JP4551933B2 - Multiple channel spatial multiplexing transmission method and communication apparatus - Google Patents

Description

  The present invention mainly controls frequency channels that share frequency channels among a plurality of communication partner devices, performs spatial multiplexing of independent signal sequences, and transmits the frequency channels that use orthogonal frequency division multiplexing. Thus, the present invention relates to a multiple channel spatial multiplexing transmission method and a communication apparatus that reduce the risk of communication degradation due to channel estimation errors.

  In recent years, as the high-speed wireless access system using the 2.4 GHz band or the 5 GHz band, the IEEE802.11g standard, the IEEE802.11a standard, and the like are remarkable. In these systems, an orthogonal frequency division multiplexing (OFDM) modulation scheme, which is a technique for stabilizing characteristics in a multipath fading environment, is used, and a transmission rate of 54 Mbps at the maximum is realized. However, since the transmission rate here is the transmission rate on the physical layer, the transmission efficiency in the MAC (Medium Access Control) layer is actually about 50% to 70%, and the upper limit of the actual throughput. The value is about 30 Mbps. On the other hand, in the world of wired LANs (Local Area Networks), the Ethernet (registered trademark) 100Base-T interface and the use of FTTH (Fiber To The Home) using optical fiber in each home have led to a high-speed line of 100 Mbps. The provision of is popular. In the world of wireless LAN, further increase in transmission speed is demanded.

As a technique for that purpose, a multi-user MIMO (Multiple Input Multiple Output) transmission technique is well known. Multi-user MIMO transmission technology is a method in which a transmitting station transmits independent signals having different frequencies at the same timing from a plurality of transmission antennas to a plurality of communication partner devices, and the entire reception antennas of the plurality of communication partner devices are arranged in a huge reception array. This is a technology for improving downlink throughput.
An example in which a multi-user MIMO transmission technique using a BD (Block Diagonalization) directivity control method is applied to OFDM is shown below.

FIG. 9 is a configuration example using a BD directivity control method in the prior art that transmits and controls the configuration to be optimal for the propagation environment and improves the transmission rate by spatial multiplexing.
The number of antenna elements of the communication device 9 is Mt, the number of communication partner devices is Ma, the number of reception antenna elements of the i-th communication partner device is Mr (i), and transmitted to the i-th communication partner device at the same time and in the same frequency band. An example of a method of determining a communication partner apparatus with L (i) as the number of communication sequences to be performed, Mf as the number of subcarriers, and Mt ≧ Mr (i) is shown.

The communication device 9 includes a data output circuit 901, a transmission signal conversion circuit 902, IFFT circuits 903-1 to 903-M _t , radio units 904-1 to 904-M _t , antenna elements 905-1 to 905-M _t , communication A partner designation circuit 906, a channel information acquisition circuit 907, and a transmission encoding determination circuit 908 are provided.
Antenna element _{905-1~905-M t} and the radio unit _{904-1~904-M t} transmits and receives radio signals. Channel information obtaining circuit 907 estimates channel information of a plurality of frequencies between each antenna element of the communication partner device with the antenna elements _{905-1~905-M t.} The method for acquiring the channel information, for example, converted into information in the frequency domain performs FFT on information obtained when performing the received known signal obtained through the antenna element 905-1~905-M _t Thus, there is a method for estimating channel information for each frequency band. There is also a method for acquiring channel information from information included in feedback information included in a received signal.

  When the communication partner specifying circuit 906 determines a plurality of communication partner devices with which to communicate, the communication partner specifying circuit 906 transmits the channel information of all the frequency bands of the communication partner device via the channel information acquisition circuit 907. Output to. The transmission coding determination circuit 908 performs scheduling to divide the communication partner device into a group in which simultaneous transmission is performed using the input channel information, and determines the transmission weight and communication quality of each signal sequence for each combination of communication partner devices. The transmission mode including the number of communication streams, the modulation scheme corresponding to the communication stream, and the coding rate is determined. Also, the transmission coding determination circuit 908 outputs the determined transmission mode to the data output circuit 901 and the transmission signal conversion circuit 902.

The data output circuit 901 generates data to be transmitted to the communication partner apparatus, and outputs the generated data to the transmission signal conversion circuit 902. Transmission signal conversion circuit 902, an input data serial - parallel conversion, application of known signal, and outputs to the IFFT circuit _{903-1~903-M t} performs encoding for error detection and error correction. IFFT circuits 903-1 to 903 -M _t convert the input transmission information in the frequency domain into transmission information for the time domain, and output the transmission information to radio units 904-1-904 -M _t . Radio unit _{904-1~904-M t} is the data of the input time domain via an antenna _{905-1~905-M t,} and transmits it as a radio signal.

Hereinafter, a BD directivity control method will be described as an example of multi-user MIMO transmission. Here, paying attention to a certain frequency channel obtained by OFDM, a transmission method is shown. A channel matrix Hi (t) (Mr (i) × Mt matrix) representing channel information for the i-th communication partner device at time t obtained in the channel information acquisition circuit 907 is a singular value decomposition as shown in Equation (1). The right singular matrix V _i (t) (Mt × Mt matrix), the left singular matrix U _i (t) (Mr (i) × Mr (i) matrix) and the square root of the eigenvalue √ (λ _{i, 1} (t )), √ (λ _{i, 2} (t)),..., √ (λ _{i, Mr (i)} (t)) as a diagonal element and a non-diagonal element as a matrix D _i (t) (Mr (I) × Mt matrix).

Here, H _{i, jk} (t) represents a transfer coefficient from the k-th antenna of the communication device 9 to the j-th antenna of the i-th communication counterpart device. Of the right singular matrix V _i (t), V ′ _i (t) is a column vector group corresponding to the eigenvalue, and V ″ _i (t) is a column vector group corresponding to 0. In eigenvector transmission, which is known as a method for obtaining the maximum frequency utilization efficiency in single-user communication, a signal that can be expressed by a corresponding eigenvalue λ _i by using a column vector of the column vector group V ′ _i (t) as a transmission weight. Electric power can be obtained (λ ₁ ≧ λ ₂ ≧... ≧ λ _{Mr (i)} ). In equation (1), the superscript H represents a conjugate complex matrix.

  Next, in the BD directivity control method, considering transmission to the Ma communication partner devices using channels of the same frequency and the same timing, attention is paid to the i-th communication partner device among the Ma communication partner devices. . First, the base station calculates a set matrix composed of channel matrices of Ma-1 communication partner devices other than the i-th communication partner device for the i-th communication partner device as shown in Expression (2).

In equation (2), matrix R ′ _j is a reception weight assumed for the j-th communication partner device, and for simplicity, it is assumed that all channels are acquired at time t. When singular value decomposition is performed on this set matrix H ⁺ _i , it can be expressed as equation (3).

Here, the matrix V ⁺ _i is a space vector corresponding to the eigenvalue D ⁺ _i , and V ⁻ _j is a null space vector corresponding to the eigenvalue 0 or no eigenvalue. In addition, when transmission is performed in the null space of V ⁻ _j , interference does not occur for reception weights formed by communication counterpart devices other than the i-th.
Therefore, in order to evaluate the communication quality obtained in this transmission space, the channel matrix of the i-th communication partner apparatus is obtained by multiplying this null space weight V ⁻ _i as shown in the following equation (4). What is necessary is just to calculate the singular value of the obtained matrix.

Therefore, the transmission weight ^{_{W i (t), V -}} i [V '''i (t)] With _{L (i),} the matrix D' null space is a square value of the diagonal elements of _{'' i} Communication quality corresponding to the eigenvalues λ ′ _i1 ,..., Λ ′ _{iL (i)} is obtained. Here, [A] _L represents an Mt × L matrix composed of L column vectors corresponding to high eigenvalues from the column vector of the right singular matrix A.
When the transmission weight for the i-th communication partner device is Wi (t) and transmission is performed to the first to Ma-th communication partner devices at time t ′, the received signal y (t ′) of the i-th communication partner device ) Can be expressed as the following equation (5).

Also, this null space eigenvalue can be increased by repetitive calculations. By using the Hermitian matrix of the left singular matrix U ′ ″ _i (t) obtained in Expression (4) as the reception weight R ′ _i used in Expression (2), communication quality can be improved, The value of the null space eigenvalues λ ′ _i1 (t),..., Λ ′ _{iMr (i)} (t), which is the square value of the diagonal component of the matrix D ′ ″ _i (t), can be increased. In addition, the communication quality can be calculated for all frequency channels of OFDM, and based on the obtained communication quality, the transmission mode such as the modulation method and coding rate, and the combination of communication partner devices that transmit simultaneously can be determined. .

  As an example of the multi-user MIMO communication, the transmission weight in the BD directivity control method and the communication quality calculation method have been described. However, the Dirty paper coding method, the Tomlinson-Harashima coding method, the SO (Successive Optimization) method, and the like are used. Thus, an encoding method on the transmission side, estimation of communication quality, and the like can also be performed (see Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3).

There is an error between the channel matrix H _i (t) estimated at time t used to determine the encoding method and the channel matrix H _i (t ′) at time t ′ when actually performing communication. When this occurs, interference occurs in the user whose channel has changed, and the communication quality deteriorates. The causes of the error include an error due to thermal noise in the estimated channel matrix, quantization error, asymmetry between the uplink and downlink, nonlinear distortion in reception or transmission, and temporal variation of the channel. When there is an estimation error in the channel, there is a possibility that communication quality is significantly deteriorated by simultaneous transmission in combination with many users. It is necessary to change the number of users and the number of streams that perform simultaneous transmission based on how much possibility of deterioration due to channel estimation error is recognized. Considering combining conventional OFDM with transmission by multi-user MIMO, when time variation occurs, there is a problem that large interference power is generated and a large bit error occurs on the receiving side.
QH Spencer, AL Swindlehurst, and M. Haardt, "Zero-Forcing Methods for Downlink Spatial Multiplexing in Multiuser MIMO Channels", IEEE Trans Sig. Processing, vol. 52, issue 2, Feb. 2004, p.461-471. M. Costa, "Writing on dirty paper", IEEE Trans. Inform. Theory, vol. 29, no. 3, May 1983, p.439-441. M. Tomlinson, "New automatic equalizer controlled modulo arithmetic", Electron. Lett., Vol. 7, p.138-139, Mar. 1971.

  The above means makes it possible to obtain high frequency utilization efficiency by spatial multiplexing in the same time and in the same frequency band by using OFDM technology and multi-user MIMO technology for a plurality of communication partner devices. However, when the channel fluctuates over time, there is a problem that communication quality is significantly degraded.

  The present invention has been made in order to solve the above-mentioned problems, and its purpose is to consider the risk of deterioration of communication quality characteristics due to channel time fluctuations, and to perform OFDM frequency band allocation adaptively so that the receiving side It is an object of the present invention to provide a multi-channel spatial multiplexing transmission method and communication apparatus that prevent a large error from occurring in information.

In order to solve the above-mentioned problem, the present invention includes a plurality of antenna elements, and applies the orthogonal wave frequency division multiplexing method to share the frequency channel common to a plurality of communication counterpart devices in some or all frequency channels. assignment, a communication method in a communication device that performs spatial multiplexing transmission, based on the reception signal received from the communication partner device, channel information indicating the information of a channel between the communication device and the respective communication partner device a channel information obtaining step of obtaining distribution, for each communication partner device, the error between the based on the channel information, the channel information of a channel transmitting signal when actually transmitting said channel information is transmitted and risk assessment step of estimating the channel estimation error information, and the reliability of the channel estimation error information is the channel information acquisition scan And Tsu the channel information acquired by the flop, the risk assessment the channel estimation error information estimated in step, and on the basis of the reliability of the channel estimation error information, assignment of frequency channels for each communication partner device, number of communication streams, modulation mode including modulation scheme and coding rate, the power distribution ratio, and a resource allocation transmission coding determining step of determining a transmission weight, have a, in the resource allocation transmission encoding decision step, the channel A multi-channel spatial multiplexing transmission method characterized by increasing the proportion of frequency channels shared by a plurality of communication partner devices among the frequency channels allocated to the corresponding communication partner device as the reliability of the estimation error information is larger It is.

Further, the present invention is the above-described invention, wherein in the channel information acquisition step, terminal information of each communication counterpart device is further acquired based on a received signal received from each communication counterpart device, and the risk evaluation step in, with the respective communication partner device, on the basis of the channel information and the terminal information, the channel estimation error information, and to estimate the reliability of the channel estimation error information, characterized in that

Further, the present invention is the invention described above, in the resource allocation transmission coding decision step, when the plurality of communication partner apparatus assigns a common said frequency channels, allocated to the communication partner device among the frequency channels, the frequencies above the norm value of the channel matrix is a channel information sequentially from the frequency channel value summed with the communication partner apparatus is smaller for multiplexing, shared by the communication partner device of the multiple It selects as a channel, It is characterized by the above-mentioned.

Further, the present invention is the invention described above, in the resource allocation transmission coding decision step, when the plurality of communication partner apparatus assigns a common said frequency channels, allocated to the communication partner device among the frequency channels, the frequencies above the norm value of the channel matrix is a channel information sequentially from the frequency channel value summed with the communication partner apparatus is large for multiplexing, shared by the communication partner device of the multiple It selects as a channel, It is characterized by the above-mentioned.

In addition, the present invention is a communication apparatus that performs spatial multiplexing transmission by applying an orthogonal wave frequency division multiplexing system, allocating the common frequency channel to a plurality of communication partner apparatuses in some or all frequency channels. , channel information between the plurality of antenna elements, a radio unit for transmitting and receiving radio signals via the antenna elements, the radio unit based on the signal received from each communication partner device, a pre-Symbol each communication partner device a channel information acquiring circuit for acquiring channel information indicating a for each communication partner device, based on the channel information, and channel information of a channel transmission signal is transmitted when actually transmitting said channel information and risk evaluation circuit for estimating channel estimation error information, and the reliability of the channel estimation error information which is the error between, preparative said channel information And the channel information acquired by the circuit, wherein the channel estimation error information estimated by the risk evaluation circuit, and on the basis of the reliability of the channel estimation error information, assignment of frequency channels for each communication partner device, a communication the number of streams, modulation mode including modulation scheme and coding rate, the power distribution ratio, and a resource allocation transmission encoding decision circuit to decide the transmission weight, comprising a, the resource allocation transmission encoding decision circuit, said channel The higher the reliability of the estimated error information, the higher the ratio of frequency channels shared by a plurality of communication partner devices among the frequency channels assigned to the corresponding communication partner device .

Further, according to the present invention, in the above-described invention, the channel information acquisition circuit further acquires terminal information of each communication counterpart device based on a received signal received from each communication counterpart device, and the risk evaluation circuit is attached to the respective communication partner device, on the basis of the channel information and the terminal information, the channel estimation error information, and to estimate the reliability of the channel estimation error information, characterized in that.

Further, the present invention is the above-described invention, wherein, when the resource allocation transmission coding determination circuit allocates the common frequency channel to a plurality of communication partner apparatuses, the frequency allocated to the communication partner apparatus of the channels, the norm value of the channel matrix is the channel information sequentially from the frequency channel value summed with the communication partner apparatus is smaller for multiplexing, as the frequency channel to be shared by the communication partner device of the multiple It is characterized by selecting.

Further, the present invention is the above-described invention, wherein, when the resource allocation transmission coding determination circuit allocates the common frequency channel to a plurality of communication partner apparatuses, the frequency allocated to the communication partner apparatus of the channels, in order from the frequency channel value summed with the communication partner apparatus is large for multiplexing the norm value of the channel matrix is the channel information, as the frequency channel to be shared by the communication partner device of the multiple It is characterized by selecting.

  According to the present invention, when transmitting data applying the OFDM technology and the multi-user MIMO technology to a plurality of communication partner devices, communication characteristics due to channel time variations are received from a signal received from the communication partner device. Based on the estimation of the deterioration risk, the number of communication streams, the ratio of frequency channels to be shared, and the power distribution ratio are determined, frequency channels are allocated, and data is transmitted. This makes it possible to reduce errors in received data due to errors in channel information on the transmission side when the communication partner apparatus receives data.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic block diagram showing the internal configuration of the communication apparatus 1 in the present embodiment. The communication device 1 includes a data output circuit 101, a transmission signal conversion circuit 102, IFFT circuits 103-1 to 103-M _t , radio units 104-1 to 104-M _t , antenna elements 105-1 to 105-M _t , communication A partner designation circuit 106, a channel information acquisition circuit 107, a resource allocation transmission encoding determination circuit 108, and a risk evaluation circuit 109 are provided.
Radio unit 104-1 to _{104-M t,} through the antenna elements 105-1 through _{105-M t,} the received signal obtained by converting the radio signal received, and outputs to the channel information acquiring circuit 107.

The channel information acquisition circuit 107 performs channel information estimation based on a known signal included in the reception signal input from the radio units 104-1 to 104-M _t , or the communication partner device included in the reception signal Channel information is estimated from a feedback signal indicating reception characteristics. For example, in Equation (5), since the transmission signal W _i (t) x _i and the reception signal y (t ′) are known, the channel matrix H (t ′) is obtained. Here, the feedback signal includes information indicating communication quality and channel time variation information indicating variation with time of a channel used for communication with the communication partner apparatus.
Also, the channel information acquisition circuit 107 acquires information indicating the accuracy of the feedback signal and uplink / downlink symmetry holding characteristic information in the channel with the communication partner apparatus from the input received signal.

  Further, the channel information acquisition circuit 107 acquires channel information and terminal information corresponding to the communication partner apparatus from the input received signal. Further, the channel information acquisition circuit 107 outputs the terminal information input from the communication partner specifying circuit 106 to the resource allocation transmission coding determination circuit 108 and the risk evaluation circuit 109. Here, the terminal information is information including a device form of a communication partner device, a power supply form, a decoding algorithm provided in the communication partner device, a quantization error of feedback information, and the like. Note that the device form of the communication partner device is information indicating whether the communication partner device is fixed, and represents, for example, a fixed personal computer or a mobile terminal that moves without being fixed. The power supply form is information indicating a form of whether a stable power supply is supplied through a wire or a battery or the like.

  The risk evaluation circuit 109 receives channel information and terminal information from the channel information acquisition circuit 107. Further, the risk evaluation circuit 109 estimates input terminal information, channel information, and channel estimation error information that is an error. Further, the risk evaluation circuit 109 outputs the input terminal information and the estimated channel estimation error information to the resource allocation transmission coding determination circuit 108.

The communication partner designation circuit 106 selects a communication partner device to be communicated, and outputs terminal information of the selected communication partner device to the channel information acquisition circuit 107.
The resource allocation transmission coding determination circuit 108 uses the channel information and channel estimation error information input from the channel information acquisition circuit 107 to determine the number of communication streams for each communication partner device and the frequency channel shared with other communication partner devices. A modulation mode and transmission weight including a ratio, a power distribution ratio, a modulation scheme, and a coding rate are determined, and frequency channels are allocated.

The resource allocation transmission coding determination circuit 108 outputs the determined modulation mode information and the input communication partner apparatus information to the data output circuit 101 and the transmission signal conversion circuit 102.
The data output circuit 101 outputs transmission information for the communication partner apparatus indicated by the communication partner apparatus information input from the resource allocation transmission coding determination circuit 108 to the transmission signal conversion circuit 102.
The transmission signal conversion circuit 102 performs serial-parallel conversion on the input transmission signal, and distributes the transmission information converted for each frequency band. The transmission signal conversion circuit 102, respectively distributed was transmitted information, based on the input modulation mode information performs modulation and coding, and outputs to the IFFT circuit 103-1 to _{103-M t.}

IFFT circuits 103-1 to _{103-M t} is the information inputted from the transmit signal conversion circuit 102 converts the frequency domain information to information in the time domain, and outputs it to the radio section 104-1 to _{104-M t.}
The radio units 104-1 to 104-M _t receive the information converted from the time domain information input from the IFFT circuits 103-1 to 103-M _t and the antenna elements 105-1 to 105- connected thereto, respectively. Transmit to the communication partner device via M _t .

  A first determination method of a transmission method including a modulation scheme, a coding rate, a transmission power distribution ratio, and frequency channel allocation in the embodiment will be described with reference to FIGS. FIG. 2 is a table showing the allocation of modulation schemes to SNR (Signal to Noise Ratio) estimated for a communication stream. FIG. 3 is a flowchart showing the frequency channel assignment operation in the present embodiment.

When initiating communication with a communication partner device, channel information acquisition circuit 107 acquires the terminal information of the communication partner device and channel information from the received signal inputted from the radio unit 104-1 to 104-M _t. The channel information acquisition circuit 107 outputs the acquired channel information and terminal information to the risk evaluation circuit 109 and the resource allocation transmission coding determination circuit 108 (step S101 in FIG. 3).

The risk evaluation circuit 109 calculates a channel estimation error coefficient having a correlation with a channel estimation error generated between the channel and the channel information at the transmission time, from the channel information and the terminal information input from the channel information acquisition circuit 107. To do. The channel estimation error coefficient is determined from a correlation value of channel information acquired at a plurality of times, information indicating a device form of a communication partner device, or both. Here, the information indicating the device form of the communication partner device is, for example, information on whether it is a fixed personal computer or a mobile terminal that moves without being fixed, the number of receiving antenna elements, and a power supply form. , Information including a decoding algorithm.
Further, the risk evaluation circuit 109 outputs the channel estimation error coefficient to the resource allocation transmission coding determination circuit 108 (step S102 in FIG. 3).

  The resource allocation transmission coding determination circuit 108 allocates a frequency channel to the selected communication partner apparatus using the input channel estimation error coefficient and channel information. When there is no information on the channel estimation error, or when the channel estimation error coefficient is the maximum, the resource allocation transmission coding determination circuit 108 allocates the frequency channel to the communication partner apparatus without duplication, and allocates the frequency channel to be shared. Not performed. This allocation may be performed by uniformly dividing continuous frequencies, or in each communication counterpart device, frequency channels are ranked in order of good communication quality, and each communication counterpart device is alternately assigned. A higher priority frequency channel may be selected, or a priority of a communication partner device may be determined in advance, and a frequency channel having a higher communication quality may be assigned from a communication partner device having a higher priority.

  FIG. 5 shows an example in which frequency channels are uniformly allocated to three communication partner devices, communication partner 1, communication partner 2, and communication partner 3 as continuous frequency channels. In the following FIGS. 5 to 8, the number of frequency channels is 15, and the numbers in the blocks indicate the data stream numbers. In FIG. 5, the frequency domain is divided into three, and only data for a single communication partner device is transmitted to each frequency channel. The number of vertically overlapping blocks indicates the spatial multiplexing number. In addition, although it is changing adaptively in each channel in the diagrams from FIG. 5 to FIG. 8, a common spatial multiplexing number may be used.

As the modulation scheme, the SNR on the receiving side is estimated for the communication stream formed in each frequency channel, and a modulation scheme corresponding to the SNR in FIG. 2 is assigned. As the SNR, for example, a ratio of the squared values λ ₁ , λ ₂ ,..., Λ _{Mr (i)} of the diagonal term of the row example Di in the formula (1) to the thermal noise dispersion value is used. At this time, Margin can also be calculated according to the SNR of the frequency channel for the determined modulation scheme. This Margin is set higher as the SNR is larger than the modulation scheme and the possibility of causing a bit error is low. The resource allocation transmission coding determination circuit 108 determines the coding rate based on the sum of the Margin value and the sum of the multiplication values of the Margin value and the number of bits of the modulation scheme. If the Margin value is small, the possibility of an error occurring in the frequency channel increases. Therefore, the error correction coding rate is set small. In addition, when the Margin value is large or small, it is possible to assign a modulation scheme other than the one corresponding to the SNR. At this time, when a high modulation scheme is assigned to the SNR of the frequency channel, the Margin value takes a smaller value, and when a low modulation scheme is assigned, a larger Margin value is taken.

When the channel estimation error coefficient is input from the risk evaluation circuit 109, the modulation scheme allocation is determined using the channel estimation error coefficient and the channel information. First, the resource allocation transmission coding determination circuit 108 calculates the SNR for each communication stream of each communication partner device when multiplexing the communication partner device in a certain frequency channel from the channel information input from the risk evaluation circuit 109. To do. For example, from the ratio between the null space eigenvalues λ ′ _{i, 1} ,..., Λ ′ _{i, L (i)} that is the square value of the diagonal component of D ′ ″ i in equation (4) and the thermal noise variance value. Obtainable. Here, when the SNR for the j-th communication stream of the i-th communication partner obtained from the null space eigenvalue and the thermal noise variance value is S _{i, j} , this is the channel when the channel information is actually transmitted. it is exactly the same, since that is the SNR when the assigned 100% power allocation to the i-th communication partner device, the S _'ij is the SNR in consideration of channel estimation error and power distribution i-th communication partner device Can be expressed by the following equation (6) using the channel estimation error coefficient φ _i defined for.

Here, α _i is a power distribution term assigned to the i-th communication partner device, and P _i is a norm value of the channel matrix H _i (t) or a value correlated with the norm value. The channel estimation error coefficient φ _i is a real number smaller than 1, and the closer to 0, the higher the quality of the estimated channel. As the channel estimation error coefficient φ _i , an error due to thermal noise at the time of channel estimation, a quantization error, and a deviation from an actual channel due to channel time variation can be considered. Further, when channel information is estimated from feedback information, it is possible to take into account channel shifts caused by uplink and downlink devices. According to equation (6), it can be seen that the SNR is greatly degraded when the channel estimation error coefficient φ _i and the channel norm value P _i are large. The resource allocation transmission coding determination circuit 108 estimates the communication partner multiplexed SNR as shown in Equation (6), and assigns a modulation scheme by using the assignment table of FIG. The resource allocation transmission coding determination circuit 108 does not multiplex the communication partner device when the obtained SNR value is lower than a preset value. In FIG. 2, a data stream having an SNR below 2 dB is not used. Further, the resource allocation transmission coding determination circuit 108 has the number of transmission bits obtained by multiplexing the communication partner devices being less than or greater than the number of bits occupied by the same communication partner device without multiplexing the communication partner devices. When the amount is small, it may be selected not to multiplex communication partner devices. Note that the resource allocation transmission coding determination circuit 108 can distribute the power allocation α _i evenly among the communication partner apparatuses, but may be set so that the sum of Margin obtained from FIG. 2 becomes large. . Further, the resource allocation transmission coding determination circuit 108 may determine the coding rate from the Margin value (step S103 in FIG. 3).
Through the above operation, the communication apparatus 1 determines the modulation scheme, coding rate, transmission power distribution ratio, and frequency channel assignment.

  The second determination method of the transmission method including the modulation scheme, coding rate, transmission power allocation ratio, and frequency channel allocation in the same embodiment will be described with reference to FIGS. FIG. 2 is a diagram illustrating the assignment of modulation schemes to the estimated SNR for a communication stream. FIG. 4 is a flowchart showing the operation of the second determination method in the embodiment.

When initiating communication with a communication partner device, channel information acquisition circuit 107 acquires the terminal information of the communication partner device and channel information from the received signal inputted from the radio unit 104-1 to 104-M _t. The channel information acquisition circuit 107 outputs the acquired channel information and terminal information to the risk evaluation circuit 109 and the resource allocation transmission coding determination circuit 108 (step S201 in FIG. 4).

  The risk evaluation circuit 109 calculates a channel estimation error coefficient having a correlation with a channel estimation error generated between the channel and the channel information at the transmission time, from the channel information and the terminal information input from the channel information acquisition circuit 107. To do. The channel estimation error coefficient is determined from the correlation value of the channel information acquired at a plurality of times, information indicating the device form of the communication partner device, or both (step S202 in FIG. 4). Here, the information indicating the device form of the communication partner device is, for example, information on whether it is a fixed personal computer or a mobile terminal that moves without being fixed, the number of receiving antenna elements, and a power supply form. , Information including a decoding algorithm.

After calculating the channel estimation error coefficient, the risk evaluation circuit 109 evaluates the reliability of the channel estimation error. When the channel error coefficient is calculated from channel information corresponding to a plurality of times, the channel error coefficient is determined from the stability of the channel estimation error obtained from a combination of channel information corresponding to three or more times. In other words, if the channel fluctuation from time t1 to time t2 and the channel fluctuation amount from time t2 to time t3 are the same, the estimation result of the channel estimation error from time t3 to the next transmission timing can be reliable. If there is a large difference in the channel fluctuation amount, it is determined that the reliability of the estimation result is low. Also, depending on the device type of the communication partner device, the reliability is highly evaluated with the expectation that it is stable if it is a fixed personal computer, but the reliability is low because it is not expected to be stable with a portable terminal. Judgment such as being evaluated may be made.
In addition, the reliability is set to the lowest initial value. After performing communication, the risk evaluation circuit 109 can determine whether the channel estimation error has been correctly estimated based on feedback information from the communication partner device, and can increase the reliability step by step. The risk evaluation circuit 109 outputs the channel estimation error coefficient and the reliability of the channel estimation error to the resource allocation transmission coding determination circuit 108 (step S203 in FIG. 4).

The resource allocation transmission coding determination circuit 108 assigns a frequency channel to the selected communication partner apparatus using the input channel estimation error coefficient, reliability of the channel estimation error, and channel information.
When the channel estimation error coefficient and the reliability of the channel estimation error are input from the risk evaluation circuit 109, the resource allocation transmission coding determination circuit 108 multiplexes the communication partner apparatuses according to the reliability of the channel estimation error. The frequency channel ratio is determined, and the modulation scheme allocation is determined using the channel estimation error coefficient and the channel information in the frequency channel in which the communication partner device is multiplexed.

  FIG. 6 shows frequency channel allocation when the channel estimation error of the communication partner 1 is large, the channel estimation error of the communication partner 2 and the communication partner 3 is small, and the reliability of the channel estimation error of the communication partner 2 and the communication partner 3 is low. Is shown. The frequency channel 9 to the frequency channel 12 are shared by the communication partner 2 and the communication partner 3, and the frequency use efficiency by multiuser MIMO communication is increased. By controlling in this way, even when communication quality deteriorates due to an unexpected estimation error in a frequency channel using the multiuser MIMO technology, an error is combined with data decoded in the frequency channel not using the multiuser MIMO technology. By using the correction, it is possible to prevent a significant deterioration in characteristics.

  FIG. 7 shows frequency channel assignment when the channel estimation error of the communication partner 1 is large, the channel estimation error of the communication partner 2 and the communication partner 3 is small, and the reliability of the channel estimation error of the communication partner 2 and the communication partner 3 is high. Is shown. The multi-user MIMO technique is used in the previous frequency channel assigned to the communication partner 2 and the communication partner 3.

FIG. 8 shows that the channel estimation error of the communication partner 1, the communication partner 2 and the communication partner 3 is small, the reliability of the channel estimation error of the communication partner device 1 is small, and the channel estimation error reliability between the communication partner 2 and the communication partner 3 The example of allocation of the frequency channel in the case where is large is shown.
The resource allocation transmission coding determination circuit 108 assigns fixed adjacent frequency channels to the subcarriers using the multiuser MIMO technique as shown in FIGS. Note that the resource allocation transmission coding determination circuit 108 may allocate a frequency channel that increases the number of transmission bits most in the allocation of the modulation scheme obtained from Equation (6). Further, the resource allocation transmission coding determination circuit 108 may assign Pi in Equation (6) in order from the frequency channel with the smallest ΣPi obtained by summing the communication partner devices that multiplex the communication partner devices. Moreover, when taking the sum, the sum may be taken after applying a weighting coefficient to Pi of each communication partner apparatus. This is because the smaller channel power is less susceptible to channel estimation errors. When the channel estimation error is small, the evaluation may be performed in order from the frequency channel with the largest ΣPi. This is because the effect of multi-user MIMO is greater when the channel power is higher. The estimation of the SNR in the frequency channel 9 to the frequency channel 12 of the communication partner apparatus can be performed in the same manner as the equation (6), and the power distribution αi, the modulation method, and the coding rate are determined (step S204 in FIG. 4).

As described above, by selecting the number of communication streams, the power distribution ratio, and the ratio of the shared frequency channel for each communication partner device, it is possible to prevent the communication characteristics from being significantly deteriorated due to the time fluctuation of the channel, and multi-user MIMO. The effect by the spatial multiplexing by can be obtained.
Note that when evaluating the channel estimation error information, the risk evaluation circuit 109 may consider the number of reception antennas of the communication partner device, the performance of the decoding algorithm, the sharing form of the power source, and the like. For example, if the communication partner device is a personal computer that is difficult to move, a communication partner device that consumes a large amount of power that can receive a stable power supply, or a communication partner device that has a complex decoding algorithm, the risk evaluation circuit In 109, the channel estimation error coefficient is evaluated to be small or the reliability of the channel estimation error information is set to be large. In addition, a communication partner device that is small and easy to move, such as a portable terminal, a communication partner device that has a power consumption limitation because it is powered by a battery, or a communication partner device that has a simple decoding algorithm due to circuit scale limitations If so, the risk evaluation circuit 109 evaluates the channel estimation error coefficient greatly or sets the reliability of the channel estimation error information small.

  In FIG. 5, the resource allocation transmission coding determination circuit 108 assigns the frequency channels by dividing them into three equal parts. However, by selecting the frequency channels according to the SNR and the size of the null space eigenvalue, the user diversity effect is obtained. As a result, the communication characteristics can be further improved. Further, in the states of FIGS. 5 to 8, it is possible to assign a frequency channel having a large SNR or null space eigenvalue or a frequency channel having a small SNR or null space eigenvalue in each communication partner apparatus. Furthermore, a frequency channel with which the correlation of the frequency channel with respect to several communication partner apparatus becomes low may be selected, and the frequency channel with which the null space eigenvalue shown by Formula (4) becomes large may be selected.

  Further, the resource allocation transmission coding determination circuit 108 may select communication partner apparatuses that transmit simultaneously using the channel estimation error information evaluated by the risk evaluation circuit 109. That is, in the examples shown in FIGS. 5 to 8, the communication partner 1 with large channel estimation error information does not transmit at the same time, and only the communication partner 2 and the communication partner 3 communicate with each other. Transmission may be performed to a communication partner device between the partner 3 and another communication partner device having small channel estimation error information, and may be transmitted to the communication partner 1 at different times. At this time, the communication partner designation circuit 106 can designate more communication partner devices as communication partner candidates than the number of communication partner devices with which the communication device 1 can communicate simultaneously.

For example, the following channel estimation error coefficients due to time variations can be used.
Here, it is assumed that the channel matrix between the i-th communication partner device and the communication device 1 at time t is H _{i, t} . The channel is estimated at times t1 and t2 (t2> t1), and channel estimation error information at the time of transmission at time t (t> t2) is evaluated using each channel information.
When the channel correlation value is used, a correlation value ρ _{i, j, t2−t1} represented by the following equation (7) is obtained.

The matrix H _{i, j, t1} and the matrix H _{i, j, t2} are matrices indicating channel transfer coefficients of the j-th frequency of the i-th communication partner device at the time t1 and the time t2. The parameter corresponding to the channel estimation error coefficient φ _{i, j} can be obtained as 1−ρ _{i, j, t2−t1} . Further, the obtained correlation value ρ _{i, j, t2−t1} and the estimated time difference Δt = t2−t1 of the channel to be evaluated, the time t2 when the channel information used for encoding at the time of transmission is acquired, and the transmission scheduled time t The channel estimation error coefficient φ _{i, j} in the j-th frequency band of the i-th communication counterpart device can be obtained by the following equation (8) with the time difference Δt ′ = t−t2.

Note that f (ρ _ijΔt , Δt, Δt ′) is a function that determines characteristic deterioration, and can be given by linear interpolation as shown in the following equation (9), for example.

Using the channel estimation error coefficient φ _{i, j} obtained by Expression (8), the resource allocation transmission coding determination circuit 108 determines, for each communication partner apparatus, the ratio between the shared frequency channel and the occupied frequency channel, The number of communication streams and the power distribution ratio for other communication partner devices in the shared frequency channel are calculated.
Further, as shown in the following equation (10), channel estimation error information can also be obtained using the correlation value of the right singular matrix corresponding to the signal space.

Here, the matrix V ′ _ijt is a matrix composed of basis vectors obtained from the channel matrix H _ijt . Moreover, and column vectors of the right singular matrix corresponding to the eigenvalue obtained when using the singular value decomposition on the channel matrix H _ijt, a column vector of complex conjugate transposed matrix channel matrix H _ijt ^H of the channel matrix H _ijt Gram Schmidt A channel estimation error coefficient can be obtained using a basis vector obtained by using the orthogonalization method.

Wherein the channel error coefficient phi _{i, j} used in (7), the average value and the channel error coefficient phi _{i, j} in all the frequency channels, one or more of the average value of the channel error coefficient phi _{i, j} in the frequency channel Is used.

  Further, by notifying the communication partner apparatus of the allocation of the frequency channels allocated as described above, a transmission method using the same frequency channel assignment can be used in the uplink from the communication partner apparatus to the communication apparatus 1. it can.

  As described above, according to the present embodiment, an orthogonal signal frequency division multiplexing system is applied, and in some or all frequency channels, the frequency channels are shared with a plurality of communication partner devices, and independent signal sequences are obtained. Is transmitted by spatial multiplexing. In addition, by determining the number of shared frequency channels, the number of data streams in the shared frequency channel, and the power distribution ratio based on channel estimation error information, transmission that realizes wireless access that reduces the risk of communication degradation due to channel estimation errors Regarding the method.

It is a schematic block diagram which shows the internal structure of the communication apparatus by this embodiment. It is an example of the modulation system correspondence table used when selecting the modulation system in the embodiment. It is a flowchart figure which defines the transmission power distribution ratio, the shared frequency channel ratio, and the allocation of a frequency channel by the communication apparatus in the embodiment. It is a flowchart figure which defines the transmission power distribution ratio, the shared frequency channel ratio, and the allocation of a frequency channel by the communication apparatus in the embodiment. It is a figure which shows the example of allocation of the frequency channel in the same embodiment, and a spatial multiplexing channel. It is a figure which shows the example of allocation of the frequency channel in the same embodiment, and a spatial multiplexing channel. It is a figure which shows the example of allocation of the frequency channel in the same embodiment, and a spatial multiplexing channel. It is a figure which shows the example of allocation of the frequency channel in the same embodiment, and a spatial multiplexing channel. It is a schematic block diagram which shows the structural example of the communication apparatus in the technique in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Communication apparatus 101 ... Data output circuit 102 ... Transmission signal conversion circuit 103-1 to 103-Mt ... IFFT circuit 104-1 to 104-Mt ... Radio | wireless part 105-1 to 105-Mt ... Antenna element 106 ... Communication Partner designation circuit 107 ... Channel information acquisition circuit 108 ... Resource allocation transmission coding determination circuit 109 ... Risk evaluation circuit

Claims (8)

Communication in a communication apparatus that includes a plurality of antenna elements, assigns the common frequency channel to a plurality of communication partner apparatuses in some or all frequency channels by applying an orthogonal wave frequency division multiplexing method, and performs spatial multiplexing transmission A method,
Based on the signal received from the communication partner device, a channel information acquiring step of acquiring channel information indicating the information of a channel between the communication device and each of the communication partner apparatus,
Based on the channel information , channel estimation error information that is an error between the channel information and channel information of a channel through which a transmission signal is transmitted when actually transmitting is transmitted for each communication counterpart device , and the channel A risk assessment step to estimate the reliability of the estimation error information ;
According to the reliability of the channel estimation error information estimated in the risk evaluation step, out of the frequency channels allocated to each communication partner device, determine the proportion of frequency channels shared by a plurality of communication partner devices, and Based on the channel information acquired in the channel information acquisition step and the channel estimation error information estimated in the risk evaluation step, frequency channel allocation, the number of communication streams, modulation scheme, and encoding for each communication counterpart device modulation modes, including rate, power distribution ratio, and a resource allocation transmission coding determining step of determining a transmission weight, was closed,
In the resource allocation transmission encoding determination step,
The greater the reliability of the channel estimation error information, the more the frequency channel allocated to the corresponding communication partner device, the proportion of frequency channels shared by a plurality of communication partner devices is increased.
And a multi-channel spatial multiplexing transmission method . In the channel information acquisition step,
Based on the received signal received from each communication counterpart device, further obtain terminal information of each communication counterpart device,
And in the risk assessment step,
For the respective communication partner device, on the basis of the channel information and the terminal information, the channel estimation error information, and to estimate the reliability of the channel estimation error information,
The multi-channel spatial multiplexing transmission method according to claim 1. In the resource allocation transmission coding decision step,
When the plurality of communication partner apparatus assigns a common said frequency channel, among the frequency channels allocated to the communication partner device, a communication partner device for multiplexing the norm value of the channel matrix is the channel information in sum in order from the frequency channel value is less took, selected as the frequency channel to be shared by the communication partner device of multiple,
The multi-channel spatial multiplexing transmission method according to claim 1 or 2, characterized by the above. In the resource allocation transmission coding decision step,
When the plurality of communication partner apparatus assigns a common said frequency channel, among the frequency channels allocated to the communication partner device, a communication partner device for multiplexing the norm value of the channel matrix is the channel information in order from the frequency channel value is greater taking the sum is selected as the frequency channel to be shared by the communication partner device of multiple,
The multi-channel spatial multiplexing transmission method according to claim 1 or 2, characterized by the above. A communication apparatus that applies orthogonal wave frequency division multiplexing, assigns the frequency channel common to a plurality of communication partner apparatuses in some or all frequency channels, and performs spatial multiplexing transmission,
A plurality of antenna elements;
A radio unit for transmitting and receiving radio signals through the antenna element;
Based on the signal received the radio unit from each communication partner device, a channel information acquiring circuit for acquiring channel information indicating the information of the channel between the previous SL each communication partner device,
Based on the channel information, channel estimation error information that is an error between the channel information and channel information of a channel through which a transmission signal is transmitted when actually transmitting is transmitted for each communication counterpart device , and the channel A risk evaluation circuit for estimating the reliability of the estimation error information ;
According to the reliability of the channel estimation error information estimated by the risk evaluation circuit, among the frequency channels allocated to each communication partner device, determine the ratio of the frequency channel shared by a plurality of communication partner devices, and based on said channel estimation error information estimated the channel information acquired by the channel information obtaining circuit and in the risk assessment circuit, assignment of frequency channels for each communication partner device, the number of communication streams, modulation scheme and coding comprising modulation modes, including rate, power distribution ratio, and a resource allocation transmission encoding decision circuit to decide the transmission weight, and
The resource allocation transmission coding determination circuit includes:
The greater the reliability of the channel estimation error information, the more the frequency channel allocated to the corresponding communication partner device, the proportion of frequency channels shared by a plurality of communication partner devices is increased.
A communication device. The channel information acquisition circuit includes:
Based on the received signal received from each communication counterpart device, further obtain terminal information of each communication counterpart device,
The risk evaluation circuit includes:
For the respective communication partner device, on the basis of the channel information and the terminal information, the channel estimation error information, and to estimate the reliability of the channel estimation error information,
The communication apparatus according to claim 5. The resource allocation transmission coding determination circuit includes:
When assigning the common frequency channel to a plurality of communication partner devices, among the frequency channels assigned to the communication partner device, a communication partner device that multiplexes the norm value of the channel matrix that is the channel information wherein in order from the frequency channel a value taking the sum is small, it is selected as the frequency channel to be shared by the communication partner device of multiple,
The communication apparatus according to claim 5 or 6, characterized by the above. The resource allocation transmission coding determination circuit includes:
When assigning the common frequency channel to a plurality of communication partner devices, among the frequency channels assigned to the communication partner device, a communication partner device that multiplexes the norm value of the channel matrix that is the channel information sequentially from the frequency channel value is greater taking the sum is selected as the frequency channel to be shared by the communication partner device of multiple,
The communication apparatus according to claim 5 or 6, characterized by the above.

Images