JP5711678B2 - Wireless communication apparatus, wireless communication system, and wireless communication method - Google Patents

Description

  The present invention relates to a radio communication apparatus, a radio communication system, and a radio communication method in which each base station performs signal transmission cooperatively in a radio access system in which a plurality of base stations perform signal transmission using the same frequency channel.

  In order to cope with various large-capacity services accompanying the recent spread of optical access and the like, it is required to improve the transmission speed of wireless communication. Since the occupied frequency band is proportional to the transmission speed, this can be realized by expanding the frequency band. However, since the actual frequency resources are limited, there is a limit to the expansion of the frequency band. Further, as a method for improving the transmission speed without causing an increase in frequency band, there is a method using a modulation method having a large modulation multi-level number such as QPSK that transmits 2 bits per symbol to 64 QAM that transmits 6 bits per symbol. is there. However, since the distance between signal points decreases as the number of multi-values increases, errors due to noise and errors due to hardware characteristics tend to occur, and a high signal-to-noise ratio is required to achieve good communication. It is difficult to greatly improve the transmission speed by this method.

  Thus, multi-user MIMO (spatial division multiplexing) as described in Non-Patent Document 1, for example, has been studied as a technique for improving the transmission efficiency by increasing the frequency utilization efficiency in combination with these methods. 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. There are actually a large number of terminal apparatuses 802 accommodated in one base station apparatus 801, but several stations are selected (three terminal apparatuses 802-1 to 802-3 in the figure) to perform communication. Hereinafter, the terminal device 802 will be referred to when any or all of the terminal devices 802-1 to 802-3 are shown. 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 in which three MIMO channels are allocated to each of the terminal devices 802-1 to 802-3 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, it is very difficult to separate all nine signal sequences in the reception process of only the three terminal devices 802-1. Therefore, signal processing for 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. 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 signals transmitted by the base station apparatus 801 are denoted as t ₁ to t _9, and column vectors having these signals as components are represented by Tx _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, the received signals at the nine antenna elements of the terminal devices 802-1 to 802-3 are expressed as r ₁ to r ₉ , and the column vector having these components as components is 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 this case, the relationship of the 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 equation (1) is rewritten as equation (2).

Furthermore, when the transmission weight matrix W is decomposed into column vectors w1 to w9 and expressed as W = (w ₁ , w ₂ , w ₃ ,..., W ₈ , w ₉ ), “H _all · W in the equation (2) "Can be expressed as in 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 in Equation (4) using a 3 × 3 partial matrix.

In equation (4), H _1,1 , H _2,2 and H _3,3 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, equation (4) can be decomposed into three relational expressions represented by 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, one base station performs MIMO communication on a one-to-one basis, so-called single user MIMO communication can be regarded as a state where three systems are communicating simultaneously in parallel.

Next, a method for determining the transmission weight vectors w _{1 to} w ₉ will be described. 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, six base 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 . Basis vectors _{e 4} is expressed as 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 equations (7-1) and (7-2).

( ^H ₅ e ₄ ^H ) in the equation (7-2) means a projection of the row vector h _{5 in} the direction of the base vector e ₄ . Similar processing is performed as in equations (8-1) and (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, 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 expressed by equation (9).

Here, j in the equation (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, if the same processing is performed for the terminal device 802-2 and the terminal device 802-3, the entire transmission weight vectors w _{1 to} w ₉ can be finally obtained. The above is the basic description of the multiuser MIMO technology.

  As a technique in which the above-described multiuser MIMO is applied to a plurality of base stations, there is base station cooperation multiuser MIMO. By cooperating with multiple base stations and performing cooperative transmission with multi-user MIMO, it is possible to eliminate interference (inter-cell interference) from adjacent base stations that would otherwise be interference sources, thus improving communication quality It becomes possible. In other words, the base station in such a system can be regarded as a wireless module or antenna unit for wireless signal transmission / reception distributed widely.

  FIG. 7 is a diagram illustrating a configuration of a wireless communication apparatus that realizes space division multiplexing by a plurality of base stations. In FIG. 7, 100 is a network, 101 is a control station that controls a base station, 102 is a communication control unit, 103 is a reception unit, 104 is a transmission unit, 105 is a network interface, and 106 is a MAC layer processing unit. The reception unit 103 includes a reception signal processing unit 107, a channel information acquisition unit 108, and a reception weight generation unit 109. The transmission unit 104 includes a transmission signal processing unit 110 and a transmission weight generation unit 111. 112a to 112d are base stations, and the control station 101 and the base stations 112a to 112d are connected by wired lines 113a to 113h such as optical fibers. 114a to 114b are terminal stations.

  Here, the configuration in FIG. 7 shows a case where each base station 112 and each terminal station 114 are each provided with two antennas, but there may be one or three or more. I do not care. Of course, the base stations 112a to 112d and the terminal stations 114a to 114b may have different numbers of antennas. In addition, each base station 112 is connected to each of the receiving unit 103 and the transmitting unit 104 through a single wired line, but each base station 112 to the control station 101 is connected through a single wired line. However, it may be configured to connect to the receiving unit 103 or the transmitting unit 104 by switching with a switch or the like.

  Next, the operation of the wireless communication apparatus shown in FIG. 7 will be described. First, the downlink for transmitting a signal from the base station 112 side to the terminal station 114 side will be described. Downlink data addressed to the terminal stations 114 a to 114 b from the network 100 is input to the control station 101 via the network interface 105, and then input to the MAC layer processing unit 106. Data input to the MAC layer processing unit 106 is temporarily stored in an individual buffer or the like. In actual hardware, the physical buffers may be the same, as long as they are logically managed individually.

  The MAC layer processing unit 106 selects a combination of the base stations 112a to 112d and the communication destination terminal stations 114a to 114b, and reads data corresponding to the terminal station 114 corresponding to the selected combination from the previous individual buffer. Then, processing in the MAC layer is performed and output to the transmission signal processing unit 110.

  The transmission signal processing unit 110 generates a wireless packet to be transmitted through a wireless line and performs modulation processing. Here, for example, if OFDM (Orthogonal Frequency Division Multiplexing) or OFDMA (Orthogonal Frequency Division Multiple Access) modulation is used, modulation processing for each frequency component is performed on the signal of each signal sequence, and multi-user MIMO transmission weight multiplication is performed. , IFFT (Inverse Fast Fourier Transform) processing that converts a signal on the frequency axis to a signal on the time axis, insertion of a guard interval and waveform shaping between OFDM symbols, D / A (digital / analog) conversion, radio frequency signal Up-conversion to the filter, filtering processing to remove out-of-band frequency components, and the like are performed to generate an electrical signal to be transmitted.

  The multiuser MIMO transmission weight at this time is generated in the transmission weight generation unit 111 based on the combination information of the terminal station 114 output from the MAC layer processing unit 106. The transmission signals that have been subjected to various types of transmission signal processing are output to the base stations 112a to 112d via the wired lines 113a to 113d and transmitted to the terminal stations 114a to 114b. As a result, signals to each radio station using the same frequency are spatially separated, and communication with each terminal station 114 can be performed at the same frequency and at the same time.

  In general, the wired lines 113a to 113d, including the case of the uplink shown below, are often configured with optical fibers. In this case, the electrical lines are electrically connected using optical / electrical conversion and electrical / optical conversion. Conversion between a simple signal and an optical signal to avoid loss on the transmission line. In addition, the generation of transmission weights by the transmission weight generation unit 111 requires channel information between the antennas of the base stations 112a to 112d and the terminal station 114a or 114b. Instead, it is assumed that it can be acquired by an existing technique related to channel feedback described later.

  Next, an uplink for transmitting a signal from the terminal station 114 side to the base station 112 side will be described. When uplink signals are received by the base stations 112a to 112d from the terminal stations 114a and 114b, the received signals are input to the received signal processing unit 107 through the wired lines 113e to 113h. The reception signal processing unit 107 performs down-conversion from a radio frequency signal to a baseband signal, filtering to remove out-of-band frequency components, A / D conversion, and FFT (or OFDMA) when using OFDM (or OFDMA). Various signal processing such as conversion of signals on the time axis into signals on the frequency axis (separation into signals of each frequency component) is performed by fast Fourier transform) processing.

  Among the signals subjected to the reception signal processing, a known signal for channel estimation separated into each frequency component (a preamble signal or the like added to the head of the radio packet) is output to the channel information acquisition unit 108, and the channel information The acquisition unit 108 estimates channel information between the antennas of the terminal stations 114 a and 114 b and the antennas of the base stations 112 a to 112 d for each frequency component, and outputs the estimation result to the reception weight generation unit 109. Reception weight generation section 109 calculates a reception weight to be multiplied by the reception signal for each frequency component based on the input channel information, and outputs it to reception signal processing section 107. The received signal processing unit 107 multiplies the received signal for each frequency component subjected to the above-described various signal processings by the received reception weight, and separates signal sequences transmitted by each terminal station at the same frequency and at the same time without interference. To do. Then, the demodulated signal is demodulated, and the reproduced data is output to the MAC layer processing unit 106.

  The MAC layer processing unit 106 performs processing related to the MAC layer (for example, conversion between data input / output to / from the network interface 105 and data transmitted / received on the wireless line, termination of header information of the MAC layer, and the like). Also, various scheduling processes including combinations of terminal apparatuses that simultaneously perform spatial multiplexing in multi-user MIMO transmission are performed, and scheduling results are output to the communication control unit 102. The reception data processed by the MAC layer processing unit 106 is output to an external device or a network via the network interface 105. In addition, the communication control unit 102 manages control related to overall communication such as management of a transmission source terminal device and overall timing control.

  FIG. 8 is a diagram showing a configuration of a terminal station that realizes space division multiplexing by a plurality of base stations 112. 8, 114 is a terminal station, 121 is a data input / output unit, 122 is a MAC layer processing unit, 123 is a communication control unit, 124 is a reception signal processing unit, 125 is a channel information acquisition unit, 126 is a transmission signal processing unit, Reference numerals 127a and 127b denote antennas. Here, the configuration in FIG. 8 shows a case where the terminal station includes two antennas, but it may be one or three or more.

  Next, the operation of the terminal station 114 shown in FIG. 8 will be described. First, the downlink for transmitting a signal from the control station 101 side to the terminal station 114 side will be described. When downlink signals addressed to the terminal station 114 from the base stations 112a to 112d are received by the antennas 127a to 127b, the received signals are input to the received signal processing unit 124. The received signal processing unit 124 is subjected to various types of signal processing for data demodulation, but the description is the same as the received signal processing unit 107 in FIG.

  Of the signals subjected to the received signal processing, a known signal for channel estimation separated into each frequency component (a preamble signal or the like added to the head of the radio packet) is output to the channel information acquisition unit 125, and the terminal station The channel information between the 114 antennas 127a and 127b and the respective antennas of the base stations 112a to 112d is estimated for each frequency component. The estimated channel information is also used for demodulation processing of the data portion of the received signal. The received signal processing unit 124 performs demodulation processing, and the reproduced data and the channel information estimated by the channel information acquisition unit 125 are output to the MAC layer processing unit 122.

  The MAC layer processing unit 122 performs processing related to the MAC layer (for example, conversion between data input / output to / from the data input / output unit 121 and data transmitted / received on a wireless line, termination of header information of the MAC layer, and the like). Do. Received data processed by the MAC layer processing unit 122 is output to an external display or the like via the data input / output unit 121. In addition, the communication control unit 102 manages communication-related controls such as transmission / reception timing control.

  Next, an uplink for transmitting a signal from the terminal station 114 side to the control station 101 side will be described. When data is input to the data input / output unit 121, it is subsequently input to the MAC layer processing unit 122. The MAC layer processing unit 122 converts the input data into data to be transmitted / received on a wireless line, performs processing such as adding MAC layer header information, and outputs the data to the transmission signal processing unit 126.

  Further, the information of the channel estimation result notified to the control station 101 acquired by the channel information acquisition unit 125 is also input to the transmission signal processing unit 126 through the processing in the MAC layer, but is included in the header information of the MAC layer, for example Alternatively, processing may be performed as a wireless packet for accommodating control information.

  The transmission signal processing unit 126 generates a wireless packet to be transmitted through a wireless line and performs modulation processing. The description is the same as that of the transmission signal processing unit 110 in FIG. The signal subjected to the transmission signal processing is transmitted to each of the base stations 112a to 112d via the antenna.

  Here, the transmission weight generation unit 111 or the reception weight generation unit 109 of the control station 101 needs channel information between the base stations 112a to 112d and the terminal stations 114a and 114b. As for the channel information of the link, the control station 101 side estimates the channel information using the received signal from the terminal station 114 side in the uplink, and for the channel information of the downlink, each terminal station 114 uses the downlink signal to make a channel. A method is used in which information is estimated, and channel information is accommodated in control information transmitted in the uplink and notified to the control station 101 by feedback.

  9 and 10 are flowcharts showing channel information acquisition processing operations in the prior art. There are roughly two methods for acquiring channel information in the prior art. Here, a method (FIG. 9) of acquiring channel information using an uplink signal and a method (FIG. 10) of acquiring using channel information will be described.

FIG. 9 is a flowchart showing a processing operation of the channel estimation method in the uplink. As shown in FIG. 9, in the case of uplink, when channel information estimation starts (step S101), a radio packet including a channel estimation training signal transmitted from each terminal station 114 to the base station 112, The control station 101 receives the data via the base station 112 (step S102). The control station 101 performs channel estimation using a training signal included in the wireless packet (step S103), and stores and manages it as a channel matrix H _{i, j} between the terminal station 114 and each base station 112 ( Step S104) and the process ends (Step S105). Here, H _{i, j} represents channel information between the i-th terminal station and the j-th base station, where the number of antennas of the terminal station is N _MT and the number of antennas of the base station is N _BS , the matrix H _{i, j} The size of _j is N _MT × N _BS .

In the estimation method using the uplink, since a plurality of base stations 112 can receive signals from the terminal station 114, a channel matrix H _ij between the terminal station i and each base station j capable of receiving a channel estimation signal is obtained. It can be acquired at the same time. The control station 101 performs the channel estimation process on a plurality of terminal stations 114 with which the base station 112 communicates in cooperation.

FIG. 10 is a flowchart showing the processing operation of the channel estimation method in the downlink. As shown in the figure, in the case of the downlink, when channel information estimation is started (step S111), the terminal station 114 receives a radio packet including a channel estimation training signal transmitted from each base station 112. (Step S112), the terminal station 114 performs channel estimation using a training signal or the like (Step S113). The terminal station 114 accommodates the channel estimation result in a “radio packet for accommodating control information” and transmits it to the base station 112 (step S114). The control station 101 receives the “radio packet for accommodating control information” transmitted from the terminal station 114 via the base station 112, and acquires channel information (step S115). Then, the received channel information is stored in a memory or the like as a channel matrix H _ij between the terminal station 114 and each base station 112, a database relating to channel information is constructed (step S116), and the process is terminated (step S117). Each base station 112 individually performs the above estimation method for each terminal station that can receive a signal in circuit design.

  If the OFDM modulation method is used, the channel information acquisition processing operation shown in FIGS. 9 and 10 may be performed for each frequency component.

  The above is an example of feedback of channel information, but there is also a method of using the estimation result of uplink channel information for downlink channel information. In general, the channel information of the downlink and the uplink in the reverse direction do not match. The combination of the high power amplifier of the base station 112 that transmits at the downlink and the low noise amplifier of the terminal station 114 on the receiving side, and the low noise amplifier of the base station 112 that receives the high power amplifier of the terminal station 114 that transmits at the uplink. This is because the combination is different and the complex phase and amplitude are different between downlink channel information and uplink channel information.

  However, this means that the downlink information is converted and estimated from the channel information of the uplink by performing a process (calibration process) that corrects the difference between the high power amplifier in the downlink and the low noise amplifier in the uplink. Is possible. Specifically, the conversion process can be performed by multiplying the channel information in the uplink by a coefficient for correcting the difference between the high power amplifier and the low noise amplifier.

  Any of the above-described channel information feedback methods may be used, but the channel information is acquired in advance in this way, and generally, based on this channel information when actually communicating. Calculate the transmission weight. As for the reception weight, the reception weight can be calculated based on the channel estimation result performed at the time of actual data reception. However, the reception weight is calculated based on the channel information obtained in advance by the above-mentioned channel feedback. It is also possible. In addition, since channel information changes with time, it is common to update periodically according to a situation, for example.

  Next, transmission / reception processing using the multiuser MIMO weight acquired by the processing operation described above will be described. FIGS. 11 and 12 are flowcharts showing reception weight calculation processing and reception signal processing of the control station in the uplink of base station cooperation multi-user MIMO.

First, the reception weight calculation processing operation will be described with reference to FIG. When a signal is received from the terminal station 114 and processing is started (step S121), information about the terminal station 114 that is a communication partner is acquired from the MAC layer processing unit 106 (step S122), and is shown in FIG. 9 and FIG. From the channel information acquired in the procedure, the partial matrices H _{i, j} corresponding to the communication partner terminal station 114 and the base station 112 are read (step S123) and synthesized to create the entire matrix H _all (step S124). ). A reception weight matrix is calculated for the entire channel matrix (step S125), the process is terminated (step S126), and reception signal separation processing of information (bit string) following the received data is continued.

In this example, the reception weight is calculated based on the channel information obtained in advance by the channel feedback described above. However, a new channel estimation is performed based on the preamble signal added to the received data. It is also possible to use the result of performing. In this case, instead of reading the partial matrix H _{i, j} from the memory in the process of step S123, it is replaced with acquisition of the partial matrix H _{i, j} by channel estimation processing.

Next, the received signal processing operation will be described with reference to FIG. When each base station 112 receives a signal from the terminal station 114 and starts reception processing (step S131), first, the control station 101 acquires the received signal R _i received by the i-th base station from all the base stations 112 ( Step S132). Here, it includes processing up to 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 signal corresponding to each base station 112 is subjected to signal processing such as separation into frequency components by an FFT circuit (step S133). Furthermore, the reception weight calculated by the processing operation shown in FIG. 11 is multiplied by the reception signal of each base station 112 for each frequency component, thereby separating the signal sequence transmitted from each terminal station 114 and multiplexed in space. Then, the estimated signal Si before the signal detection process for the separated signal is calculated (step S134). Finally, a signal detection process for each signal series is performed (step S135), the process is terminated, and the signal is output to the MAC layer (step S136).

FIGS. 13 and 14 are flowcharts illustrating the transmission weight calculation processing operation and the transmission signal processing operation of the control station in the downlink of the base station cooperation multi-user MIMO. First, the transmission weight calculation processing operation will be described with reference to FIG. When data is input from the MAC layer processing unit 106 and processing is started (step S141), information about the terminal station 114 that is a communication partner is acquired from the MAC layer processing unit 106 (step S142). From the channel information acquired in the described procedure, the partial matrices H _{i, j} corresponding to the communication partner terminal station 114 and the base station 112 are read (step S143), and they are combined to create the entire matrix H _all ( Step S144). A transmission weight matrix is calculated for the entire channel matrix (step S145), the processing is terminated (step S146), and signal processing relating to transmission data is continued.

  Next, transmission signal processing will be described with reference to FIG. When the process is started (step S151), data to be transmitted to each terminal station 114 is input from the MAC layer processing unit 106 (step S152). Transmission data processing such as various modulation processing is performed on the data to be transmitted for each destination terminal station 114 to generate transmission signals of each frequency component (step S153). Then, the transmission weight calculated by the process shown in FIG. 13 is multiplied by the transmission signal of each destination for each frequency component to generate a signal transmitted by each base station 112 (step S154). In addition, a series of signal processing such as conversion to signals on the time axis by IFFT, provision of guard intervals, waveform shaping between OFDM symbols, D / A conversion, etc., for signals transmitted by each base station 112 This is transferred to the base station 112 and a signal is transmitted to each terminal station 114 via each base station 112 (step S155), and the transmission process is completed (step S156).

  In general, if the total number of antennas included in the base station 112 is K and the number of spatially multiplexed signal sequences (that is, the total number of antennas included in the terminal station 114) is L, K and L need not match, If the value of L is equal to or less than the value of K, signals of a large number of signal sequences can be spatially multiplexed.

Here, the total channel matrix H _all used when performing space division multiplexing is obtained by using the obtained partial channel matrix H _ij in the case of uplink (10), and in the case of downlink (11). Synthesize like equation.

Then, transmission / reception weights in the uplink and the downlink are calculated using the channel matrix H _all shown in the equations (10) and (11).

Note that there are various calculation methods for the transmission / reception weights used in the above signal processing in addition to the Gramschmitt orthogonalization method described using the equations (6) to (9). For example, a method (Zero Forcing, ZF) for obtaining a pseudo inverse matrix of the channel matrix H _all can be expressed as the following equations (12) and (13) in the case of the downlink and uplink.

For MMSE weights known as similar transmission / reception weights, equations (14) and (15) may be used if the noise power is σ ² .

  In addition, nonlinear signal processing such as MLD (Maximum Likelihood Detection) may be performed.

  The above is the explanation of the base station cooperation multi-user MIMO. However, the important point in the present technology is that the channel information between other cells that would otherwise cause inter-cell interference is mutually acquired, and transmission / reception weights for space division multiplexing are obtained. There is a place to calculate. For this reason, it is desirable to acquire all channel information with other cells that cause interference due to the arrival of signals in the circuit design in order to suppress the inter-cell interference.

  As described above, a typical feature of multi-user MIMO is that each time transmission / reception is performed based on channel information between the transmission side and the reception side in transmission / reception processing in the control station 101 in the uplink. The latest channel information is read (steps S123 and S143), and a transmission / reception weight is calculated based on the read channel information (steps S125 and S145). That is, the calculation of the transmission weight and the reception weight is performed at every transmission or reception. This is due to channel time variation, and it is necessary to periodically perform channel information estimation processing in order to obtain good channel estimation accuracy. As the channel estimation cycle is set shorter, transmission / reception of control information for channel estimation becomes necessary and overhead increases.

  In addition, when base stations arranged over a wide area cooperate to perform spatial multiplexing by multiuser MIMO, channel information between the base station of each cell and the terminal stations existing in each cell is individually estimated. This requires a desired number of orthogonal training signals. In general, it is preferable that the pattern of the training signal itself is 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 cooperative base stations The overhead increases with the increase. Such overhead becomes a factor that gives an estimation error of channel information in a propagation environment that varies from moment to moment.

  In addition, in a reception environment with a small SNR or SINR, errors due to noise and interference are reflected in the channel estimation result. In general, the greater the distance between the terminal station and the base station, the smaller the SNR and the greater the channel estimation error. FIG. 15 shows an example of arrangement of cooperative base stations and terminal stations in the prior art. For example, as shown in FIG. 15, the cells are arranged in a regular hexagonal densely packed state, and the base station is arranged at the center of each cell. Each base station is connected to the control station via a wired line, but this is omitted here. Further, in the presence of a large number of terminal stations, attention is paid to one cell existing in the central cell, and the path between the terminal and the peripheral base station is illustrated.

  In this case, with respect to the propagation distance between the terminal station existing in the center cell and the nearest 6-cell base station adjacent to it (solid line arrow in the figure), the propagation distance between the next adjacent 12-cell base station (Dotted arrow in the figure) is large, and the SNR of the signal from the next adjacent cell is small with respect to the nearest neighbor. For this reason, the channel estimation error between the terminal station of the center cell and the base station of the next adjacent 12 cells is larger than the channel estimation error between the base stations of the adjacent 7 cells. In addition, since the SNR can be significantly lowered due to the influence of fading or the like, channel estimation cannot be performed with sufficient accuracy in such an environment. When multiuser MIMO weights are generated in a state where errors are included in channel estimation, suppression of interference to terminal stations belonging to other cells, that is, null control is destroyed due to the influence of errors, and nulls are further directed to such interference sources. For this reason, transmission / reception power to a desired terminal station serving as a communication partner is lost, leading to a decrease in frequency utilization efficiency.

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

  By the way, in order to operate the above-described technique in which a plurality of base stations cooperate to perform multi-user MIMO transmission in an actual system, a design based on channel estimation errors is required. The channel estimation between the terminal station and the distant base station will reduce the estimation accuracy with attenuation on the propagation path. Estimate is required.

  However, since this increase in overhead reduces transmission efficiency, a method for allowing insufficient channel estimation accuracy is established, and a technique for suppressing the influence of channel estimation errors and improving frequency utilization efficiency is required. . Therefore, it is required to perform multi-user MIMO transmission in which interference is sufficiently reduced even in a situation where a highly accurate estimated value and a less accurate estimated value are mixed.

  The present invention has been made in view of such circumstances, and in a process related to space division multiplex transmission in which a plurality of cells cooperate with each other and communicate with a plurality of terminal stations using the same time and the same frequency, a channel estimation error is provided. An object of the present invention is to provide a wireless communication apparatus, a wireless communication system, and a wireless communication method that suppress the influence of the above and improve the frequency use efficiency.

  The present invention includes a plurality of base stations equipped with antennas, a control station connected to each of the base stations, and a plurality of terminal stations equipped with antennas communicating with any of the base stations, A wireless communication apparatus operating as the control station in a wireless communication system in which a base station communicates on the same frequency at the same time as the plurality of terminal stations connected to the base station, wherein the plurality of base stations and the plurality of base stations In all or part of the combination of terminal stations, channel information acquisition means for acquiring channel information between antennas provided in the base station and the terminal station, and the estimation accuracy of the channel information acquired by the channel information acquisition means is Channel information zero replacement means for replacing the channel information with zero when the threshold information is lower than a predetermined threshold, the plurality of base stations, and the plurality of terminals Weight calculation means for calculating a transmission weight and / or reception weight in space division multiplex transmission using the entire channel matrix having the channel information between the antennas included in the antenna, and the transmission weight calculated by the weight calculation means and Alternatively, communication control means for performing space division multiplex transmission between the plurality of base stations and the plurality of terminal stations using the reception weight is provided.

  In the present invention, the channel information acquisition means acquires the channel information only for a combination of the base station and the terminal station whose estimation accuracy calculated from a circuit design exceeds a predetermined threshold, The information zero replacement means performs zero replacement on the channel information only for a combination of the base station and the terminal station that does not acquire the channel information.

  The present invention includes a plurality of base stations equipped with antennas, a control station connected to each of the base stations, and a plurality of terminal stations equipped with antennas communicating with any of the base stations, A wireless communication system in which a base station communicates on the same frequency at the same time as the plurality of terminal stations connected to the base station, wherein the control station is a combination of the plurality of base stations and the plurality of terminal stations In all or part of the above, channel information acquisition means for acquiring channel information between the antennas of the base station and the terminal station, and the estimation accuracy of the channel information acquired by the channel information acquisition means is lower than a predetermined threshold Channel information zero replacement means for replacing the channel information with zero in the case of low, and a channel between the antennas provided in the plurality of base stations and the plurality of terminal stations Using weight calculation means for calculating a transmission weight and / or reception weight in space division multiplex transmission using the entire channel matrix having information as elements, and using the transmission weight and / or reception weight calculated by the weight calculation means Communication control means for performing space division multiplex transmission between the plurality of base stations and the plurality of terminal stations is provided.

  The present invention includes a plurality of base stations equipped with antennas, a control station connected to each of the base stations, and a plurality of terminal stations equipped with antennas communicating with any of the base stations, A radio communication method performed by the control station in a radio communication system in which a base station communicates on the same frequency at the same time as the plurality of terminal stations connected to the base station, wherein the plurality of base stations and the plurality of base stations In all or a part of the combination of terminal stations, a channel information acquisition step for acquiring channel information between antennas provided in the base station and the terminal station, and an estimation accuracy of the channel information acquired by the channel information acquisition step is predetermined. A channel information zero replacement step of replacing the channel information with zero, the plurality of base stations, and the plurality of base stations A weight calculation step of calculating a transmission weight and / or a reception weight in space division multiplex transmission using an entire channel matrix having channel information between antennas included in a terminal station as an element, and the transmission weight calculated by the weight calculation step And / or a communication control step of performing space division multiplex transmission between the plurality of base stations and the plurality of terminal stations using the reception weight.

  According to the present invention, in the processing related to space division multiplex transmission in which a plurality of cells communicate with a plurality of terminal stations using the same time and the same frequency, the influence of channel estimation error is suppressed, and the frequency utilization efficiency is improved. The effect that it becomes possible to improve is acquired.

It is a flowchart which shows the channel information estimation process operation | movement in the 1st Embodiment of this invention. It is a flowchart which shows the channel information estimation processing operation in the 2nd Embodiment of this invention. It is a flowchart which shows the channel information estimation process operation | movement in the 3rd Embodiment of this invention. It is a flowchart which shows the channel information estimation process operation | movement in the 3rd Embodiment of this invention. It is explanatory drawing which shows the effect of this invention in the frequency utilization efficiency in a channel estimation error environment. It is a block diagram which shows the structural example of a multiuser MIMO system. It is a block diagram which shows the structural example of a radio | wireless communication apparatus. It is a block diagram which shows the structural example of a terminal station. It is a flowchart which shows the acquisition processing operation | movement of the channel information in a prior art. It is a flowchart which shows the acquisition processing operation | movement of the channel information in a prior art. It is a flowchart which shows the reception weight calculation processing operation of the control station in the uplink of base station cooperation multiuser MIMO. It is a flowchart which shows the received signal processing operation | movement of the control station in the uplink of base station cooperation multiuser MIMO. It is a flowchart which shows the transmission weight calculation processing operation of the control station in the downlink of base station cooperation multiuser MIMO. It is a flowchart which shows the transmission signal processing operation | movement of the control station in the downlink of base station cooperation multiuser MIMO. Example of arrangement of cooperative base stations and terminal stations in the prior art

Hereinafter, a wireless communication apparatus according to an embodiment of the present invention will be described with reference to the drawings. First, the basic concept of the present invention will be described. In conventional base station cooperation multi-user MIMO, in order to generate transmission / reception weights, all channel information relating to the entire channel matrix H _all , that is, a partial channel matrix is required. However, when a channel estimation error due to channel estimation overhead or poor reception environment occurs, the frequency utilization efficiency decreases as described above.

Therefore, in the present invention, the channel information quality does not satisfy a certain condition, that is, when the estimation accuracy is low, the channel information is replaced with 0, and this new entire channel partially replaced with 0 Generate weights based on information. As a result, for example, the entire channel matrix of the uplink partially substituted with 0 as shown in the equation (16) is generated.

  Here, in order to examine the expression (16) in detail, the sub-matrices of the first column and the L-th column of this matrix are compared. For the first column (strictly speaking, if the sub-matrix is a multi-column matrix, it becomes a vertically long matrix extending over a plurality of rows, but here this block matrix is collectively referred to as the first row), 3 rows All the components are zero in the lines below the eye. Regarding the Lth column, all the components are zero in the first to K-2th rows. Actually, the position of each base station and other base stations may not be so cleanly arranged that the diagonal components of the entire matrix are near zero and the other parts are zero. Since the range to reach is limited, it is possible to easily find a column component in which one row component is non-zero and the other row component is zero.

At this time, for example, the column vector included in the first row submatrix and the column vector included in the Lth row submatrix have a relationship that all become zero when taking the inner product. That is, since the column vectors are orthogonal to each other, it is not necessary to waste the degree of freedom of the multidimensional vector space especially for mutual orthogonalization, and no orthogonalization loss is caused. In other words, since it means that null is not directed to the terminal station of the i-th cell, the interference from the terminal station of the j-th cell to the i-th base station is suppressed for the channel information H _{i, j} replaced with 0. It will remain as it is.

  On the other hand, if the channel information contains a large estimation error, the inner product of those column vectors does not become zero, so even a slight interference wastes a degree of freedom to form a null in the calculation, and is orthogonal. This will cause a loss. Furthermore, since the null formation performed up to that point is also the null formation performed including the estimation error, there is a risk of causing new interference as a result unlike the accurate null formation. In some cases, it is expected that the amount of interference will be increased without reducing the original interference power. In such a case, interference from the terminal station is tolerated to some extent, unnecessary power is not wasted due to useless null formation, and sufficient power for the desired signal is secured to reduce SIR. Suppression is effective.

  FIG. 5 shows the result of calculating the frequency utilization efficiency achieved by the base station cooperation MU-MIMO in the present invention by computer simulation. The horizontal axis represents frequency utilization efficiency, and the vertical axis represents the cumulative probability distribution function (CDF). In this simulation, 37 cells are arranged in a hexagonal shape as shown in FIG. The dotted line in the figure shows the frequency utilization efficiency when channel information including estimation errors between the base station and the terminal station of all cells is used, and the solid line shows channel information including estimation errors from the own cell and the nearest cell. The frequency utilization efficiency CDF when only channel information is non-zero and zero substitution is performed on other channel information is shown. In this evaluation, channel estimation accuracy and signal propagation attenuation are given by a predetermined approximate expression, and transmission power, noise power, and the range of channel information to be zero-substituted are evaluated as parameters. Although it showed only a tendency, the same effect can be seen for other conditions.

  With regard to this example, in the application of the present invention, the channel information between the base stations and terminal stations of all 37 cells arranged is not used, but there are seven bases in 6 cells adjacent to the own cell, which are smaller than that. Only channel information between the station and the terminal station is used, and other channel information is replaced with 0. At this time, when there is a channel estimation error, it can be seen that the CDF characteristic of frequency utilization efficiency according to the present invention in which a part of the channel matrix is replaced with 0 is superior (located on the right side in the graph).

Based on the above principle of operation, a specific embodiment of the present invention will be described below.
<First Embodiment>
FIG. 1 is a flowchart showing channel information acquisition processing operation in the uplink according to the first embodiment of the present invention. The configuration of the wireless communication apparatus in this embodiment is the same as that shown in FIGS. 7 and 8, and the signal processing operation in transmission / reception is the same as that shown in FIGS. A feature of the present embodiment is that the channel information acquisition unit 108 of the control station 101 measures the quality of the acquired channel information, and if the condition is not satisfied, the channel information is replaced with 0 and stored, and transmitted / received It is used for weight generation.

  As a result, the channel information with low reliability is replaced with 0, and the weight is calculated without using the channel information including the estimation error, and the reduction of the desired power can be suppressed and the frequency utilization efficiency can be improved. Become.

  Next, the channel information estimation processing operation will be described with reference to FIG. There are several variations of downlink channel estimation (feedback of channel information) as described above, but for uplink, channel estimation is performed based on the signal received by the base station 112. Hereinafter, the description will focus on uplink channel estimation.

  First, when channel information estimation processing is started (step S1), a radio packet including a channel estimation training signal transmitted from each terminal station 114 to the base station 112 is transmitted via the base station 112 to the control station 101. Is received (step S2). The control station 101 performs channel estimation using a training signal included in the wireless packet (step S3). Then, the estimated quality of the channel information is measured (step S4), and it is determined whether or not the quality of the measured channel information satisfies the condition (step S5).

  Here, for example, EVM (Error Vector Magnitude) is used as the quality. The EVM is a value indicating a difference from the reference point of the received symbol. As a condition, a certain value is set as a threshold, EVM is measured from the difference from the reference point of the training symbol shared by the transmitting and receiving stations, and the condition may be satisfied if the measured EVM is smaller than the threshold. Any other means such as using the reception level itself, estimating the signal quality from the characteristics of SNR (Signal to Noise Power Ratio), SINR (Signal to Interference and Noise Power Ratio), and BER (Bit Error Rate) It may be used as an index of

If Yes in step S5 (the quality of the channel information satisfies the condition), the estimated channel information is stored and managed as it is as the channel matrix H _{i, j} between the terminal station i and the base station j (step S7), and processing Is finished (step S8). On the other hand, if No in step S5 (the condition is not satisfied), the channel information is all replaced with 0, the process proceeds to step S7, and is stored as the channel matrix H _{i, j} , and the process is terminated (step S8). .

  With this operation, the entire channel matrix partially replaced with 0 is generated, and a transmission / reception weight of multi-user MIMO based on base station cooperation is generated using the channel matrix. Thereby, it is possible to suppress the influence due to the channel estimation error and improve the frequency utilization efficiency.

  Although the above description is about the uplink, the same processing is possible for the downlink. Regarding downlink channel estimation, as explained earlier, there are variations between the method of using the uplink channel estimation result and the method of feeding back the downlink channel estimation result on the terminal side in the control information. Regardless of which one is used, the equivalent of uplink processing is performed by performing zero replacement of channel information with low estimation accuracy for downlink channel information determined after those processing. Is possible. Hereinafter, a case where channel information is fed back from the terminal station 114 side will be described in detail.

<Second Embodiment>
FIG. 2 is a flowchart showing channel information acquisition processing operation in the downlink according to the second embodiment of the present invention. In the description of the first embodiment, it is assumed that the base station 112 also performs zero replacement when the estimation accuracy for downlink channel information is reduced. However, downlink channel estimation is illustrated in FIG. In the case where the terminal station 114 performs the above, it is also possible to perform the zero substitution to the downlink channel information on the terminal station 114 side. The configuration of the wireless communication apparatus in this embodiment in this case is the same as that shown in FIGS. 7 and 8, and the signal processing operation in transmission / reception is the same as that shown in FIGS. The feature of this embodiment is that the channel information acquisition unit 125 of the terminal station 114 measures the quality of the acquired channel information, and if the condition is not satisfied, the channel information is replaced with 0 and fed back to the control station 101. By the way.

  As a result, the channel information with low reliability is replaced with 0 and notified to the control station, so that the null control collapses and the desired power is reduced by forcibly calculating the weight using the channel information including the estimation error. It becomes possible to suppress and improve the frequency utilization efficiency.

  The channel information estimation processing operation will be described with reference to FIG. First, when the channel information estimation process is started (step S11), a radio packet including a channel estimation training signal transmitted from any of the base stations 112 of the control station 101 to the terminal station 114 is transmitted to the terminal station 114. Is received (step S12). The terminal station 114 performs channel estimation using a training signal included in the wireless packet (step S13). Then, the estimated quality of the channel information is measured (step S14), and it is determined whether the measured quality of the channel information satisfies the condition (step S15).

If Yes in step S15 (the quality of the channel information satisfies the condition), the terminal station 114 accommodates this channel estimation result in the “radio packet for accommodating control information” and transmits it to the base station 112 (step S15). S17). The control station 101 receives the “radio packet for accommodating control information” transmitted from the terminal station 114 via the base station 112, and acquires channel information (step S18). Then, the received channel information is stored in a memory or the like as a channel matrix H _{i, j} between the terminal station i and the base station j (step S19), and the process ends (step S20).

  On the other hand, in the case of No (does not satisfy the condition) in Step S5, the channel information is replaced with 0 (Step S16), the process proceeds to Step S17, and Steps S17 to S19 are performed as processing, and the processing is terminated ( Step S20). The above operation is performed for each base station connected to the control station.

  Through this operation, the entire channel matrix partially replaced with 0 is acquired, and the transmission / reception weights of multi-user MIMO by base station cooperation are generated using the channel matrix. Thereby, it is possible to suppress the influence due to the channel estimation error and improve the frequency utilization efficiency.

  In step S17, the channel information replaced with 0 is notified to the control station 101. However, the notification itself may not be performed. At that time, the control station 101 generates transmission / reception weights with the channel information for the terminal station 114 set to 0, and the effect intended by the present invention can be obtained similarly.

<Third Embodiment>
In the first and second embodiments, after obtaining channel information, the estimation accuracy is evaluated to determine whether or not to perform zero substitution. However, since the arrangement of the base stations 112 is known, the first neighboring cell, the second neighboring cell, the third neighboring cell, etc. It is predictable from what cell and at what level the signal can be received. To be precise, rather than predicting, it is determined whether the channel estimation accuracy is higher than the desired level in the circuit design, and between the cells within the range where channel estimation is possible with the accuracy higher than the desired level. In consideration of only the mutual interference, it is possible to cope with other cells by performing zero insertion (corresponding to zero substitution in the above example) without actually performing channel estimation processing.

  Alternatively, when the number of cells in which channel estimation can be performed is limited due to system design, zero insertion may be performed on channel information between cells in which channel estimation exceeding the upper limit number cannot be performed.

  Although not described in the description of the prior art, the acquisition of the channel information in FIGS. 9 and 10 requires transmission / reception of wireless packets for acquiring each channel information. In order to avoid packet collision, it is necessary to make adjustments so that wireless packets are not transmitted on the same frequency and at the same time. However, if only one signal transmission is allowed at a certain frequency at a certain time, the signal transmission / reception must be performed in order over an enormous amount of time. Channel estimation is performed while allowing overlapping of timing and frequency. The operation of the entire system is designed so that the cells with overlapping timing and frequency have a sufficiently small mutual interference. In this embodiment, the necessity of channel estimation is determined through this design, and zero insertion is performed for cells in which channel estimation is not performed.

  FIG. 3 is a flowchart showing the calculation processing operation of the transmission / reception weight according to the third embodiment of the present invention. The configuration of the wireless communication apparatus in the present embodiment is the same as that shown in FIGS. 7 and 8, and the signal processing flow in transmission / reception is the same as that shown in FIGS. The feature of this embodiment is that the cells to be subjected to channel estimation are limited in terms of circuit design or system design, channel estimation is performed only between those cells, and the channel information is managed with non-zero values. The channel information that is not acquired is managed as 0.

  As a result, part of the channel information is managed as 0, thereby suppressing the collapse of null control and the decrease in the desired power due to the forced calculation of the weight using the channel information including the estimation error, and improving the frequency utilization efficiency. It becomes possible to improve.

  The reception weight calculation processing operation will be described with reference to FIG. The basic operation is the same as that of FIG. 11, and zero insertion is performed between step S123 and step S124 as a submatrix that is not subject to channel estimation as step S127.

Similarly, the transmission weight calculation processing operation will be described with reference to FIG. The basic operation is the same as in FIG. 13, and zero insertion is performed as a submatrix that is not subject to channel estimation as step S147 between step S143 and step S144. In this way, the entire matrix H _all including the partial matrix for which channel information is not measured can be acquired, and transmission / reception weights can be calculated.

In addition, the process of step S127 and step S147 here can implement | achieve completely equivalent process also with another method. For example, in the channel information acquisition flow related to the prior art shown in FIG. 9 and FIG. 10, sub-matrices H _{i, j} for all combinations are prepared regardless of the presence or absence of actual channel information estimation processing. In this case, zeros are inserted as initial values. In the actual operation state, the channel information measured every time channel estimation is recorded as a non-zero value in the submatrix _{Hi, j} . In this state, when step S123 and step S143 in FIG. 11 and FIG. 13 are performed, a matrix in which each component is zero is read as the value of the partial matrix H _{i, j} for which channel estimation is not performed. The operation is equivalent to the processing of steps S123 and S127 of FIG. 3 and steps S143 and S147 of FIG.

  However, most of the sub-matrixes of the matrix represented by the equation (16) are originally low in estimation accuracy, that is, channel information between cells in which channel estimation is not performed due to channel design. Then, it is necessary to secure an excessively large memory area. In the case of the processing shown in FIG. 3, since it is sufficient to manage only non-zero components that actually perform channel estimation, the processing can be performed while the memory capacity is reduced accordingly.

  Through the above operation, the entire channel matrix in which 0 is partially inserted is generated, and the transmission / reception weights of multi-user MIMO based on base station cooperation are generated using the channel matrix. Thereby, it is possible to suppress the influence due to the channel estimation error and improve the frequency utilization efficiency.

  As described above, multi-user MIMO is a technique in which one base station transmits to a plurality of terminals simultaneously by beam forming, and signals do not reach terminals other than the terminal that is the destination of each data signal. By performing beam forming in this way, simultaneous transmission can be performed without causing interference. As an application form, when a plurality of base stations perform transmission simultaneously, beam forming is performed so that signals do not reach terminals other than the terminal that is the destination of each data signal, thereby suppressing interference between cells. There is a form of simultaneous transmission. In order to perform beam forming, it is necessary to estimate the channel information between all base stations and all terminals to form a beam. However, in the case of a wide range system including a large number of base stations and terminals, Some combinations have low channel information estimation accuracy. For example, if beam forming is performed using channel information with low estimation accuracy as in the case where the distance between the base station and the terminal is far away, a correct beam cannot be formed, and interference may be generated. is there.

  In this embodiment, each piece of channel information is evaluated, and channel information determined to have low accuracy is replaced with 0 to form a beam. If the channel information is 0, the base station does not perform control to direct a null toward the direction of the terminal, but it is possible to reduce the risk that the beam is directed in the wrong direction. In addition, since the degree of freedom of the antenna increases by ignoring the direction, the degree of freedom can be directed to beam control between the base station and the terminal from which other highly accurate channel information has been acquired, Furthermore, it becomes possible to form a beam with high accuracy.

  A program for realizing the functions shown in FIGS. 1 to 4 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read by a computer system and executed to execute wireless communication processing. May be performed. Here, the “computer system” includes an OS and hardware such as peripheral devices. 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, what is called a difference file (difference program) may be sufficient.

  As mentioned above, although embodiment of this invention has been described with reference to drawings, the said embodiment is only the illustration of this invention, and it is clear that this invention is not limited to the said embodiment. is there. Accordingly, additions, omissions, substitutions, and other changes of the components may be made without departing from the technical idea and scope of the present invention.

  In a radio access system in which a plurality of base stations perform signal transmission using the same frequency channel, it can be applied to applications in which it is indispensable for each base station to perform signal transmission cooperatively.

  DESCRIPTION OF SYMBOLS 100 ... Network, 101 ... Control station, 102, 123 ... Communication control part, 103 ... Reception processing part, 104 ... Transmission processing part, 105 ... Network interface, 106, 122. ··· MAC layer processing unit, 107, 124 ... reception signal processing unit, 108, 125 ... channel information acquisition unit, 109 ... reception weight generation unit, 110, 126 ... transmission signal processing unit, 111 Transmission weight generation unit 112a to 112d Base station 113a to 113h Wired line 114, 114a to 114b Terminal station 121 Data input / output unit 127a to 127b ..Antenna, 801 ... Base station, 802-1, 802-2, 802-3 ... Terminal equipment

Claims (4)

A plurality of base stations each including an antenna; a control station connected to each of the base stations; and a plurality of terminal stations including an antenna that communicates with any of the base stations. A wireless communication device that operates as the control station in a wireless communication system that performs communication on the same frequency at the same time as the plurality of terminal stations connected to a base station,
Channel information acquisition means for acquiring channel information between antennas of the base station and the terminal station in all or part of the combination of the plurality of base stations and the plurality of terminal stations;
Channel information zero replacement means for replacing the channel information with zero when the estimation accuracy of the channel information acquired by the channel information acquisition means is lower than a predetermined threshold;
Weight calculation means for calculating transmission weights and / or reception weights in space division multiplex transmission using an entire channel matrix having the channel information between antennas of the plurality of base stations and the plurality of terminal stations as elements;
Communication control means for performing space division multiplex transmission between the plurality of base stations and the plurality of terminal stations using the transmission weight and / or the reception weight calculated by the weight calculation means. A wireless communication device. The channel information acquisition means performs the acquisition of the channel information only for a combination of the base station and the terminal station whose estimation accuracy calculated from circuit design exceeds a predetermined threshold value,
2. The radio communication according to claim 1, wherein the channel information zero replacement unit performs zero replacement on the channel information only for a combination of the base station and the terminal station that does not acquire the channel information. apparatus. A plurality of base stations each including an antenna; a control station connected to each of the base stations; and a plurality of terminal stations including an antenna that communicates with any of the base stations. A wireless communication system for performing communication on the same frequency at the same time as the plurality of terminal stations connected to a base station,
The control station
Channel information acquisition means for acquiring channel information between antennas of the base station and the terminal station in all or part of the combination of the plurality of base stations and the plurality of terminal stations;
Channel information zero replacement means for replacing the channel information with zero when the estimation accuracy of the channel information acquired by the channel information acquisition means is lower than a predetermined threshold;
Weight calculation means for calculating transmission weights and / or reception weights in space division multiplex transmission using an overall channel matrix having channel information between antennas of the plurality of base stations and the plurality of terminal stations as elements;
Communication control means for performing space division multiplex transmission between the plurality of base stations and the plurality of terminal stations using the transmission weight and / or the reception weight calculated by the weight calculation means. A wireless communication system. A plurality of base stations each including an antenna; a control station connected to each of the base stations; and a plurality of terminal stations including an antenna that communicates with any of the base stations. A wireless communication method performed by the control station in a wireless communication system that performs communication on the same frequency at the same time as the plurality of terminal stations connected to a base station,
Channel information acquisition step for acquiring channel information between antennas of the base station and the terminal station in all or part of the combination of the plurality of base stations and the plurality of terminal stations;
A channel information zero replacement step of replacing the channel information with zero when the estimation accuracy of the channel information acquired by the channel information acquisition step is lower than a predetermined threshold;
A weight calculation step of calculating a transmission weight and / or a reception weight in space division multiplex transmission using an entire channel matrix having elements of channel information between antennas of the plurality of base stations and the plurality of terminal stations;
A communication control step of performing space division multiplex transmission between the plurality of base stations and the plurality of terminal stations using the transmission weight and / or the reception weight calculated in the weight calculation step. A wireless communication method.

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