WO2009096145A1 - Radio communication device, radio communication system, and radio communication method - Google Patents

Abstract

It is possible to improve the code word transmission quality upon retransmission when precoding is employed in the MIMO. A receiver for an MCW type MIMO precoding system includes: a parameter selection unit (604) which selects parameters Δi, δi for setting a power adjustment offset value of each code word according to a channel matrix H based on a channel estimation result and an ACK/NACK signal of each code word; and a precoding matrix selection unit (606) which selects and decides a precoding matrix C for precoding beam formation in accordance with the channel matrix H and the parameters Δi, δi. The receiver feeds back and reports to the transmitter, the index information specifying the parameters Δi, δi and the precoding matrix C together with the ACK/NACK signal of each code word.

Description

Wireless communication apparatus, wireless communication system, and wireless communication method

The present invention relates to a wireless communication apparatus, a wireless communication system, and a wireless communication method applicable to a MIMO (Multiple Input Multiple Output) system that performs communication using a plurality of antennas.

In communication systems, hybrid ARQ (HARQ: Hybrid Automatic Repeat Re- Quest) technology is widely adopted as a retransmission control method in order to improve transmission reliability. In a typical implementation employing HARQ technology, in a wireless communication device, a transmitter transmits each data packet with a cyclic redundancy check (CRC) bit for error detection. The receiver receives each data packet transmitted from the transmitter, and checks the contents of these data packets through the CRC. If the received data packet fails the CRC check, the receiver returns a NACK (Negative Acknowledgment) signal to the transmitter and requests retransmission. When the transmitter receives the retransmission request, the transmitter retransmits the data packet to which reception and decoding have failed in the receiver. Subsequently, the receiver decodes the retransmitted data packet together with the previous reception failure data packet to improve the decoding performance. On the other hand, if the received data packet passes the CRC check, the receiver returns an ACK (Acknowledgement) signal to the transmitter and acknowledges the successful reception and decoding of the data packet.

In recent years, MIMO (Multiple Input Multiple Output) has attracted attention as a technology for realizing high-speed and large-capacity communication in wireless communication technology. MIMO technology uses multiple antennas for both transmission and reception, and simultaneously transmits individual data streams via multiple antennas (spatial multiplexing transmission), thereby improving frequency utilization efficiency without additional bandwidth and power consumption. Promising in terms of improvement. That is, by applying MIMO, the transmission capacity can be improved without expanding time / frequency resources. If the channel information is known at both the transmitter and receiver, the capacity of the MIMO system increases linearly with the minimum number of antennas implemented in the transmitter and receiver.

When performing spatial multiplexing, the prior art includes both single codeword (hereinafter referred to as “SCW”) transmission and multiple codeword (hereinafter referred to as “MCW”) transmission. Was being considered. A data series which is a control unit such as HARQ is called a code word (CW), and a transmission method using a plurality of code words for controlling a code word for each spatially multiplexed stream is called MCW.

In the SCW type MIMO system, at the transmitter, the input information bit sequence is CRC-encoded, channel-encoded, and mapped to data symbols to form a data packet. The data packets are then segmented into multiple (spatial) data streams and transmitted in parallel via multiple transmit antennas. At the receiver, all detected data space streams are multiplexed into a single data packet and channel decoding and CRC checking are performed through the channel decoder and CRC checking module, respectively. Subsequently, an ACK / NACK signal is transmitted to the transmitter according to the CRC check result, and the reception quality of the transmission data packet is acknowledged.

On the other hand, in the MCW type MIMO system, at the transmitter, the input information bit sequence is CRC encoded, channel encoded, and individually mapped to data symbols to form a plurality of data packets. Then, a multi-input information bit sequence using a plurality of data packets is transmitted in parallel via a plurality of antennas. The receiver first reconstructs a plurality of data packets using the detected data space stream, and independently performs channel decoding and CRC check for each data packet. Subsequently, a plurality of ACK / NACK signals are fed back to the transmitter according to the CRC check result for each data packet, and the reception quality of the plurality of data packets is acknowledged.

In MIMO, there is a beam transmission method for forming a beam by transmitting weighted data from each antenna when transmitting from a plurality of antennas. Beam transmission has the effect of increasing received power at the terminal due to beam gain. In addition, spatial multiplexing using a plurality of beams is possible, and transmission capacity can be improved with respect to spatial multiplexing by an antenna by performing beam transmission suitable for the condition of the propagation path. In this case, it is necessary to notify the transmitting side of beam information suitable for the propagation path condition on the receiving side. Such a transmission beam technique is called Precoding (hereinafter referred to as “precoding”). In precoding, in order to reflect the observation status (propagation channel status) of the received signal at the receiving point, a feedback signal including beam information is transmitted from the receiver to the transmitter, and the transmitter controls the beam using the feedback signal. To do.

As a method for obtaining the transmission capacity of the MIMO system, a right matrix of singular value decomposition (SVD) of the MIMO channel in the transmitter, that is, a precoding matrix obtained from the right singular matrix, is applied during the SVD. It is known to allocate power to each spatial stream based on eigenvalues. To achieve this, the right singular matrix and eigenvalues are first quantized and then fed back to the transmitter. However, it is impractical for the receiver to send the exact right singular matrix and eigenvalues to the transmitter over the uplink, which results in enormous signaling overhead. In contrast to the right singular matrix and the immediate quantization of the eigenvalues, a more efficient method predetermines a codebook consisting of precoding sets that are optimally designed to reflect the statistics of the MIMO fading channel. The precoding matrix is selected from a codebook based on channel conditions and some predetermined criteria. The receiver transmits an index corresponding to the selected precoding matrix to the transmitter. This requires very few bits for signaling the index of the precoding matrix to the transmitter. If the precoding matrix set (codebook) is optimally designed, capacity loss can be achieved at an acceptable level.

Precoding can be used for both SCW transmission and MCW transmission. In MCW transmission, when precoding is applied at the transmitter, data packets from different codewords contribute to signals transmitted via multiple antennas with different weight values. For this reason, each codeword has different link conditions. As a result, the decoding quality varies with the codeword. In the MCW type MIMO system, some codewords are correctly decoded and pass the CRC check, while others are not decoded correctly and are likely to require retransmission.

Most of the precoding designs currently employed are optimal for initial communications, ie concentrate on maximizing MIMO capacity without considering HARQ. For retransmission, the retransmission codeword has higher transmission quality requirements as opposed to initial communication where the codeword has the same requirements and transmission quality. A precoding design for retransmission must address the challenges of higher transmission quality requirements in order to reduce the number of retransmissions and improve system capacity.

As a prior art for adapting precoding to retransmission, as disclosed in Non-Patent Document 1, there is a method in which precoding vectors used for MCW codewords are replaced during retransmission.
3GPP TSG RAN WG1 # 49, R1-072384, Nortel, "HARQ performance enhancement", May 7th-11th, 2007

As in the prior art of Non-Patent Document 1, simply replacing the precoding vector used for each codeword at the time of retransmission cannot guarantee whether sufficient transmission quality requirements can be obtained at each codeword at the time of retransmission. In particular, when the temporal change of the propagation path condition does not occur very much (when the temporal channel correlation is high), even if the precoding vector is replaced, the improvement of the reception quality in each codeword cannot be expected. In addition, when there is no temporal change in the propagation path condition and a significant reduction in received power due to fading occurs in one propagation path, the newly transmitted codeword fails to be decoded (decoding result) May be NACK).

The present invention has been made in view of the above circumstances, and a radio communication apparatus, a radio communication system, and a radio communication capable of improving the transmission quality of each codeword at the time of retransmission when precoding is employed in MIMO. It aims to provide a method.

The present invention provides, as a first aspect, a wireless communication apparatus that performs communication using a plurality of codewords using a plurality of antennas, and that receives a signal of a plurality of codewords transmitted from a plurality of antennas of a transmission apparatus A decoding unit that decodes each of the received multiple codewords, a channel estimation unit that estimates a propagation state of each of the received multiple codewords, and a future transmission based on the propagation state of each codeword A precoding matrix selection unit for selecting a precoding matrix for beam forming by precoding and a decoding result of each of the decoded codewords to adjust the power of each codeword in the precoding matrix A parameter determination unit for determining the parameters of each of the codewords Issue result, the feedback information including the information for specifying the precoding matrix and the parameter, to provide a radio communication apparatus and a feedback information output unit to be transmitted to the transmission device.

Moreover, the present invention provides, as a second aspect, the wireless communication apparatus described above, wherein the parameter determination unit adjusts the power of each codeword as the parameter while keeping the power of all codewords constant. Includes those that calculate offset values.

Further, the present invention provides, as a third aspect, the above wireless communication apparatus, wherein the parameter determination unit converts a code word that needs to be retransmitted when the decoding result is negative based on the decoding result of each code word. Including those that determine parameters to allocate more power to.

According to a fourth aspect of the present invention, there is provided the wireless communication apparatus according to the above aspect, wherein the parameter determination unit determines whether a codeword that needs to be retransmitted based on a decoding result of each codeword is negative. In the case where there are a plurality of codewords, a parameter for allocating more power to codewords having poor decoding reliability is included.

Moreover, the present invention provides, as a fifth aspect, the above-described wireless communication device, wherein the parameter determination unit is configured to detect an antenna having a good channel condition based on a channel condition for each of a plurality of antennas of the transmission device. To determine parameters to allocate more power.

In addition, the present invention provides, as a sixth aspect, the wireless communication apparatus described above, wherein the parameter determination unit needs to retransmit based on the decoding result and the number of retransmissions of each codeword, with no decoding result This includes determining a parameter for assigning more power to a large codeword as the number of retransmissions increases.

Further, the present invention provides, as a seventh aspect, the above wireless communication apparatus, wherein the parameter determination unit calculates a decoding quality of each codeword, and a codeword that needs to be retransmitted because the decoding result is negative On the other hand, a parameter for adaptively allocating power so as to obtain the best decoding quality is included.

Moreover, the present invention provides, as an eighth aspect, a wireless communication apparatus that performs communication using a plurality of codewords using a plurality of antennas, and an encoding unit that encodes a plurality of codewords to be transmitted to a receiving apparatus; A precoding processing unit that performs precoding to form a predetermined beam by weighting signals output to a plurality of antennas for a plurality of encoded codewords, and a signal after the precoding processing via a plurality of antennas A transmitter for transmitting to the receiver, and the precoding processor includes a precoding matrix for the precoding included in feedback information from the receiver and each codeword in the precoding matrix. Based on the information that specifies the parameters for adjusting the power, To provide a radio communication apparatus for performing the loading.

Further, the present invention provides, as a ninth aspect, the above wireless communication apparatus, wherein the precoding processing unit uses each codeword as a parameter in the precoding matrix while maintaining the power of all codewords constant. Including pre-coding using an offset value for adjusting the power of.

Moreover, the present invention provides, as a tenth aspect, the wireless communication apparatus described above, wherein the precoding processing unit needs to retransmit based on a decoding result of each of the plurality of codewords with no decoding result. This includes precoding that allocates more power to codewords.

Moreover, the present invention provides, as an eleventh aspect, the wireless communication apparatus described above, wherein the precoding processing unit needs to retransmit based on a decoding result of each of the plurality of codewords with no decoding result. In the case where there are a plurality of codewords, precoding in which more power is allocated to codewords having poor decoding reliability in these codewords is included.

Further, the present invention provides, as a twelfth aspect, the wireless communication apparatus described above, wherein the precoding processing unit is based on a channel condition for each of the plurality of antennas and has an excellent channel condition. This includes precoding that allocates a lot of power.

According to a thirteenth aspect of the present invention, there is provided the wireless communication apparatus, wherein the precoding processing unit re-determines whether the decoding result is negative based on each decoding result and the number of retransmissions of the plurality of codewords. This includes codewords that need to be transmitted and that perform precoding with more power allocated as the number of retransmissions increases.

Moreover, the present invention provides, as a fourteenth aspect, the wireless communication apparatus described above, wherein the precoding processing unit needs to retransmit based on the decoding quality of each of the plurality of codewords with no decoding result. This includes codewords that are precoded with adaptively assigned power so that the decoding quality is best.

Moreover, this invention provides a radio | wireless communication base station apparatus provided with the radio | wireless communication apparatus in any one of the above as a 15th aspect.
Moreover, this invention provides a radio | wireless communication mobile station apparatus provided with the radio | wireless communication apparatus in any one of the above as a 16th aspect.

According to a seventeenth aspect of the present invention, there is provided a wireless communication system that performs communication using a plurality of codewords using a plurality of antennas, and receives a plurality of codeword signals transmitted from a plurality of antennas of a transmission apparatus. A receiving unit, a decoding unit that decodes each of the received multiple codewords, a channel estimation unit that estimates the propagation status of each of the received multiple codewords, and a future based on the propagation status of each codeword And a precoding matrix selection unit for selecting a precoding matrix for beam forming by precoding in transmission, and adjusting the power of each codeword in the precoding matrix based on the decoding result of each of the decoded codewords A parameter determining unit for determining a parameter for performing the reception An encoding unit for encoding a plurality of codewords to be transmitted to a device, and forming a predetermined beam by weighting signals output to a plurality of antennas based on the precoding matrix and the parameters for the encoded plurality of codewords There is provided a wireless communication system comprising: a precoding processing unit that performs precoding to transmit; and a transmission unit that transmits a signal after the precoding processing to the reception device via a plurality of antennas.

According to an eighteenth aspect of the present invention, there is provided a wireless communication method in a wireless communication system that performs communication using a plurality of codewords using a plurality of antennas, wherein a plurality of codewords transmitted from a plurality of antennas of a transmission apparatus are transmitted. A reception step of receiving a signal; a decoding step of decoding each of the received multiple codewords; a channel estimation step of estimating a propagation path condition of each of the received multiple codewords; and a propagation path condition of each codeword A precoding matrix selecting step for selecting a precoding matrix for beamforming by precoding in future transmission, and each codeword in the precoding matrix based on a decoding result of each of the decoded codewords For adjusting the power of A parameter determining step for determining data, an encoding step for encoding a plurality of codewords to be transmitted to the receiving device, and a plurality of antennas based on the precoding matrix and the parameters for the encoded plurality of codewords A precoding processing step of performing precoding to form a predetermined beam by weighting of a signal to be output to, and a transmission step of transmitting the signal after the precoding processing to the receiving device via a plurality of antennas. A wireless communication method is provided.

With the above configuration, the power of the precoding matrix is adjusted so that more power is allocated to the retransmission codeword when retransmission occurs based on the decoding result of each of the multiple codewords. It becomes possible to do. Thereby, it is possible to improve the transmission quality of each codeword at the time of retransmission.

According to the present invention, it is possible to provide a radio communication apparatus, a radio communication system, and a radio communication method that can improve the transmission quality of each codeword at the time of retransmission when precoding is employed in MIMO.

Block diagram illustrating a configuration of a transmitter for MCW MIMO precoding system Block diagram illustrating the configuration of a receiver for MCW MIMO precoding system A diagram illustrating a more efficient way to achieve precoding in a MIMO system under limited feedback The figure which shows the relationship of parameter (DELTA) i and (delta) i determined based on the signaling condition of ACK / NACK, the channel conditions of a transmission antenna, and decoding reliability A flowchart showing a procedure for determining the parameters Δi and δi shown in FIG. A block diagram showing a configuration of a receiver for an MCW MIMO precoding system according to the present embodiment Block diagram showing the configuration of a transmitter for the MCW MIMO precoding system according to the present embodiment The figure which shows the method of acquiring the coefficient b in Numerical formula (18) by simulation. The figure which shows the processing procedure of static parameter adjustment The figure which shows the processing procedure of dynamic parameter adjustment

Explanation of symbols

106, 108 CRC encoding unit 110, 112 Channel encoding / symbol mapping unit 130, 730 Precoding processing unit 122, 124 Transmitting antenna 202, 204 Receiving antenna 214, 216 Demapping and decoding unit 218, 220 CRC checking unit 602 Channel estimation unit 604 Parameter selection unit 606 Precoding matrix selection unit

In the present embodiment, as an example of the wireless communication apparatus, the wireless communication system, and the wireless communication method according to the present invention, in a wireless communication system employing MIMO, precoding is performed by weighting a plurality of antennas to form a beam. A configuration example in the case of performing is shown. At this time, it is assumed that the transmission device and the reception device perform signal transmission using a plurality of CWs using a plurality of antennas, and perform retransmission control (adaptive retransmission control) using HARQ in MCW. In the present embodiment, it is assumed that in a cellular system, a signal is transmitted from a base station to a user terminal, and ACK / NACK indicating whether reception is possible is fed back from the user terminal to the base station. In this case, the base station (wireless communication base station device) becomes a transmitting device (wireless communication device having a transmitter function), and the user terminal (wireless communication mobile station device) is a receiving device (wireless communication device having a receiver function). ) The following embodiment is an example for description, and the present invention is not limited to this.

In the present embodiment, a precoding method capable of improving the transmission quality of a spatial stream at the time of retransmission when MCW is simultaneously transmitted in a MIMO system and retransmission control by HARQ is performed is presented. By adjusting the input power of the precoding matrix based on the ACK / NACK signal of multiple codewords when one codeword does not pass the CRC check at the receiver and becomes NACK and re-transmission is required, The transmission quality of the retransmission data stream can be improved.

In this embodiment, when adjusting the power distribution among a plurality of codewords, the input power of the precoding matrix is adjusted while keeping the transmission power of all the codewords and the physical antenna constant. At this time, the receiver first decodes the initial transmission codeword. If there is a codeword that fails the CRC check and needs to be retransmitted, the receiver will, for each input of the precoding matrix included in the codeword for initial transmission, based on the ACK / NACK signal and / or the decoding quality We will add an offset value. This offset value will be used to allocate more power retransmission codewords for antennas with good channel conditions and less power for antennas with poor channel conditions. The transmission quality of the retransmission codeword is improved as compared with the precoding method that does not use input adjustment of the precoding matrix while keeping the transmission power of the codeword and the physical antenna constant. Then, the receiver feeds back the offset value together with the precoding matrix to the transmitter. This offset value can be either predetermined based on channel statistics or adaptively determined based on instantaneous channel conditions.

As an example of a method for determining an offset value when adjusting power distribution among a plurality of codewords, in a static adjustment method determined in advance based on channel statistics, a set of offset values with respect to a precoding matrix input for retransmission is expressed as ACK / NACK. The signal is determined in advance according to the case, and the index of the offset value set to be used next time is fed back to the transmitter for notification from the receiver according to the ACK / NACK signal. As another example of the offset value determination method, in the dynamic adjustment method adaptively determined based on the instantaneous channel condition, the offset value for the input of the precoding matrix is adapted based on the decoding quality at the receiver. To be determined and fed back to the transmitter for notification.

In the following, an exemplary implementation for precoding design of data retransmission trust in a MIMO system will be described first, followed by a detailed description of the exemplary implementation followed by a separate and extensive description of transmitters and receivers in the MIMO system.

In the present embodiment, the transmitter and the receiver will be described extensively for each having two transmission antennas and reception antennas individually. However, the transmitter and the receiver each having three or more transmission antennas and reception antennas are illustrated. Those skilled in the art will appreciate that the implementation can be applied. In the following description, a new codeword refers to a codeword that has not been transmitted before, whereas a retransmission codeword refers to a codeword that is retransmitted based on the previous transmission codeword.

FIG. 1 is a block diagram illustrating the configuration of a transmitter for an MCW MIMO precoding system having two transmission antennas and two reception antennas. Here, a precoding matrix is applied at the transmitter, and a beam of a data sequence corresponding to each codeword is formed by precoding. Each block shown in the following drawings has a function realized by a hardware circuit in the wireless communication apparatus or a software program operating on the processor.

The CRC encoding units 106 and 108 perform CRC encoding on the input bit sequences CW1 (102) and CW2 (104), respectively. Channel coding and symbol mapping sections 110 and 112 perform channel coding and symbol mapping for the respective input bit sequences CW1 and CW2, and generate _two codewords s ₁ (114) and s ₂ (116). The precoding processing unit 130 receives data symbols from two code words, multiplies the weights specified by the precoding matrix, and outputs an output signal x ₁ (118) which is a weighted sum of the code words s ₁ and s _2. ) And x ₂ (120). These output signals x ₁ and x ₂ are transmitted via physical transmission antennas Tx1 (122) and Tx2 (124). At this time, the transmitter performs retransmission control by HARQ based on the ACK / NACK signal fed back from the receiver, and retransmits the codeword notified of NACK.

The output signals x ₁ and x ₂ are mathematically expressed by the following formula (1).

The signal transmitted via the antenna Tx1 and the antenna Tx2 is given by the following formula (2).

Here, N _S and N _T are the number of codewords and the number of transmission antennas, respectively, N _S ≦ min (N _T , N _R ), and N _R is the number of reception antennas.

The transmission power of the data symbol s _j distributed to the antenna Txi is expressed by the following mathematical formula (3).

In short, a part of the power of the data symbol s _j having the same value as the following formula (4) is allocated to the antenna Txi.

Thereby, the contribution of the code word s _j to the signal transmitted via the i-th antenna Txi is defined by the weight value | c _ij | ² , and the large | c _ij | ² is the majority of the power of the code word s _j. Is assigned to antenna Txi.

In general, transmitter output signals x ₁ and x ₂ propagate through a MIMO channel given by a matrix of N _R rows and N _T columns to reach the receiver. The input / output relationship of the precoding MIMO channel is given by the following equation (5).

Here, r, H, and n represent a received signal vector, a channel matrix, and an additive white Gaussian noise (AWGN) vector, respectively.

FIG. 2 is a block diagram illustrating a configuration of a receiver for an MCW MIMO precoding system having two transmission antennas and two reception antennas.

Reception signals r ₁ (206) and r ₂ (208) received by reception antennas Rx1 (202) and Rx2 (204) are input to MIMO detection section 208, respectively. The MIMO detection unit 208 separates the independent data symbols and generates codewords s ₁ (210) and s ₂ (212). Here, the MIMO detection unit 208 uses a known detection system, such as a linear least mean square error (LMMSE) decoder (not shown), and the precoding matrix C is known at the receiver through signaling transmission (not shown). Assuming that the channel matrix H is also known through channel estimation (not shown), MIMO detection may be performed. Demapping and decoding sections 214 and 216 receive detected codewords s ₁ and s ₂ and perform symbol demapping and channel decoding, respectively. Then, the CRC checkers 218 and 220 perform CRC check on the decoded codewords. As a result, two output bit sequences CW1 (222) and CW2 (224) are output. Further, depending on the output result of the CRC check, for each codeword, an ACK signal issued when the detected codeword passes the CRC check, or the detected codeword fails the CRC check. Any one of the NACK signals emitted at a time is transmitted and fed back to the transmitter via the uplink of the wireless communication system.

Theoretically, assuming singular value decomposition (SVD) of the MIMO channel matrix H, the following equation (6) is obtained.

The optimal precoding matrix C that maximizes the capacity of the MIMO system is obtained as a right singular matrix, that is, C = V. To achieve optimal precoding, the matrix C is first quantized and then immediately fed back to the transmitter via the uplink. Because of the irregular characteristics of the MIMO channel, the right singular matrix changes every moment. In this case, since a huge signaling overhead is caused, it is not practical to feed back a strict right singular matrix.

FIG. 3 is a diagram illustrating a more efficient method of implementing precoding in a MIMO system under limited feedback. FIG. 3 shows a precoding matrix output procedure. The codebook ３０４ (304) consisting of a finite set of precoding matrices is predetermined based on MIMO channel characteristics using some known techniques (for example, linear interpolation not shown). The size of the codebook Ξ is defined by N _c (number of codes or number of antennas). The number of binary bits of log ₂ N _c characterizes the codebook Ξ ⁽ⁱ⁾ as a whole. Here, at the receiver, for a given MIMO channel matrix H (302), one precoding matrix C is selected from the codebook for each transmission, and a metric (for example, capacity or SNR (Signal to Noise ratio, Signal-to-noise ratio)) is maximized (306). Then, as an example of information specifying the selected precoding matrix C, an index of the precoding matrix C is fed back to the transmitter 310 via the uplink of the wireless communication system (308).

In a precoding design for a MIMO system, in order to keep the transmission power of each codeword and each physical antenna constant and reduce the processing complexity, the precoding matrix is represented by, for example, the unitary shown in Equation (7) below. Must be a matrix.

The above precoding design is mainly for initial transmission where two transmission codewords become new codewords.

By using HARQ, the codeword whose decoding result is NACK is retransmitted according to a specific HARQ scheme (Chase scheme or IR (incremental redundancy) scheme, not shown). The retransmitted codeword is combined with the initial transmission codeword to obtain retransmission composite gain and improve decoding performance. When retransmission is performed in the MCW type MIMO system, the retransmission codeword requires higher transmission quality than the new codeword in order to improve the decoding performance after retransmission synthesis. The precoding scheme for retransmission needs to be designed to meet this requirement. The present embodiment proposes a precoding design method by adjusting the input power of the precoding matrix in the codebook based on the ACK / NACK signal or the decoding quality that achieves this goal.

Assume that s ₁ is a retransmission codeword and s ₂ is a new codeword to be transmitted simultaneously with s ₁ on the MIMO channel. The signal received by the receiver is given by the following equations (8) and (9).

Since a signal obtained by combining the above signals is observed at the receiver, the codeword s ₂ actually interferes with the retransmission codeword s ₁ .

From the above equations (8) and (9), the received signal power from the transmission antenna Tx1 of the retransmission codeword s ₁ is given by the following equation (10).

Also, the received signal power from the transmission antenna Tx2 of the retransmission codeword s ₁ is given by the following formula (11).

Interference power from new codeword s ₂ transmitted via the transmission antennas Tx1 to retransmission codeword s _1, that is, the reception signal power from the transmission antenna Tx1 new codeword s ₂ is given by the following equation (12) It is done.

Further, the interference power from the new codeword s ₂ transmitted to the retransmission codeword s ₁ via the transmission antenna Tx ₂ , that is, the received signal power from the transmission antenna Tx ₂ of the new codeword s ₂ is expressed by the following equation (13). Given in.

From the above equations (10) - (13), the fading gain of a given MIMO channel, for example, _{i∈ {1, ···, N R} } i∈ in {1, ···, N _T} to h _ij of On the other hand, the precoding matrix c _pq of q∈ {1,..., N _S } with p∈ {1,..., N _T } determines the power of the codeword transmitted through the transmitting antenna.

The channel conditions of the transmission antenna Tx1 and the transmission antenna Tx2 are given by the following equations (14) and (15), respectively.

The above description suggests a way to improve the transmission quality of the retransmission data stream. Assign more power of the retransmission codeword s _{1 to} the transmit antenna with better channel conditions given by equations (14) and (15), and assign a new codeword s ₂ with less power to equations (10) and ( By assigning to transmit antennas with better channel conditions based on 11), the received SNR of retransmission codeword s ₁ will be improved compared to the case without using the power adjustment. This power adjustment is performed when the received code is greatly reduced due to fading in the propagation path or when the temporal channel correlation is high. This is particularly useful when decoding failure results in failure.

Next, the precoding design of this embodiment for implementing the above method will be described in detail in the following description.

Assume that a codebook Ξ ⁽⁰⁾ consisting of a unitary matrix precoding matrix designed for initial transmission is given by the following equation (16).

Here, A can be a real value or an imaginary value. The first column of the precoding matrix is the weight coefficient of the code word s ₁ through the transmission antenna, and the second column of the precoding matrix is the weight coefficient of the code word s ₂ through the transmission antenna. The structure of the precoding matrix in the codebook ensures unitarity of the precoding matrix.

In the MCW type MIMO system, the decoding quality varies with the codeword. For 2 rows by 2 columns (2 × 2) MIMO using two codewords, the following four cases occur.
(1) When both transmission antennas Tx1 and Tx2 have good channel conditions sufficient for correct decoding and both codewords s ₁ and s ₂ are ACK (2) Both transmission antennas Tx1 and Tx2 are correct decoding the has a poor channel condition can not be performed, the code word s _1, s ₂ if both the NACK (3) transmit antennas Tx1, codewords s ₁ of the signal power from Tx2 codeword s ₂ and additive white When the code word s ₁ becomes NACK and the code word s ₂ becomes ACK when the interference power from the Gaussian noise AWGN is not sufficient, (4) The signal power of the code word s ₂ from the transmission antennas Tx1 and Tx2 is codewords s ₁ and additive not sufficient to counteract the interference power from white Gaussian noise AWGN, codeword s ₁ is ACK next code If the word s ₂ is NACK based on different combinations of decoding quality for the codewords s ₁ and codeword s _2, pre-encoding processor needs to have a different design for the quality improvement of retransmission codeword .

If at least one codeword is NACK and needs to be retransmitted, for the i-th transmission of a particular codeword, codebook Ξ ⁽ⁱ⁾ is designed as equation (17) below.

Here, Δ _i and δ _i are real numbers and satisfy 0 ≦ Δ _i , δ _i ≦ | A |.

The structure of the precoding matrix in Equation (17) continues to have unitary nature of the precoding matrix given by Equation (16). The purpose of introducing the parameters Δ _i and δ _i is to adjust the power of each input of the precoding matrix in retransmission. Here, Δ _i > δ _i means that more power of the codeword s ₁ is assigned to the transmission antenna Tx1, and less power is assigned to the transmission antenna Tx2. On the other hand, Δ _i <δ _i means that more power of the codeword s ₂ is assigned to the transmission antenna Tx1, and less power is assigned to the transmission antenna Tx2. Δ _i = δ _i indicates that the equal power of both codewords s ₁ and s ₂ is assigned to the transmitting antenna, where Δ _i and δ _i provide the difference between the initial transmission and the retransmission. It is only used for.

In Equation (17), the first column A + Δ _i , A + δ _i of the matrix is related to the weight of the code word s ₁ , and the second column A + δ _i , − (A + Δ _i ) of the matrix is related to the weight of the code word s _2. . The first row of the matrix is related to the weight of the transmission antenna Tx1, and the second row is related to the weight of the transmission antenna Tx2. Here, attention is paid to one of the codeword strings in accordance with the ACK / NACK signal, and more weight is assigned to the codeword that becomes NACK and needs to be retransmitted, and the weight of the other codeword is reduced. Also, pay attention to the row of any antenna depending on whether the channel condition of the transmitting antenna is good or bad. That is, the magnitude relationship between the parameters Δ _i and δ _i is determined according to the condition of the ACK / NACK signal and the channel condition of the transmitting antenna. When both codewords s ₁ and s ₂ are NACK, the parameters Δ _i and δ _i are adjusted according to the decoding reliability, which is one of decoding quality.

FIG. 4 is a diagram showing the relationship between the ACK / NACK signaling of the decoding result of each codeword, the channel condition of the transmitting antenna, and the parameters Δ _i and δ _i determined based on the decoding reliability.

When both the code word s ₁ and the code word s ₂ are ACK, the parameters Δ _i and δ _i are set to Δ _i = δ _i = 0 regardless of the channel conditions of the transmission antennas Tx1 and Tx2.

When the codeword s ₁ is ACK and the codeword s ₂ is NACK, the parameter is set to δ _i > Δ _i ≧ 0 when the transmission antenna Tx1 has better channel conditions than the transmission antenna Tx2. Also, when the channel condition of the transmission antenna Tx2 is better than that of the transmission antenna Tx1, Δ _i > δ _i ≧ 0 is set.

When the codeword s ₁ is NACK and the codeword s ₂ is ACK, the parameter is set to Δ _i > δ _i ≧ 0 when the transmission antenna Tx1 has better channel conditions than the transmission antenna Tx2. Further, when the channel condition of the transmission antenna Tx2 is better than that of the transmission antenna Tx1, δ _i > Δ _i ≧ 0 is set. That is, the power distribution is adjusted so that more power is allocated to the code word that needs to be retransmitted because the decoding result is NACK. At this time, a lot of power is allocated to the antenna having a good channel condition.

When both the code word s ₁ and the code word s ₂ are NACK, adjustment is made according to the decoding reliability of both the code words s ₁ and s ₂ . Decoding reliability is one metric that indicates decoding quality, and each codeword is measured by comparing the average LLR (Log Likelihood Ratio) or SNR of decoded bits with each other for comparison. Here, when the reliability of the codeword s ₁ is higher and the channel condition of the transmission antenna Tx1 is better than that of the transmission antenna Tx2, the parameter is set to δ _i > Δ _i ≧ 0. Also, when the channel condition of the transmission antenna Tx2 is better than that of the transmission antenna Tx1, Δ _i > δ _i ≧ 0 is set. On the other hand, when the reliability of the codeword s ₂ is higher, the parameter is set to Δ _i > δ _i ≧ 0 when the transmission antenna Tx1 has better channel conditions than the transmission antenna Tx2. Further, when the channel condition of the transmission antenna Tx2 is better than that of the transmission antenna Tx1, δ _i > Δ _i ≧ 0 is set. That is, the power distribution is adjusted so that more power is allocated to the codeword having the lower decoding reliability.

FIG. 5 is a flowchart showing a procedure for determining the parameters Δ _i and δ _i shown in FIG. The receiver first determines whether the _two codewords s ₁ and s ₂ both have an ACK signal (502). When the code words s ₁ and s ₂ are both ACK, the parameters Δ _i and δ _i are set to Δ _i = δ _i = 0 (504).

If both codewords s ₁ and s ₂ are not ACK in step 502, the receiver determines whether codeword s ₁ has a NACK signal (506). If the code word s ₁ is NACK, it is determined whether the code word s ₂ has a NACK signal (514). If the code word s ₁ is ACK, that is, the code word s ₁ is ACK and the code word s ₂ is NACK. In this case, the channel conditions of the two transmission antennas Tx1 and Tx2 are determined (508).

In step 508, if the transmission antenna Tx1 has better channel conditions than the transmission antenna Tx2, the parameter is set to δ _i > Δ _i ≧ 0 and more of the power of the codeword s ₂ is assigned to the antenna Tx1 (510). If the channel condition of the transmission antenna Tx2 is better than that of the transmission antenna Tx1, the parameter is set to Δ _i > δ _i ≧ 0, and more power of the codeword s ₂ is assigned to the antenna Tx2 (512).

If the code word s ₂ is NACK in step 514, that is, if both the code words s ₁ and s ₂ are NACK, the decoding reliability determined by the average LLR or SNR of the decoded bits is determined. Here, when the code word s ₁ has higher reliability than the code word s ₂ , the processing of steps 508, 510, and 512 is performed, and the transmission antenna Tx 1 has better channel conditions than the transmission antenna Tx 2. The parameter is set to δ _i > Δ _i ≧ 0, and the parameter is set to Δ _i > δ _i ≧ 0 when the transmission antenna Tx2 has better channel conditions than the transmission antenna Tx1. On the other hand, if the code word s ₁ has a lower reliability than the code word s ₂ , the process proceeds to step 516.

If the code word s ₂ is not NACK in step 514, that is, if the code word s ₁ is NACK and the code word s ₂ is ACK, channel conditions of the two transmission antennas Tx1 and Tx2 are determined (516). If the transmit antenna Tx1 has better channel conditions than the transmit antenna Tx2 at step 516, the parameter is set to Δ _i > δ _i ≧ 0 and more of the power of the codeword s ₁ is assigned to the antenna Tx1 (518). If the channel condition of the transmission antenna Tx2 is better than that of the transmission antenna Tx1, the parameter is set to δ _i > Δ _i ≧ 0, and more power of the codeword s ₁ is allocated to the antenna Tx2 (520).

The above parameters Δ _i and δ _i are based on ACK / NACK signaling, decoding reliability information (average LLR and SNR of decoded bits), and channel conditions of the transmitting antenna given by equations (14) and (15). Based on this, it is determined by either a static adjustment method or a dynamic adjustment method described later.

FIG. 6 is a block diagram showing a configuration of a receiver for the MCW type MIMO precoding system according to the present embodiment. FIG. 6 is an example in which constituent elements characteristic to the present embodiment are added to the configuration of FIG. The receiver includes a channel estimation unit 602, a parameter selection unit 604, and a precoding matrix selection unit 606. In addition, a transmission unit 608 including a transmission signal processing unit for transmitting feedback information, a transmission RF unit, and the like is provided. Others are the same as FIG.

The channel estimation unit 602 performs channel estimation based on the received signals r ₁ (206) and r ₂ (208) received by the receiving antennas Rx1 (202) and Rx2 (204), and a channel matrix H corresponding to the channel estimation result Is output. The parameter selection unit 604 receives the channel matrix H and the ACK / NACK signal output according to the CRC check result of each codeword decoded in the CRC check units 218 and 220. The parameter selection unit 604 selects and determines the parameters Δ _i and δ _i as described above based on the channel matrix H and the ACK / NACK signal. The precoding matrix selection unit 606 selects and determines the precoding matrix C based on the channel matrix H and the parameters Δ _i and δ _i . The receiver feeds back the index information specifying the determined parameters Δ _i and δ _i and the precoding matrix C to the transmitter via the transmitter 608 together with the ACK / NACK signal of each codeword. To do. In the receiver of FIG. 6, the receiving antennas 202 and 204 and a receiving RF unit (not shown) realize the function of the receiving unit. In addition, the MIMO detection unit 208 and the demapping and decoding units 214 and 216 realize the function of the decoding unit. The parameter selection unit 604 implements the function of the parameter determination unit. Further, the transmission unit 608 and the transmission antenna (usually also serving as a reception antenna) implement the function of the feedback information output unit.

FIG. 7 is a block diagram illustrating a configuration of a transmitter for the MCW MIMO precoding system according to the present embodiment. FIG. 7 is an example in which components characteristic to the present embodiment are added to the configuration of FIG. The transmitter has a characteristic function in the precoding processing unit 730. In addition, a reception unit 710 including a reception RF unit for receiving feedback information, a reception signal processing unit, and the like is provided. The transmitter acquires the precoding matrix C fed back from the receiver and the index information of the parameters Δ _i and δ _i via the receiving unit 710. Pre-encoding processor 730 uses the precoding matrix C and the parameter delta _i, the index information of [delta] _i, determining the precoding matrix C after power adjustment, pre for the two codewords s _1, s ₂ Perform the coding process. Here, the code words s ₁ and s ₂ are respectively multiplied by the weights specified by the precoding matrix C and the parameters Δ _i and δ _i to generate output signals x ₁ and x ₂ . In the transmitter of FIG. 7, the CRC encoding units 106 and 108 and the channel encoding and symbol mapping units 110 and 112 realize the function of the encoding unit. The transmission antennas 122 and 124 and a transmission RF unit (not shown) realize the function of the transmission unit. In addition, the reception unit 710 and the reception antenna (usually also serving as the transmission antenna) realize the function of the feedback information reception unit.

Next, a specific example of a method for adjusting the parameters Δ _i and δ _{i in} the above-described precoding matrix C will be described. Here, a static adjustment method and a dynamic adjustment method are illustrated.

(1) Static Parameter Adjustment In static adjustment, a parameter set {Δ _i , δ _i } is defined based on the number of retransmissions of two codewords and ACK / NACK signaling.

In the i-th retransmission, one codeword is assumed. The parameters Δ _i and δ _i can be determined by the following mathematical formula (18).

Here, the coefficient b is a positive value parameter and can be determined in advance from a simulation based on the channel statistics and the quality of service (QOS) of the data packet. In addition, w = 1,..., N−1 takes a positive value and represents the difference between the number of retransmissions of two code words. For example, if codeword s ₁ is the i-th retransmission and codeword s ₂ is the p-th retransmission, w = | ip |. N represents the maximum number of transmissions including initial transmission. Therefore, the upper limit of the coefficient b is b ≦ | A | / N.

Based on Equation (18) above, the parameter set {Δ _i , δ _i } is one of the sets given on the right side of Equation (18) based on the number of retransmissions of two codewords and ACK / NACK signaling. I will take. When w> 0, the first parameter set given on the right side of Equation (18) indicates that more power of codeword s ₁ will be allocated to transmit antenna Tx1. The second parameter set also indicates that more power of codeword s ₂ will be allocated to transmit antenna Tx1.

Here, the reason for selecting the parameter set given by Equation (18) is as follows. At w = 0, the two codewords are both at the same number of retransmissions. Since the transmission quality requirements for the two retransmission codewords are the same, equal power distribution is applied to the power of the two codewords for the transmission antenna.

For w> 0, a codeword having a larger number of retransmissions must have higher requirements regarding transmission quality. For this reason, in the code word having the larger number of retransmissions, more power of the code word is allocated to the transmission antenna having better channel conditions. As w increases or as the difference in the number of retransmissions of two codewords increases, codewords having a larger number of retransmissions have even higher retransmission quality requirements. For this reason, in the codeword to be retransmitted, it is necessary to allocate much greater power of the codeword to the transmit antenna with better channel conditions. Accordingly, as the number of retransmissions increases, the power distribution is made to differ between codewords.

FIG. 8 is a diagram illustrating a method for obtaining the coefficient b in the equation (18) by simulation. Here, the coefficient b is determined based on a given MIMO channel statistic and packet error rate (PER: PacketPackError Rate) performance.

First, random coefficients b are generated irregularly according to a uniform distribution in the range of b ≦ | A | / N (802). Then, for each coefficient b, MCW input information bits relating to the code words s ₁ and s ₂ are generated (804), and based on the given coefficient b, a transmitter for encoding, modulation and precoding is generated. Processing is performed (806). A MIMO channel is then randomly generated based on given channel statistics (average and deviation) (808). Then, a signal is transmitted from the transmitter via the MIMO channel (810), and the receiver processes the receiver to perform MIMO detection, demodulation, and decoding (812).

Subsequently, the decoding bits of the codeword that has passed the CRC check (becomes ACK) at the receiver are collected (814). Thereafter, the procedure between steps 804 to 814 is repeated until the MIMO channel is sufficiently simulated in this simulation. Next, the average throughput for a given coefficient b is calculated using the decoded information pits collected in step 814 (816). Thereafter, the procedure between steps 802 to 816 is repeated in this simulation to obtain an average throughput for different coefficients b. The coefficient b that provides the best average throughput is the final selection result.

FIG. 9 is a diagram showing a processing procedure for static parameter adjustment. The receiver first detects and decodes the received signal (902). Then, based on the given MIMO channel estimation result, the channel conditions of the transmission antennas Tx1 and Tx2 are calculated from the equations (14) and (15) (904). Next, w is acquired based on the CRC check result of the current transmission and the number of retransmissions of all codewords (906). Then, a parameter set {Δ _i , δ _i } given by Equation (18) is selected as power adjustment parameters Δ _i , δ _i to be used for the next transmission based on ACK / NACK signaling of two code words. (908). The index of the selected parameter set {Δ _i , δ _i } is fed back to the transmitter via the uplink.

(2) In the dynamic parameter adjustment dynamic adjustment, the relationship between the SNR of decoded reliability and every bit, that is the average LLR and the average LLR and SNR with _{D r} representing the relationship between the PER = f _{(D r} ) Must be determined in advance by simulation.

FIG. 10 is a diagram illustrating a processing procedure for dynamic parameter adjustment. The receiver first detects and decodes the received signal (1002). The decoding failure to a mean LLR of decoded bits of the code word becomes NACK, is calculated by _{D r} (1004). At this time, _Dr is obtained by the following equation (19).

Here, p (r | 1) and p (r | 0) represent information probabilities to be decoded as 1 and 0, respectively.

Next, the required average LLR corresponding to the required PER is calculated based on the relationship between the average LLR and PER defined in advance (1006). Based on the relationship between the SNR and the average LLR, the required SNR for the next retransmission credit is extracted (1008). Subsequently, a parameter set {Δ _i , δ _i } is determined by solving the following mathematical formulas (20), (21), and (22) based on the required SNR (1010). The index of the selected parameter set {Δ _i , δ _i } is fed back to the transmitter via the uplink.

When determining the parameter set {Δ _i , δ _i }, first, a combination of parameters Δ _i , δ _i (for example, four ways) is temporarily set. Then, the precoding matrix C based on the temporarily set parameters Δ _i and δ _i is substituted into the equations (20), (21), and (22), and the SNR for each parameter Δ _i and δ _i is calculated. Thereafter, the parameter delta _i, the parameter set of the largest SNR from the combinations of _{δ i {Δ i, δ i} } selects. The SNR calculated here can be used as the decoding reliability at the time of parameter determination in FIGS. 4 and 5 described above.

As described above, in the present embodiment, when precoding is applied in MCW MIMO system and retransmission control is performed by HARQ, retransmission of a plurality of codewords is required according to ACK / NACK of each codeword. A precoding matrix is determined so that more power is allocated to a simple codeword and more power is allocated to a high quality antenna among a plurality of antennas. As a result, the transmission quality of retransmission codewords that require high transmission quality can be improved, and reception quality such as decoding quality at the receiver can be improved. Therefore, it is possible to further improve the transmission efficiency and transmission capacity in the wireless communication system.

It should be noted that the present invention is not limited to those shown in the above-described embodiments, and those skilled in the art can also make changes and applications based on the description in the specification and well-known techniques. Yes, included in the scope of protection.

In each of the above embodiments, the case where the present invention is configured by hardware has been described as an example, but the present invention can also be realized by software.

Further, each functional block used in the description of each of the above embodiments is typically realized as an LSI that is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

Further, the method of circuit integration is not limited to LSI, and implementation with a dedicated circuit or a general-purpose processor is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

Furthermore, if integrated circuit technology that replaces LSI emerges as a result of advances in semiconductor technology or other derived technology, it is naturally also possible to integrate functional blocks using this technology. Biotechnology can be applied.

This application is based on a Japanese patent application (Japanese Patent Application No. 2008-017524) filed on January 29, 2008, the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY The present invention has an effect of improving the transmission quality of each codeword at the time of retransmission when precoding is employed in MIMO, and is applied to a MIMO system that performs communication using a plurality of antennas. It is useful as an applicable wireless communication device, wireless communication system, wireless communication method, and the like.

Claims (18)

1. A wireless communication device that performs communication using a plurality of codewords using a plurality of antennas,
   A receiving unit that receives signals of a plurality of codewords transmitted from a plurality of antennas of the transmitting device;
   A decoding unit for decoding each of the received multiple codewords;
   A channel estimator for estimating the propagation path condition of each of the received multiple codewords;
   A precoding matrix selection unit that selects a precoding matrix for beam forming by precoding (Precoding) in future transmission based on a propagation path state of each codeword;
   A parameter determining unit that determines a parameter for adjusting the power of each codeword in the precoding matrix based on the decoding result of each of the plurality of decoded codewords;
   A feedback information output unit for transmitting feedback information including a decoding result of each codeword and information specifying the precoding matrix and the parameter to the transmission device;
   A wireless communication device comprising:
2. The wireless communication device according to claim 1,
   The parameter determination unit is a wireless communication apparatus that calculates, as the parameter, an offset value for adjusting the power of each codeword while keeping the power of all codewords constant.
3. The wireless communication device according to claim 1,
   The parameter determination unit is a wireless communication apparatus that determines a parameter for allocating more power to a codeword that needs to be retransmitted when the decoding result is negative based on a decoding result of each codeword.
4. The wireless communication device according to claim 1,
   Based on the decoding result of each codeword, the parameter determination unit may determine whether or not there is a plurality of codewords that need to be retransmitted because the decoding result is negative, and for these codewords, the decoding reliability is inferior. A wireless communication device that determines parameters for allocating much power.
5. The wireless communication device according to claim 3 or 4,
   The said parameter determination part is a radio | wireless communication apparatus which determines the parameter which allocates more power with respect to the antenna which has favorable channel conditions based on the channel conditions for every several antenna of the said transmitter.
6. The wireless communication device according to claim 1,
   The parameter determination unit determines a parameter for allocating more power as the number of retransmissions increases for a codeword that needs to be retransmitted because the decoding result is negative based on the decoding result and the number of retransmissions of each codeword. Wireless communication device.
7. The wireless communication device according to claim 1,
   The parameter determination unit calculates a decoding quality of each codeword, and determines a parameter to which power is adaptively allocated so that the decoding quality is the best for a codeword that is not decoded and needs to be retransmitted. Wireless communication device.
8. A wireless communication device that performs communication using a plurality of codewords using a plurality of antennas,
   An encoding unit for encoding a plurality of codewords to be transmitted to the receiving device;
   A precoding processing unit that performs precoding for forming a predetermined beam by weighting signals output to a plurality of antennas with respect to the plurality of encoded codewords,
   A transmission unit that transmits the signal after the precoding process to the reception device via a plurality of antennas,
   The precoding processing unit is information specifying a precoding matrix for the precoding and a parameter for adjusting the power of each codeword in the precoding matrix, which are included in the feedback information from the receiving device. A wireless communication device that performs precoding based on the above.
9. The wireless communication device according to claim 8,
   The precoding processing unit is a wireless communication apparatus that performs precoding using an offset value that adjusts the power of each codeword while maintaining the power of all codewords as a parameter in the precoding matrix.
10. The wireless communication device according to claim 8,
    The precoding processing unit is a wireless communication apparatus that performs precoding by allocating more power to a codeword that needs to be retransmitted because the decoding result is negative based on the decoding result of each of the plurality of codewords.
11. The wireless communication device according to claim 8,
    Based on the decoding results of the plurality of codewords, the precoding processing unit converts codewords having inferior decoding reliability in these codewords when there are a plurality of codewords that are not decoded and need to be retransmitted. A wireless communication device that performs precoding with more power allocated to the device.
12. The wireless communication device according to claim 10 or 11,
    The precoding processing unit is a wireless communication apparatus that performs precoding by assigning more power to an antenna having a good channel condition based on the channel condition for each of the plurality of antennas.
13. The wireless communication device according to claim 8,
    The precoding processing unit allocates more power as the number of retransmissions increases, based on the decoding result and the number of retransmissions of each of the plurality of codewords, to a codeword that needs to be retransmitted because the decoding result is negative A wireless communication device that performs precoding.
14. The wireless communication device according to claim 8,
    The precoding processing unit adaptively allocates power based on the decoding quality of each of the plurality of codewords so that the decoding quality is not good and the codeword that needs to be retransmitted needs the best decoding quality. A wireless communication device that performs precoding.
15. A wireless communication base station apparatus comprising the wireless communication apparatus according to any one of claims 1 to 14.
16. A wireless communication mobile station device comprising the wireless communication device according to any one of claims 1 to 14.
17. A wireless communication system that performs communication by a plurality of codewords using a plurality of antennas,
    A receiving unit that receives signals of a plurality of codewords transmitted from a plurality of antennas of the transmitting device;
    A decoding unit for decoding each of the received multiple codewords;
    A channel estimator for estimating the propagation path condition of each of the received multiple codewords;
    A precoding matrix selection unit that selects a precoding matrix for beam forming by precoding (Precoding) in future transmission based on a propagation path state of each codeword;
    A parameter determining unit that determines a parameter for adjusting the power of each codeword in the precoding matrix based on the decoding result of each of the plurality of decoded codewords;
    An encoding unit for encoding a plurality of codewords to be transmitted to the receiving device;
    A precoding processing unit that performs precoding to form a predetermined beam by weighting signals output to a plurality of antennas based on the precoding matrix and the parameters with respect to the plurality of encoded codewords;
    A transmission unit that transmits the signal after the precoding process to the reception device via a plurality of antennas;
    A wireless communication system comprising:
18. A wireless communication method in a wireless communication system that performs communication using a plurality of codewords using a plurality of antennas,
    A receiving step of receiving signals of a plurality of codewords transmitted from a plurality of antennas of the transmitting device;
    A decoding step of decoding each of the received multiple codewords;
    A channel estimation step of estimating a propagation path state of each of the received multiple codewords;
    A precoding matrix selection step of selecting a precoding matrix for beam forming by precoding (Precoding) in future transmission based on a propagation path condition of each codeword;
    A parameter determining step for determining a parameter for adjusting the power of each codeword in the precoding matrix based on the decoding result of each of the decoded codewords;
    An encoding step of encoding a plurality of codewords to be transmitted to the receiving device;
    A precoding processing step for performing precoding to form a predetermined beam by weighting signals output to a plurality of antennas based on the precoding matrix and the parameter with respect to the plurality of encoded codewords;
    A transmission step of transmitting the signal after the precoding process to the reception device via a plurality of antennas;
    A wireless communication method.

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