channel estimation, etc. There is a need to effectively implement spatial multiplexing.

(Requirement 4)
The above description has been basically focused on signal processing in the physical layer. However, in actual radio system operation, in addition to physical layer processing, the operation of the MAC layer that manages access control is also important. For example, WiFi (registered trademark, the same shall apply hereinafter) or the like employs autonomous distributed CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance). In this CSMA / CA, the presence / absence of signal transmission from another radio device is grasped by carrier sense, a random number is generated according to a predetermined rule so that the transmission of radio packets does not collide, and the time of signal negative detection by carrier sense Transmission starts at the stage when the accumulated value coincides with the time length corresponding to the random number (this control is referred to as “random backoff”). By such independent distributed control, the base station apparatus can avoid the bandwidth allocation scheduling process and realize simple access control. Even if this control is a case where a plurality of signal sequences are spatially multiplexed, if the base station apparatus and one terminal apparatus perform single-user MIMO transmission on a one-to-one basis, this CSMA / CA autonomous distributed type Access control can be used as it is. However, in the technology such as multi-user MIMO described above, the base station device needs to centrally manage combinations of terminal devices that perform spatial multiplexing simultaneously, and the centralized control type (hereinafter referred to as base station) in a base station device different from the autonomous distributed type Access control of centralized control type) is required.

  Taking the uplink as an example, in order for the base station apparatus to simultaneously separate the spatially multiplexed signals, it is necessary to estimate channel information for each terminal apparatus. For this channel estimation, it is necessary to receive a pilot signal (preamble signal) for orthogonal channel estimation for each terminal device and to manage which pilot signal corresponds to which terminal device. This pilot signal orthogonal relationship is generally realized by setting a combination of time axis (OFDM symbol) and frequency axis (subcarrier) that does not overlap with other terminal apparatuses, This is realized by addition synthesis by multiplying a predetermined coefficient of the received signal. However, for example, in a situation where there are 100 or more terminal devices, it is difficult (or inefficient) to prepare different orthogonal preambles for each terminal device. Generally, pilot signals are reused. That is, it is necessary to instruct the terminal device in accordance with the conditions of the pilot signal to be used at the time of band allocation, and perform transmission / reception while synchronizing the pilot signals for channel estimation. For this reason, at least for the uplink, it is necessary for the base station apparatus to select a terminal apparatus to which a band is allocated and to instruct transmission start timing and pilot signal usage conditions. As a result, the base station centralized control type It must work.

  In this base station centralized control, the base station device needs to grasp the bandwidth required for each terminal device to transmit data on the uplink. That is, the base station apparatus is notified using some control information packet. For such base station centralized control, application of a TDMA (Time Division Multiple Access) system is generally assumed. WiMAX is an example of a system in which multi-user MIMO is partially introduced into the standard, but here too, a TDMA frame is used, and a terminal device makes a bandwidth request using an assigned slot. The terminal device transmits control information including information on a necessary bandwidth (for example, the number of bytes of information to be accommodated and a transmission mode at that time) to the base station device, and the base station device allocates the bandwidth in response to the request. assign. Even when the terminal device does not need to be assigned, the base station device must assign a slot for transmitting the control information for bandwidth request. Therefore, when the base station apparatus accommodates a very large number of terminal apparatuses having a relatively low traffic density, the bandwidth for transmitting / receiving control information such as a bandwidth request becomes an overhead, thereby reducing the efficiency of the MAC layer. Become. In the autonomous distributed CSMA / CA scheme, the time for performing random backoff cannot be used for transmission / reception, and therefore the efficiency of the MAC layer is lowered by this amount. Since only data transmission is performed, when a very large number of terminal devices having a relatively low traffic density are accommodated, it is rather efficient. For example, assuming a wireless system that accommodates a wide area in a conditionally disadvantageous area as described above with a single base station device, a large number of terminal devices scattered in a very wide service area can be accommodated collectively. become. For this reason, there is a need for an access control method that can be operated efficiently without reducing the efficiency of the MAC layer even when operating under such conditions.

Yusuke Hara et al., "Reduction of power consumption by coherent transmission", IEICE Society Conference BS-3-1, September 2009 Daiki Matsuda et al., “A Study on Channel Capacity of Distributed Antenna System Using Maximum Ratio Transmission”, IEICE RCS2007-196, pp. 61-66, February 2008 Takehiko Tsukiji, “Introduction to Radio and Antenna Engineering”, General Electronic Publishing Company, pp. 166-168, March 2002 Taiji Takatori et al., "Application of downlink multi-user MIMO technology to next-generation high-speed wireless access systems" IEICE Transactions B, Communication J93-B (9), pp 1127-1139, September 2010 Edited by Takashi Shono, "WiMAX Textbook", published by Impress R & D, Inc., July 21, 2008

  In the multi-user MIMO transmission technology, in addition to the calculation load of transmission / reception weights for transmission / reception directivity control and the calculation load of selecting a combination of users with high orthogonality, problems related to the MAC layer remain. Among the issues related to the MAC layer, it is important to establish a scheduling technique for efficiently allocating bandwidth while taking into account the variation in traffic between terminal devices.

  For example, consider the case where a 1500-byte packet and a 64-byte packet are spatially multiplexed in spatial multiplexing for two different terminal apparatuses. Since the time required for transmitting a 64-byte packet is overwhelmingly shorter than the time for transmitting a 1500-byte packet, if spatial multiplexing is simply performed side by side, the spatial multiplexing is effectively performed for 64 bytes. It becomes only the first half. Most of the time, 1500 bytes of data are transmitted independently (not spatially multiplexed). Therefore, when scheduling is not performed while taking into account traffic variations, the effect of improving the transmission dose by spatial multiplexing is extremely limited.

  In general, since the amount of transmitted / received data of each terminal device varies in terms of time, it is necessary to devise in order to maintain the MAC layer efficiency high. As a method that can flexibly cope with such a variation in the amount of data for each terminal device, an OFDMA method can be applied among existing methods. As mentioned above, this OFDMA scheme is also adopted in WiMAX that partially adopts multi-user MIMO as a standard. In the OFDMA system applied to WiMAX, as shown in Non-Patent Document 5, after grasping the band that needs to be allocated for each terminal device, the number of subcarriers allocated is changed in accordance with the band. A large number of subcarriers may be allocated to a terminal apparatus with a large amount of information, and a small number of subcarriers may be allocated to a small terminal apparatus.

  Further, in the OFDMA method, an allocation area is set in a patchwork form in a two-dimensional array of a frequency axis and a time axis. For example, in the previous example, 1500 bytes is about 23.4 times 64 bytes. If 2 subcarriers are allocated for 64 bytes of data, transmission is completed in an equivalent time if 47 subcarriers are allocated for 1500 bytes. In this example, the comparison is made only on the frequency axis, but it is also possible to adjust by the number of allocated arrays represented on the frequency axis and the time axis. As described above, the OFDMA scheme is expected to be an efficient method for accommodating a plurality of terminal devices in a base station centralized control system since the degree of scheduling is increased.

However, in the OFDMA scheme, due to the flexibility of scheduling, it is necessary to select an optimal allocation from among a large number of allocation options, and the processing load is unexpectedly large. For example, when N terminal devices are simultaneously spatially multiplexed on the same frequency, the scheduling processing load is at least N times. Further, if the relationship between the combination of terminal devices and the spatial multiplexing characteristics is also taken into account, the calculation load becomes even larger.
When the OFDMA system is used in the transmission unit 81 (FIG. 9) and the reception unit 85 (FIG. 10) of the base station apparatus 80 shown in FIGS. 9 and 10, the transmission signal processing circuits 811-1 to 811 are used. -L (FIG. 9) and the terminal devices associated with the received signal processing circuits 858-1 to 858-L (FIG. 10) are different for each subcarrier and each time. The control for appropriately switching the circuit becomes very complicated. Further, when the transmission unit 81 (FIG. 9) and the reception unit 85 (FIG. 10) shown in FIG. 8 are implemented by fixed circuits, the MAC layer processing circuit 88 receives and inputs an instruction from the communication control circuit 820. The corresponding relationship between the data # 1 to #L and the individual transmission signal processing circuits 811-1 to 811-L or the reception signal processing circuits 858-1 to 858-L. Processing becomes very complicated.

As described above, in both the scheduling process and the signal process, there is a problem that the MAC layer process is complicated and the response performance is deteriorated.
Furthermore, as described in (Requirement 4) above, when assuming a wireless system in which a wide area is accommodated by one base station device in a disadvantageous area, etc., it is scattered within a very wide service area. Thus, a large number of terminal devices having a relatively low traffic density are accommodated together. In this case, there is a need for a base station centralized control type access control method that obtains bandwidth information indicating the bandwidth required by each terminal device and performs efficient operation without impairing the efficiency of the MAC layer. However, in such a base station centralized control type access control method, even if the terminal device does not have data to be transmitted, the bandwidth request information must be periodically transmitted and received. There is a possibility that the amount of overhead becomes a non-negligible amount compared to the actual amount of data flowing. As a result, the transmission efficiency in the MAC layer is lowered, which may hinder the increase in capacity of the wireless system.

  The present invention has been made in view of such a situation, and a base station device, a wireless communication method, and a wireless communication system capable of performing spatial multiplexing transmission with a plurality of terminal devices without impairing the efficiency of the MAC layer Is to provide.

  In order to solve the above problem, the present invention comprises a base station apparatus having a plurality of antenna elements and a plurality of terminal apparatuses, and the base station apparatus and the terminal apparatus are at the same time on the same frequency. A base station apparatus in a radio communication system capable of performing spatial multiplexing transmission, each for synthesizing in-phase signals received by a plurality of antenna elements based on a training signal transmitted from the terminal apparatus A reception weight for a frequency component is calculated for each combination of the terminal device and the antenna element, a transmission / reception weight calculation unit that stores the calculated reception weight, and a reception signal that is provided for each antenna element and is received by the antenna element. A radio signal processing unit that separates a signal for each frequency component; and a frequency component and an antenna provided for each terminal device and corresponding to the terminal device. Multiplying the reception weight according to the combination with the element by the signal of each frequency component separated by each of the radio signal processing units, a reception weight multiplication unit for adding and combining the multiplication results for each frequency component, and for each terminal device The presence / absence of a signal from the corresponding terminal device is determined based on the result of addition synthesis by the reception weight multiplication unit corresponding to the terminal device, and if there is a signal from the terminal device, And a reception signal processing unit that performs reception processing.

  Further, the present invention provides the transmission signal processing unit provided for each of the terminal devices, wherein the signal transmitted to the terminal device is separated into signals for each frequency component, and provided for each of the terminal devices. The signal for each frequency component separated by the transmission signal processing unit corresponding to the terminal device is multiplied by a transmission weight corresponding to the combination of the frequency component corresponding to the terminal device and the antenna element, and corresponds to the multiplied transmission weight A transmission weight multiplication unit that outputs a multiplication result to the radio signal processing unit connected to an antenna element, wherein the transmission / reception weight calculation unit is either the training signal or channel information fed back from the terminal device. Each of the rounds for synthesizing the signals transmitted from the plurality of antenna elements in the terminal device. The transmission weights for several components are calculated for each combination of the terminal device and the antenna element, the calculated transmission weights are stored, and the wireless signal processing unit corresponds to each of the terminal devices. Are added and combined for each frequency component, converted to a signal on the time axis based on the addition result for each frequency component, and transmitted from the corresponding antenna element.

  Also, in the present invention described above, when frequency division duplex is used for spatial multiplexing transmission with the terminal device, the radio signal processing unit is always in the period in which the terminal device is communicating. The reception signal is separated into signals for each frequency component, and the reception weight multiplication unit always performs multiplication of the reception weight and addition synthesis.

  Also, in the present invention described above, in the case where time division duplex is used for spatial multiplexing transmission with the terminal device, the radio signal processing unit is always in a period allocated for reception of the terminal device. The reception signal is separated into signals for each frequency component, and the reception weight multiplication unit always performs multiplication and addition synthesis of the reception weights.

  In addition, the present invention includes a base station apparatus including a plurality of antenna elements and a plurality of terminal apparatuses, and the base station apparatus and the terminal apparatus perform spatial multiplexing transmission at the same time on the same frequency. A wireless communication method performed by a base station apparatus in a wireless communication system capable of performing in-phase synthesis of signals received by a plurality of antenna elements based on a training signal transmitted from the terminal apparatus A reception weight for a component is calculated for each combination of the terminal device and the antenna element, and a transmission / reception weight calculation step for storing the calculated reception weight; and for each antenna element, a reception signal received by the antenna element is a frequency component A radio signal processing step for separating each signal, and for each terminal device, a frequency component and an antenna corresponding to the terminal device In the reception weight multiplication step, the reception weight multiplication step of multiplying the signal of each frequency component separated in the radio signal processing step by the combination with the child, and adding and combining the multiplication results for each frequency component, in the reception weight multiplication step Based on the result of addition synthesis corresponding to each terminal device, the presence / absence of a signal from the terminal device is determined, and when there is a signal from the terminal device, reception signal processing for performing reception processing on the addition synthesis result A wireless communication method comprising: steps.

  In addition, the present invention includes a base station apparatus including a plurality of antenna elements and a plurality of terminal apparatuses, and the base station apparatus and the terminal apparatus perform spatial multiplexing transmission at the same time on the same frequency. The base station apparatus receives each frequency component for in-phase combining signals received by the plurality of antenna elements based on a training signal transmitted from the terminal apparatus. A weight is calculated for each combination of the terminal device and the antenna element, a transmission / reception weight calculation unit for storing the calculated reception weight, and a reception signal provided for each antenna element and received by the antenna element for each frequency component A combination of a radio signal processing unit that separates signals and a frequency component provided for each of the terminal devices and an antenna element corresponding to the terminal device The reception weight multiplication unit that multiplies the corresponding reception weight by the signal of each frequency component separated by each of the radio signal processing units, and adds and synthesizes the multiplication result for each frequency component, and the terminal device provided for each terminal device The presence / absence of a signal from the corresponding terminal device is determined based on the result of addition / synthesis by the reception weight multiplication unit corresponding to, and if there is a signal from the terminal device, reception processing is performed on the addition / synthesis result A wireless communication system comprising a reception signal processing unit.

According to the present invention, prior to actual data communication, the base station apparatus acquires channel information by receiving a predetermined training signal from the terminal apparatus, and further acquires multiple times at different timings. By averaging the relative components of the received channel information, the channel information is accurately estimated, and a fixed reception weight to be used when simultaneously multiplexing multiple terminal apparatuses simultaneously in actual data communication using this channel information is obtained in advance. And reception processing is performed using this spatially multiplexed reception weight.
According to the present invention, the base station device includes a reception weight multiplication unit and a reception signal processing unit that correspond one-to-one with each terminal device to be communicated. Each reception weight multiplication unit performs addition synthesis using reception weights corresponding to a combination of a terminal device corresponding to itself, an antenna element, and a frequency component, and each reception signal processing unit receives a signal from the terminal device corresponding to itself. It is determined whether or not the signal is included in the addition-combined signal by multiplying the reception weight, and demodulation is performed when the signal is included.
As a result, the base station apparatus can demodulate the spatially multiplexed signal without knowing the band allocation to each terminal apparatus. That is, since the base station apparatus can perform one-to-one communication with each terminal apparatus in parallel without being particularly conscious of communication with other terminal apparatuses, the base station apparatus performs spatial multiplexing as a whole for each terminal apparatus. There is no need to perform conscious bandwidth allocation, and it is not necessary to grasp the bandwidth information required by each terminal device. As a result, the base station apparatus can perform spatial multiplexing transmission with each terminal apparatus without impairing the efficiency of the MAC layer for grasping the band information of each terminal apparatus.

It is a schematic block diagram which shows the structure of the base station apparatus 400 in embodiment which concerns on this invention. It is a figure which shows the outline | summary of the radio relay system in a prior art. It is a figure which shows the outline | summary of the distributed antenna system in a prior art. It is a flowchart which shows the process of the channel feedback in a prior art. It is a figure which shows the principle of a phased array antenna. It is the schematic which shows the structural example of a multiuser MIMO system. It is a flowchart which shows the procedure which calculates the transmission weight matrix W in a multiuser MIMO system. It is a schematic block diagram which shows an example of a structure of the base station apparatus 80 in a multiuser MIMO system. It is a schematic block diagram which shows an example of a structure of the transmission part 81 in the base station apparatus 80 in a multiuser MIMO system. It is a schematic block diagram which shows an example of a structure of the receiving part 85 in the base station apparatus 80 in a multiuser MIMO system. It is a flowchart which shows the transmission process of the base station apparatus 80 in multiuser MIMO. It is a flowchart which shows the reception process of the base station apparatus 80 in multiuser MIMO. It is a figure which shows the example of the communication system used in this embodiment. It is a figure which shows the example of installation of the base station apparatus with which the radio | wireless communications system which concerns on this invention comprises. It is a figure which shows the operation example of the signal synthesis | combination which the base station apparatus which concerns on this invention performs. It is a figure which shows the example of the training signal in this invention. It is a figure which shows the asymmetry of the channel information of an uplink and a downlink. It is a figure which shows the outline | summary of calibration. It is a schematic block diagram which shows the structure of the base station apparatus 10 in the structural example of related technology. It is a figure which shows an example of a structure of the receiving part 100 with which the base station apparatus 10 in the same structural example is provided. It is a schematic block diagram which shows the structural example of the transmission / reception weight calculation part 120 in the same structural example. It is a figure which shows an example of a structure of the transmission part 140 in the base station apparatus 10 in the same structural example. It is a flowchart which shows the short time averaging process which acquires the channel information of the uplink in the same structural example. It is a flowchart which shows the relative component acquisition process which acquires the relative component of the uplink channel information in the example of a structure. It is a flowchart which shows the long-time averaging process of the uplink channel information in the same configuration example. It is a flowchart which shows the process which acquires the channel information of the downlink in the same structural example. It is a flowchart which shows the process which calculates the transmission weight and the reception weight in the base station apparatus 10 of the same structural example. It is a flowchart which shows the transmission process of the base station apparatus 10 in the same structural example. It is a flowchart which shows the reception process of the base station apparatus 10 in the same structural example. It is a flowchart which shows the other relative component acquisition process which acquires the relative component of the channel information of uplink in each structural example. It is a schematic block diagram which shows the structural example (in the case of TDD) of the radio signal processing circuit 410 in this embodiment. It is a schematic block diagram which shows the structural example (in the case of FDD) of the radio | wireless signal processing circuit 410a in this embodiment. It is a flowchart which shows the reception process of the base station apparatus 400 in this embodiment. It is a flowchart which shows the transmission process of the base station apparatus 400 in this embodiment.

[Operational principle of the present invention]
One of the essences of the present invention is that the base station apparatus calculates an estimated value of channel information indicating channel characteristics between a large number of wireless modules provided in the base station apparatus and the terminal apparatus over a long period of time. By using transmission weights and reception weights that are measured and calculated based on the average value of the estimated channel information, it is possible to reduce the effects of channel time fluctuations using multiple wireless modules while coherent using in-phase synthesis. The purpose is to obtain a line gain associated with transmission and to realize high-order spatial multiplexing using a low line gain in an area other than the region where the same phase synthesis is performed at a pinpoint.

  In addition, the present invention steadily performs transmission processing and reception processing for each terminal device using fixed transmission weights and reception weights calculated based on the estimated values obtained by averaging the above channel information. To do. The reception weight at this time is a reception weight for combining signals transmitted from a certain terminal apparatus received by a plurality of antennas of the base station apparatus in the same phase. Similarly, the transmission weight is a transmission weight for allowing signals transmitted from a plurality of antennas of the base station apparatus to be combined and received by the terminal apparatus in the same phase. That is, it is a transmission / reception weight that can be set independently in each terminal device, without depending on the combination of terminal devices that perform spatial multiplexing simultaneously. Using these reception weights and transmission weights, the base station apparatus performs transmission processing using transmission weights regardless of whether there is a transmission signal to be transmitted to a certain terminal apparatus, and should also receive from a certain terminal apparatus. Reception processing using reception weights is performed regardless of the presence or absence of reception signals.

  Specifically, the base station device converts each received signal received by a plurality of antennas into a signal on the frequency axis, and for each frequency component obtained by the conversion, for each assumed terminal device, antenna, and frequency component Is multiplied by the reception weight corresponding to each antenna, and the multiplication result of the reception weight corresponding to each antenna in each frequency component is added and synthesized over all antennas. At this time, the reception weight multiplied by each frequency component is calculated in advance corresponding to the combination of the antenna, the frequency component, and the terminal device.

  Here, consider a case where only a certain terminal device transmits a signal to the base station device. In the base station apparatus, when the reception signal corresponding to the terminal apparatus that transmitted the signal is multiplied by the reception signal, the reception signals received by the multiple antennas are combined in phase to detect a signal having a significant reception level. be able to. On the other hand, when the reception signal corresponding to another terminal device is multiplied by the reception signal, the signals of each antenna are added and synthesized with a random phase, and the reception level of the resulting signal is a very low signal. The signal cannot be detected. That is, when the signals of all frequency components (or a part of the frequency components may be used) are synthesized using the reception weight corresponding to each terminal device, the synthesis obtained using the reception weight corresponding to the terminal device that transmitted the signal As a result, a signal having a significant reception level can be detected, and it can be grasped that the signal is transmitted from the terminal device. On the other hand, when the terminal device does not transmit a signal, a signal having a significant reception level is not detected even in the synthesis result obtained using the above-described reception weight, and no signal is transmitted from the terminal device. I can understand that.

  The base station apparatus can grasp whether or not each terminal apparatus has transmitted a signal by performing the reception process using the above-described reception weight, so it can grasp in advance whether or not each terminal apparatus has transmitted a signal. Without being able to receive the signal from each terminal device. That is, the base station device includes a reception signal processing circuit that performs reception processing corresponding to each of all the accommodated terminal devices, so that each terminal can be determined without knowing in advance whether or not there is a signal transmitted from each terminal device. As a result, it becomes possible to receive a signal from the device, and as a result, it is possible to omit the assignment management of the radio resource to each terminal device.

  Similarly, when transmitting a signal from a base station apparatus to a terminal apparatus, the signals transmitted from a plurality of antennas are in-phase synthesized by a desired terminal apparatus by performing the transmission processing using the transmission weight described above. The signal addressed to the terminal device can be detected by the terminal device as a signal having a significant reception level. At this time, in other terminal apparatuses, since the phase synthesis is not random phase synthesis but random phase synthesis, it is not detected as a signal having a significant reception level. In other words, by using a transmission weight calculated based on an estimated value obtained by averaging channel information, a signal addressed to a desired terminal apparatus is transmitted regardless of the presence / absence of a signal addressed to another terminal apparatus. be able to.

  As described above, in the base station apparatus according to the present invention, base station centralized control is performed by regularly performing transmission / reception processing using transmission weights and reception weights calculated based on estimated values obtained by averaging channel information. Therefore, it is possible to perform spatially multiplexed transmission with each terminal device without performing the allocation management of radio resources to each terminal device. Furthermore, since the base station device individually includes a processing unit that performs reception processing and transmission processing for each terminal device to be communicated, communication with each terminal device can be performed independently and in parallel. This eliminates the need to grasp the bandwidth required for each terminal device using bandwidth request control information, avoids overhead due to transmission / reception of unnecessary control signals, and does not impair the efficiency of the MAC layer. Spatial multiplexing transmission can be performed with a plurality of terminal devices.

[Outline of related technology on which the present invention is based]
In order to realize the outline of the operation of the present invention described above, the related technology as a base will be described below. The related technology in the following description does not refer to the conventional technologies such as the wireless relay system, the distributed antenna system, the phased array antenna technology, and the multiuser MIMO technology in the coherent transmission described above. This means the base technology used in combination. In other words, the present invention is based on the operation shown in the configuration example of the related technology described below in terms of processing and operation principle in the physical layer. And while utilizing the feature, it is possible to simplify the processing of the MAC layer by correcting a part of the apparatus configuration and processing contents. In the processing shown in the configuration example of the related technology that forms the basis of the present invention described below, the transmission / reception weight used for spatial multiplexing does not depend on the combination of terminal devices that perform spatial multiplexing, and does not vary with time. Due to the weight, the control is greatly simplified.
In the following, description will be made in order starting from the preconditions and system installation examples.

(Prerequisite)
First, the precondition of the present invention is premised on communication in which a signal to be transmitted and a signal to be received in the base station apparatus do not interfere with each other. FIG. 13 is a diagram illustrating an example of a communication method used in the present embodiment. In order to avoid this interference, this wireless communication system is a communication method used in WiMAX and the like, and time-division duplex (in which transmission and reception times shown in FIG. Either the Time Division Duplex (TDD) method or the Frequency Division Duplex (FDD) method using different frequency bands for transmission and reception shown in FIG. 13B is used. Thus, the present invention assumes a wireless communication system in which transmission and reception are separated in terms of time or frequency.

  Further, it is assumed that the OFDM symbol timing is synchronized in timing between the base station apparatus and the terminal apparatus. As a method for achieving this timing synchronization, for example, synchronization using a system such as GPS may be used, or any other method may be used. As the accuracy of symbol timing synchronization, the timing synchronization error only needs to be sufficiently smaller than the guard interval length included in the OFDM symbol. For example, in WiMAX or the like, one OFDM symbol length is about 100 μs and a guard interval length is about 20 μs. Therefore, it is possible to use a radio clock or other various methods having a synchronization accuracy lower than that of GPS.

  Further, in the present invention, it is not always necessary to ensure the prospect of each wireless module and the terminal device, but it is recommended that the wireless module and the terminal device are fixed at a relatively high place. In this case, the transmission path (channel) between each wireless module and the terminal device is a “direct line-of-sight wave”, a “stable reflected wave” by a fixed huge building, etc. ) It can be regarded as a mixture of “multiple reflected waves from objects with movement” such as nearby cars and people. In this case, the “direct line-of-sight wave” and the “stable reflected wave” have a relatively high reception level and smaller time fluctuation than the “multiple reflected wave from the moving object”. On the other hand, “multiple reflected waves from a moving object” has a lower reception level and a large fluctuation with time compared to “direct line-of-sight waves” and “stable reflected waves”.

  A signal for channel estimation (hereinafter referred to as “training signal”) is transmitted continuously or intermittently over a long period of time, and the received signal is averaged over a long period of time. Because of the randomness of the “multiple reflected wave from the object with movement” signal, the average value of the variation of the complex phase and amplitude approaches zero. On the other hand, components related to “direct line-of-sight wave” and “stable reflected wave” converge to a non-zero constant value. As a result, a channel estimation result corresponding to a stable path with a relatively small time variation component is extracted.

In the description of coherent transmission in the prior art, the “wireless module” is “relay station” or “remote base station” in the distributed antenna system. Of course, these are physically located away from the control station or base station in the prior art. Taking a distributed antenna system as an example, a remote base station is located at the center of a plurality of cells, and if it is a relay station using radio, it is far enough to use radio Become. However, in the same phase synthesis (for both transmission and reception) of signals from individual radio modules intended in the present invention, it is not always necessary to separate the radio modules as far as remote base stations and relay stations. Absent.
In addition, if the distance between the antenna elements of each wireless module is smaller than the wavelength of the carrier frequency of communication, the assumed in-phase synthesis of signals may be disturbed due to mutual coupling between the antenna elements. However, this problem can be avoided if an interval of approximately one wavelength or more is ensured between the antenna elements.

That is, the basic configuration of the present invention is that a large number of antenna elements each having an interval of one wavelength or more are secured to one base station apparatus. Of course, since the signals transmitted and received from each antenna element have different transmission and reception weight coefficients, each antenna element has a separate RF (Radio Frequency) circuit in the radio frequency band such as a high power amplifier, low noise amplifier, and filter. And are connected to each other to constitute one wireless module.
In the description so far, each wireless module is physically arranged discretely at a location different from the control station or the like, so the term “wireless module” is intended to be a wireless module that is almost integrated with the antenna element. Although various explanations have been given, in the present invention, a control station and a large number of wireless modules are integrated in one place, and generally, a form of one base station apparatus is natural. The expression “wireless module” may not be appropriate.

  For example, functionally, a function corresponding to a control station such as baseband signal processing and a function of an RF circuit in a radio frequency band such as a plurality of high power amplifiers, low noise amplifiers, filters, etc. are mounted in one casing, If a configuration is assumed in which a casing and a large number of antenna elements are connected by a coaxial cable, it is necessary to consider correction for fluctuations in amplitude / complex phase in amplifiers and filter systems during transmission and reception. In many cases, the expression “channel information between the wireless module and the wireless module” is substantially expressed as “channel information between the antenna element of the terminal device and the antenna element of the wireless module”. Therefore, hereinafter, in the description of the channel, the term “antenna element” will be used instead of the term “wireless module”.

(Installation example of wireless communication system and basic principle of related technology)
FIG. 14 is a diagram illustrating an installation example of the base station apparatus included in the wireless communication system according to the present invention. In the same figure, the code | symbol 11 shows the building in which the base station apparatus is installed, the code | symbols 12-1 to 12-2 shows a terminal device, and the code | symbols 13-1 to 13-4 are equipped with the base station apparatus. An antenna element is shown, the code | symbol 14-1 to 14-3 shows the mobile body on the ground, and the code | symbols 15-1 to 15-2 have shown the large sized building (naturally a stationary state).

  Here, the antenna elements 13-1 to 13-4 included in the base station apparatus are installed in a very high place such as the roof of the building 11. The terminal devices 12-1 to 12-2 may be relatively lower than the antenna elements 13-1 to 13-4 of the base station device such as a telephone pole or a general building rooftop. However, it is installed at a relatively high place. On the other hand, the mobile units 14-1 to 14-3 on the ground are located in places relatively lower than the antenna elements 13-1 to 13-4 and the terminal devices 12-1 to 12-2 of the base station apparatus. In addition to cars, there are many starting points (reflective points) of reflected waves that fluctuate randomly, such as people and trees swaying in the wind.

  For example, the terminal device 12-1 and the antenna elements 13-1 to 13-4 of the base station device are in a line-of-sight environment (direct waves are indicated by thick solid arrows in the figure). On the other hand, although the terminal device 12-2 and the antenna elements 13-1 to 13-4 of the base station device are not in the line-of-sight environment due to the shielding of the large building 15-2, the large building 15-1 or the like And a stable reflected wave (indicated by a thick solid arrow in the figure) has reached.

In addition, for the terminal device 12-1 in the line-of-sight environment, there may be a situation where a stable reflected wave due to a large building exists in addition to the line-of-sight wave, and these signals are always combined to reach the signal. A signal represented by such a thick solid arrow is regarded as a stable incident wave. On the other hand, the reflected waves from the mobile bodies 14-1 to 14-3 on the ground have many signals that arrive as many random multiple reflections, and the level of the signal received is relatively low, and the complex phase component And the amplitude varies randomly with time.
When a number of weak and random waves are combined, the resulting signal has a relatively low signal strength relative to a stable incident wave. Therefore, the “time-varying incident wave” obtained by combining the “stable incident wave” with the “random multiple reflected wave” is a signal in which a minute error is added around the “stable incident wave”. Can see.

Next, signal synthesis performed by the base station apparatus in such a situation will be described.
FIG. 15 is a diagram illustrating an example of signal combining operation performed by the base station apparatus according to the present invention. Here, as an example, when signals transmitted from terminal apparatus 12-1 in FIG. 14 are received by antenna elements 13-1 to 13-4 of the base station apparatus, they are combined using appropriate reception weights. Shows the case.
The antenna elements 13-1 to 13-4 of the base station apparatus receive the “incident wave that varies with time”. The reception weight used when combining these signals is determined so that the signals at the respective antenna elements are combined in phase with the “stable incident wave” as a reference. The signal indicated by the dotted line in FIG. 15 is a signal in which the “stable incident wave” is multiplied by the reception weight and the phase is aligned in the same phase in each of the antenna elements 13-1 to 13-4.

The actual “time-varying incident wave” multiplied by the reception weight, that is, the “time-varying incident wave” indicated by the thin solid line in FIG. 15 is slightly shifted from the “stable incident wave” indicated by the dotted line. Strictly speaking, each antenna element does not have the same phase composition, but the “time-varying incident wave” behaves close to a “stable incident wave”. When combined using the reception weight set with “stable incident wave” as a reference, a combined signal having a large amplitude indicated by a thick solid line is obtained. In other words, if the number of antenna elements used in the base station apparatus is increased to an enormous number, the “stable incident wave” component of each antenna element is in-phase synthesized as a statistical effect, and the “random multiple reflected wave” is In order to cancel each other, the time-varying component with respect to the “stable incident wave” is relatively suppressed to a very small level.
Here, in the description of FIG. 14 and FIG. 15, the case where the base station apparatus is provided with four antenna elements has been described for the sake of simplicity. A statistical effect can be obtained by providing the antenna element.

  The in-phase synthesis of a statistical signal based on this “stable incident wave” can be used in the same way for both the transmission weight used during transmission and the reception weight used during reception. The transmission / reception weight used in the base station apparatus is calculated based on the channel estimation result. Even if the channel estimation is performed by receiving the training signal transmitted by the base station apparatus by the terminal apparatus, the signal transmitted by the terminal apparatus May be received by the base station apparatus to estimate the channel. In general, downlink and uplink channel information is asymmetric because amplifiers / filters used for transmission / reception are different, but a predetermined conversion formula is used for the uplink channel estimation result and the downlink channel estimation result. If the calibration process described later is used, the training signal transmitted by the terminal device is simultaneously received by all the antenna elements of the base station device, and uplink channel information is obtained by channel estimation using the result, By applying a predetermined conversion formula to this, channel information in the downlink direction can be acquired.

As explained above, by the averaging process over a long time for the channel information between each antenna element of the base station apparatus and the antenna element of each terminal apparatus, random time-varying components are suppressed, It is possible to extract a stable incident wave from no line-of-sight wave or a stable structure. Based on the extracted long-term average channel information, high phase gain can be obtained by performing in-phase synthesis on the target terminal device. In general, when an amplitude when a signal transmitted from one antenna element is received by one antenna element in another location is 1, signals transmitted from N antenna elements are in phase. When combined, the expected value of the amplitude of the received signal becomes N times. Since the received power is proportional to the square of the amplitude, the received power is N ² times. That is, a gain of ₁₀ Log ₁₀ (N ² ) [dB] can be obtained. If N is 100, the line gain associated with coherent transmission by in-phase combining corresponds to 40 [dB].

Next, high-order spatial multiplexing using reduction of given / interfered will be described. The in-phase synthesis described above is performed with a specific terminal device as a target, and a high line gain can be obtained pinpoint only for the terminal device. For example, if in-phase combining is performed on the terminal device 12-1 in FIG. 14, random phase combining is performed at other points where in-phase combining is not performed, such as the terminal device 12-2. Although FIG. 14 shows a case where the antenna elements 13-1 to 13-4 of the base station apparatus are four elements, when N antenna elements are used, the received power is increased N times as an expected value as a result of random phase synthesis. Become. In such a situation, when two signal sequences are simultaneously spatially multiplexed, the desired signal having the same phase composition is interfered with the line gain being N ² times per transmission antenna element. For undesired signals, the line gain is N times per transmission antenna element. Therefore, the relative SIR value is ₁₀ Log ₁₀ (N) [dB].

Thus, if the number (N) of transmitting antenna elements is 100, an SIR of 20 [dB] can be earned as an expected value while performing spatial multiplexing. That is, using the two paths indicated by thick solid lines in FIG. 14, it is possible to simultaneously perform communication between both the terminal device 12-1 and the terminal device 12-2 and the base station device in the same frequency band. .
Usually, when the number of antennas is enormous, when performing spatial multiplexing with a general multi-user MIMO technique, the amount of computation of signal processing proportional to the cube of the number of antennas is expected. Operation with a large number of antenna elements has been forced. Particularly important is null control to prevent a signal to a certain terminal device from interfering with other terminal devices. In the present invention, calculation of transmission / reception weights for realizing this null control is performed in real time. The signal processing in communication can be realized by reading the weight calculated in advance. For this reason, it is possible to realize high-order spatial multiplexing with a reduced calculation amount and circuit scale during operation while using a large number of antenna elements. Furthermore, in the present invention, a high SIR can be secured originally without performing the above-described null control. For this reason, even if the null control is broken to some extent due to channel fluctuation, the SIR value remains relatively high and stable. It also has the feature of being able to perform spatial multiplexing.

  If the number of transmitting antennas (N) is 100, the interference power will be approximately 10 times relatively large when 10 signals are spatially multiplexed. The expected value is about 10 [dB]. Of course, even if the average SIR value is 10 [dB], there is a certain extent of distribution. Therefore, even when the required SIR value is 10 [dB], in order to perform 10 or more spatial multiplexing, the SIR characteristic is good. It is preferable to combine a scheduling function for combining terminal devices and a directivity control function for performing interference suppression. However, the scheduling function and directivity control function performed here do not need to be premised on real-time control reflecting channel information that varies with time, and the time-varying component is averaged by the long-time averaging described above. Channel information can be used. Therefore, avoiding performing complicated signal processing sequentially every time communication is performed, in the pre-processing performed before the start of communication, by completing the heavy processing, and using the processing results, The load during operation can be reduced. As described above, the present invention constructs a stable condition that excels in SIR characteristics without null control as described above, and further stabilizes higher-order spatial multiplexing by combining a directivity control function for performing interference suppression. To be feasible.

Thus, in the present invention, instead of aiming at strict in-phase synthesis using real-time channel information, transmission / reception that can be suppressed within a certain amount of error even if there is a transmission / reception weight with a slight error from the strict transmission / reception weight. The first important point is to aim at quasi-optimal in-phase synthesis that draws stable and high line gain by a statistical effect by combining weights and using many antenna elements.
Furthermore, in the present invention, since the transmission / reception weight is a fixed value without being conscious of channel time fluctuations, for example, if it is acquired in advance before starting the operation of the communication service, Even if the number of antenna elements used for communication is increased to an enormous number, it is possible to keep the signal processing load low because it is only necessary to read the transmission / reception weights stored in the memory without performing individual calculations. This is the second important point.
Furthermore, in the present invention, channel estimation between individual antenna elements is not performed every time communication is performed, so that it is not necessary to assign the same number of channel estimation preamble signals as the spatial multiplexing number. For this reason, taking the case of using the OFDM modulation method as an example, conventionally, a preamble signal for channel estimation of 10 different symbols is required for 10 spatial multiplexing, but in the present invention, spatial multiplexing is used. A preamble signal for channel estimation of one symbol is sufficient without depending on the number. As a result, it is possible to perform higher-order spatial multiplexing while suppressing a decrease in the efficiency of the MAC layer, which is a third important point.
With respect to the above operating principle, supplementary matters for realizing these will be briefly described below before describing the detailed embodiment.

(About channel estimation averaging processing)
The base station apparatus according to the present invention is characterized by using a transmission / reception weight for performing in-phase synthesis of a statistical signal based on a “stable incident wave”. An overview of the corresponding channel estimation will now be described.
As described above, the base station apparatus extracts a component related to a “stable incident wave” by removing the influence of multiple reflected waves that are reflected on a mobile object and randomly vary. In order to extract a component related to “stable incident wave” in each antenna element as a pre-stage to obtain a statistical effect by a large number of antenna elements, the base station apparatus extracts each antenna element and terminal apparatus Channel information corresponding to a “stable incident wave” is acquired by performing channel estimation of individual channels with the antenna element over a long period of time and averaging the results.

  Before describing the specific acquisition method, first, the influence of reflection reflected on the moving bodies 14-1 to 14-3 such as a car in FIG. 14 will be considered. The situation of the reflected waves from these moving bodies does not change so much in a short time when the positions of the moving bodies are not displaced so much, but if these moving bodies move to physically different positions, the influence of the reflected waves is absolutely not. Expect to be different. In other words, even if the channel information is averaged in a short period of time, where the state of multiple multiple reflections reflected on the mobile object does not change so much, the mobile object that is the basis of the random reflected wave moves greatly. Is expected to be in another channel state.

  Next, how to obtain the long-term average channel information will be described focusing on points to be noted. In general, the clock signal of the base station apparatus and the clock signal of the terminal apparatus are not completely synchronized, and there is some frequency error. For example, when performing block transmission such as OFDM modulation scheme or SC-FDE transmission technology, the symbol timing (or block cycle) of one symbol is slightly shifted between the base station apparatus and the terminal apparatus. This symbol timing shift appears as a common complex phase rotation at all frequencies. Note that the clock signal of the base station device and the clock signal of the terminal device are A / D conversion and a clock signal that determines a sampling period when performing D / A conversion.

A similar problem of complex phase rotation is that the local oscillation signal output from the local oscillator used for up-conversion and down-conversion between the baseband signal and the radio frequency signal is not synchronized between the base station device and the terminal device. A frequency error also becomes a problem.
When transmission and reception are asynchronous and accompanied by a frequency error, the channel information measured at different times is complex depending on the time difference and the frequency error even if there is no time variation in the channel information in space. The phase component fluctuates.

  This is because, for example, the initial complex phase of the local oscillation signal input from the local oscillator that is multiplied in the mixer in the down-conversion process on the reception side cannot be matched every time communication is performed. In signal detection processing in communication, when channel estimation is performed with a training signal, channel information as a result including the influence of the initial complex phase is acquired, which causes a problem in signal detection processing of a signal subsequent to the training signal. There is nothing. However, when averaging in discrete time, there is a problem because even if there is no time variation in the channel information, it appears that there is time variation due to the uncertainty of the initial complex phase.

  However, the channel information required to calculate the transmission weight and reception weight for realizing in-phase synthesis at the time of reception is not the absolute value itself including the complex phase of the channel information indicating the characteristics of the transmission path, but the antenna information. It is sufficient to know the relative relationship of complex phases in channel information for each element. Therefore, when averaging channel estimation results measured at discrete times, one reference antenna element is set from a plurality of antenna elements of the base station apparatus, and channel information estimated by the antenna element is set. It is only necessary to add a minus offset to the complex phase component of the channel information in each antenna element for the complex phase component.

Specifically, when the base station apparatus includes K antenna elements, channel information of the k-th frequency component observed by antenna element #i (i = 1,..., K) is A _i · Exp ( Let φ _i ^(k) j). Here, j represents an imaginary unit, A _i represents the amplitude component of the channel information of the antenna element #i, and φ _i ^(k) represents the complex phase of the channel information of the k-th frequency component of the antenna element #i.
At this time, if the complex phase −φ ₁ ^(k) is added to all the antenna elements using the complex phase φ ₁ ^(k) of the antenna element # 1, the channel information of the antenna element #k corrected by the offset A _i · Exp {(φ _i ^(k) −φ ₁ ^(k) ) j} is obtained. If the channel information in space is unchanged, the corrected channel information is influenced by the frequency error of the clock signal and the local oscillation signal between the base station device and the terminal device (that is, the uncertainty of the initial phase of the complex phase). Not affected. In the following description, the corrected channel information for removing the uncertainty of the initial phase is referred to as “relative component (of channel information)”. This correction is performed individually for each frequency component.

  Therefore, when channel information is averaged, it is necessary to perform such correction to eliminate the uncertainty of the complex phase component and to perform averaging. In addition, in the area where the line gain shown in (Problem 1) of the problem of the present invention is greatly insufficient in performing this averaging, the channel information obtained by the channel estimation is based on the basis before the averaging. Note that it may be difficult to obtain information. In such a situation, even if any kind of channel estimation training signal is received, it is generally impossible to detect the reception of the signal. Taking the case of the OFDM modulation method as an example, it means that OFDM symbol timing cannot be detected. Of course, if the guard interval cannot be removed, FFT cannot be performed. A channel estimation averaging method in such a low SNR environment and an example of a specific training signal are shown below.

(Example of training signal in the present invention)
FIG. 16 is a diagram illustrating an example of a training signal in the present invention. In the figure, reference numerals 1-1 to 1-3 denote general OFDM symbols, reference numerals 2-1 to 2-3 denote effective signal areas not including guard intervals, and reference numerals 3-1 to 3-3 denote In the present invention, training signals are shown. Reference numerals 4-1 to 4-3 denote end regions of the signals, reference numerals 5-1 to 5-3 denote guard intervals, and reference numerals 6-1 to 6-3 denote actual channels. The signal period used for estimation is shown. Although the OFDM signal includes a plurality of subcarrier components, in the figure, one subcarrier is extracted and illustrated as a sine wave.

  In the case of a conventional OFDM signal, a signal having a period of OFDM symbols (1-1 to 1-3) generates a signal region (2-1 to 2-3) effective as actual data, and the tail region of this signal. (4-1 to 4-3) are copied and pasted as guard intervals (5-1 to 5-3) in the head area of the signal to generate the entire OFDM symbols (1-1 to 1-3). It was. In normal communication, information on the amplitude and complex phase when the timing of the leading portion of the effective signal area (2-1 to 2-3) from which the guard interval is removed is extracted by timing detection and the timing is used as a starting point. Are obtained in the channel estimation.

  However, since it is sufficient to obtain the relative phase relationship of each antenna element in the calculation of the transmission / reception weight according to the present invention, it is not necessary to accurately grasp the initial complex phase, and an appropriate value such as the head of the OFDM symbol is used. There is no need to start from a specific timing. Therefore, it is not necessary to be an OFDM signal in which a guard interval is set, and training signals (3-1 to 3-3) which are signals obtained by extracting effective signal regions (2-1 to 2-3) of OFDM symbols and continuing them. ) May be repeated many times. Here, since the sections are continuously connected, the symbol timing does not substantially make sense in the training signal over a plurality of periods. On the receiving side, the received training signals (3-1 to 3-3) are cut out at arbitrary start timings, for example, signal periods (6-1 to 6-3) used for actual channel estimation, and the section 6 -1, section 6-2, and section 6-3 may be added.

(Compensation of local oscillator frequency error between base station and terminal)
In the channel averaging using the training signal, a relatively short time average of a plurality of continuous sections 6-1, 6-2, and 6-3 is performed. The quantitative meaning of “time” is the influence that depends on the frequency error of the clock signal and the local oscillation signal between the base station device and the terminal device (strictly speaking, the residual frequency error remaining after the frequency error compensation processing shown below) Mean in a range that can be ignored.
For example, in a local oscillation signal having a center frequency of 2.4 [GHz], the frequency error of the local oscillator is 1 p. p. m. In this case, the maximum value of the frequency error of the local oscillation signal is 2.4 [kHz]. That is, this is an error that the phase rotates by 2π in 416 μsec. At this time, if it is desired to suppress the rotation of the complex phase accompanying the frequency error within 1/10 of one period (2π) in the time length for averaging, the time length usable for averaging is about 40 μsec. Become.
However, in the WiMAX example where the wide area is the service area, one symbol period for eliminating the influence of the long delay wave is set to about 100 μsec, which is not sufficient as the time for the averaging process. In order to solve these problems, the following correction processing for compensating for the frequency error is performed here.

  In general, frequency error correction can be dealt with by signal processing called AFC (Automatic Frequency Control). If the same signal is repeatedly received like the current training signal, it is generally possible to extract the frequency error component by multiplying the signal shifted by one period. By applying this AFC process, it is possible to extract a frequency error and perform correction to cancel the frequency error. However, when the received signal has a low SNR, even if an attempt is made to extract a frequency error from adjacent symbols by applying AFC processing, there is a possibility that an erroneous frequency error is extracted due to being buried in noise. Therefore, the AFC processing also needs to be performed for a length of time that can improve the SNR of the original signal.

For example, if sampling data represented by a complex number at time t is represented as S (t) and a frequency error is represented as Δf, the amount of rotation of the complex phase at time t is 2πΔf · t. Therefore, when the frequency compensation is ideally performed on the sampling data S (t), the frequency-compensated sampling data is S (t) · Exp (−2πjΔf · t).
If the sampling period is represented by Δt and the period of one symbol is T, the number of data in one period is given by N = T / Δt. At this time, if the time t = m ′ · Δt, and m and M are m = mod (m ′, N) and M = Int (m ′ / N), the sampling data S (t) is discrete. It can be expressed as a sequence {S _m ^(M) } determined by a specific time. Here, the function “mod (x, y)” is a function for obtaining a remainder when x is divided by y. The function “Int (x)” is a function (a function for truncating the decimal part) for obtaining the integer part of x.
Further, a number sequence obtained by ideally frequency-compensating the sampling data S (t) can be expressed as {S _m ^(M) · Exp (−2πjΔf · Δt · [M × N + m]}, where M ₀ symbol period as a whole. Sampling shall be performed.

The frequency compensated number sequence {S _m ^(M) · Exp (−2πjΔf · Δt · [M × N + m]}) obtained by adding a large number of M for each m to S _m is expressed by the following equation (10). Here, in Formula (10), S with “˜ (tilde)” added thereto is represented as “˜S”.

To improve the SNR by AFC process may be determined to Δf to maximize the amplitude of the to S _m of formula (10). Therefore, an evaluation function G (Δf) expressed by the following equation (11) is determined.

  ^ S (M, M ′) in the equation (11) is expressed by the following equation (12).

  Since Δf that maximizes the evaluation function G (Δf) may be obtained, a conditional expression represented by the following expression (13) is obtained.

  If the real number Δf satisfying the conditional expression (13) is obtained numerically, the frequency error between the base station apparatus and the terminal apparatus is calculated, and using this Δf, the addition for one cycle given by the expression (10) Channel estimation may be performed using averaged sampling data. In the case of the OFDM modulation method, channel information of each subcarrier component is calculated by FFT processing based on the sampling data of one cycle.

Note that even if the equation (13) is not necessarily used, if the possible range of Δf is limited, Δf is set with an appropriate step size within the range, and the equation (11) is set for those Δf. Δf that gives the maximum value may be searched. In this case, the center frequency to be used is 2.4 GHz and the frequency error is 1 p. p. m. In this case, the range of Δf is from −2.4 kHz to +2.4 kHz. The optimum value of the step size varies depending on the required accuracy. For example, if Δf is set in increments of 10 Hz and equation (11) is calculated, true Δf that maximizes equation (11) is obtained. It is possible to search for Δf within the range of residual frequency error within ± 5 Hz. That is, the frequency error is suppressed within 5 Hz, and even if the time length (M ₀ × T) for averaging the M ₀ period is assumed to be about 5 milliseconds, the phase error within the averaging period is It falls within 1/40 of 2π (angle is 9 degrees). Considering that the phase rotates constantly during the averaging period, it is possible to calculate the channel information with an accuracy that does not hinder the operation. In other words, the time length (that is, the value of M ₀ ) during averaging of the M ₀ period is limited within a range in which the phase error within the averaging period can be suppressed to a predetermined value. It will be.

In this way, when performing the averaging process, averaging on a continuous relatively short time scale and averaging on the result of channel estimation in discrete time are performed in two stages. It should be noted that the time length for averaging on a relatively short time scale is subject to the above-mentioned limitations. Also, in the discrete time channel estimation result, by using the complex phase φ ₁ ^(k) of the antenna element # 1 as described above, an offset of the complex phase −φ ₁ ^(k) is added to all the antenna elements. The problem of the uncertainty of the initial complex phase can be avoided.

(Effects of individual amplifier differences (calibration))
In an actual wireless communication apparatus, in signal processing on the transmission side, signal amplification is often performed by a high power amplifier immediately before transmission. In this case, there is an error in the amplification factor due to the individual difference of the high power amplifier, and the complex phase may rotate at a different value for each high power amplifier in the high power amplifier. Similarly, in signal processing on the reception side, signal amplification is often performed by a low noise amplifier immediately after reception. In this case, there is an error in the amplification factor due to individual differences among the low noise amplifiers, and the complex phase may rotate with a different value for each low noise amplifier in the low noise amplifier.

  In particular, the amplification factor and phase rotation amount of the high power amplifier and the low noise amplifier have frequency dependency. If the individual difference in the amplification factor with frequency dependency and the amount of rotation of the complex phase is so large that it cannot be ignored, it is necessary to perform calibration processing when estimating the downlink channel information from the uplink channel information. is there. Since the error of the amplification factor and the amount of phase rotation is almost stable in time, measure the error of the amplification factor and the amount of phase rotation in advance, and use a coefficient to cancel the influence of the error. Converts link channel information to downlink channel information.

  In the base station apparatus in the following embodiment, the transmission weight and the reception weight are calculated using channel information obtained by performing long-time averaging on the uplink channel estimation result. Also in the above description, the amplitude and the complex phase may actually be changed by a high power amplifier or a low noise amplifier (strictly speaking, a transmission system and a reception system circuit including other circuits such as a filter). In this case, it has been described that a calibration coefficient for correcting in accordance with a change in amplitude or complex phase is acquired in advance and used for correction. Although a known technique may be used for the calibration process, an example of the calibration process will be described below.

FIG. 17 is a diagram illustrating asymmetry of channel information between the uplink and the downlink. In the figure, reference numerals 25-1 to 25-3 denote wireless modules, reference numerals 21-1 to 21-3 denote high power amplifiers (HPA), and reference numerals 22-1 to 22-3 denote low noise amplifiers (LNA). Reference numerals 23-1 to 23-3 denote time division switches (TDD-SW), and reference numerals 24-1 to 24-3 denote antenna elements.
Here, since only functions that affect channel information are extracted in the base station apparatus, configurations other than those illustrated are omitted, but the wireless modules 25-1 to 25-3 include other functions. Further, when the signal passes through each of the high power amplifiers 21-1 to 21-3, the amplitude and the complex phase are Z _{HPA # 1} (f _k ), Z _{HPA # 2} (f _k ), Z _{HPA # 3} (f _k ). Further, when the signal passes through each of the low noise amplifiers 22-1 to 22-3, the amplitude and the complex phase are Z _{LNA # 1} (f _k ), Z _{LNA # 2} (f _k ), and Z _{LNA # 3} (f _k ). Here, it is assumed that there is frequency dependency as a general condition, and the frequency “(f _k )” is expressed for the k-th frequency component.

Here, for example, channel information when signals are transmitted from the wireless module 25-1 and the wireless module 25-2 to the test wireless module 25-3 will be described. Here, spatial channel information between the antenna element 24-1 of the wireless module 25-1 and the antenna element 24-3 of the wireless module 25-3 is represented by h ₁ (f _k ), and the wireless module 25 Channel information on the space between the antenna element 24-2 of -2 and the antenna element 24-3 of the wireless module 25-3 is represented by h ₂ (f _k ).

At this time, the channel information when the signal is actually transmitted from the wireless module 25-1 to the wireless module 25-3 indicates a change accompanying the passage of the high power amplifier 21-1 at h ₁ (f _k ) in space. A coefficient Z _{HPA # 1} (f _k ) and a coefficient Z _{LNA # 3} (f _k ) indicating a change accompanying the passage through the low noise amplifier 22-3 are observed as multiplied values.
Similarly, the channel information when transmitting a signal from the wireless module 25-2 to the wireless module 25-3 is a coefficient Z indicating a change accompanying passage of the high power amplifier 21-2 at h ₂ (f _k ) in space. _{HPA # 2} (f _k ) and a coefficient Z _{LNA # 3} (f _k ) indicating a change accompanying passage through the low noise amplifier 22-3 are observed as multiplied values.

Therefore, the channel from the wireless module 25-1 to the wireless module 25-3 is represented by Z _{HPA # 1} (f _k ) · h ₁ (f _k ) · Z _{LNA # 3} (f _k ). A channel from the wireless module 25-2 to the wireless module 25-3 is represented by Z _{HPA # 2} (f _k ) · h ₂ (f _k ) · Z _{LNA # 3} (f _k ). Therefore, in addition to the difference between the channel information h ₁ (f _k ) and h ₂ (f _k ), the wireless module 25-1 and the wireless module 25-2 have relatively Z _{HPA # 2} (f _k ) / Z _{HPA # 1} (f _k ) difference occurs.

This situation is the same on the receiving side. When the signal transmitted from the wireless module 25-3 is received by the wireless module 25-1, the channel information is stored in the high power amplifier 21 in h ₁ (f _k ) in space. Observed as a value obtained by multiplying the coefficient Z _{HPA # 3} (f _k ) indicating the change accompanying the passage of −3 and the coefficient Z _{LNA # 1} (f _k ) indicating the change accompanying the passing of the low noise amplifier 22-1 Is done.
Similarly, when the signal transmitted from the wireless module 25-3 is received by the wireless module 25-2, the channel information changes in space h ₂ (f _k ) due to the passage of the high power amplifier 21-3. It is observed as a value obtained by multiplying the indicated coefficient Z _{HPA # 3} (f _k ) by the coefficient Z _{LNA # 2} (f _k ) indicating the change accompanying the passage of the low noise amplifier 22-2.

Therefore, the channel from the wireless module 25-3 to the wireless module 25-1 is represented by Z _{HPA # 3} (f _k ) · h ₁ (f _k ) · Z _{LNA # 1} (f _k ). A channel from the wireless module 25-3 to the wireless module 25-2 is represented by Z _{HPA # 3} (f _k ) · h ₂ (f _k ) · Z _{LNA # 2} (f _k ). Therefore, in addition to the difference between the channel information h ₁ (f _k ) and h ₂ (f _k ), the wireless module 25-1 and the wireless module 25-2 have relatively Z _{LNA # 2} (f _k ) / Z _{LNA # 1} (f _k ) difference occurs.

As described above, the base station apparatus according to the embodiment includes a channel including changes caused by the low noise amplifiers 22-1 to 22-3 connected to each antenna element by taking a long-time average with respect to the received training signal. Information can be acquired on the uplink.
However, the base station apparatus cannot directly obtain channel information in the downlink. Therefore, downlink channel information is obtained by conversion from uplink channel information. For this conversion, the influence of individual differences between the low-noise amplifiers 22-1 to 22-3 and the high-power amplifiers 21-1 to 21-3 connected to the antenna elements 24-1 to 24-3 is canceled. There is a need.

  Therefore, in the manufacturing stage of the base station apparatus, a test radio module 25-3 serving as a reference is prepared. And channel information including changes by the high power amplifiers 21-1 to 21-3 and the low noise amplifiers 22-1 to 22-3 are measured in an environment where the channel information on the propagation path is a common value. Then, correction is performed using the measured channel information.

FIG. 18 is a diagram showing an outline of calibration. In the figure, reference numerals 26-1 to 26-3 indicate antenna terminals, and reference numeral 27 indicates a coaxial cable. In addition, the same code | symbol is attached | subjected to the function part same as the function part shown in FIG.
FIG. 18A shows a configuration in which the wireless module 25-3 and the wireless module 25-1 are connected by a coaxial cable. FIG. 18B shows a configuration in which the wireless module 25-3 and the wireless module 25-2 are connected by a coaxial cable. FIG. 17 shows a state in which a signal propagates in an actual space, whereas FIG. 18 shows a state in which a signal propagates on a coaxial cable without passing through an antenna element.

The channel information of the coaxial cable 27 serving as a propagation path connecting the wireless modules 25-1 and 25-2 and the wireless module 25-3 is h ₀ (f _k ).
At this time, the channel information from the wireless module 25-1 to the wireless module 25-3 is expressed by Z _{HPA # 1} (f _k ) · h ₀ (f _k ) · Z _{LNA # 3} (f _k ). The channel information from the wireless module 25-2 to the wireless module 25-3 is expressed by Z _{HPA # 2} (f _k ) · h ₀ (f _k ) · Z _{LNA # 3} (f _k ).
Further, the channel information from the wireless module 25-3 to the wireless module 25-1 is represented by Z _{HPA # 3} (f _k ) · h ₀ (f _k ) · Z _{LNA # 1} (f _k ), and the wireless module 25 -3 to the wireless module 25-2 is represented by Z _{HPA # 3} (f _k ) · h ₀ (f _k ) · Z _{LNA # 2} (f _k ).

Therefore, after measuring these channel information, calibration coefficients C ₁ (f _k ) and C ₂ (f _k ) represented by the following equations (14) and (15) are calculated.

The channel information from the wireless module 25-3 to the wireless module 25-1 is represented by Z _{HPA # 3} (f _k ) · h ₁ (f _k ) · Z _{LNA # 1} (f _k ), and the wireless module 25- It has been described that the channel information from 3 to the wireless module 25-2 is represented by Z _{HPA # 3} · (f _k ) · h ₂ (f _k ) · Z _{LNA # 2} (f _k ). When these are multiplied by the calibration coefficients C ₁ (f _k ) and C ₂ (f _k ) of the equations (14) and (15), the following equations (16) and (17) are obtained.

The right sides of Expression (16) and Expression (17) are the channel information from the wireless module 25-1 to the wireless module 25-3 and the channel information from the wireless module 25-2 to the wireless module 25-3 described above. It matches.
As described above, the calibration coefficients corresponding to the equations (14) and (15) are acquired at the manufacturing stage of the base station apparatus, and stored in the base station apparatus, thereby calibrating them. The downlink channel information can be calculated from the uplink channel information using the coefficient.

  In the following embodiment, these calibration coefficients are acquired in advance, and the description will be made mainly on the case where the values are used in digital signal processing.Naturally, these calibration coefficients are displayed on an analog circuit. If calibration is performed in the base station apparatus so that all values are almost constant (if the complex phase is constant, the absolute value itself may be different), all calibration coefficients are It can also be read as a process regarded as 1. Similarly, even when the complex phases of the uplink and downlink are adjusted to be constant values, as a result, the complex phases of the calibration coefficients expressed by the equations (14) and (15) are all Since the antenna element has a substantially constant value, the same effect can be obtained.

  As described above, it is possible to acquire uplink and downlink channel information between the antenna element of the base station device and the antenna element of each terminal device by extracting a line-of-sight wave and a stable reflected wave. become. By using this channel information, it is possible to obtain a transmission weight and a reception weight used fixedly in communication. This transmission weight is set so that the plurality of signals transmitted from the plurality of antenna elements of the base station apparatus to the antenna element of the terminal apparatus are in-phase combined in the antenna element of the terminal apparatus. The reception weight is set so that a signal transmitted from the antenna element of the terminal apparatus can be combined in phase with a plurality of signals received by the plurality of antenna elements of the base station apparatus. That is, the transmission weight and the reception weight can be set independently for each terminal device without depending on the combination of terminal devices that perform spatial multiplexing simultaneously. Details of the apparatus configuration and processing flow will be described below for the technology related to the present invention performed using these transmission weights and reception weights.

[Configuration example of related technology as a base of the present invention]
In the configuration example of the related technology that forms the basis of the present invention, a radio communication system including a base station apparatus including a plurality of antenna elements and a plurality of terminal apparatuses that communicate with the base station apparatus will be described as an example. First, before describing a specific embodiment of the present invention, a configuration example of related technology which is a base of the embodiment will be described first.

(Configuration example of base station apparatus in the technology related to the present invention)
FIG. 19 is a schematic block diagram showing the configuration of the base station apparatus 10 in the configuration example of the technology related to the present invention. As shown in the figure, the base station apparatus 10 includes a reception unit 100, a transmission unit 140, a transmission / reception weight calculation unit 120, an interface circuit 170, a MAC layer processing circuit 180, a communication control circuit 110, and a storage circuit 115. The MAC layer processing circuit 180 has a scheduling processing circuit 181.
The base station apparatus 10 inputs and outputs data with an external device or a network via the interface circuit 170. The interface circuit 170 detects data to be transferred on the wireless line among the input data, and outputs the detected data to the MAC layer processing circuit 180. The MAC layer processing circuit 180 performs processing related to the MAC layer in accordance with an instruction from the communication control circuit 110 that performs management control of the operation of the entire base station apparatus 10. Here, the processing related to the MAC layer includes conversion of data input / output by the interface circuit 170 and data transmitted / received on the wireless line, addition of MAC layer header information, and the like. In this process, the scheduling processing circuit 181 performs various scheduling processes including a combination of terminal apparatuses that simultaneously perform spatial multiplexing. The scheduling processing circuit 181 outputs the scheduling result to the communication control circuit 110.

In the spatial multiplexing transmission, a signal is transmitted to a plurality of terminal devices at a time at the time of transmission, so that a plurality of signal sequences are output from the MAC layer processing circuit 180 to the transmission unit 140. In addition, a plurality of signal sequences transmitted from a plurality of terminal devices are output from the receiving unit 100 to the MAC layer processing circuit 180 during reception. The transmission / reception weight calculation unit 120 manages reception weights and transmission weights used when the reception unit 100 and the transmission unit 140 spatially multiplex and transmit / receive data.
The storage circuit 115 stores in advance various information (for example, SNR information, information on the degree of time variation, information on the optimum transmission mode, etc.) of each terminal device in the wireless communication system. Information such as the SNR information and optimum transmission mode of the terminal device stored in the storage circuit 115 is used when scheduling is performed. Note that the memory circuit 115 is not necessarily required in both the embodiment of the present invention and related technology, and may be omitted in some cases.
Hereinafter, the configuration (reception unit 100) related to reception (uplink) in the base station apparatus 10 and the configuration (transmission unit 140) related to transmission (downlink) will be described separately.

  FIG. 20 is a schematic block diagram illustrating an example of the configuration of the receiving unit 100 included in the base station device 10 in the configuration example of the technology related to the present invention. As shown in the figure, the receiving unit 100 includes antenna elements 101-1 to 101-K, TDD switches 102-1 to 102-K, low noise amplifiers (LNA) 103-1 to 103-K, a local oscillator 104, a mixer. 105-1 to 105-K, filters 106-1 to 106-K, A / D converters 107-1 to 107-K, FFT circuits 108-1 to 108-K, and received signal processing circuits 109-1 to 109 -L is provided. Reception signal processing circuits 109-1 to 109-L and TDD switches 102-1 to 102-K are connected to communication control circuit 110 shown in FIG. The FFT circuits 108-1 to 108-K and the reception signal processing circuits 109-1 to 109-L are connected to the transmission / reception weight calculation unit 120 shown in FIG. The antenna elements 101-1 to 101-K correspond to the antenna elements 13-1 to 13-4 in FIG. In this configuration example, the description will be made on the assumption that the TDD system is used. However, as shown in the embodiments described later, the present invention can be extended to the FDD system in principle.

  The base station apparatus 10 of this configuration example includes A / D converters 107-1 to 107-K from TDD switches 102-1 to 102-K corresponding to the K antenna elements 101-1 to 101-K, respectively. Are provided in parallel, and the FFT circuits 108-1 to 108-K are connected to the outputs of the A / D converters 107-1 to 107-K. In order to estimate downlink channel information from uplink channel information, the same antenna elements 101-1 to 101-K are used for transmission and reception. The TDD switches 102-1 to 102-K switch the flow of transmission signals and reception signals.

  The TDD switches 102-1 to 102-K output the signals received via the antenna elements 101-1 to 102-K to the low noise amplifiers 103-1 to 103-K. The low noise amplifiers 103-1 to 103-K amplify the signals output from the TDD switches 102-1 to 102-K and output the amplified signals to the mixers 105-1 to 105-K. The local oscillator 104 generates a local oscillation signal having a predetermined frequency, and outputs the generated local oscillation signal to each of the mixers 105-1 to 105-K. Here, the local oscillation signals input to the mixers 105-1 to 105-K are the same signal, and the local oscillation signals having the same frequency and phase are input to the mixers 105-1 to 105-K.

  The mixers 105-1 to 105-K multiply the signals input from the low noise amplifiers 103-1 to 103-K by the local oscillation signal input from the local oscillator 104, down-convert them, and perform filters 106-1. 106-K. Filters 106-1 to 106-K remove signals outside the band of the channel to be received, included in the signals down-converted by mixers 105-1 to 105-K, and A / D converters 107-1 to 107-. Output to K.

  The A / D converters 107-1 to 107-K digitize the baseband signals input from the filters 106-1 to 106-K. If the digital baseband signal input from the A / D converters 107-1 to 107-K is a signal including a normal data communication signal, the FFT circuits 108-1 to 108-K correspond to the digital baseband. The signal is separated into signals for each frequency component. At this time, the FFT circuits 108-1 to 108-K remove the guard interval for each OFDM signal (or block transmission block) for each frequency component signal, and perform FFT processing on the remaining sampling data. The signal on the time axis is converted into a signal on the frequency axis, and the signal is output to the reception signal processing circuits 109-1 to 109-L. Furthermore, if the input digital baseband signal is a training signal for channel estimation different from a normal data communication signal in accordance with the control of the communication control circuit 110, the FFT circuits 108-1 to 108-K The signal is output to transmission / reception weight calculation section 120. The communication control circuit 110 determines whether the digital baseband signal input to the FFT circuits 108-1 to 108-K is a signal including a data communication signal or a different training signal.

  Here, the “training signal for channel estimation different from the normal data communication signal” refers to the training signals 3-1 to 3-1 shown in FIG. 16 that are used in the channel information estimation process used in the transmission / reception weight calculation in this configuration example. The 3-3 signal is completely different from a radio packet containing user data or various control information in radio communication. In this related technology, except for some configuration examples, it is necessary to perform signal processing (such as short-time averaging processing of channel information shown in FIG. 23 below) different from normal data communication. As described above, since it differs from a conventional OFDM signal or the like, the contents of signal processing are also slightly different. For this reason, in the FFT circuits 108-1 to 108-K, a series of processing associated with FFT is not performed on the training signal for channel estimation different from the normal data communication signal, and the digital baseband signal remains as it is. It is assumed that a function that outputs to the transmission / reception weight calculation unit 120 and performs processing including FFT in the transmission / reception weight calculation unit 120 is implemented. However, although details will be described later, in order to realize the functions described herein, it is of course possible to substitute other functional blocks by performing equivalent processing, and this is also a method for realizing the related technology. Is considered part of

  Reception signal processing circuits 109-1 to 109-L are each associated with a terminal device that transmits data using spatial multiplexing or a spatially multiplexed signal sequence, and detects data of the corresponding terminal device from the received signal. A signal detection process is performed. Specifically, the received signal processing circuits 109-1 to 109-L output the received weights corresponding to the transmission source terminal devices assigned to the respective frequency components to the transmission / reception weight calculation unit 120. Is multiplied by the reception weight for each frequency component. The reception signal processing circuits 109-1 to 109-L add and synthesize the signals multiplied by the reception weights for each of the antenna elements 101-1 to 101-K for each frequency component, and signal the added and synthesized signals. The detection process is performed, and the obtained data outputs # 1 to #L are output to the MAC layer processing circuit 180.

  Specifically, when the OFDM (A) modulation method is used, reception signal processing circuits 109-1 to 109-L perform demodulation processing for each subcarrier on the added and synthesized signal, and SC- When FDE is used, signal equalization processing on the frequency axis is performed on the frequency component signals added and synthesized, and demodulation processing is performed on the signal synthesized by IFFT processing. The demodulation processing here includes channel estimation for the signal after signal processing such as addition synthesis, and signal detection processing is performed based on the channel information estimated here. Furthermore, it performs decoding processing for error correction as necessary, and outputs data. The signal processing on the MAC layer in the MAC layer processing circuit 180 is the same as the processing using a known technique, and the description is omitted here.

  When the reception signal processing circuits 109-1 to 109-L perform signal processing, it is necessary to use different reception weights for each terminal device as a transmission source. The communication control circuit 110 manages overall control related to a series of communications. In particular, the communication control circuit 110 manages which terminal device receives a signal at which timing and which reception weight is used. Therefore, access control between the base station apparatus 10 and the terminal apparatus in this configuration example is managed by centralized control of the base station apparatus 10.

As a supplement, the communication control circuit 110 uses absolute time / timing synchronization using GPS or the like for timing synchronization between its own device (base station device 10) and the terminal device. May be.
In addition to absolute time synchronization, if a rough distance between the base station apparatus 10 and the terminal apparatus is known, a propagation delay corresponding to the distance is set in the terminal apparatus in advance. The terminal device may start transmission of the uplink signal at a time obtained by subtracting the propagation delay as a predetermined offset from the reception time of the signal serving as a timing reference of the base station device 10.

  Specifically, if an example of access control using time division multiple access (Time Division Multiple Access (TDMA)) is used, the terminal device is based on the frame timing obtained by timing detection such as a preamble at the beginning of the TDMA frame, The contents of slot assignment in the frame are grasped and communication operation is performed. Normally, a signal is transmitted at the timing of the uplink time slot. However, in the so-called time alignment control, the terminal is ahead of the timing that the terminal recognizes by considering the propagation delay. The transmission of the signal is started at the timing of the time, and as a result, the time at which the signal arrives at the base station apparatus 10 is adjusted so as to match the timing recognized by the base station.

The amount of adjustment required at this time is that the actual signal is reciprocated from the base station device 10 to the terminal device and then to the base station device 10, so the terminal device transmits it ahead of time by twice the propagation delay. Will start. Note that this timing adjustment does not necessarily have to be performed by the terminal device. If the base station device 10 can grasp the distance between the own device and the terminal device or the propagation delay corresponding to the distance, the base station device 10 It is also possible to adjust the timing by adjusting the time at which the signal is received backward by that amount (twice the propagation delay). Alternatively, the base station apparatus may directly instruct the terminal apparatus that the time advanced by that time is the transmission timing.
In this way, the base station apparatus 10 can start reception processing at a timing grasped by any means such as absolute time synchronization or time alignment control using GPS, and can perform processing with a known symbol timing. It is. The communication control circuit 110 controls and manages all of these timing control, access control, switching of the TDD switches 102-1 to 102-K, provision of terminal device information that is a transmission source when reading the reception weight, and the like. I do.

Next, the configuration of the transmission / reception weight calculation unit 120 will be described.
FIG. 21 is a schematic block diagram illustrating a configuration example of the transmission / reception weight calculation unit 120 in the configuration example of the technology related to the present invention. As shown in the figure, the transmission / reception weight calculation unit 120 includes a channel information short-time average circuit 121, a relative component acquisition circuit 122, a channel information long-time average circuit 123, a reception weight calculation circuit 124, a reception weight storage circuit 125, and calibration. A circuit 126, a transmission weight calculation circuit 127, a transmission weight storage circuit 128, and a calibration coefficient storage circuit 129 are included. Note that channel information, transmission / reception weights, calibration coefficients, and the like in the following description are all different for each frequency component, and are individually calculated, processed, recorded, and managed for each frequency component.

  The channel information short-time averaging circuit 121 performs a short-time averaging process of the training signal on the signals input from the FFT circuits 108-1 to 108-K according to instructions from the communication control circuit 110 (frequency error compensation is performed if necessary). And further separating the signal on the time axis for each frequency component by FFT processing), and for each terminal device, information on the uplink channel between the terminal device and each of the antenna elements 101-1 to 101-K is obtained. Acquired for each frequency component. The relative component acquisition circuit 122 acquires, for example, the relative component of each antenna element 101-1 to 101-K with respect to the antenna element 101-1, using the complex phase of the antenna element 101-1 as a reference. The channel information long-time average circuit 123 determines, for each terminal device, the antenna elements from the relative components for each of the plurality of antenna elements 101-1 to 101-K acquired at discrete times acquired by the relative component acquisition circuit 122. A long-time averaging process for calculating an average value of relative components for each of 101-1 to 101-K is performed, and the calculated average value is output as channel information.

  The reception weight calculation circuit 124 calculates a reception weight corresponding to each combination of the antenna element and the frequency component for each terminal device based on the channel information output from the channel information long-time average circuit 123, and receives the calculated reception weight. The data is output to the weight storage circuit 125. The reception weight storage circuit 125 stores the reception weight output from the reception weight calculation circuit 124 in association with the combination of the terminal device, the antenna element, and the frequency.

The calibration circuit 126 obtains downlink channel information by multiplying the channel information output from the channel information long-time average circuit 123 by a predetermined calibration coefficient. Based on the downlink channel information acquired by the calibration circuit 126, the transmission weight calculation circuit 127 calculates a transmission weight corresponding to each combination of antenna element and frequency component for each terminal device, and transmits the calculated transmission weight. The data is output to the weight storage circuit 128. The transmission weight storage circuit 128 stores the transmission weight output from the transmission weight calculation circuit 127 in association with the combination of the terminal device, the antenna element, and the frequency.
The calibration coefficient storage circuit 129 stores, for each antenna element 101-1 to 101 -K, each frequency used for calculating downlink channel information from the uplink channel information and the calibration coefficient for each antenna element. Pre-stored. Note that the transmission weight storage circuit 128 is also a part of the configuration related to the uplink included in the base station apparatus 10.

Note that a series of processes related to channel information estimation performed by the transmission / reception weight calculation unit 120 and a subsequent series of processes such as calculation and storage of transmission / reception weights are all performed for each frequency component. That is, after estimating the frequency error using Equation (11) or Equation (13), the sampling data for each m to S _m after short-time averaging given by Equation (10) corrected for the frequency error On the other hand, after FFT processing is performed and channel information averaged for a short period of time is acquired by separating the frequency components, a series of processing is performed on each frequency component based on the acquired channel information.

  FIG. 22 is a diagram illustrating an example of the configuration of the transmission unit 140 in the base station apparatus 10 in the configuration example of the background art of the present invention. As shown in the figure, the transmission unit 140 includes transmission signal processing circuits 141-1 to 141-L, addition synthesis circuits 142-1 to 142-K, IFFT & GI adding circuits 143-1 to 143-K, and D / A conversion. 144-1 to 144-K, a local oscillator 145, mixers 146-1 to 146-K, filters 147-1 to 147-K, and high power amplifiers (HPA) 148-1 to 148-K. . Transmission signal processing circuits 141-1 to 141-L and TDD switches 102-1 to 102-K are connected to communication control circuit 110 shown in FIG. The transmission signal processing circuits 141-1 to 141-L are connected to the transmission / reception weight calculation unit 120 shown in FIG. Here, the antenna elements 101-1 to 101-K and the TDD switches 102-1 to 102-K are used in common with the configuration related to the uplink (reception side). Actually, in the base station apparatus 10, the configuration related to the uplink and the configuration related to the downlink operate integrally, but for the convenience of description, they are described separately.

  Each of the transmission signal processing circuits 141-1 to 141-L is associated with a destination terminal device that transmits data using spatial multiplexing, and performs signal processing on data to be transmitted to the associated terminal device. Do. Specifically, the transmission signal processing circuits 141-1 to 141-L receive the OFDM (A) modulation scheme or SC-FDE when the data inputs # 1 to #L to be transmitted are input from the MAC layer processing circuit 180. The predetermined transmission process in is performed. Data inputs # 1 to #L are data corresponding to each destination terminal device or spatially multiplexed signal sequence, and are input to transmission signal processing circuits 141-1 to 141-L associated with the destination terminal device. The When the base station apparatus 10 uses the OFDM (A) modulation scheme, the transmission signal processing circuits 141-1 to 141-L perform signal modulation processing for each subcarrier after error correction coding. The transmission signal processing circuits 141-1 to 141-L correspond to the antenna elements 101-1 to 101-K corresponding to the destination terminal devices assigned to the transmission weights stored in the transmission weight storage circuit 128, respectively. Each transmission weight is read from the transmission weight storage circuit 128, and the signal for each subcarrier subjected to the modulation process is multiplied by the read transmission weight for each subcarrier.

Further, when SC-FDE is used in the base station apparatus 10, the transmission signal processing circuits 141-1 to 141-L transmit a signal subjected to single carrier modulation processing after error correction coding to a block of the transmission signal. Each frequency component is separated by FFT in units. The transmission signal processing circuits 141-1 to 141-L read out the transmission weight corresponding to the destination terminal device from among the transmission weights stored in the transmission weight storage circuit 128, and read out the signals separated into frequency components. The transmitted weight is multiplied for each frequency component.
Thereafter, the transmission signal processing circuits 141-1 to 141-L add the signal of each frequency component for each antenna element multiplied by the transmission weight, regardless of which of the OFDM (A) modulation scheme and SC-FDE is used. The data is output to the synthesis circuits 142-1 to 142-K. Addition synthesis circuits 142-1 to 142-K synthesize the signals generated by transmission signal processing circuits 141-1 to 141-L for each frequency component, and output them to IFFT & GI adding circuits 143-1 to 143-K. IFFT & GI adding circuits 143-1 to 143-K perform IFFT processing on the signals synthesized in the adder / synthesizing circuits 142-1 to 142-K, convert the signals from the frequency axis to the signals on the time axis, and further guard intervals , And waveform shaping as necessary to generate a digital baseband signal to be transmitted and output it to the D / A converters 144-1 to 144-K. The digital baseband signal corresponds to each of the antenna elements 101-1 to 101 -K and is individually signal processed.

The D / A converters 144-1 to 144-K convert the signals input from the IFFT & GI adding circuits 143-1 to 143-K into analog signals and output the analog signals to the mixers 146-1 to 146-K.
The local oscillator 145 outputs a local oscillation signal used for up-conversion and having a predetermined frequency to the mixers 146-1 to 146-K.
The mixers 146-1 to 146-K multiply the analog signals input from the D / A converters 144-1 to 144-K by the local oscillation signals input from the local oscillator 145 and up-convert them to radio frequencies. The signal is output to the filters 147-1 to 147-K. The local oscillation signals input to the mixers 146-1 to 146-K are the same signal, and local oscillation signals having the same frequency and phase are input to the mixers 146-1 to 146-K.

Filters 147-1 to 147 -K remove signals outside the band of the channel to be transmitted included in the signals input from mixers 146-1 to 146 -K and provide high-power amplifiers 148-1 to 148 -K. Output.
The high power amplifiers 148-1 to 148-K amplify the signals input from the filters 147-1 to 147-K, and the antenna elements 101-1 to 101-K via the TDD switches 102-1 to 102-K. Send more.
The communication control circuit 110 further controls transmission timing, destination terminal device management, and switching of the TDD switches 102-1 to 102-K.

  In the above description, the case where the signal processing performed in the IFFT & GI adding circuits 143-1 to 143-K is processed in the subsequent stage of the adding / combining circuits 142-1 to 142-K has been described. However, the IFFT & GI adding circuit 143 has been described. The signal processing performed in -1 to 143-K is performed in the transmission signal processing circuits 141-1 to 141-L to obtain digital sampling data on the time axis, and the sampling data at each sampling time is added and synthesized Even if it replaces with the process of carrying out addition synthesis over all the destination terminal stations in 142-1 to 142-K, equivalent signal processing is possible, and either configuration may be selected. However, in this case, the number of times IFFT is performed is larger than that described above, and therefore the configuration of FIG. 22 is considered preferable from the viewpoint of overall circuit scale suppression.

(Calculation processing of transmission / reception weight from channel estimation)
Hereinafter, processing from channel estimation to calculation of transmission weights and reception weights in the base station apparatus 10 of this configuration example will be described with reference to FIGS. These series of processes are basically performed before starting communication with the terminal device, but once these processes are performed, the accuracy of channel information is improved while performing sequential learning, that is, transmission weight and It is also possible to improve the accuracy of the reception weight.
In addition, the base station apparatus 10 is intended for use in a broadband service and is intended for communication with a certain bandwidth. For this reason, assuming that an OFDM (A) modulation method or a communication method such as SC-FDE is used, an explanation is given of performing signal processing by separating each frequency component in units of blocks.

In uplink channel estimation, for example, a training signal as shown in FIG. 16 is continuously transmitted from the terminal device, and the base station device 10 receives the training signal and performs an averaging process in a relatively short time (see FIG. 16). 23). Further, the base station apparatus 10 acquires a relative component indicating a difference in relative channel information of each of the antenna elements 101-1 to 101-K (FIG. 24), and performs an averaging process for a long time (FIG. 25). Three-stage signal processing is performed.
The uplink channel information thus obtained is multiplied by a calibration coefficient to obtain downlink channel information (FIG. 26), and transmission weights and reception weights are obtained based on the uplink and downlink channel information. Is calculated (FIG. 27).
Hereinafter, each processing will be described.

FIG. 23 is a flowchart showing short-time averaging processing for acquiring uplink channel information in the configuration example of the background art of the present invention.
In the base station device 10, the channel information short-time averaging circuit 121 starts receiving a training signal for channel estimation for short-time averaging from the terminal device (step S 101), and sets m and M as sampling counters. Reset to zero (step S102). Here, the counter means m and M in Equation (10), and means the m-th sample of the M-th symbol. The channel information short-time averaging circuit 121 samples the training signals input from the FFT circuits 108-1 to 108-K, and sets the sampled signal as S _m ^(M) (step S103).

The channel information short-time averaging circuit 121 adds “1” to the counter m every time the sampling period Δt elapses (step S104), and checks whether the counter m matches the number of data N (m = N). When the determination is made (step S105) and the counter m does not match the number of data N (m ≠ N) (step S105: NO), the process returns to step S103, and steps S103 to S105 are repeated. Here, the data number N is the number of samples per symbol, and is a predetermined value.
On the other hand, when the counter m coincides with the number of data N (step S105: YES), the channel information short-time averaging circuit 121 considers that sampling for one symbol has been completed, and in order to sample the next symbol, the counter m 0 is substituted into “1”, and “1” is added to the counter M (step S106).

The channel information short-time averaging circuit 121 determines whether or not the sampling is finished depending on whether or not the counter M has reached a predetermined value (M _{0 in} Expression (10)) (step S107), and a series of samplings Is not completed (step S107: NO), the process returns to step S103, and the processes of steps S103 to S106 are repeated. Here, the sampling of a series is that the predetermined sampling number of symbols M _0.
On the other hand, when a series of sampling is completed (step S107: YES), the channel information short-time averaging circuit 121 calculates ^ S (M, M ′) using equation (12) (step S108). A frequency error Δf that maximizes the solution of (13) or equation (11) is calculated (step S109).

The channel information short-time averaging circuit 121 uses the calculated frequency error Δf to calculate sampling data to S _m that are added and averaged over a plurality of periods from Equation (10) (step S110).
Channel information short-time average circuit 121, a short time performs an FFT on averaged sampled data to S _m, calculates information of each frequency component (step S111), and terminates the processing in the short-term average (step S112).
When it is known in advance that the frequency error Δf is negligibly small (in the case of such a setting in the design), or the time for performing short-time averaging (T × M ₀ ) is If it is set sufficiently short, steps S108 and S109 corresponding to the correction of the frequency error Δf can be omitted, and step S110 can be directly executed with Δf = 0.
The channel information short-time averaging circuit 121 separates training signals over a plurality of periods for each of the antenna elements 101-1 to 101 -K and synthesizes the separated training signals for a short-time averaging process. I do. Furthermore, each frequency component signal having a different period included in the signal received by each antenna element 101-1 to 101 -K is separated for each frequency component by FFT, and each antenna element is separated from the separated signal for each frequency component. Channel information of each frequency component in the uplink between 101-1 to 101-K and the terminal device is acquired.

FIG. 24 is a flowchart showing a relative component acquisition process for acquiring a relative component of uplink channel information in the configuration example of the technology related to the present invention. The relative component acquisition circuit 122 completes the short-time averaging process for the signals corresponding to the first antenna element 101-1 to the K-th antenna element 101 -K by the channel information short-time average circuit 121 (step S 1). S121-1 to S121-K), k-th frequency components ^ h ₁ ^(k) , ..., ^ h _K ⁽ in channel information corresponding to the antenna elements 101-1 to 101-K for which the short-time averaging processing has been completed. ^k) is input from the channel information short-time averaging circuit 121 (steps S122-1 to 122-K).

The relative component acquisition circuit 122 ^calculates the offset value e ^{−jφ (k} from the channel information (^ h ₁ ^(k) ) in the first antenna element 101-1 and its complex conjugate (^ h ₁ ^(k) ) ^{*. )} (= (^ H ₁ ^(k) ) ^* / ‖ ^ h ₁ ^(k) ‖) is calculated (step S123). Here, “‖x‖” represents the absolute value of x. This offset value is obtained individually for each frequency component.
The relative component acquisition circuit 122 uses the calculated offset value e ^{−jφ (k)} for the k-th frequency component as the k-th frequency component corresponding to each of the antenna elements 101-1 to 101 -K ^ h ₁ ^(k) ,. multiplying the h _K ^{(k) (step} S124-1~S124-K), the channel information _{to h} ¹ indicating the relative complex phase relationships (k), ..., determine the _~h ^{K (k),} the process ends (Steps S125-1 to S125-K).
As described above, the relative component acquisition circuit 122 uses the channel information of the first antenna element 101-1 as a reference, and the relative channel information of the antenna elements 101-1 to 101-K to h ₁ ^(k) , ..., ~ h _K ^(k) is calculated. The relative component acquisition circuit 122 performs the processing from step S121-1 to step S125-K for all frequency components for each terminal device, and performs a short-time average channel for all frequency components for each terminal device. relative components _{to h} ¹ information (k), ..., and calculates the _~h ^{K (k).}

FIG. 25 is a flowchart showing long-time averaging processing of uplink channel information in the configuration example of the technology related to the present invention. Each of the processes shown in FIGS. 23 and 24 is performed a plurality of times in continuous or discrete time, and long-time averaging is performed in the long-time averaging process based on the short-time average channel information calculated in each process. Calculated channel information is calculated.
When the channel information long-time averaging circuit 123 completes the first to Q-time short-time averaging processing (including relative component acquisition) (steps S131-1 to S131-Q), the short-time average is calculated from the relative component acquisition circuit 122. , H ₁ ^{(k) [q]} ,..., H _K ^{(k) [q]} (q = 1,..., Q) are input (steps S132-1 to S132-Q). . Here, the relative component of short-term average channel information to h ₁ ^{(k) [q]} is the relative component of the channel information with respect to the k-th frequency component of the first antenna element 101-1 calculated for the q-th time. . Therefore, steps S132-1 to S132-Q correspond to processing performed at different timings. Note that the number Q of times subjected to long-time averaging processing is determined in advance based on the environment in which the wireless communication system is operated.
The channel information long-time average circuit 123 calculates long-time average channel information h _i ^(k) (i = 1,..., K) using the following equation (18) (step S133). Since steps S132-1 to S132-Q are completed at different timings, the relative component of this channel information is temporarily stored in the memory until step S133, which is a long-time averaging process, is performed. You may memorize | store and implement step S133 at once. Alternatively, the individual summation processing by Σ in step S133 is performed every time the individual processing in steps S132-1 to S132-Q is completed, and is stored in the memory until the next processing. You may read them each time and may implement step S133.

The channel information long-time averaging circuit 123 calculates long-time average channel information h _i ^{(k) obtained} by averaging the channel information of each frequency component for each antenna element 101-1 to 101 -K. The averaging process ends (step S134). The reception weight calculation described with reference to FIG. 27 described later is performed using the uplink channel information acquired here. However, when these processes are performed, the reception weight is temporarily stored in a memory. You can leave it.
Through the above processing, uplink channel information can be acquired directly. In this configuration example, since the relative component acquisition process (FIG. 24) is performed, the long-time average channel information is obtained without being affected by the phase shift in each short-time average process from the first time to the Q-th time. Can be calculated. Note that the superscript k on the right shoulder of the channel information h _i ^(k) described above represents a number for identifying a frequency component.

  FIG. 26 is a flowchart showing a process of acquiring downlink channel information in the configuration example of the technology related to the present invention. Since it is difficult for the base station apparatus 10 to obtain channel information directly as in the uplink for the downlink from the base station apparatus 10 to the terminal apparatus, the downlink channel is based on the uplink channel information. Estimate information.

In the base station apparatus 10, the calibration circuit 126 receives the uplink channel information h _i ^(k) from the channel information long-time averaging circuit 123 (step S 142), and the calibration circuit 126 performs the first operation on the input channel information h _i ^(k) . The calibration coefficient C _i ^(k) corresponding to the k-th frequency component in the antenna element 101-i of i is read from the calibration coefficient storage circuit 129 (step S143).
The calibration circuit 126 multiplies the input channel information h _i ^(k) by the read calibration coefficient C _i ^(k) (step S144), and uses the multiplication result as downlink channel information to complete the process. (Step S145). Also in this case, the calculation of the transmission weight described with reference to FIG. 27 described later is performed using the downlink channel information acquired here, but is temporarily stored in the memory when performing these processes. It does not matter.
The calibration circuit 126 performs the processing from step S142 to step S144 described above for each frequency component for each of the antenna elements 101-1 to 101-K.

  FIG. 27 is a flowchart showing processing for calculating a transmission weight and a reception weight in the base station apparatus 10 according to the configuration example of the present invention. Since the processing for calculating the reception weight for the channel information in the uplink and the processing for calculating the transmission weight for the channel information in the downlink are the same, the processing for calculating the transmission weight in the downlink will be described here. A specific description of the process of calculating the reception weight will be omitted.

When the transmission weight calculation circuit 127 starts the processing (step S451), the channel information h _i ^(k) in the downlink of the k-th frequency component related to the terminal device of interest in the i-th antenna element 101-i is the calibration circuit. 126 (step S452).
The transmission weight calculation circuit 127 calculates a complex conjugate (h _i ^(k) ) ^* of the channel information h _i ^(k) input from the calibration circuit 126 and calculates the calculated complex conjugate (h _i ^(k) ) ^* . The value divided by the absolute value of the channel information h _i ^(k) is set as the transmission weight w _i ^(k) (step S453). That is, the transmission weight calculation circuit 127 calculates the transmission weight w _i ^(k) using the following equation (19) (step S453).

The transmission weight calculation circuit 127 stores the calculated transmission weight w _i ^(k) in the transmission weight storage circuit 128 (step S454), and ends the process (step S455).
The transmission weight calculation circuit 127 performs the processing from step S452 to step S453 described above for all the terminal devices for each frequency component for each of the antenna elements 101-1 to 101 -K.
The reception weight calculation circuit 124 calculates the reception weight from the channel information h _i ^(k) input from the channel information long-time average circuit 123 by the same operation as the transmission weight calculation circuit 127, and calculates the calculated reception weight. The data is stored in the reception weight storage circuit 125.
In general, as a weight for signal synthesis when signals are received by a plurality of antennas, there may be a large difference in the signal reception level for each antenna due to the influence of fading or the like. In this case, the reception level is low. In order to suppress the influence of noise of the received signal of the antenna element, the maximum ratio combining weight shown below is often used. Therefore, in the present configuration example, the following equation (20) can be used instead of the equation (19).

  The difference between the two weights of Expression (19) and Expression (20) is the difference in whether the magnitude (absolute value) of the coefficient of the i-th antenna element is slightly different or the same for each antenna element. (20) incorporates an effect of reducing the weight of a signal having a relatively high noise level (that is, a low reception level). However, both are common in that both are adjusted so that the complex phase becomes zero or a constant value after multiplication with channel information averaged for a long time. In a broad sense, equation (20) is also a kind of weight for in-phase synthesis. In this configuration example, the same effect can be obtained even if other weights are used as long as the complex phase is zero or a constant value after multiplication with the channel information averaged for a long time.

In general, it is preferable to use the weight of Expression (19) as the transmission weight and the weight of Expression (20) as the reception weight. In this configuration example, it is recommended that the system be installed so that a line of sight can be secured between the base station apparatus and the terminal apparatus. Since this is a dominant environment, the difference in reception level for each antenna element is relatively difficult. As a result, the weight obtained by Expression (20) is effectively a weight equivalent to Expression (19).
In the transmission / reception weight, the direction indicated by a vector (weight vector) having the weight value for each antenna element as a component of each element has an effective meaning. For this reason, a vector obtained by multiplying a certain weight vector by a predetermined coefficient is the same in direction, so that a weight vector multiplied by a constant coefficient for each antenna element is all equivalent without depending on the coefficient to be multiplied. is there. That is, all the weights obtained by multiplying the entire components of the vectors given by the equations (19) and (20) by the common coefficient are equivalent to the weights in the technology related to the present invention.
The above description regarding FIG. 27 was related to the calculation of the transmission weight, but the circuit corresponding to the reception weight (for example, the channel information long-time averaging circuit 123 for the calibration circuit 126 and the transmission weight calculation circuit 127). Thus, the reception weight calculation circuit 124 and the transmission weight storage circuit 128 can be replaced with the reception weight storage circuit 125), and the reception weight calculation processing can be performed by performing the same processing.

  The above-described processing shown in FIGS. 23 to 27 is performed in advance, and the transmission weight and the reception weight obtained there are stored in the transmission weight storage circuit 128 and the reception weight storage circuit 125, respectively. Note that the processing shown in FIGS. 23 and 27 can be executed after temporarily suspending communication at an appropriate cycle even after the start of communication. The processing shown in FIGS. 25 to 27 may be performed using the short-time average channel information obtained there, and the transmission weight and the reception weight may be updated sequentially.

(Transmission process)
Next, signal transmission processing in the base station apparatus 10 will be described with reference to the drawings.
FIG. 28 is a flowchart showing a transmission process of the base station apparatus 10 in the configuration example of the technology related to the present invention. As mentioned above, here, a case where the OFDM (A) modulation method or SC-FDE is used will be described.
When the base station apparatus 10 starts transmission processing (step S161), the communication control circuit 110 or the scheduling processing circuit 181 selects a terminal apparatus to be subjected to spatial multiplexing using a known technique (step S162). It should be noted that here, a detailed description of a method for selecting a terminal device that performs spatial multiplexing simultaneously, that is, a scheduling method is omitted. The transmission signal processing circuits 141-1 to 141-L generate transmission signals of each frequency component from the input data inputs # 1 to #L (step S163).

  The processing performed by the transmission signal processing circuits 141-1 to 141-L in step S163 is necessary for a bit string constituting a wireless packet subjected to MAC layer signal processing, for example, when the OFDM (A) modulation method is used. Depending on the error, encoding processing for error correction, overhead information (preamble signal) including timing detection signals, channel estimation signals, and the like are applied, and bits are divided for each subcarrier and a predetermined modulation scheme (for example, BPSK) , QPSK, 16QAM, etc.). In addition, when SC-FDE is used, transmission signal processing circuits 141-1 to 141-L are necessary for a bit string constituting a radio packet subjected to MAC layer signal processing in the same manner as the OFDM (A) modulation method. In accordance with the above, an encoding process for error correction, overhead information (preamble signal) including a timing detection signal, a channel estimation signal, and the like are applied, and a predetermined modulation scheme (for example, BPSK, QPSK, 16QAM, etc.) Single-carrier transmission signal processing such as signal point mapping processing is performed, and FFT is performed in units of blocks in order to perform transmission weight multiplication processing on the frequency axis, thereby generating each frequency component of the transmission signal.

The transmission signal processing circuits 141-1 to 141-L correspond to the antenna elements 101-1 to 101-1 corresponding to the terminal device assigned to the own circuit among the transmission weights corresponding to the terminal device selected by the communication control circuit 110. The transmission weight of each frequency component of 101-K is read from the transmission weight storage circuit 128 (step S164).
The transmission signal processing circuits 141-1 to 141-L respectively transmit the transmission signals separated in the frequency components generated in step S163 for each transmission signal transmitted by the antenna elements 101-1 to 101-K, and step S164. Is multiplied by the transmission weight of each frequency component read out in step S165, and the result is output to the adder / synthesizer circuit 142-1 to 142-K (step S165).

Each of the adder / synthesizers 142-1 to 142-K adds and synthesizes the signals input from the transmission signal processing circuits 141-1 to 141-L, and the IFFT & GI adding circuits 143-1 to 143-K. A signal on the frequency axis is converted to a signal on the time axis, and a guard interval is given, and a series of processing such as waveform shaping is performed as necessary (steps S166-1 to S166-K). For each of these signals, D / A conversion of sampling data by the D / A converters 144-1 to 144-K, up-conversion to a radio frequency by the mixers 146-1 to 146-K, and filters 147-1 to 147-1 147-K removes the out-of-band signal, performs amplification by the high power amplifiers 148-1 to 148-K, and transmits from each of the antenna elements 101-1 to 101-K (steps S167-1 to S167-K). The transmission process ends (steps S168-1 to S168-K).
These series of processes (from step S163 to steps S167-1 to S167-K), when a wireless packet spans a plurality of symbols or a plurality of blocks, the processing in units of blocks of OFDM symbols or SC-FDEs is the number of symbols. The transmission signal processing of the entire wireless packet is performed by continuing the execution for the number of blocks.

A characteristic of the transmission processing of the base station apparatus 10 in this configuration example is that the transmission weight corresponding to the terminal apparatus stored in the transmission weight storage circuit 128 is read out and used in step S164, and is slightly subtle. This is to use a fixed transmission weight calculated in advance for each terminal device without being conscious of the channel information that changes. Thereby, it is possible to perform transmission processing without calculating a transmission weight each time transmission is performed.
In addition, the signals transmitted in this manner are received at the antenna elements of the respective terminal apparatuses, with the signals transmitted from the antenna elements 101-1 to 101-K of the base station apparatus 10 being approximately in phase for each frequency component. Will be. The signal received at each terminal device can be processed as a normal signal that can be received without being conscious of various signal processing performed by the base station device 10 in particular.
In addition, in the provision of overhead information (preamble signal) such as a channel estimation signal performed by the transmission signal processing circuits 141-1 to 141-L in step S163, signals having a common pattern are used for a plurality of terminal devices. It is possible. This is because transmission by the transmission weight performed in step S165 allows each terminal device to receive a signal destined for another terminal device in a sufficiently suppressed state. Therefore, it is necessary to assign a separate preamble signal to each terminal device. Because there is no. As a result, it is not necessary to assign a preamble signal having the number of symbols depending on the number of spatial multiplexing while performing high-order spatial multiplexing, and it is possible to suppress a decrease in MAC layer efficiency.

(Reception processing)
FIG. 29 is a flowchart showing a reception process of the base station device 10 in the configuration example of the technology related to the present invention. The signal transmitted by the terminal device is transmitted as a normal signal without being conscious of various signal processing performed by the base station device 10 in this configuration example. Here, although details of a method for selecting a terminal device that performs spatial multiplexing simultaneously, that is, a scheduling method, are omitted, the MAC layer processing circuit 180 selects a terminal device that performs spatial multiplexing and transmits data using a known technique.

  In the base station apparatus 10, when the reception process is started (step S171), the communication control circuit 110 selects a combination of terminal apparatuses that perform spatial multiplexing and transmit data (step S172), and sets scheduling contents related to the uplink. The selected terminal device is notified (step S173). For example, in the case of a system such as WiMAX that employs base station centralized control using a TDMA frame, the notification method here is an UL-MAP (uplink allocation map) at the head of the frame, which is assigned to The carrier number, time slot (OFDM symbol position), and the continuous time (number of OFDM symbols) are notified. Of course, the assignment may be notified to the terminal device by another method, and step S173 of notifying the terminal device may be omitted depending on the access control method.

In accordance with the processing of step S173, among the reception weights corresponding to the transmission source terminal apparatus, the reception weights of the respective frequency components of the respective antenna elements 101-1 to 101-K corresponding to the terminal apparatus allocated to the own circuit. Is read from the reception weight storage circuit 125 (step S176).
In parallel with this, signals are received via the respective antenna elements 101-1 to 101-K from a predetermined timing when the assignment instruction (transmission instruction to the terminal device) is given (steps S174-1 to S174-K). . Here, reception includes processing for performing analog / digital conversion on a received signal or a signal obtained by down-converting the received signal. Thereafter, the FFT circuits 108-1 to 108-K extract signals in symbol units, remove guard intervals, perform FFT processing, and convert signals on the time axis into signals on the frequency axis. The received signal processing is performed (steps S175-1 to S175-K).

  Further, the reception signal processing circuits 109-1 to 109-L multiply the reception weight read from the reception weight storage circuit 125 and the reception signal separated for each frequency component (steps S177-1 to S177-K). The reception signal processing circuits 109-1 to 109-L add and synthesize the multiplication results for each transmission source terminal device (steps S178-1 to S178-L). The processing in steps S177-1 to S177-K and steps S178-1 to S178-L corresponds to the operation of multiplying the reception signal vector by the reception weight matrix as a whole.

Reception signal processing circuits 109-1 to 109-L perform predetermined reception signal processing on each signal series (data output # 1 to #L) thus separated (step S179-1 to S179-1). S179-L), a series of processing ends (steps S180-1 to S180-L).
Here, the predetermined received signal processing is processing after signal separation of a spatially multiplexed signal. Therefore, the signal processing is the same as that of normal SISO communication. The received signal processing includes demodulation processing for each subcarrier when the OFDM (A) modulation method is used, and when SC-FDE is used, the frequency axis for the received signal of each frequency component It includes a single carrier demodulation process for a signal obtained by performing the above signal equalization process and synthesizing the signal by IFFT process. Furthermore, a decoding process for error correction may be performed as necessary. Naturally, signal processing such as a MAC layer is also performed after the above processing, but it is omitted here because it is the same as the processing by a known technique.

  Regarding the symbol timing, when the reception level of the reception signal at each of the antenna elements 101-1 to 101-K is very weak, it may be difficult to detect the timing from the reception signal. In this case, for example, in addition to absolute time synchronization using GPS, a subsequent frame using a periodic frame configuration with reference to the timing obtained from the immediately preceding frame timing detection signal, etc. The reception timing and symbol timing of the received signal may be determined using any synchronization means such as estimating the reception timing of the received signal. At this time, when determining the transmission timing, the terminal device may transmit a signal at a predetermined timing in accordance with an instruction from the base station based on the synchronized reception timing.

(Effects of the technology related to the present invention)
As described above, in the wireless communication system of this configuration example, both the base station apparatus 10 and the terminal apparatus are installed at relatively high places, and as a result, stable from a line-of-sight or a fixed huge building or the like. Channel information corresponding to a stable incident wave component given by combining a line-of-sight wave and a stable reflected wave is acquired in an environment where a reflected wave is expected between the base station apparatus and the terminal apparatus. The base station device 10 generates a transmission weight and a reception weight based on the acquired channel information, and realizes in-phase synthesis of signals in the base station device and the terminal device by using the reception weight. Further, by transmitting signals from the plurality of antenna elements 101-1 to 101 -K using the transmission weight generated by the base station apparatus 10, the terminal apparatus aligns the phases of the signals synthesized on the propagation path with high accuracy. Received as a received signal.

Moreover, in the acquisition of channel information in the base station apparatus 10, the estimation accuracy of channel estimation is improved by performing short-time averaging. Further, by combining a plurality of reception signals at discrete times received via the antenna elements 101-1 to 101-K, random signals in the reception signals received via the antenna elements 101-1 to 101-K can be obtained. The relative ratio of the time variation component to the stable component can be statistically suppressed, and the influence of the time variation can be reduced.
As a result, even in an environment where the line gain by each of the antenna elements 101-1 to 101-K is insufficient such that acquisition of channel information between the terminal device and the antenna elements 101-1 to 101-K is difficult. Thus, it is possible to calculate transmission weights in which the signals transmitted from the antenna elements 101-1 to 101-K are combined in phase in the terminal device.

  Further, in the feedback of channel information related to the calculation of transmission weights and reception weights, it is possible to avoid a decrease in transmission efficiency due to overhead for channel estimation, which is a problem when real-time channel information feedback is frequently performed. . Actually, if the average channel information is acquired for a long time before the service is started, it is possible to operate without performing any channel information feedback during the data communication service. Furthermore, since the calculation load associated with the calculation of the transmission weight and the reception weight, which has been performed sequentially in the past, only needs to be calculated once at the start of operation of the wireless communication system, the load during normal operation can be reduced. It is also possible to plan. The calculation of these transmission weights and reception weights is often required to complete arithmetic processing in a short time in the conventional technology premised on real-time processing. For this reason, hardware processing capable of high-speed arithmetic is assumed. There were many. However, although the conventional technique has a problem that the hardware scale increases due to the enormous amount of computation, the base station apparatus 10 is allowed to perform computation processing over time at the start of operation of the wireless communication system. Therefore, even software processing with a slow calculation processing time can be dealt with, and a secondary effect of reducing the overall hardware scale can be obtained.

Thus, by performing transmission / reception using K antenna elements (wireless modules) using the transmission weight and reception weight described above, the maximum transmission power is ₁₀ Log ₁₀ K [dB] at a maximum under a certain condition. Can be obtained. As a result, it is possible to obtain an energy saving effect that reduces the total transmission power, an economic effect that allows an inexpensive amplifier to be used instead of a high output, high linearity, high gain amplifier, and the like. At the same time, the L signal series can be simultaneously spatially multiplexed on the same frequency, thereby increasing the transmission capacity, that is, improving the frequency utilization efficiency.

Also, the receiving unit 85 of the base station apparatus 80 shown in FIG. 10 sends a preamble signal or the like used for channel estimation from the A / D converters 856-1 to 856-K to the channel information estimation circuit 861 every time a signal is received. The channel information estimation circuit 861 performs channel estimation of the received signal. The result of channel estimation is input to multi-user MIMO reception weight calculation circuit 862, where reception weights are calculated from a predetermined calculation process for the MIMO channel matrix, and are received by reception signal processing circuits 858-1 to 858-L. The received signal is detected based on the output. In the most typical processing example, an inverse matrix or pseudo inverse matrix of a MIMO channel matrix is calculated as a reception weight, but of course, if the destination terminal device combination is different, the channel information (channel vector) of the terminal device to which attention is paid. Even if the same vector is selected, the row vectors corresponding to the corresponding terminal devices constituting the reception weight matrix obtained by the inverse matrix calculation are different when the other channel vectors are different, and the reception weights are different.
On the other hand, every time a base station apparatus 10 in this configuration example receives a signal, it performs channel estimation for the purpose of acquiring information for generating a reception weight for separating a spatially multiplexed signal sequence, and performs estimation. It is not necessary to calculate the reception weight from the result. This point is essentially different from the receiving unit 85 of the base station apparatus 80 shown in FIG. In particular, the base station apparatus 10 uses reception weights calculated in advance based on channel information corresponding to a large number of antenna elements 101-1 to 101-K subjected to long-time averaging.

The reception weight is calculated every time a signal is received in the conventional multi-user MIMO technology, and the level of the interference signal from each of the spatially multiplexed signal sequences (data inputs # 1 to #L) is not negligible. This is because, in order to suppress this, it is necessary to calculate a coefficient for canceling a signal of another terminal device at the time of synthesis as null control. The signal processing for signal suppression is the calculation of the (pseudo) inverse matrix shown above, but the calculation load increases in proportion to the cube of the matrix size, and real-time processing tends to be impossible. .
When the base station apparatus 10 in this configuration example determines the terminal apparatus to receive, the base station apparatus 10 only needs to read out the reception weight corresponding to the terminal apparatus and perform reception signal processing, and thus does not need real-time processing for the reception weight calculation calculation. (In other words, the reception weight can be simply read from the memory.) Therefore, even if an enormous number of antenna elements is assumed, it can be realized with a realistic hardware configuration.

  Further, every time a signal is received in the multi-user MIMO technology, the base station apparatus 80 needs to perform channel estimation individually for each terminal apparatus that is simultaneously spatially multiplexed, and uses the result to calculate the reception weight. It was. For this individual channel estimation, the same number of orthogonal preambles as the spatial multiplexing number or the preamble signal of the channel estimation signal having the same number of symbols as the spatial multiplexing number is required. In this case, overhead corresponding to the number of symbols equal to the number of spatial multiplexing occurs, leading to a decrease in MAC layer efficiency. However, in the technology related to the present invention, the reception weight is multiplied by the reception signal in steps S177-1 to S177-K without performing channel estimation for each spatially multiplexed terminal device, and as a result, the transmission source terminal Signal separation is performed for each device. Thus, in the received signal processing for each signal sequence performed in steps S179-1 to S179-L, a single channel estimation preamble signal (for example, one symbol) is as if the spatial multiplexing number is 1. If there is, signal detection processing can be performed. As a result, it is not necessary to assign a preamble signal having the number of symbols depending on the number of spatial multiplexing while performing high-order spatial multiplexing, and it is possible to suppress a decrease in MAC layer efficiency.

Further, when the number of antenna elements 101-1 to 101-K provided in the base station apparatus 10 is a very large number, even if there is a time variation of the channel of each transmitting antenna element versus receiving antenna element, If it changes randomly between a large number of antenna elements, it can be regarded as a statistically averaged state as a whole, and the influence of time fluctuation can be reduced.
Further, by storing the transmission weight calculated for each terminal device in the transmission weight storage circuit 128 in advance, when transmitting data by spatial multiplexing, the transmission weight corresponding to the terminal device is read and transmission signal processing is performed. Therefore, it is possible to transmit data by spatial multiplexing without calculating the transmission weight each time transmission is performed, and high-order spatial multiplexing using a huge number of antenna elements is realized with simple processing, and as a result As a result, the frequency utilization efficiency of the downlink can be improved.

(Supplement regarding configuration example)
The above is the description of the configuration example of the technology related to the present invention. The following are supplementary items common to these configuration examples.
In the base station apparatus 10 in the configuration example of the technology related to the present invention, the configuration in which the short-time averaging process illustrated in FIG. 23 is performed when acquiring the channel information in the uplink has been described. However, this was premised on the response to (Requirement 1). For example, although channel estimation is at a level where channel estimation is feasible in terms of channel design, when the base station apparatus 10 is used as a means for further obtaining channel gain for communication at a higher transmission rate, it is not necessarily short. There is no need to perform time averaging. In this case, the short-time averaging process (FIG. 23) for acquiring uplink channel information can be simply replaced with a channel estimation process.

  Similarly, in the base station apparatus 10 in the configuration example of the technology related to the present invention, when calculating the downlink channel information from the uplink channel information, the calibration coefficients shown in the equations (14) and (15) are used. The configuration used is described. However, as described above, the frequencies in the low noise amplifiers 103-1 to 103-K, the filters 106-1 to 106-K, the high power amplifiers 148-1 to 148-K, the filters 147-1 to 147-K, and the like. Adjust by analog signal processing so that the relative value (angle difference of complex phase) between the uplink and downlink of the amount of complex phase rotation for each component becomes a constant value in the circuit corresponding to all antenna elements. (For example, the complex phase of the uplink and downlink may be adjusted to be a constant value), it is not necessary to perform the process using the calibration coefficient. In this case, the process of acquiring downlink channel information (FIG. 26) can be omitted, and the uplink channel information and the downlink channel information are equivalent, so the transmission weight and the reception weight are common. Value. In this case, the circuit related to the calculation of the transmission weight in the downlink and the circuit related to the calculation of the reception weight in the uplink can be shared.

In this case, in the base station apparatus in the configuration example of the technology related to the present invention, the reception weight calculation circuit 124 and the reception weight storage circuit 125 are configured to perform both calculation and storage of the transmission weight and the reception weight. As a result, the calibration circuit 126, the transmission weight calculation circuit 127, the transmission weight storage circuit 128, and the calibration coefficient storage circuit 129 are omitted. However, the present invention is not limited to this, and with the same configuration as that of the base station apparatus 10 in the configuration example of the present invention, the calibration coefficient is regarded as “1” in all combinations of antenna elements and frequency components, and the transmission weight is set. You may make it calculate.
Furthermore, in this case, the rotation amount of the complex phase does not necessarily have to be the same (or the calibration coefficient is 1) in all the antenna elements of each frequency component, and this condition is exceptional in some small number of antenna elements. Even in a situation that is not satisfied, as long as at least half of the antenna elements satisfy this condition, the operation intended by the present invention can be realized as a whole.

Further, in the OFDM modulation scheme, all subcarriers are used for communication with the same terminal apparatus, and therefore, transmission / reception weights for the terminal apparatuses of a combination common to all subcarriers are used. However, in OFDMA, since allocations to different combinations of terminal devices in a patchwork pattern on the time axis and the frequency axis are gathered together, terminals allocated for each time (OFDM symbol) and frequency (subcarrier) It is necessary to use transmission / reception weights for the device. In this case, the reception signal processing circuits 109-1 to 109-L and the transmission signal processing circuits 141-1 to 141-L configured by a plurality of surfaces correspond to the terminal device that is the communication partner regardless of the frequency and time. However, it should be understood that it corresponds to a terminal device that is a communication partner when attention is paid to each frequency component or each time (OFDM symbol). However, except for the difference, OFDM and OFDMA can be processed in exactly the same way. In this specification, the description has been focused on OFDM, but the present invention is also applied to OFDMA. can do.
In addition, there are various operational variations regarding SC-FDE, but reception signal processing and reception after signals transmitted from each antenna element are combined in space are multiplied by transmission weights on the transmission side. In any of the received signal processings after the reception weights are multiplied on the side and the signals of the respective antenna elements are added and combined, the processing performed in the conventional SC-FDE is applied as it is in each of the above-described configuration examples. Therefore, the present invention is applicable to all variations of SC-FDE.

Furthermore, when adding and combining signals multiplied by reception weights over multiple antenna elements, it is not always necessary to add and combine over all antenna elements, and add and combine over some antenna elements in the whole. Even if it performs, it is possible to implement | achieve the operation | movement which the technique relevant to this invention intends as a whole, and can obtain the same effect as a result. Similarly, when adding and combining signals for a plurality of terminal devices multiplied by transmission weights for each antenna element, addition combining is not performed for all the antenna elements, and addition and combining is performed for some antenna elements. Even if the above is performed, it is possible to realize the intended operation of the technology related to the present invention as a whole.
Similarly, in the technology related to the present invention, the preamble signal for channel estimation used for data communication can be a common preamble signal in all terminal devices, but other preambles are used in some terminal devices. It is of course possible to employ a configuration using a signal. If a common preamble is used when transmitting and receiving a signal by spatially multiplexing at least a plurality of terminal devices at the same time, it is intended by the technology related to the present invention. Corresponds to the action.

  Furthermore, in the channel information acquisition process shown in FIGS. 23 to 25 in the technology related to the present invention, what is the exchange process between the base station apparatus and the terminal apparatus for various control information such as an instruction for starting these processes? It may be realized by a method. These processes are basically performed before the start of service operation. In this case, since an appropriate transmission / reception weight is unknown at the beginning, a sufficient line gain is secured between the base station apparatus and the terminal apparatus. It is assumed that various controls are performed in a situation where it is impossible. However, before the start of service operation, for example, an operator can manually instruct the start of processing in the installation work of the terminal device, or temporarily control using other wireless standards It doesn't matter. Therefore, it is possible to implement the technology related to the present invention regardless of various control processing methods such as an instruction for starting the acquisition processing of channel information.

Furthermore, the offset value φ ^(k) of the complex phase used when acquiring the relative component can be acquired by a method other than the processing shown in FIG.
FIG. 30 is a flowchart showing another relative component acquisition process for acquiring a relative component of uplink channel information in each configuration example of the technology related to the present invention described above. The difference between the processing shown in FIG. 24 and the processing shown in FIG. 24 is that the complex phase offset value φ ^(k) used when acquiring the relative component is based on the complex phase of the specific antenna element 101-1. Instead, in step S193, an average value of complex phases (that is, angles represented by 0 to 2π) of all the antenna elements 101-1 to 101-K is used. Based on the k-th frequency components ^ h ₁ ^(k) ,..., ^ H _K ^(k) in the channel information corresponding to the antenna elements 101-1 to 101-K in steps S122-1 to S122-K, Using (21), the average value φ ^(k) of the complex phases of all antennas for the k-th frequency component is obtained, and this is used in steps S124-1 to S124-K, thereby obtaining the relative component. This offset value is obtained individually for each frequency component.
Even when the complex phase component of each of the antenna elements 101-1 to 101-K includes an error, the equation (21) averages the error, and as a result, a highly accurate relative component is obtained. Can do.

  As a method of acquiring downlink channel information, in addition to the method using uplink channel information shown in this specification, as shown in the direct method of FIG. A method is also conceivable in which a training signal is directly transmitted on the downlink and channel information acquired by a terminal device that has received the training signal is fed back to the base station device in a form of feedback. In this case, the training signals shown in FIG. 16 are sequentially transmitted one by one from the antenna elements provided in the base station apparatus, and the same processes as those shown in FIGS. 23 to 25 are performed in the terminal apparatus. The same effect can be obtained when the averaged channel information for each antenna element and each frequency component is set by feeding back to the base station by some method, and the base station apparatus uses this to calculate the transmission weight. It is possible to get However, even in this case, transmission of a training signal from each terminal device is indispensable for acquiring uplink channel information, and this point is exactly the same as the above-described technology related to the present invention.

Further, for example, is performed a process of extracting the complex phase of the formula (21) in the channel information ^ h i ^_(k), the angle of the complex phase from the ratio of the real and imaginary parts of the channel information ^ h i ^_(k) It is also possible to acquire information and calculate a value equivalent to the equation (21) based on the angle information. Although this appears to be mathematically different, it is mathematically equivalent, and of course it is possible to substitute processing with such mathematically equivalent alternatives for all arithmetic operations. It is.
Similarly, in the base station apparatus 10 in the configuration example of the technology related to the present invention, after performing the long-time averaging process shown in FIG. 25 as the process after obtaining the relative component of the uplink channel information shown in FIG. The transmission / reception weight calculation process shown in FIG. 27 was performed. However, since the weights shown in the equations (19) to (20) correspond to simple complex phase component extraction, the weight calculation processing shown in FIG. 27 is performed after the relative components shown in FIG. By replacing steps S131-1 to S131-Q with acquisition of individual reception weights and replacing the long-time averaging target shown in step S133 with this reception weight, an approximately equivalent long-time average reception weight is acquired. It is possible to do. That is, in the configuration example of the related art of the present invention, the physical quantity that is subject to long-term averaging is a relative component of channel information, but the reception weight calculated from the relative component of channel information is subject to long-term averaging. It is also possible to replace it with a physical quantity.

  Furthermore, in the installation example of the base station apparatus included in the wireless communication system according to the present invention illustrated in FIG. 14, the terminal apparatuses 12-1 to 12-2 are illustrated as including one antenna. Even if a plurality of antennas are provided, the same processing can be performed. In principle, if the terminal apparatuses 12-1 to 12-2 are provided with a plurality of antennas, a plurality of signal sequences can be spatially multiplexed in one terminal station. In this case, it is possible to similarly implement the technology related to the present invention by regarding each antenna of the terminal devices 12-1 to 12-2 as an antenna element of each terminal station. However, in the present invention, since it is assumed that the terminal devices 12-1 to 12-2 and the antenna elements 13-1 to 13-4 of the base station device are in a line-of-sight environment, generally, It is often difficult to perform MIMO transmission between one terminal station (after the second eigenvalue approaches zero).

Therefore, when the terminal station is provided with a plurality of antennas, it is practical to operate transmission / reception of a single signal sequence as a diversity configuration of a plurality of antennas. In this case, by combining a plurality of antennas with appropriate weights, it can be regarded as a virtual one antenna, and the same processing is realized with this virtual one antenna. Then, it is possible to apply the technology related to the present invention in exactly the same way.
Furthermore, in the above description of the operation principle and the configuration example of the technology related to the present invention, the channel information and transmission / reception weight corresponding to each antenna element have been described. However, the channel information or transmission / reception weight of each antenna element is used as a component. In the constructed vector, the direction indicated by the vector has an effective meaning. For this reason, the vector obtained by multiplying a certain vector by a predetermined coefficient is the same in direction, so that a vector obtained by multiplying a certain coefficient for each antenna element has all equivalent meanings without depending on the coefficient to be multiplied. Will have.

  On the other hand, as described in the preconditions of the present invention, since the antennas of the base station apparatus and the terminal apparatus are assumed to be a line-of-sight environment or an environment close to the line-of-sight environment, the intensity and amplitude of the signal received by each antenna element. Is expected to be roughly constant. For this reason, for example, the vector of channel information of each antenna element is effectively not so significant in the absolute value of each component of the vector, and the channel information value is normalized (the channel information is the absolute value). (Complex number obtained by dividing by) is significant information. For this reason, the processing in which the “channel information” used in the description of the operation principle and the above is approximately regarded as the “value obtained by normalizing the value of the channel information” is the present invention and related technology of the present invention. In this sense, the above-mentioned “channel information” includes up to “a value obtained by standardizing the value of channel information” in a broad sense.

Furthermore, in the specification of the present invention, for convenience of explanation, “row vector” and “column vector” are treated without being distinguished from each other. For example, the channel information vector h _i in the expression (3) is a row vector, the transmission weight vector w _j is a column vector, and “transpose” or the like if it is a strict mathematical notation that unifies the direction of vector arrangement. Should be written using the symbol etc. However, the information required in the practice of the present invention is the value of each component of the vector, and it does not make much sense whether the vector is a row vector or a column vector. The description does not distinguish between “vector” and “column vector”.

  Still further, the main feature of the related technology described above is that, as pre-processing prior to actual communication, uplink and / or downlink channel information is acquired in advance, and reception weight and / or transmission weight is determined in advance based on that information. In actual communication, transmission / reception signal processing is performed with reference to the reception weight or transmission weight acquired in advance. As a result, even when the number of antenna elements becomes enormous, it is possible to perform real-time processing while reducing the circuit scale without accompanying a very heavy calculation load in the transmission / reception weight acquisition processing. It becomes possible. Therefore, acquisition of relative components for each antenna element of channel information is not necessarily performed, and averaging processing thereof is not performed. Even if transmission / reception weights are acquired using a single channel information acquisition result as preprocessing, signal separation is not performed. Therefore, the accuracy of signal separation due to the transmission / reception weight may be somewhat lowered, but it is also possible to obtain the intended effect of the related technology. In the present invention, the use of this related technique is mainly assumed. However, acquisition of the relative component of the channel information and the averaging process are not necessary as an essential condition for obtaining the effect of the present invention.

Furthermore, regarding the scheduling process shown in step S162 of FIG. 28 and step S172 of FIG. 29, for example, the SINR (Signal to Interference and Noise Power Ratio) of each terminal device that deteriorates due to the influence of time variation or the like. The ratio may be determined by determining whether the expected value of the ratio can satisfy a predetermined condition. For example, the SNR value of the i-th terminal device which is the i-th terminal device is x _i [dB], the SIR value corresponding to the class value of the time variation index is y _i [dB], and the required SINR value of the transmission mode to be applied is z _{It is} assumed that _i [dB]. In this case, in order to satisfy the desired communication quality, it is necessary to satisfy the following equation (22).

Here, the range in which the sum of Σ in the second term on the left side of equation (22) is taken is that only the i-th terminal that is subject to quality evaluation of equation (22) with respect to the terminal number j assumed as the object of spatial multiplexing transmission. The excluded range (j ≠ j). For example, when all of the terminal devices that are assumed to be spatially multiplexed at a certain stage of scheduling are subject to spatial multiplexing, if Equation (22) is not satisfied for a terminal device of a certain number j, the i-th terminal is In addition to being excluded from the target of spatial multiplexing transmission, the terminal number may be excluded from the range in which the summation of Σ in the determination of the feasibility of the following equation (22) is taken. As long as such a condition can be satisfied, the scheduling processing circuit 181 narrows down the terminal devices to be spatially multiplexed. Here, since the required SINR value (z _i [dB]) of the transmission mode to be applied that appears on the right side of the equation (22) changes depending on the transmission mode to be applied, the adaptation of such a transmission mode is applied. It may be dealt with by a change. As described above, various conditions are determined and scheduling processing for combinations of terminal devices is required for scheduling. However, the related technology of the present invention can be applied without depending on the scheduling processing, and there are particularly limited conditions. It is not necessary.

[Specific Embodiment of the Present Invention Based on Related Technology]
Based on the above principle of operation, a specific embodiment of the present invention will be described below. The embodiments of the present invention are implemented in combination with related technologies on which the present invention is based. Hereinafter, the number of terminal devices that the base station device is subject to spatial multiplexing transmission is N, and the number of antenna elements provided in the base station device is K (in the case of the FDD system, the number of pairs of transmitting antenna elements and receiving antenna elements) Is described as K group).

(Configuration example of base station device)
FIG. 1 is a schematic block diagram showing a configuration of a base station apparatus 400 in an embodiment according to the present invention. Base station apparatus 400 performs spatial multiplexing transmission at the same time on the same frequency as a plurality of terminal apparatuses. Further, as shown in the figure, the base station apparatus 400 includes K antenna elements 401-1 to 401 -K, K radio signal processing circuits 410-1 to 410 -K, and N transmission / reception signals. Processing units 430-1 to 430 -N, a transmission / reception weight calculation unit 402, a communication control circuit 403, and an interface circuit 404 are provided. Hereinafter, the whole or any one of the antenna elements 401-1 to 401 -K is referred to as the antenna element 401. Similarly, when the whole or any one of the wireless signal processing circuits 410-1 to 410-K is shown, the whole or any one of the wireless signal processing circuit 410 and the transmission / reception signal processing units 430-1 to 430-N is used. In this case, it is referred to as a transmission / reception signal processor 430.

The antenna elements 401-1 to 401 -K are associated with the wireless signal processing circuits 410-1 to 410 -K on a one-to-one basis, and are connected to the corresponding wireless signal processing circuits 410-1 to 410 -K. .
The radio signal processing circuits 410-1 to 410 -K perform signal amplification on the received signals received via the connected antenna elements 401-1 to 401 -K, frequency conversion to a baseband, and filters Out-of-band component removal, sampling processing (A / D conversion processing), guard interval removal, FFT processing are performed to convert each frequency component into a digital signal, and the digital signal obtained by the conversion is transmitted / received signal processing section 430- 1 to 430-N.

  The radio signal processing circuits 410-1 to 410 -K add and synthesize digital signals of respective frequency components input from the transmission / reception signal processing units 430-1 to 430 -N, and each frequency obtained by the addition synthesis. The component signal is converted to a baseband digital signal by IFFT processing and a guard interval, and this is D / A converted and further converted to a radio frequency band analog signal (including removal of out-of-band components), It transmits via the antenna elements 401-1 to 401-K connected after signal amplification. Hereinafter, specific configuration examples of the radio signal processing circuits 410-1 to 410-K will be described.

  FIG. 31 is a schematic block diagram showing a configuration example (in the case of the TDD system) of the wireless signal processing circuit 410 in the present embodiment. As shown in the figure, the radio signal processing circuit 410 includes a TDD switch 411, a low noise amplifier (LNA) 412, a local oscillator 413, a mixer 414, a filter 415, an A / D converter 416, an FFT circuit 417, and an addition synthesis circuit 421. , IFFT & GI adding circuit 422, D / A converter 423, local oscillator 424, mixer 425, filter 426, and high power amplifier (HPA) 427.

The TDD switch 411, the low noise amplifier 412, the local oscillator 413, the mixer 414, the filter 415, the A / D converter 416, and the FFT circuit 417 are the TDD switch 102-1 and the low noise amplifier 103- in the receiving unit 100 illustrated in FIG. 1 corresponds to the local oscillator 104, the mixer 105-1, the filter 106-1, the A / D converter 107-1, and the FFT circuit 108-1, and performs the same processing.
Signals obtained by separating by the FFT circuit 417 and having each frequency component included in the received signal are output to the transmission / reception signal processing units 430-1 to 430-N shown in FIG.

  Also, the addition synthesis circuit 421, IFFT & GI adding circuit 422, D / A converter 423, local oscillator 424, mixer 425, filter 426, and high power amplifier (HPA) 427 are addition synthesis in the transmission unit 140 shown in FIG. Corresponding to the circuit 142-1, IFFT & GI adding circuit 143-1, D / A converter 144-1, local oscillator 145, mixer 146-1, filter 147-1, and high power amplifier 148-1, the same processing is performed. Do. In addition, each frequency component of each transmission signal generated in each transmission / reception signal processing section 430-1 to 430-N shown in FIG.

  Each local oscillator 413 in each of the radio signal processing circuits 410-1 to 410-K generates a synchronized local oscillation signal (F1). At this time, since the mixer 414 normally uses a local oscillation signal synchronized in each of the radio signal processing circuits 410-1 to 410-K, each of the radio signal processing circuits 410-1 to 410-K uses a common reception signal. A local oscillation signal obtained by branching the output of the local oscillator 413 is used. That is, the local oscillator 413 is arranged inside any one of the radio signal processing circuits 410-1 to 410-K, or one local oscillator 413 is arranged outside the radio signal processing circuits 410-1 to 410-K. The The local oscillation signal (F1) output from the local oscillator 413 may be branched and input to each of the radio signal processing circuits 410-1 to 410-K.

  In addition, each local oscillator 424 in each of the radio signal processing circuits 410-1 to 410-K generates a synchronized local oscillation signal (F1). At this time, since the mixer 425 normally uses a local oscillation signal synchronized in each of the radio signal processing circuits 410-1 to 410-K, each of the radio signal processing circuits 410-1 to 410-K uses a common transmission signal. A configuration is used in which a signal obtained by branching the output of the local oscillator 424 is used. That is, the local oscillator 424 is disposed inside one of the wireless signal processing circuits 410-1 to 410-K, or one local oscillator 424 is disposed outside the wireless signal processing circuits 410-1 to 410-K. The The local oscillation signal (F1) output from the local oscillator 424 may be branched and input to the wireless signal processing circuits 410-1 to 410-K.

Further, when the TDD system shown in FIG. 31 is employed, the frequency used for up-conversion / down-conversion frequency conversion is common, so that the local oscillator 413 and the local oscillator 424 can be shared. In this case, a local oscillation signal used in each of the radio signal processing circuits 410-1 to 410-K is generated by one local oscillator. If the signal intensity is reduced by branching a local oscillation signal generated by one local oscillator, the signal may be amplified using an amplifier as appropriate.
In addition, here, the configuration of the wireless signal processing circuit 410 when the TDD method is applied is shown, but the FDD method can also be applied as described above.

  FIG. 32 is a schematic block diagram showing a configuration example (in the case of FDD) of the wireless signal processing circuit 410a in the present embodiment. FIG. 31 shows the radio signal processing circuit 410 when the TDD scheme is applied to the base station apparatus 400, but FIG. 32 shows the radio signal processing circuit 410a when the FDD scheme is applied to the base station apparatus 400. The radio signal processing circuit 410a to which the FDD method is applied includes a reception system (low noise amplifier 412, local oscillator 413, mixer 414, filter 415, A / D converter 416, and FFT circuit 417) and a transmission system (addition synthesis circuit). 421, IFFT & GI adding circuit 422, D / A converter 423, local oscillator 424a, mixer 425, filter 426a, and high power amplifier (HPA) 427), and different antenna elements (receiving antenna element 401r and transmitting antenna element 401t) And the TDD switch 411 is unnecessary. In FIG. 1, as shown by antenna elements 401-1 to 401 -K, each radio signal processing circuit 410 has been illustrated with a TDD system in which one antenna element is arranged, but in the case of the FDD system As shown in FIG. 32, a radio signal processing circuit 410a to which two antenna elements are connected is provided. The frequency of the local oscillation signal generated by the local oscillator 413 is F1, whereas the frequency of the local oscillation signal generated by the local oscillator 424a is F2, which is different from F1. For this reason, in the case of the FDD system, the local oscillator 413 and the local oscillator 424a cannot be shared. Further, since the filter 426a uses different frequencies for the uplink and the downlink in the case of the FDD system, a filter having a different pass band and a different design from that in the TDD system is used.

Returning to FIG. 1, the description of the base station apparatus 400 will be continued.
The radio signal processing circuits 410-1 to 410 -K are connected to the communication control circuit 403, and various control information is input from the communication control circuit 403. For example, the communication control circuit 403 controls the TDD switches 411 of the radio signal processing circuits 410-1 to 410 -K when switching between reception and transmission in the base station apparatus 400. Information on frame timing and transmission / reception symbol timing is also input from the communication control circuit 403 to the radio signal processing circuits 410-1 to 410-K, and signal processing such as FFT and IFFT is performed according to the symbol timing.

  The transmission / reception signal processing units 430-1 to 430 -N are associated one-to-one with the terminal device to be subjected to spatial multiplexing transmission by the base station device 400, and process signals transmitted / received to / from the corresponding terminal device I do. As shown in FIG. 1, each of the transmission / reception signal processing units 430-1 to 430-N includes a reception weight multiplication circuit 431, a reception signal processing circuit 432, a MAC layer processing circuit 433, a transmission signal processing circuit 434, and a transmission weight. A multiplication circuit 435 is provided.

The reception weight multiplication circuit 431 includes a terminal device associated with its own circuit and each of the antenna elements 401-1 to 401 -K for the signals input from the wireless signal processing circuits 410-1 to 410 -K. The signal obtained by multiplying the reception weight corresponding to each combination for each frequency component and adding and synthesizing each multiplication result for each frequency component is output to the reception signal processing circuit 432.
The received signal processing circuit 432 performs processing such as channel estimation processing, received signal detection processing, demodulation and error correction decoding, acquires data transmitted from the terminal device associated with the own circuit, and receives the MAC layer. The data is output to the processing circuit 433.

  The MAC layer processing circuit 433 performs MAC layer signal processing related to termination and access control such as a MAC header on the data input from the received signal processing circuit 432, and the obtained signal is transmitted to the communication control circuit 403 or the interface. Output to one of the circuits 404. The MAC layer processing circuit 433 performs MAC layer signal processing related to addition of a preamble signal, termination of a MAC header, and access control on data input from either the communication control circuit 403 or the interface circuit 404. And output to the transmission signal processing circuit 434.

  The transmission signal processing circuit 434 performs processing such as error correction coding and modulation and addition of a preamble signal on the data input from the MAC layer processing circuit 433, and sends the obtained signal to the transmission weight multiplication circuit 435. Output. The transmission weight multiplication circuit 435, for the signal input from the transmission signal processing circuit 434, transmits a transmission weight corresponding to a combination of the terminal device associated with its own circuit and each of the antenna elements 401-1 to 401-K. Is multiplied for each frequency component. The transmission weight multiplication circuit 435 outputs a result for each frequency component obtained by multiplying the transmission weight to the radio signal processing circuit 410 corresponding to the transmission weight used for the multiplication.

  Similarly to the radio signal processing circuit 410, the transmission / reception signal processing unit 430 is connected to the communication control circuit 403, and various control information is input and output. For example, information on frame timing and transmission / reception symbol timing is also input to transmission / reception signal processing sections 430-1 to 430-N, and individual signal processing of each terminal apparatus with which base station apparatus 400 communicates according to this symbol timing. I do. Signal processing performed here includes reception signal processing of the physical layer such as reception weight multiplication, addition synthesis processing, channel estimation processing, reception signal signal detection / demodulation processing, error correction processing as necessary, etc. Includes physical layer transmission signal processing such as error correction coding, signal modulation processing, preamble signal addition, transmission weight multiplication, and MAC layer signal processing related to termination and access control of control information and MAC header It is. When the control signal is received by the MAC layer processing circuit 433, this is also notified to the communication control circuit 403 as necessary. When control information to be transmitted to the terminal device is input from the communication control circuit 403, the MAC layer processing circuit 433 appropriately processes the MAC layer and outputs it to the transmission signal processing circuit 434.

Since the transmission / reception weight calculation unit 402 has the same configuration as the transmission / reception weight calculation unit 120 shown in FIG. 21, a description of a specific configuration of the transmission / reception weight calculation unit 402 is omitted.
The communication control circuit 403 has the same configuration as the communication control circuit 110 shown in FIG. 19, and as described above, the radio signal processing circuits 410-1 to 410-K and the transmission / reception signal processing units 430-1 to 430- N.
The interface circuit 404 has the same configuration as the interface circuit 170 shown in FIG. 19, and is connected to each of the transmission / reception signal processing units 430-1 to 430-N and an external network. The interface circuit 404 performs data relay processing between the transmission / reception signal processing units 430-1 to 430-N and the network.

  The difference between the base station apparatus 400 in the present embodiment and the base station apparatus 10 in the configuration example of the technology related to the present invention corresponds one-to-one with respect to all terminal apparatuses that the base station apparatus 400 communicates with. The transmission / reception signal processing units 430-1 to 430-N are provided. By fixing a terminal device corresponding to each transmission / reception signal processing unit 430-1 to 430-N, each transmission / reception signal processing unit 430-1 to 430-N receives a reception weight from the transmission / reception weight calculation unit 402 every time reception processing is performed. There is no need to read. The same applies to the transmission weight. Therefore, in this embodiment, the reception weight calculated by the transmission / reception weight calculation unit 402 may be stored in the reception weight multiplication circuit 431. Similarly, the transmission weight may be stored in the transmission weight multiplication circuit 435.

(Reception processing)
FIG. 33 is a flowchart showing reception processing of the base station device 400 in the present embodiment. The reception process in the base station apparatus 400 is basically performed in units of symbols that are synchronized between the base station apparatus 400 and each terminal apparatus. In the case of communication using a general OFDM method, the start of the reception process is determined by determining whether or not the timing detection of the reception signal using a predetermined preamble signal is performed. The reception process is always repeated for each symbol without making such a determination.

When reception processing is started in the base station apparatus 400, a signal received by the first antenna element 401-1 is input to the first radio signal processing circuit 410-1 (step S 401-1). Similarly, signals received from the second antenna element 401-2 to each of the Kth antenna elements 401-K correspond to the radio signal processing circuits 410-2 to 410-2 corresponding to the antenna elements 401-2 to 401-K. 410-K (steps S401-2 to S401-K).
Each of the wireless signal processing circuits 410-1 to 410 -K amplifies the input signal by the low noise amplifier 412, downconverts the amplified signal to the baseband by the mixer 414, and removes out-of-band components by the filter 415. Then, the result is digitized by the A / D converter 416. Further, the FFT circuit 417 removes the guard interval from the digitized baseband signal, and converts the signal on the time axis to the signal on the frequency axis (steps S402-1 to S402-K).

  The baseband signals on the frequency axis calculated by the wireless signal processing circuits 410-1 to 410-K in steps S402-1 to S402-K are copied, and the transmission / reception signal processing unit 430- corresponding to each of the N terminal devices. 1 to 430-N. The reception weight multiplication circuit 431 multiplies each baseband signal input to the first transmission / reception signal processing unit 430-1 by a reception weight corresponding to each baseband signal for each frequency component, and the multiplication result is a frequency component. Each is added and synthesized over all antenna elements and output to the received signal processing circuit 432 (step S403-1). Similarly, in each of the second transmission / reception signal processing unit 430-2 to the Nth transmission / reception signal processing unit 430-N, each reception weight multiplication circuit 431 multiplies the reception weight by the reception component for each frequency component. Then, the multiplication results are added and synthesized over all antenna elements for each frequency component and output to the received signal processing circuit 432 (steps S403-2 to S403-N).

  The reception weight corresponding to the baseband signal is a combination of the antenna element 401 connected to the radio signal processing circuit 410 that acquired the baseband signal and the terminal device associated with the transmission / reception signal processing unit 430. Corresponding reception weights for each frequency component.

  In the transmission / reception signal processing unit 430-1, the reception signal processing circuit 432 determines whether or not a significant signal is detected from the signals obtained by the addition and synthesis by the reception weight multiplication circuit 431 (step S404-1). If no significant signal is detected (step S404-1: NO), the reception process is terminated. Similarly, in each of the second transmission / reception signal processing unit 430-2 to the Nth transmission / reception signal processing unit 430-N, has each reception signal processing circuit 432 detected a significant signal from the signals obtained by addition synthesis? If no significant signal is detected (steps S404-2 to S404-N: NO), the reception process is terminated.

  On the other hand, when the transmission / reception signal processing unit 430-1 detects a significant signal from the signals obtained by addition synthesis (step S404-1: YES), the reception signal processing circuit 432 receives the received signal with respect to the detected signal. The process is performed (step S405-1), and the reception process is terminated. Similarly, in the transmission / reception signal processing units 430-2 to 430-N, when a significant signal is detected from signals obtained by addition synthesis (steps S404-2 to S404-N: YES), the reception signal processing circuit 432 Performs reception processing on the detected signal (steps S405-2 to S405-N), and ends the reception processing.

  In addition, the detection of a significant signal in steps S404-1 to S404-N is a value obtained by squaring the absolute value of a signal obtained by addition synthesis (for example, a signal represented by a complex number) and adding up all frequency components. This is performed depending on whether or not the obtained received signal level (or an approximate amount of the received signal level obtained by another method) is equal to or higher than a predetermined threshold level. Alternatively, it is possible to evaluate whether or not the absolute value of each frequency component value exceeds a certain threshold value, and to detect a significant signal when a predetermined number or more frequency components exceed a predetermined threshold value. Similarly, any method that can determine the presence or absence of a signal may be used.

The received signal processing here refers to channel estimation processing that considers the frame format, signal detection processing (demodulation processing, etc.) based on the channel estimation results, and error correction processing as necessary. Refers to processing centered on. Here, when OFDM is used, demodulation processing for each subcarrier is performed on the added and combined signal, and when SC-FDE is used, the signal of each frequency component that is added and combined is on the frequency axis. The signal equalization process is performed, and the demodulation process is performed on the signal synthesized by the IFFT process. Of course, higher layer processing such as the MAC layer and processing of the interface unit are also necessary, but these are processed in the same manner as in the prior art as appropriate according to the presence or absence of signals, etc., unlike the processing in units of symbols. It is.
Further, in the processing of steps S403-2 to S403-N, it has been described that the signals corresponding to all the antenna elements are added and synthesized. However, it is possible to obtain a received signal level capable of performing significant signal detection, demodulation, decoding, and the like. In this case, signals corresponding to some antenna elements may be added and synthesized.

  Note that the significant signal detection here and the reception signal processing performed by the transmission / reception signal processing units 430-1 to 430-N are integrally determined for a series of wireless packets. For example, if there is a change from a state where there is no significant signal detection to a state where there is signal detection, it is regarded as the start of reception of a wireless packet, processing is started, control information representing the data length, for example, is acquired according to the frame format, and the data During the length, the received signal processing may be continued even if there is no significant signal detection. Furthermore, when it is determined that the reception of a wireless packet starts from the change in the reception level, processing for determining whether or not it is truly the start of the wireless packet is added, and this determination definitely determines that it is the start of the wireless packet. In this case, the above reception signal processing may be continued. This determination method may be, for example, a check using an error detection code (for example, CRC check) or the like, or may be determined by using a unique word pattern after channel estimation and matching with the pattern.

  Further, the component on the frequency axis of the channel estimation result is positioned at the head in the impulse response or delay profile obtained by performing the inverse process of the modulation process performed on the preamble signal and performing the IFFT process on the result. Approximate timing detection may be performed when the sum of the squares of the absolute values of the components in the predetermined region is equal to or greater than a predetermined ratio with respect to the sum of the squares of the components in the remaining region. Furthermore, the signal of the frequency component may be returned to the component on the time axis, and processing equivalent to conventional timing detection may be performed on the signal on the time axis. The present invention can be implemented by a combination of various existing techniques, and the present invention can be implemented by any method.

(Transmission process)
FIG. 34 is a flowchart showing the transmission processing of the base station apparatus 400 in the present embodiment. Also in the transmission processing, the following processing is regularly performed in units of symbols that are basically synchronized between the base station device 400 and each terminal device. In general, the transmission process is a process performed only when there is a signal to be transmitted. However, the transmission process in the base station apparatus 400 of the present invention always performs a symbol unit without determining whether there is a signal to be transmitted. The following transmission process is repeated.

  When transmission processing is started in the base station apparatus 400, in the first transmission / reception signal processing section 430-1, the transmission signal processing circuit 434 determines whether there is a signal to be transmitted to the terminal apparatus corresponding to itself (strictly speaking, the MAC layer). The presence / absence of a signal input from the processing circuit 433 is determined (step S411-1), and when there is no signal to be transmitted (step S411-1: NO), transmission processing in the first transmission / reception signal processing unit 430-1 End. Similarly, in the second transmission / reception signal processing unit 430-2 to the Nth transmission / reception signal processing unit 430-N, the transmission signal processing circuit 434 individually determines whether or not there is a signal to be transmitted to the terminal device corresponding to itself. If there is no signal to be transmitted (steps S411-2 to S411-N: NO), the second to Nth transmission / reception signal processing units 430-2 to 430-N The transmission signal processing is terminated.

  On the other hand, when there is a signal to be transmitted to the terminal device corresponding to the first transmission / reception signal processing unit 430-1 (step S411-1: YES), the transmission signal processing circuit 434 transmits the signal. Signal processing is performed (step S412-1). The transmission signal processing here refers to processing similar to that of the prior art, such as so-called modulation processing or addition of a preamble signal given as necessary. For example, in the case of OFDM, error correction coding is performed as necessary on transmission data to which MAC layer control information and the like are given, and the result is divided into bit strings for each subcarrier. The signal is mapped to a signal point and formed as a transmission signal on the frequency axis. In addition, in the case of SC-FDE, error correction coding is performed on transmission data to which MAC layer control information and the like are added as necessary, and a single carrier modulation process is performed on the result, and a block of a transmission signal is further processed. Each frequency component is separated by FFT in units. Similarly, in the second to Nth transmission / reception signal processing units 430-2 to 430-N, when there is a signal to be transmitted to a terminal device corresponding to itself (steps S411-2 to S411-N: YES), The transmission signal processing circuit 434 performs transmission signal processing on the signal (steps S412-2 to S412-N).

  In each of the transmission / reception signal processing units 430-1 to 430-N, the transmission weight multiplication circuit 435 applies each antenna element 401- to the signal of each frequency component subjected to the transmission signal processing in steps S412-1 to S412-N. Every 1 to 401-K, the transmission weight corresponding to the antenna element is multiplied, and the multiplication result is output to the radio signal processing circuit 410 to which the antenna element is connected (steps S413-1 to S413-N).

In the first radio signal processing circuit 410-1, the addition / combination circuit 421 converts each frequency component signal (signal on the frequency axis) input from each of the transmission / reception signal processing units 430-1 to 430-N for each frequency component. Are added and synthesized (step S414-1). Similarly, in the second to K-th radio signal processing circuits 410-2 to 410-K, the addition / combination circuit 421 also receives the signals of the frequency components input from the transmission / reception signal processing units 430-1 to 430-N. Are added and synthesized for each frequency component (steps S414-2 to S414-K).
In each of the radio signal processing circuits 410-1 to 410 -K, each IFFT & GI adding circuit 422 performs IFFT processing on the added and synthesized signal, gives a guard interval, and converts it to a signal on the time axis (step S 415-). 1-S415-K). At this time, waveform shaping between symbols may be performed if necessary.

  Further, in each of the radio signal processing circuits 410-1 to 410-K, the D / A converter 423 converts the signal on the time axis into an analog signal, and the mixer 425 upconverts the analog signal to the radio frequency band. The filter 426 removes out-of-band frequency components included in the upconverted signal (steps S416-1 to S416-K). The high power amplifier 427 amplifies the signal from which the out-of-band frequency component has been removed by the filter 426, transmits the signal from the antenna elements 401-1 to 401-K (steps S417-1 to S417-K), and performs transmission processing. finish

  In Steps S411-1 to S411-N, when there is no signal to be transmitted (Steps S411-1 to S411-N: NO), the transmission process is ended, but the transmission / reception signal processing units 430-1 to 430- N does not perform the processing of steps S412-1 to S412-N to steps S413-1 to S413-N, and outputs all-zero signals in the respective frequency components to the radio signal processing circuits 410-1 to 410-K. You may make it output. Also in this case, each of the wireless signal processing circuits 410-1 to 410-K performs the processing from step S414-1 to 414-K to steps S417-1 to S417-K as described above. Further, although completely equivalent to this, the transmission signal to be multiplied by the transmission weight in the processing of steps S413-1 to S413-N is set as a signal “0 (zero)”, and steps S413-1 to S413-N are performed. The process may be shifted to. Even if this processing is performed, in addition synthesis, only zero is added, and there is no substantial effect, which is effectively equivalent to not transmitting a valid signal.

(Supplementary items related to this embodiment)
As a supplementary matter in the present embodiment, if the FDD scheme is used, the channel estimation results between the uplink and the downlink have no correlation at all. Therefore, it is not possible to estimate downlink channel information by performing calibration from the uplink channel estimation result. Therefore, the downlink channel estimation may require additional processing such as realization by a direct method of channel feedback. However, if such processing is performed, the FDD scheme is used. Is equally applicable. In downlink channel estimation when the FDD scheme is used, it is necessary to sequentially transmit training signals and the like from all the antenna elements 401 one by one from the base station apparatus 400 one by one. However, all of the terminal devices can perform channel estimation in parallel with respect to transmission of a channel estimation signal from the base station device 400. On the other hand, in the case of the uplink, each terminal apparatus transmits the signal separately at different timings so that the signal does not interfere as in the case of the related art of the present invention. It should be noted that this is a target process.

  As described above, the base station apparatus 400 according to the present embodiment includes N transmission / reception signal processing units 430-1 to 430-N that correspond one-to-one to all N terminal apparatuses to be communicated. . Further, each of the transmission / reception signal processing units 430-1 to 430-N performs short-time averaging processing (FIG. 23), relative component acquisition processing (FIG. 24), and long-time averaging processing (FIG. 25) on the channel information. Using the reception weights obtained in this way, the reception signals received by the plurality of antenna elements 401-1 to 401 -K are always in-phase synthesized to determine whether or not a significant signal is included. That is, each of the transmission / reception signal processing units 430-1 to 430-N can determine whether or not the corresponding terminal device has transmitted a signal, and can perform reception processing when there is a transmitted signal. Thereby, uplink communication can be performed in parallel without grasping the allocation of radio resources to each terminal device.

  Each transmission / reception signal processing unit 430-1 to 430 -N performs short-time averaging processing, relative component acquisition processing, and long-time averaging processing when there is a signal to be transmitted to the corresponding terminal device. Using the obtained transmission weight, a signal to be synthesized in phase at the terminal device is transmitted. As a result, the transmission / reception signal processing units 430-1 to 430-N perform parallel processing according to the presence / absence of signals to be transmitted to the corresponding terminal devices even when performing spatial multiplexing transmission with a plurality of terminal devices. Can be done.

  Thereby, the base station apparatus 400 can perform spatial multiplexing transmission with each terminal apparatus, without performing the scheduling process which allocates a radio | wireless resource to each terminal apparatus. That is, when viewed between the transmission / reception signal processing units 430-1 to 430-N in the base station apparatus 400 and each terminal apparatus, it is as if Point-to-Point type communication is being performed, and symbol timing synchronization is performed. In the case of conditions and TDD system, wireless communication may be interrupted due to restrictions on transmission / reception sections, maintenance work, etc., but data transmission and reception may be performed at any timing except those it can. Therefore, in base station apparatus 400, it is possible to reduce a load related to processing associated with scheduling.

Furthermore, since the bandwidth allocation management for the terminal device becomes unnecessary, it becomes unnecessary to transmit / receive control information for inquiring each terminal device about the required bandwidth, or for requesting bandwidth allocation to the base station device by each terminal device, The processing in the MAC layer can be reduced, and the efficiency of the MAC layer can be improved by omitting unnecessary control information. For example, in the case of normal multiple access among a plurality of terminal devices, it is unavoidable to exchange control signals for bandwidth request and bandwidth allocation with the exception of random access control that allows signal collision. Therefore, the decrease in the efficiency of the MAC layer due to the overhead cannot be ignored. In particular, since the overhead tends to be proportional to the number of terminal devices, it is fatal in multiple access with the majority of terminal devices. However, the base station device 400 does not reduce the efficiency of the MAC layer due to such overhead even when there is a large bias in traffic for each terminal device or when there is a large bias in traffic according to time, Spatial multiplexing transmission can be performed with each terminal device. Further, in base station apparatus 400, access control for avoiding interference of signals transmitted from each terminal apparatus is unnecessary, so in practice, for example, slot assignment processing in the TDMA system, CSMA / CA system, or the like. Control such as random back-off in is unnecessary.
As a result, in the wireless communication system including the base station apparatus 400, it is possible to expect improvement in MAC layer efficiency and accompanying improvement in throughput characteristics.

  If the base station device 400 operates in accordance with the existing wireless standard, there is no problem even if such access control is performed in the MAC layer processing circuit. Specifically, if the terminal device is a terminal device that complies with WiMAX of the wireless standard, each MAC layer processing circuit 433 of the base station device 400 is connected to WiMAX, although it is effectively point-to-point communication. Broadcast information related to scheduling, such as UL-Map and DL-Map, in the frame configuration may be generated.

  In addition, when the FDD method is used, if a modification is performed in which transmission and reception are performed using different frequency channels, even a terminal device that complies with the wireless standard WiFi can perform the same processing as before. . In the case of WiFi, random back-off control for avoiding the collision of transmission timings of a plurality of terminal devices is indispensable. However, in the case of applying the present invention, wireless packet transmission between different terminal devices is basically different. Since no collision (interference) occurs, it is sufficient that the random backoff control can avoid only the collision between the base station apparatus and the terminal apparatus.

Further, the operation defined in the present invention does not necessarily have to be performed constantly in all time zones. For example, in the case of using the TDD method and the FDD method, similarly, a time zone in which a base station centralized control operation instructing allocation of both uplink and downlink bandwidths from the base station apparatus at a certain period is performed. And the time zone in which each terminal device and base station device defined in the present invention operate autonomously distributed Point-to-Point communication in parallel by time division, and only in the determined time zone A configuration using the present invention may be used. As a specific example, only the bandwidth request signal in the uplink may be transmitted using the present invention, and user data may be transmitted / received by base station centralized control as in the past. In this case, the effect of reducing the scheduling load associated with the central station centralized control cannot be expected, but the scheduling process is not necessary for the control signal for bandwidth request, and if the bandwidth request information is transmitted only when necessary. For good, it is possible to reduce unnecessary overhead and increase the efficiency of the MAC layer.
Further, although the circuit corresponding to the storage circuit 115 of the configuration example in the technology related to the present invention shown in FIG. 19 is not specified in the present embodiment, these circuits are mounted and various setting information stored therein are stored. Of course, it is possible to utilize this for communication.
Furthermore, in FIG. 1, the local oscillators 413 and 424 (or 424a) described in the configuration example of the radio signal processing circuit 410 in FIG. 31 or the configuration example of the radio signal processing circuit 410a in FIG. Not. However, as described in the above description, the local oscillators 413 and 424 included in each of the radio signal processing circuits 410-1 to 410-K in FIG. 1 are generally shared by the entire base station. Originally, it is appropriate to illustrate the local oscillators 413 and 424 outside the wireless signal processing circuit 410. However, here, for convenience of explanation, these are described in each radio signal processing circuit 410, and the whole operation is explained as being shared.

[Other supplementary items]
Note that a program for realizing the functions of the base station apparatus according to the present invention is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed, thereby transmitting weights. In addition, a process of calculating a reception weight and a transmission / reception weight may be performed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer system” includes a WWW system having a homepage providing environment (or display environment). The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

1-1, 1-2, 1-3 OFDM symbol 2-1, 2-2, 2-3 Effective signal region 3-1, 3-2, 3-3 Training signal 4-1, 4-2, 4 -3 Trailing area 5-1, 5-2, 5-3 Guard interval 6-1, 6-2, 6-3 Signal period 10 Base station device 11 Building 12-1, 12-2 Terminal device 13-1, 13-2, 13-3, 13-4 Antenna elements of base station apparatus 14-1, 14-2, 14-3 Ground moving body 15-1, 15-2 Building 21-1, 21-2, 21 -3 High power amplifier (HPA)
22-1, 22-2, 22-3 Low noise amplifier (LNA)
23-1, 23-2, 23-3 Time division switch (TDD-SW)
24-1, 24-2, 24-3 Antenna elements 25-1, 25-2, 25-3 Radio module 26-1, 26-2, 26-3 Antenna terminal 27 Coaxial cable 80 Base station device 81 Transmitter 85 Receiving unit 87 Interface circuit 88 MAC layer processing circuit 100 Receiving unit 101-1, 101-2, 101-K Antenna element 102-1, 102-2, 102-K TDD switch 103-1, 103-2, 103-K Low noise amplifier (LNA)
104 local oscillators 105-1, 105-2, 105-K mixers 106-1, 106-2, 106-K filters 107-1, 107-2, 107-K A / D converters 108-1, 108-2 , 108-K FFT circuit 109-1, 109-2, 109-L Reception signal processing circuit 110 Communication control circuit 115 Storage circuit 120 Transmission / reception weight calculation unit 121 Channel information short time averaging circuit 122 Relative component acquisition circuit 123 Channel information long time Average circuit 124 Reception weight calculation circuit 125 Reception weight storage circuit 126 Calibration circuit 127 Transmission weight calculation circuit 128 Transmission weight storage circuit 129 Calibration coefficient storage circuit 140 Transmitters 141-1, 141-2, 141-L Transmission signal processing circuit 142-1, 142-2, 142-K addition synthesis circuit 143-1, 143-2, 143-K IFFT & GI adding circuit 144-1, 144-2, 144-K D / A converter 145 local oscillator 146-1, 146-2, 146-K Mixers 147-1, 147-2, 147-K Filters 148-1, 148-2, 148-K High power amplifier (HPA)
170 Interface circuit 180 MAC layer processing circuit 181 Scheduling processing circuit 400 Base station apparatus 401, 401-1, 401-2, 401-K Antenna element 402 Transmission / reception weight calculation unit 403 Communication control circuit 404 Interface circuit 410, 410a, 410-1 410-2, 410-K Wireless signal processing circuit (wireless signal processing unit)
411 TDD switch 412 Low noise amplifier (LNA)
413, 424, 424a Local oscillator 414, 425 Mixer 415, 426, 426a Filter 416 A / D converter 417 FFT circuit 421 Addition synthesis circuit 422 IFFT & GI adding circuit 423 D / A converter 427 High power amplifier 430, 430-1, 430-2, 430-N transmission / reception signal processing unit 431 reception weight multiplication circuit (reception weight multiplication unit)
432 Received signal processing circuit (received signal processing unit)
433 MAC layer processing circuit 434 transmission signal processing circuit (transmission signal processing unit)
435 Transmission weight multiplication circuit (transmission weight multiplication unit)
801 Base station device 802-1, 802-2, 802-3 Terminal device 811-1, 811-2, 811-L Transmission signal processing circuit 812-1, 812-2, 812-K Addition / synthesis circuit 813-1 813-2, 813 -K IFFT & GI adding circuit 814-1, 814-2, 814 -K D / A converter 815 Local oscillator 816-1, 816-2, 816 -K mixer 817-1, 817-2, 817 -K filters 818-1, 818-2, 818-K high power amplifier (HPA)
819-1, 819-2, 819-K Antenna element 820 Communication control circuit 830 Transmission weight processing unit 831 Channel information acquisition circuit 832 Channel information storage circuit 833 Multi-user MIMO transmission weight calculation circuit 851-1, 851-2, 851- K antenna element 852-1, 852-2, 852-K Low noise amplifier (LNA)
853 Local oscillators 854-1, 854-2, 854-K mixers 855-1, 855-2, 855-K filters 856-1, 856-2, 856-K A / D converters 857-1, 857-2 857-K FFT circuit 858-1, 858-2, 858-L reception signal processing circuit 860 reception weight processing unit 861 channel information estimation circuit 862 multiuser MIMO reception weight calculation circuit 881 scheduling processing circuit 901 transmitting station 902-1 902-2, 902-3, 902-N ₁ relay station 903 receiving station 911-1, 911-2, 911-3 cell 912-1, 912-2, 912-3 remote base station 913-1, 913-2 , 913-3, 913-4, 913-5, 913-6 terminal device 914 control station 915 optical fiber 96 -1,961-2,961-3,961-4,961-5 antenna element

Claims (6)

A wireless communication system comprising a base station device having a plurality of antenna elements and a plurality of terminal devices, wherein the base station device and the terminal devices can perform spatial multiplexing transmission at the same time on the same frequency A base station apparatus in which
Based on the training signal transmitted from the terminal device, for each combination of the terminal device and the antenna element, a reception weight for each frequency component for in-phase synthesis of signals received by the plurality of antenna elements is calculated, A transmission / reception weight calculation unit for storing the calculated reception weight;
A radio signal processing unit that is provided for each antenna element and separates a received signal received by the antenna element into a signal for each frequency component;
The reception weight corresponding to the combination of the frequency component and the antenna element corresponding to the terminal device provided for each terminal device is multiplied by the signal of each frequency component separated by each of the radio signal processing units, and the multiplication result is the frequency. A reception weight multiplier for adding and combining each component;
Based on the result of addition synthesis by the reception weight multiplier provided for each terminal device and corresponding to the terminal device, the presence / absence of a signal from the corresponding terminal device is determined, and when there is a signal from the terminal device, A base station apparatus comprising: a reception signal processing unit that performs reception processing on the addition synthesis result. The base station apparatus according to claim 1,
A transmission signal processing unit that is provided for each terminal device and separates a signal to be transmitted to the terminal device into signals for each frequency component;
A signal for each frequency component provided for each terminal device and separated by the transmission signal processing unit corresponding to the terminal device is multiplied by a transmission weight corresponding to a combination of the frequency component corresponding to the terminal device and the antenna element. A transmission weight multiplier for outputting a multiplication result to the radio signal processor connected to the antenna element corresponding to the multiplied transmission weight;
Further comprising
The transmission / reception weight calculation unit includes:
Based on either the training signal or the channel information fed back from the terminal device, the transmission weight for each frequency component for in-phase combining the signals transmitted from the plurality of antenna elements in the terminal device. Calculate for each combination of the terminal device and the antenna element, store the calculated transmission weight,
The wireless signal processor is
The antennas corresponding to each of the terminal devices are added and synthesized for each frequency component by the multiplication results inputted from the transmission weight multiplication unit, and converted to a signal on the time axis based on the addition synthesis result for each frequency component. A base station apparatus that transmits from an element. The base station apparatus according to claim 1 or 2,
When using frequency division duplex for spatial multiplexing transmission with the terminal device, in the period of communication with the terminal device,
The radio signal processing unit always separates the received signal into signals for each frequency component,
The base station apparatus, wherein the reception weight multiplication unit always performs multiplication and addition synthesis of the reception weights. The base station apparatus according to claim 1 or 2,
When using time division duplex for spatial multiplexing transmission with the terminal device, in a period allocated to reception of the terminal device,
The radio signal processing unit always separates the received signal into signals for each frequency component,
The base station apparatus, wherein the reception weight multiplication unit always performs multiplication and addition synthesis of the reception weights. A wireless communication system comprising a base station device having a plurality of antenna elements and a plurality of terminal devices, wherein the base station device and the terminal devices can perform spatial multiplexing transmission at the same time on the same frequency A wireless communication method performed by a base station apparatus in
Based on the training signal transmitted from the terminal device, for each combination of the terminal device and the antenna element, a reception weight for each frequency component for in-phase synthesis of signals received by the plurality of antenna elements is calculated, A transmission / reception weight calculation step for storing the calculated reception weight;
For each antenna element, a radio signal processing step for separating a received signal received by the antenna element into a signal for each frequency component;
For each terminal device, the reception weight corresponding to the combination of the frequency component corresponding to the terminal device and the antenna element is multiplied by the signal of each frequency component separated in the radio signal processing step, and the multiplication result for each frequency component A reception weight multiplication step to add and synthesize,
The presence / absence of a signal from the terminal device is determined based on the addition / combination result corresponding to each of the terminal devices in the reception weight multiplication step, and when there is a signal from the terminal device, the addition / combination result is received. And a received signal processing step for performing processing. A wireless communication system comprising a base station device having a plurality of antenna elements and a plurality of terminal devices, wherein the base station device and the terminal devices can perform spatial multiplexing transmission at the same time on the same frequency Because
The base station device
Based on the training signal transmitted from the terminal device, for each combination of the terminal device and the antenna element, a reception weight for each frequency component for in-phase synthesis of signals received by the plurality of antenna elements is calculated, A transmission / reception weight calculation unit for storing the calculated reception weight;
A radio signal processing unit that is provided for each antenna element and separates a received signal received by the antenna element into a signal for each frequency component;
The reception weight corresponding to the combination of the frequency component and the antenna element corresponding to the terminal device provided for each terminal device is multiplied by the signal of each frequency component separated by each of the radio signal processing units, and the multiplication result is the frequency. A reception weight multiplier for adding and combining each component;
Based on the result of addition synthesis by the reception weight multiplier provided for each terminal device and corresponding to the terminal device, the presence / absence of a signal from the corresponding terminal device is determined, and when there is a signal from the terminal device, A wireless communication system, comprising: a reception signal processing unit that performs reception processing on the addition synthesis result.

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