JP5213044B2 - Communication apparatus, radio communication system, estimation information feedback method, and program - Google Patents

Description

  The present invention relates to a communication device, a wireless communication system, a method for feedback of estimation information, and a program.

  As a next-generation communication method, attention is paid to MIMO (Multi Input Multi Output) -OFDM (Orthogonal Frequency Division Multiplexing) such as LTE (Long Term Evolution) standardized by 3GPP (3rd Generation Partnership Project). In MIMO-OFDM, MIMO precoding is used as a technique for improving reception characteristics. Here, precoding means a technique for improving received signal characteristics by performing linear processing suitable for a channel state between transmission and reception in advance on the transmission side.

  In MIMO precoding, an optimal precoding matrix (hereinafter referred to as a precoding matrix) is estimated in a receiving apparatus according to a channel state, and the estimation result is transmitted to a transmitting apparatus as feedback information. The transmission apparatus that has received the feedback information multiplies the transmission signal by a precoding matrix based on the feedback information. In this way, the transmission device and the reception device cooperate to compensate for transmission channel distortion and improve reception characteristics. As literatures related to MIMO precoding, there are Patent Literature 1 and Patent Literature 2.

JP2007-214995 Special table 2005-502223

  In MIMO precoding, it is necessary to calculate an optimal precoding matrix according to channel conditions. For this reason, there exists a problem that the calculation amount in a receiver increases.

Hereinafter, this problem will be described by taking the case of LTE as an example. In the case of LTE, there are mainly three pieces of feedback information from the receiving device to the transmitting device. That is, CQI (Channel Quality Indicator) representing reception quality in the reception band, PMI (Precoding Matrix Indicator) representing an indicator of an optimal precoding matrix for the channel state, and optimum when transmitting information from the transmission apparatus to the reception apparatus RI (Rank which represents accurate rank information
Indicator).

In 3GPP TS36.213 v8.3.0, when feedback information is transmitted using PUSCH (Physical Uplink Shared Channel) and PUCCH (Physical Uplink Control Channel), transmission is performed from each receiving apparatus as shown in FIGS. 11 and 12, respectively. A reporting mode to the device is specified. That is, the horizontal direction in FIGS. 11 and 12 is the mode type. For example, it is written as 1-0, 1-1, 2-0, 2-1, 2-2, 3-0, 3-1. On the other hand, the vertical direction is the type of feedback information. Wideband shown in FIG. 11 and FIG.
CQI (PMI) is common CQI (PMI) information in all bands, Subband CQI (PMI) shown in FIG. 11 is CQI (PMI) information in a specific subband, and Best-M CQI shown in FIG. Information from which M CQIs are extracted from the better one, UE Selected in FIG.
Subband CQI is CQI information in the subband selected by UE (User Equipment), Best-M shown in FIG.
PMI is PMI information in the subband selected for Best-M CQI report, Index shown in FIG.
r represents information on the band selected by Best-M, and Index j shown in FIG. 12 represents information on the band selected by the UE. Here, what is indicated by double circles indicates feedback information that needs to be reported.

  As can be seen from FIG. 11 and FIG. 12, Wideband PMI and RI need to be reported in many modes, and reducing this amount of computation greatly contributes to reducing the amount of computation for calculating feedback information in the receiving apparatus. .

  That is, in MIMO precoding, since it is necessary to calculate an optimal precoding matrix according to the channel state, the amount of calculation in the receiving apparatus increases. In particular, among Wideband PMI and RI among feedback information from the receiving apparatus, SNR (hereinafter referred to as Effective SNR) when each PMI indicated by Codebook prepared in advance is applied in all bands. There is a need. For this reason, there is a problem that the amount of calculation in the receiving apparatus becomes enormous.

  An object of the present invention is to provide a communication apparatus, a wireless communication system, a method of estimating information feedback, and a program that can reduce the amount of calculation of feedback information. And

  The communication apparatus of the present invention estimates a precoding matrix according to a channel state of a received signal, and in a communication apparatus that feeds back a value thereof to another communication apparatus, a plurality of pieces generated by dividing a reception band into a predetermined number Means for selecting N (M> N) subbands from M subbands based on a predetermined criterion, and means for estimating a precoding matrix based on the N subbands It is.

  Alternatively, the communication apparatus according to the present invention includes a control unit that estimates a precoding matrix according to a channel state of a received signal and feeds back the value to another communication apparatus. N sub-bands (M> N) are selected from a plurality of M sub-bands generated by dividing into a number based on a predetermined criterion, and a precoding matrix is selected based on the N sub-bands. Is estimated.

  The wireless communication system of the present invention includes the communication apparatus of the present invention and another communication apparatus that multiplies a transmission signal by a precoding matrix fed back from the communication apparatus and transmits the transmission signal to the communication apparatus.

  The estimation information feedback method of the present invention estimates a precoding matrix according to the channel state of a received signal and feeds back the estimation information applied to a communication apparatus that feeds back to a transmission apparatus of a wireless communication system using MIMO precoding. , Selecting N (M> N) subbands based on a predetermined criterion from among a plurality of M subbands generated by dividing the reception band into a predetermined number, and the N subbands Estimating a precoding matrix based on a band.

  The program of the present invention is a program characterized in that the function of the communication apparatus of the present invention is realized in the information processing apparatus by being installed in the information processing apparatus.

  According to the present invention, for example, in MIMO precoding, the amount of calculation of feedback information can be reduced.

(Configuration of wireless communication system according to first embodiment of the present invention)
The configuration of the wireless communication system 1 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block configuration diagram of the wireless communication system 1. A transmission apparatus 10 serving as a wireless communication apparatus includes a channel encoding unit 11, a modulation unit 12, a layer mapping unit 13, a precoding unit 14, a RE (Resource Element) mapping unit 15, and an IFFT (Inverse Fast Fourier Transform) unit 16. To do. The receiving device 20 serving as a wireless communication device includes an FFT (Fast Fourier Transform) unit 21, an RE demapping unit 22, a channel estimation unit 23, a demodulation unit 24, a channel decoding unit 25, and a CQI / PMI / RI estimation unit 30. It has.

  Note that there are two channel encoding units 11, modulation units 12, RE mapping units 15, IFFT units 16, FFT units 21, RE demapping units 22, demodulation units 24, and channel decoding units 25, respectively. This is because different components of the two inner codewords are processed in parallel.

  FIG. 2 shows a configuration example of the CQI / PMI / RI estimation unit 30. The CQI / PMI / RI estimation unit 30 includes an SNR estimation unit 31, a determination unit 32, an effective SNR estimation unit 33, and a CQI / PMI / RI estimation unit 34.

  Each unit of the transmission device 10 and the reception device 20 may be configured by a general-purpose computer device (CPU, DSP, microprocessor (microcomputer), or the like) that operates by predetermined software. Further, in the transmission device 10 and the reception device 20, illustration of a control unit for controlling each unit is omitted.

(Description of operation of wireless communication system according to first embodiment of the present invention)
Operations of the transmission device 10 and the reception device 20 of the wireless communication system according to the first embodiment of the present invention will be described. In the transmission apparatus 10, transmission data is first subjected to a desired encoding operation in the channel encoder 11. For example, error detection coding and error correction coding are performed. Subsequently, the modulation unit 12 performs mapping into an I component (in-phase component) and a Q component (quadrature phase component) based on the designated modulation method. The modulated data is mapped to the transmission layer by the layer mapping unit 13 based on the feedback information 40 from the receiving device 20. Then, the data mapped to the transmission layer is multiplied by a designated precoding matrix in the precoding unit 14. Subsequently, the RE mapping unit 15 performs DFT (Discrete Fourier transform) processing, and maps the RE on the frequency resource. Subsequently, the IFFT unit 16 converts the signal into a time domain signal, and then transmits the signal as a transmission signal from the transmission antenna.

  On the other hand, in the receiving device 20, the signal received by the receiving antenna is first divided into frequency component data by Fourier transform in the FFT unit 21, and then demapped from the frequency resource by the RE demapping unit 22. That is, the RE demapping unit 22 performs the reverse process of the RE mapping unit 15. The channel estimation unit 23 estimates a channel estimation matrix representing a channel state using a known signal (reference signal) mapped in advance on a frequency resource. The demodulator 24 demodulates the I component and the Q component into likelihood information based on the channel estimation matrix estimated by the channel estimator 23, and the channel decoder 25 performs error correction decoding and error detection. .

  The CQI / PMI / RI estimation unit 30 in the reception device 20 estimates CQI / PMI / RI based on the channel estimation matrix estimated by the channel estimation unit 23 and transmits the CQI / PMI / RI as feedback information 40 to the transmission device 10. The feedback information 40 is reflected in the processing in the layer mapping unit 13 and the precoding unit 14 in the transmission apparatus 10.

  Next, the operation of the CQI / PMI / RI estimator 30 will be described with reference to FIGS. 2 and 3 in the case of Closed Loop Spatial Multiplexing. First, the SNR estimation unit 31 divides the entire band into a predetermined number of fine bands. Hereinafter, each divided band is referred to as a subband. Then, an SNR (Signal to Noise power Ratio) for each subband is calculated based on the channel estimation matrix calculated by the channel estimation unit 23 (step S1).

  Based on the SNR information for each subband calculated by the SNR estimation unit 31, the determination unit 32 determines a subband to be used for Effective SNR calculation (step S2). Details of this determination process will be described later.

The effective SNR estimation unit 33 estimates an effective SNR that represents an SNR value when each PMI indicated by the codebook indicator prepared in advance is applied to the selected subband (step S3). FIG. 4 shows an example of the case where the number of transmitting antennas is 1 or 2 in the LTE Codebook, and details are defined in 3GPP TS 36.211 v8.3.0. Here, the Effective SNR (= SINR (P _R , L, f, K)) is calculated according to Equation 1.
_{SINR (P R, L, f} , K) = (SNR (K) / [SNR (K) -1 I R + V H PR H (f) H H (f) V PR] LL -1) -1 ... ( 1)

However, P _R represents a PMI indicated by the P-th Codebook in the case of rank R, L represents a layer number, f is represents a subcarrier number RS on the frequency axis (Reference Signal) is mapped, K Represents a subband number, I _R represents an R × R identity matrix, V _PR represents a precoding matrix represented by the P-th codebook in the case of rank R, and H (f) represents the f-th subcarrier. Represents a channel estimate. [] _LL represents a component of L rows and L columns in the matrix.

The CQI / PMI / RI selection unit 34 first calculates the communication capacity C (P _R , L, f, K) of the entire system when each PMI is applied according to Shannon's theorem according to the following equation (2): Step S4). Steps S3 and S4 are performed for all PMIs, all layers, selected subbands, and all RSs.
C (P _R , L, f, K) = log ₂ (1 + SINR (P _R , L, f, K)) (2)

Next, Wideband PMI = P ^ _w and RI = R ^ that maximize the communication capacity calculated above are selected according to Equation 3 (step S5).
_{R ^, P ^ w = arg} max Re (1,2) max PR∈ΩR Σ K Σ f Σ L = 1toR C (P R, L, f, K) ... (3)
However, Ω _R represents a set of all PMIs in rank R.

Here, as shown in FIG. 3, the effective SNR estimator 33 performs processing for all PMIs (loop 2), all layers (loop 3), selected subbands (loop 4), and all RSs (loop 5). Since the maximum number of PMI is P _max , the maximum number of layers is L _max , and the maximum number of subcarriers including RS is K _{max in} order to perform an effective SNR calculation process, the maximum is (P _max × L _max × K _max ). Processing is required. When 4 × 2 MIMO is applied in the LTE system used as the embodiment, P _max = 16, L _max = 1, K _max = 200 for rank 1, P _max = 16, L for rank 2 _{Since max} = 2 and K _max = 200, 16 × (1 + 2) × 200 = 9600 effective SNR calculation processes are required at the maximum. In addition, since calculation of communication capacity is performed for all PMIs, all layers, etc., enormous processing is required. The above processing (steps S1, S3 to S5) is a well-known technique except for processing in the determination unit 32, which will be described in detail later, that is, processing for selecting a subband used for calculation in step S2.

  Below, the characteristic of the radio | wireless communications system 1 is demonstrated. Conventionally, there is no step S2, and the effective SNR is calculated for all subbands. However, in the wireless communication system 1, the determination unit 32 reduces the subbands used for the effective SNR calculation. Thereby, the amount of calculation in Wideband PMI and RI calculation can be reduced.

  For the high SNR subband, the reception characteristics are good and the selected PMI has little influence on the reception characteristics. Also, the low SNR subband has a small influence on the overall characteristics because the reception characteristics are originally poor. Therefore, there is no significant difference in the reception characteristics of the entire system as a result of calculating Wideband PMI and RI by selecting only subbands close to the average of the bands and calculating all bands. Therefore, the amount of calculation can be reduced by this method without deteriorating the reception characteristics.

  FIG. 5 shows an outline of specific determination processing (processing in step S2) in the determination unit 32. First, the determination unit 32 calculates an average SNR in all bands based on the SNR information from the SNR estimation unit 31 (step S10). Next, the determination unit 32 selects N subbands close to the average SNR from all the subbands (step S11). An image of subband selection is shown in FIG. In FIG. 6, six subbands (that is, B2, B8, B9, B4, B10, and B6) are selected in order from the SNR in the subbands (B1 to B10) that is close to the average SNR.

  Finally, the determination unit 32 notifies the selected subband to the Effective SNR estimation unit 33 (step S12). As described above, since the effective SNR estimation unit 33 performs the effective SNR calculation process (step S3) only for the selected subband, the amount of calculation can be reduced as compared with the case where all the subbands are used.

(Description of the operation according to the second embodiment of the present invention)
In the first embodiment of the present invention, the number of subbands extracted by the determination unit 32 is fixed, but in the second embodiment of the present invention, this number is dynamically controlled. In addition, the structure of the radio | wireless communications system which concerns on 2nd embodiment is the same as that of 1st embodiment, and has a structure shown in FIG. 1, FIG.

  As a parameter for dynamic control, the degree of SNR variation in the subbands in the band is used. An image of this embodiment is shown in FIG. That is, when the SNR variation in the band is large as in the case of (b) in FIG. 7, the number of subbands N used for calculating the effective SNR is increased (N = 6), thereby degrading the reception characteristics. prevent. Further, when the SNR variation is small as in the case of (a) in FIG. 7, the number of subbands N used for calculating the effective SNR is reduced (N = 3), thereby eliminating unnecessary Effective SNR calculation processing. The amount of calculation in the receiving device 20 can be reduced. For example, a configuration using a standard deviation as shown in FIG. 7 is conceivable as an indicator of the degree of variation, but other indicators may be used.

(Description of operation according to the third embodiment of the present invention)
In the second embodiment of the present invention, the number of subbands is dynamically controlled. In this case, subbands close to the average SNR are extracted and used for the effective SNR calculation process. In contrast, in the third embodiment of the present invention, all subbands are divided into high, medium, and low SNR regions, and A, B, and C subbands are extracted from each of the subbands to obtain an effective SNR. The configuration is used for calculation processing. Thereby, the amount of calculation in the receiver can be reduced while the deterioration of the reception characteristic is prevented by reflecting the value of each area in Wideband PMI and RI. In addition, the structure of the radio | wireless communications system which concerns on 3rd embodiment is the same as that of 1st embodiment, and has a structure shown in FIG. 1, FIG.

  An image of the third embodiment of the present invention is shown in FIG. At this time, the high, medium, and low SNR regions are divided so that, for example, the number of subbands included in each region becomes a predetermined number. In the example of FIG. 8, there are three, four, and three high, medium, and low SNR regions, respectively. In the example of FIG. 8, two subbands are selected from each region. That is, subbands B6 and B8 are selected in the high SNR region, subbands B2 and B9 are selected in the medium SNR region, and subbands B4 and B10 are selected in the low SNR region, respectively. However, instead of two, two, three, and two may be selected for high, middle, and low, or the number of subbands in each region may be the same or may be different.

  Also, as shown in FIG. 9, the upper A subbands with SNR are divided into high SNR regions, and the lower C subbands with SNR are divided into low SNR regions. Then, B pieces are selected from subbands not included in either the high or low SNR region. Alternatively, A, B, and C subbands (A = B = C, A = B, A = C, and B = C may be selected) are selected from each area determined in this way. Good. Further, the high, medium, and low SNR regions may be divided according to a predetermined threshold. This threshold value may always be a fixed value, or may be dynamically controlled by the average SNR value over the entire band. An image of the embodiment in the case of dynamic control is shown in FIG.

  That is, control is performed so that the threshold value is large when the average SNR is high and the threshold value is small when the average SNR is low. Further, the values of A, B, and C may be fixed or variable. In the case of making it variable, for example, a control method based on the bandwidth can be considered. That is, if the bandwidth of the subband is large, the values of A, B, and C are decreased. Conversely, if the bandwidth of the subband is small, the values of A, B, and C are increased. Of course, other indicators may be used. In addition, it is sufficient if there are a plurality of regions, and the regions are not high, medium, low, but are divided into six regions of high high, high low, medium high, medium low, low high, low low, and the central three regions or four You may select from the area.

(Program embodiment)
Next, an embodiment of a program that realizes the functions of the transmission device 10 and the reception device 20 according to the embodiment of the present invention by installing in the information processing device will be described. Here, the information processing apparatus is, for example, a general-purpose computer apparatus, and includes a CPU, a DSP (Digital Signal Processor), a microprocessor (microcomputer), and the like.

  For example, the microprocessor has a memory, a CPU, an input / output port, and the like. The CPU of the microprocessor reads and executes a control program as a predetermined program from a memory or the like. Thereby, the microprocessor performs the function of each unit of the transmission device 10 and the reception device 20 as a channel encoding unit 11, a modulation unit 12, a layer mapping unit 13, a precoding unit 14, an RE mapping unit 15, an IFFT unit 16, and an FFT unit. 21, an RE demapping unit 22, a channel estimation unit 23, a demodulation unit 24, a channel decoding unit 25, and a CQI / PMI / RI estimation unit 30 are realized.

  Even if the control program executed by the microprocessor is stored in the memory of the microprocessor before shipment of the transmission device 10 and the reception device 20, the control program is executed after the transmission of the transmission device 10 and the reception device 20. It may be stored in a processor memory or the like. Further, a part of the control program may be stored in a memory of a microprocessor or the like after shipment of the transmission device 10 and the reception device 20. The control program stored in the memory of the microprocessor after shipment of the transmission device 10 and the reception device 20 is, for example, an installation of what is stored in a computer-readable recording medium such as a CD-ROM. Alternatively, it may be an installed version downloaded via a transmission medium such as the Internet.

  Note that the program according to the present embodiment includes not only a program that can be directly executed by the information processing apparatus but also a program that can be executed by being installed on a hard disk or the like. Also included are those that are compressed or encrypted.

(Effect according to the embodiment of the present invention)
According to the wireless communication system 1, a band having a certain width close to the average reception quality in the reception band is extracted, or a certain band is extracted from high, medium, and low reception quality in the reception band, and the extracted band The PMI and RI calculated from the information about only are reported as Wideband PMI and RI. Thereby, the calculation calculation amount of Wideband PMI and RI can be reduced.

(Modification)
The above-described embodiment of the present invention can be variously modified without departing from the gist thereof. For example, in the above-described embodiment, the calculation calculation amount of both Wideband PMI and RI is reduced, but only one of them may be reduced by the method described above.

  Further, when all subbands are divided into high, medium, and low SNR regions, all subbands that fall within the medium SNR region may be selected. As described above, an area within a certain width range close to the average reception quality in the entire band may be extracted, and all subbands in the area may be selected. In addition, the predetermined criterion may select N (M> N) subbands in order from the closest to the average reception quality of M subbands.

  Further, when the SNR variation of the subbands is large, the number of subbands selected from the same number of regions of high, medium, and low may be increased in the middle and decreased in the high and low. Conversely, when the variation is small, the number of subbands selected from each region may be the same. In addition, dynamic control based on the average SNR value when dividing the region in consideration of the degree of variation may be used in combination, and such dynamic control may be used when the average SNR is calculated. And can be used as appropriate when not calculated.

  In addition, the above description has been given for communication in a mobile phone using LTE. However, the same method can be applied to a wireless communication system using MIMO precoding such as a mobile phone using FDM or OFDM, or a wireless LAN. Is possible. Alternatively, the technique according to the embodiment of the present invention can be applied to any communication system that notifies feedback information to a transmission device based on reception quality at the reception device. In this case, the wireless communication system is not necessarily required.

It is a block block diagram of the radio | wireless communications system which concerns on 1st embodiment of this invention. It is a block block diagram of the CQI / PMI / RI estimation part of the communication apparatus (reception apparatus) shown in FIG. 3 is a flowchart showing an optimal PMI / RI selection operation of the CQI / PMI / RI estimation unit shown in FIG. It is a figure showing the example regarding the case where the number of transmitting antennas is 1 or 2 among Codebook in LTE used for the Effective SNR estimation part shown in FIG. 3 is a flowchart showing feedback information transmission operation of the CQI / PMI / RI estimation unit shown in FIG. FIG. 3 is a diagram for explaining subband selection in a CQI / PMI / RI estimation unit shown in FIG. 2. It is a figure for demonstrating the example which changes the selection number of a subband by the variation in SNR at the time of subband selection in the CQI / PMI / RI estimation part in the radio | wireless communications system which concerns on 2nd embodiment of this invention. It is a figure for demonstrating the example which provides the high, middle, and low SNR area | region at the time of the subband selection in the CQI / PMI / RI estimation part in the radio | wireless communications system which concerns on 2nd embodiment of this invention. It is a figure for demonstrating the subband selection in a high, middle, and low SNR area | region at the time of the subband selection in the CQI / PMI / RI estimation part in the radio | wireless communications system which concerns on 2nd embodiment of this invention. The figure for demonstrating the example which changes the threshold value in the case of providing the high, middle, and low SNR area | region in the case of subband selection in the CQI / PMI / RI estimation part in the radio | wireless communications system which concerns on 2nd embodiment of this invention. It is. It is a figure which shows prescription | regulation of the report mode from the receiver to a transmitter in LTE PUSCH, and is a figure which shows WidebandCQI, Subband CQI, Best-MCQI, Wideband PMI, SubbandPMI, Best-MPMI, RI, and Indexr. It is a figure which shows prescription | regulation of the report mode from the receiver to a transmitter in LTE PUCCH, and is a figure which shows Wideband CQI, UE Selected Subband CQI, Wideband PMI, RI, and Index j.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wireless communication system, 10 ... Transmission apparatus (communication apparatus), 11 ... Channel decoding part, 12 ... Modulation part, 13 ... Layer mapping part, 14 ... Precoding part, 15 ... RE mapping part, 16 ... IFFT part, DESCRIPTION OF SYMBOLS 20 ... Reception apparatus (communication apparatus), 21 ... FFT part, 22 ... RE demapping part, 23 ... Channel estimation part, 24 ... Demodulation part, 25 ... Channel decoding part, 30 ... CQI / PMI / RI estimation part 30 ( Calculating means, selecting means, estimating means, determining means, classifying means), 31... SNR estimating section, 32... Determining section (calculating means, selecting means, determining means, classification means), 33 ... Effective SNR estimator (means for estimating), 34 ... CQI / PMI / RI selector

Claims (13)

In a communication device that estimates a precoding matrix according to the channel state of a received signal and feeds back the value to another communication device,
Means for selecting N (M> N) subbands based on a predetermined criterion from among a plurality of M subbands generated by dividing a reception band into a predetermined number;
Means for estimating the precoding matrix based on the N subbands;
Means for calculating an average reception quality within the reception band ,
The means for selecting the subbands selects the N subbands having reception quality close to the average reception quality.
A communication device. The communication device according to claim 1 .
Means for determining a variation in reception quality between the subbands;
The means for selecting sets the value of N greater when the degree of variation is determined to be large by the determining means than when it is determined that the degree of variation is small.
A communication device. The communication device according to claim 1 or 2 ,
Means for classifying the reception quality into a plurality of ranks for each subband;
The selecting means selects a predetermined number of the subbands for each rank from the subbands.
A communication device. The communication device according to claim 3 .
The means for classifying sets the reception quality threshold value for classification into the rank higher when the average reception quality of the entire band is high than when the average reception quality of the entire band is low.
A communication device. The communication device according to claim 3 or 4 ,
Changing the number of subbands selected for each rank according to the number of subbands for each rank classified by the means for classifying;
A communication device. In a communication device having a control unit that estimates a precoding matrix according to a channel state of a received signal and feeds back the value to another communication device,
The control unit selects N (M> N) subbands based on a predetermined criterion from among a plurality of M subbands generated by dividing a reception band into a predetermined number,
Estimating the precoding matrix based on the N-number of the subbands,
The communication apparatus according to claim 1, wherein the predetermined criterion is to select N subbands in order from the closest to the average reception quality of the M subbands . The communication device according to claim 6 .
The predetermined criterion is to divide the M subbands into a plurality of classifications according to reception quality, and to select at least one or more subbands from all of the classifications or an area having a medium reception quality. A communication device. The communication device according to any one of claims 1 to 7 ,
Another communication device that multiplies the transmission signal by the precoding matrix fed back from this communication device and transmits it to the communication device; and
A wireless communication system using MIMO precoding, comprising: In a feedback method of estimation information applied to a communication apparatus that estimates a precoding matrix according to a channel state of a received signal and feeds back to a transmission apparatus of a wireless communication system using MIMO precoding,
Selecting N (M> N) subbands based on a predetermined criterion from among a plurality of M subbands generated by dividing a reception band into a predetermined number;
Estimating the precoding matrix based on the N subbands;
Determining a variation in reception quality between the subbands ,
The estimation step is characterized in that the step of selecting sets the value of N greater when the variation degree is determined to be large by the process of the determination step than when it is determined that the variation degree is small. Feedback method. The estimation information feedback method according to claim 9 ,
Classifying the reception quality into a plurality of ranks for each subband;
The selecting step selects a predetermined number of the subbands for each rank from the subbands.
An estimation information feedback method characterized by the above. The estimation information feedback method according to claim 10 ,
In the classifying step, when the average reception quality of the entire band is high, the reception quality threshold value for classification into the rank is set higher than when the average reception quality of the entire band is low.
An estimation information feedback method characterized by the above. The estimation information feedback method according to claim 10 or 11 ,
Changing the number of subbands selected for each rank according to the number of subbands for each rank classified by the processing of the classifying step;
An estimation information feedback method characterized by the above. A program characterized in that the function of the communication device according to any one of claims 1 to 7 is realized in the information processing device by being installed in the information processing device.

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