JP5121368B2 - Receiver - Google Patents

Description

  The present invention relates to a receiving apparatus. In particular, the present invention relates to a receiving apparatus included in a multi-user MIMO (Multiple-Input and Multiple-Output) system in a mobile communication system.

  As one technique for increasing the communication speed between wireless devices, a multi-input / multi-output transmission system is known. This method is literally based on signal input / output using a plurality of antennas. The feature of this method is that a plurality of transmission data can be transmitted at the same time and at the same frequency using a plurality of different antennas. Therefore, as the number of channels that can be transmitted simultaneously increases, the amount of information that can be transmitted per unit time can be increased by the increased number of channels. Further, this method has an advantage that the occupied frequency band does not increase when the communication speed is improved.

  However, since a plurality of modulated signals having carrier components of the same frequency are transmitted at the same time, a means for separating the interfering modulated signals on the receiving side is necessary. Therefore, on the receiving side, a channel matrix representing the transmission characteristics of the wireless transmission path is estimated, and the transmission signal corresponding to each substream is separated from the received signal based on the channel matrix. The channel matrix is estimated using pilot symbols or the like.

  However, special measures are required to accurately remove the influence of noise added in the transmission path, interference generated between substreams, and the like and accurately reproduce the transmission signal for each substream. In recent years, various techniques related to MIMO signal detection have been developed. In particular, recently, attention has been focused on a topic related to a multi-user MIMO system including a plurality of communication apparatuses capable of MIMO signal transmission. As a signal detection method in the multi-user MIMO system, for example, a method using MMSE (Minimum Mean Squared Error) detection is known. In this method, SINR (Signal power to Interference plus Noise power Ratio) after MMSE detection is calculated on the reception side, and the transmission is returned to the transmission side, and transmission control parameters are set based on the SINR after MMSE detection. It is a technology that improves the characteristics.

  Further, as a method capable of improving transmission characteristics as compared with the above MMSE detection method, there is a demand to use, for example, an MLD (Maximum Likelihood Detection) detection method or the like on the receiving side of the multiuser MIMO system. Therefore, a technique for separating subchannels for each receiving apparatus is required. In relation to this, for example, a technique for calculating a beamforming matrix by performing singular value decomposition on a subchannel matrix fed back from each receiving apparatus is known.

  When the above technique is applied, each receiving apparatus needs to feed back information on the subchannel matrix used for calculating the beamforming matrix to the transmitting apparatus. However, enormous amount of communication is consumed to return the subchannel matrix information as it is. Therefore, a technique called vector quantization has been devised to reduce the amount of feedback information. For example, as described in Non-Patent Document 1 below, this technique compares a channel vector for each antenna estimated by a receiving apparatus with a preset quantization vector, and compares the channel vector with the channel vector. An index of a quantization vector having a small angle difference between them is fed back to the transmission device. Therefore, when this technique is used, the amount of feedback information can be greatly reduced.

  By the way, as another technique related to the MIMO system, there is known a retransmission control technique called a hybrid ARQ (Automatic Repeat reQuest) scheme using MIMO cyclic permutation (for example, see Non-Patent Document 2 below). . This method relates to a technique for performing retransmission control by detecting an error in retransmission data for each stream for which a MIMO signal is detected on the receiving side, and feeding back NACK / ACK to the transmitting side. In particular, it is characterized in that different channel gains can be obtained each time a packet is retransmitted by cyclically replacing the combination of antennas assigned to each transmission symbol on the transmission side. That is, the diversity effect due to antenna switching can be obtained by combining the retransmitted packets on the receiving side.

Nihar Jindal, “Antenna combining for the MIMO downlink channel”, Submitted to IEEE wireless communications, April 2007. T.A. Koike, H.M. Murata and S.M. Yoshida, “Evaluation of HARQ scheme with antenna permutation and TCM regimen- forment-time transmission in slow Nakami-Rice funding EMO”. Commun. , Vol. E87-B, no. 6, pp. 1487-1494, June 2004.

  However, it is difficult to apply the hybrid ARQ scheme as described in Non-Patent Document 2 to the technique described in Non-Patent Document 1. This is because the technique described in Non-Patent Document 1 multiplies each stream to be transmitted on the transmission side by multiplying the beamforming weight and transmits from all antennas, so there is no degree of freedom of stream allocation to each antenna. As a result, even when hybrid ARQ is applied, different channel gains cannot be received between the retransmitted packet and the same packet transmitted before retransmission, and the effect of hybrid ARQ cannot be effectively utilized. is there.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a novel that can enjoy the diversity effect obtained by retransmission control while reducing the amount of feedback information. Another object of the present invention is to provide an improved receiving apparatus.

  In order to solve the above-described problem, according to an aspect of the present invention, a receiving apparatus having N (N ≧ 4) antennas and capable of retransmission control is provided. The receiving apparatus combines M channel vectors corresponding to M antennas (2 ≦ M ≦ N−2), and selects a predetermined quantization vector corresponding to the combined vector of the M channel vectors. A combination switching unit that switches the combination of the channel vectors combined by the combination quantization unit to the combination of the channel vectors corresponding to another combination of the antennas, and The index of the predetermined quantization vector selected by the synthesis quantization unit is fed back to a transmission device.

  The combination switching unit switches the channel vector combination when an error is detected in the reproduction data. And the said synthetic | combination quantization part newly selects the said predetermined | prescribed quantization vector based on the combination of the said channel vector switched by the said combination switching part. Further, the receiving apparatus feeds back the index of the newly selected predetermined quantization vector to the transmitting apparatus.

  Further, the receiving apparatus can receive a transmission signal that has been subjected to beam forming based on a predetermined quantization vector corresponding to the index. Corresponding to this, the receiving apparatus synthesizes M reception signals received via the M antennas corresponding to the combined quantization units, and combines signals corresponding to the combined quantization units. And a signal detection unit that detects a transmission signal for each stream based on a channel matrix estimated from a plurality of the combined signals corresponding to the plurality of combined quantization units. Good.

  In addition, the reception device may receive a stream corresponding to a received signal for each stream corresponding to the reproduction data in which an error is detected, and a retransmission signal beamformed based on the newly selected predetermined quantization vector. You may further provide the detection signal synthetic | combination part which synthesize | combines each received signal.

  Further, the receiving device may be a user terminal included in a multiuser MIMO system. In that case, a beamforming matrix for block diagonalizing the channel matrix is calculated for each user terminal based on the index of the predetermined quantization vector fed back from the receiving device, and the beamforming matrix is calculated by the transmitting device. When a transmission signal beamformed by a matrix is transmitted, the signal detection unit can detect a transmission signal for each stream using a channel matrix estimated based on the combined signal.

  As described above, according to the present invention, it is possible to enjoy the diversity effect obtained by retransmission control while reducing the amount of feedback information.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[Purpose and Overview]
First, prior to describing preferred embodiments according to the present invention, technologies related to the embodiments of the present invention described below will be briefly described with reference to FIGS.

[Antenna cyclic permutation type automatic retransmission control method]
A configuration of a communication system 1 capable of antenna cyclic permutation type automatic retransmission control will be described with reference to FIG. FIG. 1 is an explanatory diagram showing a system configuration of a communication system 1 capable of antenna cyclic permutation type automatic retransmission control.

  As illustrated in FIG. 1, the communication system 1 is a MIMO system that employs a hybrid ARQ scheme, and mainly includes a transmission device 10 and a reception device 40.

(Functional configuration of transmitting apparatus 10)
First, the functional configuration of the transmission device 10 will be described. The transmission apparatus 10 mainly includes a retransmission control unit 12, an error detection coding unit 14, an error correction coding unit 16, a modulation mapping unit 18, an antenna cyclic replacement unit 20, and a plurality of antennas 22. Is done.

  First, transmission data is generated for each stream and input to each retransmission control unit 12. The retransmission control unit 12 inputs new transmission data or previously transmitted transmission data to the error detection coding unit 14 in accordance with an ACK / NACK (ACKnowledgement / Non-ACKnowledgement) signal fed back from the receiving device 40. The error detection encoding unit 14 adds a predetermined error detection code to the input transmission data. As the error detection code, for example, a cyclic code, a Hamming code, a Reed-Solomon code, a turbo code, or the like is used. The transmission data to which the error detection code is added is input to the error correction encoding unit 16.

  The error correction encoding unit 16 adds a predetermined error correction code to the transmission data. The transmission data to which the error correction code is added is input to the modulation mapping unit 18. The modulation mapping unit 18 performs modulation mapping of transmission data based on a predetermined modulation scheme, and generates a transmission symbol for each stream. A transmission symbol vector whose component is a transmission symbol for each stream is input to the antenna cyclic permutation unit 20. The antenna cyclic replacement unit 20 performs cyclic replacement for the combination of antennas 22 to which each transmission symbol is assigned. Therefore, even if the same packet is transmitted, an effect that a different channel gain can be obtained at each cyclic replacement can be expected.

(Functional configuration of receiving device 40)
Next, the functional configuration of the receiving device 40 will be described. The receiving device 40 mainly includes a plurality of antennas 42, a MIMO signal detection unit 44, a packet synthesis unit 46, an error correction decoding unit 48, and an error detection unit 50.

  The MIMO signal detection unit 44 detects a transmission signal for each stream from reception signals received via the plurality of antennas 42 based on a channel matrix estimated in advance. The detected transmission signal is input to the packet combining unit 46. When the input transmission signal is retransmitted, the packet combining unit 46 combines the transmission signal before retransmission in which an error is detected and the input new transmission signal. The combined transmission signal is input to the error correction decoding unit 48.

  The error correction decoding unit 48 performs error correction decoding using a predetermined error correction code added by the transmission apparatus 10 and restores transmission data. The restored transmission data is input to the error detection unit 50. The error detection unit 50 detects an error in the transmission data based on a predetermined error detection code added by the transmission device 10. When an error is detected, the error detection unit 50 returns NACK to the transmission device 10. When no error is detected, the error detection unit 50 returns an ACK to the transmission device 10.

(Flow of automatic retransmission control processing)
Next, the flow of automatic retransmission control processing by the transmission apparatus 10 and the reception apparatus 40 having the above configuration will be briefly described with reference to FIG. FIG. 2 is an explanatory diagram showing the flow of automatic retransmission control processing in the communication system 1.

First, the transmission device 10 transmits a transmission symbol vector s = [s ₁ , s ₂ , s ₃ , s ₄ ] ^T to the reception device 40 (initial transmission). When an error is detected in the transmission data (reproduction data) reproduced from the transmission symbol vector s, the reception device 40 returns NACK to the transmission device 10. Transmitting apparatus 10 cyclically replaces transmission symbols assigned to each transmission antenna by antenna cyclic permutation unit 20 and retransmits transmission symbol vectors s = [s ₄ , s ₁ , s ₂ , s ₃ ] ^T. As described above, every time an error is detected in the retransmission data, the retransmission of the packet is repeated between the transmission device 10 and the reception device 40.

  Further, when an error is detected in the reproduction data, the receiving device 40 returns NACK to the transmitting device 10 again. Transmitting apparatus 10 performs cyclic permutation of antennas every retransmission interval, and changes the assigned antenna of each transmission symbol retransmitted in response to NACK. Therefore, the retransmitted packet is transmitted from a different antenna from the same packet transmitted before that time. As a result, the retransmission packet and the previously transmitted same packet have different channel gains, and the diversity effect due to antenna switching is obtained by combining the packets in the receiving device 40.

[Synthetic quantization method of channel vector]
Next, a method of combining and quantizing channel vectors will be described with reference to FIGS. According to this method, the quantization accuracy can be improved without increasing the number of quantization bits by combining and quantizing a plurality of channel vectors.

  First, with reference to FIG. 3, a functional configuration of the receiving apparatus 60 provided with means for combining and quantizing a plurality of channel vectors will be described.

  As illustrated in FIG. 3, the reception device 60 mainly includes channel estimation units 62 and 64, a storage unit 66, and a combined quantization unit 68 as channel estimation blocks. Furthermore, the receiving device 60 includes a signal synthesis unit 70 and a synthesis coefficient acquisition unit 72 in addition to the channel estimation block.

The channel estimation unit 62 estimates a channel vector h ₁ = [h ₁₁ , h ₁₂ , h ₁₃ ] ^T having a vector component corresponding to each antenna of the transmission device 10 based on a signal received from one antenna. Similarly, the channel estimation unit 64 calculates channel vectors h ₂ = [h ₂₁ , h ₂₂ , h ₂₃ ] ^T having vector components corresponding to the respective antennas of the transmission device 10 based on signals received from other antennas. presume. Channel vectors h ₁ and h ₂ estimated by the channel estimation units 62 and 64 are input to the synthesis quantization unit 68.

Next, the combined quantization unit 68 combines the two channel vectors h ₁ and h ₂ estimated by the channel estimation units 62 and 64, and generates a combined channel vector h ′ = a × h ₁ + b × h ₂ . However, a and b are synthesis coefficients. Further, the synthesis quantization unit 68 refers to the quantization code book recorded in the storage unit 66, selects a quantization vector that matches the synthesis channel vector h ′, and feeds back the index to the transmission apparatus 10. For example, as shown in FIG. 4, the synthetic quantization unit 68 selects a quantization vector q = [q ₁ , q ₂ , q ₃ ] ^T that minimizes the angular difference from the synthetic channel vector h ′. .

In the example of FIG. 4, three axes corresponding to each antenna of the transmission apparatus 10 are set, and a plurality of quantization vectors and channel estimation units 62 and 64 are estimated in a space defined by the three axes. The channel vectors h ₁ and h ₂ and the combined channel vector h ′ are described. As shown in FIG. 4, the combined quantization unit 68 selects a quantization vector q that minimizes the angle difference from the combined channel vector h ′. At this time, the synthesis quantization unit 68 determines the synthesis coefficients a and b so that the synthesis channel vector h ′ approximates the quantization vector q, for example. As a method for synthesizing the channel vectors h ₁ and h ₂ , for example, a selective synthesis method, a maximum ratio synthesis method, a minimum quantization error synthesis method, or the like can be used.

Next, the synthesis coefficient acquisition unit 72 acquires the synthesis coefficients a and b determined by the synthesis quantization unit 68 and inputs them to the signal synthesis unit 70. The synthesis coefficients a and b may be calculated by the synthesis coefficient acquisition unit 72 based on the information on the quantization vector q selected by the synthesis quantization unit 68 and the information on the channel vectors h ₁ and h _2. . In this case, the synthesized quantization unit 68 may determine the quantization vector q based on a synthesized channel vector obtained by simply synthesizing the channel vectors h ₁ and h ₂ , for example.

When the above method is applied, the angle difference between the combined channel vector h ′ and the quantized vector q is adjusted using the combined coefficients a and b, so that the quantization accuracy can be increased without increasing the number of quantization bits. It becomes possible to improve. When receiving a transmission signal beamformed based on the feedback index, the receiving device 60 multiplies the signal received by each antenna by a synthesis coefficient by the signal synthesis unit 70 and then synthesizes each signal. To do. For example, the synthesis coefficient a multiplied by the channel vector h ₁ is multiplied by the signal received via the antenna corresponding to the channel vector h ₁ .

  By using the method described above, it is possible to feed back information on the subchannel matrix used for beamforming or the like in the transmission apparatus 10 with a small number of feedback bits. Next, as an application example of this method, a configuration of a multi-user MIMO communication system 1000 capable of obtaining multiple gains with a plurality of antennas while reducing the amount of feedback information will be described.

[System configuration of communication system 1000]
The system configuration of the communication system 1000 will be described with reference to FIGS. FIG. 5 is an explanatory diagram showing a system configuration of the communication system 1000 and a functional configuration of the transmission apparatus 100 included in the communication system 1000. FIG. 6 is an explanatory diagram illustrating a functional configuration of the reception device 200 included in the communication system 1000.

(Functional configuration of transmitting apparatus 100)
First, the functional configuration of the transmission apparatus 100 included in the communication system 1000 will be described with reference to FIG.

  In the example of FIG. 5, the number of antennas of the transmission device 100 is four and the number of antennas of each reception device 200 is four. However, the number of antennas of the transmission device 100 and each reception device 200 is not limited to this. . Furthermore, the number of antennas of the receiving device 200 may be different between the receiving device 200 (# 1) and the receiving device 200 (# 2). In the example of FIG. 5, since each receiving device 200 uses two antennas for antenna combination, the number of streams transmitted to the selected pair of receiving devices 200 (# 1, # 2) is two. Please note that.

  As illustrated in FIG. 5, the transmission apparatus 100 mainly includes a quantization vector reproduction unit 102, a user selection unit 104, a subset matrix setting unit 106, an inverse matrix calculation unit 108, a beamforming matrix generation unit 110, and the like. , A serial / parallel converter 112, a channel encoder 114, a modulation mapping unit 116, a beamforming processor 118, and a plurality of antennas 120.

(Quantized vector reproduction unit 102)
The quantization vector reproducing unit 102 refers to the quantization code book and selects a quantization vector corresponding to the channel vector estimated by each receiving device 200 based on the codebook index fed back from each receiving device 200. . Information about the quantization vector selected by the quantization vector reproducing unit 102 is input to the user selection unit 104.

(User selection unit 104)
First, the user selection unit 104 has a large channel capacity after beamforming based on the quantization vectors q _{(# 1)} and q _{(# 2)} corresponding to each receiving apparatus 200 input from the quantization vector reproducing unit 102. In such a manner, a combination of receiving apparatuses 200 that are transmission destinations to which signals are simultaneously transmitted is selected. The user selection unit 104 notifies the subset matrix setting unit 106 of the combination of the reception devices 200 using the user index indicating each reception device 200. Further, the transmission apparatus 100 determines data (data u ₁ , data u ₂ ) to be assigned to each stream according to the combination of the reception apparatuses 200 (the combination of user indexes) selected by the user selection unit 104, and serial / parallel Input to the conversion unit 112.

  The serial / parallel converter 112 performs serial / parallel conversion on data for each stream, distributes the data to a plurality of substreams, and inputs the substreams to the channel encoder 114. Next, channel coding section 114 channel codes the data for each substream input from serial / parallel conversion section 112 and inputs the data to modulation mapping section 116. Next, the modulation mapping unit 116 performs modulation mapping on the data of each channel-coded substream with a predetermined modulation order based on a predetermined modulation scheme, determines a transmission symbol for each substream, and performs a beamforming processing unit 118. To enter.

(Subset matrix setting unit 106)
Subset matrix setting section 106 sets a subset matrix Hi ′ related to one antenna (i) possessed by one receiving apparatus 200 and all antennas possessed by another receiving apparatus 200 based on the elements of the quantization vectors. At this time, the subset matrix setting unit 106 sets a subset matrix for every antenna included in each receiving device 200 with respect to all receiving devices 200 included in the communication system 1000. However, (i) is an index indicating the i-th antenna when the antennas of all receiving apparatuses 200 are numbered.

For example, as shown in the following formula (1), the subset matrix setting unit 106 includes the antenna (1) of the reception device 200 (# 1), the antenna (3) and the antenna (4) of the reception device 200 (# 2). ) And a subset matrix H ₁ ′. Similarly, the subset matrix setting unit 106 includes a subset matrix H ₂ ′ related to the antenna (2) of the receiving apparatus 200 (# 1) and the antennas (3) and (4) of the receiving apparatus 200 (# 2) (formula (2)). ), Subset matrix H ₃ ′ (equation (3)) regarding antenna (3) of receiving apparatus 200 (# 2) and antenna (1) (2) of receiving apparatus 200 (# 1), and receiving apparatus 200 (#) A subset matrix H ₄ ′ (equation (4)) relating to the antenna (4) of 2) and the antennas (1) and (2) of the receiving apparatus 200 (# 1) is set. Then, the subset matrix setting unit 106 inputs the set subset matrix information to the inverse matrix calculation unit 108.

(Inverse matrix calculation unit 108)
The inverse matrix calculation unit 108 performs an inverse matrix calculation shown in the following equation (5) on each subset matrix H _i ′ set by the subset matrix setting unit 106 to perform a beamforming weight for each subset matrix H _i ′. W _i ′ is calculated. Then, the inverse matrix calculation unit 108 inputs the calculated beamforming weight W _i ′ to the beamforming matrix generation unit 110.

(Beam forming matrix generator 110)
The beamforming matrix generation unit 110 uses the beamforming weight W _i ′ calculated for each subset matrix H _i ′, and the beam forming matrix W ′ for diagonalizing the channel matrix H in units of the receiving device 200. Is generated. First, the beamforming matrix generation unit 110 selects an antenna (hereinafter referred to as a weight vector) of the beamforming weights W _i ′ = {w _j ⁽ⁱ⁾ ; j = 1, 2,. A weight vector w _k ⁽ⁱ⁾ corresponding to ⁱ⁾ is extracted. However, k represents the index of the component corresponding to the antenna (i). Then, the beamforming matrix generation unit 110 generates a beamforming matrix W ′ using the extracted weight vectors w _k ⁽ⁱ⁾ (k = 1, 2,...).

As an example, consider a method of selecting weight vector w _k ⁽ⁱ⁾ corresponding to antenna (1) of receiving apparatus 200 (# 1). First, referring to the above equation (1), it can be seen that there is a matrix element corresponding to the antenna (1) of the receiving apparatus 200 in the first row of the subset matrix H ₁ ′ corresponding to the antenna (1). . When an inverse matrix operation is performed on the subset matrix H ₁ ′ according to the above equation (5), the following equation (6) is obtained. At this time, the first row component of the subset matrix H ₁ ′ corresponds to the first column component of the beamforming weight W ₁ ′. Therefore, the beamforming matrix generation unit 110 extracts a vector w ₁ ⁽¹⁾ positioned first in the beamforming weight W ₁ ′ as a weight vector.

Similarly, the beamforming matrix generation unit 110 also performs weight vectors (w ₁ ⁽²⁾ , w ₃ ⁽³⁾ , w ₃ ⁽⁴ ) for the antenna (i) (i = 2, 3, 4) of the receiving apparatus 200. ⁾⁾ ). Then, the beamforming matrix generation unit 110 uses the extracted weight vectors w ₁ ⁽¹⁾ , w ₁ ⁽²⁾ , w ₃ ⁽³⁾ , and w ₃ ⁽⁴⁾ to represent the following equation (7). Thus, the beam forming matrix W ′ is generated.

(Beam forming processing unit 118)
The beamforming processing unit 118 performs beamforming on the transmission symbol vector s using the beamforming matrix W ′ generated by the beamforming matrix generation unit 110 and transmits the result. As a result, the received symbol vector r is expressed as the following equation (8). As shown in the following equation (8), the effective channel matrix HW ′ after beam forming is block-diagonalized for each receiving device, and interference components between the receiving devices are removed. Further, in this effective channel matrix HW ′, interference components between a plurality of antennas included in the receiving apparatus 200 remain. In the following equation (8), for example, ρ ₂₁ corresponds to the weight vector for the antenna (1) and the cross-correlation component included in the channel vector of the antenna (2), and is received by the antenna (2). It is an ingredient.

  This effect is obtained as a result of selecting the subset matrix by the subset matrix setting unit 106 so as to leave the MIMO subchannel. According to this method, a beam directed to one antenna of receiving apparatus 200 does not form a null with respect to another antenna, and further, a beam directed toward another antenna forms a null with respect to the one antenna. It is controlled not to. As a result, the channel matrix of the multi-user MIMO channel is block-diagonalized so that the receiving apparatus 200 does not interfere with each other while forming a MIMO channel for a plurality of antennas included in each receiving apparatus 200. Is possible.

(Functional configuration of receiving apparatus 200)
Next, the functional configuration of the receiving apparatus 200 will be described with reference to FIG.

  As illustrated in FIG. 6, the reception apparatus 200 mainly includes channel estimation units 202, 204, 214, 222, 224, and 234, synthesis quantization units 206 and 226, storage units 208 and 228, and synthesis coefficient acquisition. Sections 210, 230, signal synthesis sections 212, 232, and MIMO signal detection section 240.

(Channel estimation units 202 and 204)
The channel estimation unit 202 has a channel vector h ₁ = [h ₁₁ , h ₁₂ , h ₁₃ , h ₁₄ ] ^T having a vector component corresponding to each antenna of the transmission device 100 based on the signal received from the antenna (1). Is estimated. Similarly, the channel estimation unit 204 has a channel vector h ₂ = [h ₂₁ , h ₂₂ , h ₂₃ , h having vector components corresponding to each antenna of the transmission device 100 based on the signal received from the antenna (2). ₂₄ ] ^T is estimated. Channel vectors h ₁ and h ₂ estimated by the channel estimation units 202 and 204 are input to the synthesis quantization unit 206.

(Synthetic quantization unit 206)
Next, the synthesis quantization unit 206 synthesizes the two channel vectors h ₁ and h ₂ estimated by the channel estimation units 204 and 206 and obtains the synthesis channel vector h ₁ ′ = a ₁ × h ₁ + b ₁ × h ₂ . Generate. However, a ₁ and b ₁ are synthesis coefficients. Further, synthesized quantization section 206 refers to the quantization codebook recorded in storage section 208, selects a quantization vector that matches synthesized channel vector h ₁ ′, and feeds back the index to transmitting apparatus 100. For example, the combined quantization unit 206 selects a quantized vector q ₁ = [q ₁₁ , q ₁₂ , q ₁₃ , q ₁₄ ] ^T that minimizes the angle difference with the combined channel vector h ₁ ′. As a method for synthesizing channel vectors, for example, a method such as selective synthesis, maximum ratio synthesis, or minimum quantization error synthesis is used.

(Channel estimation units 222 and 224)
Based on the signal received from the antenna (3), the channel estimation unit 222 has channel vectors h ₃ = [h ₃₁ , h ₃₂ , h ₃₃ , h ₃₄ ] ^T having vector components corresponding to the respective antennas of the transmission device 100. Is estimated. Similarly, the channel estimation unit 224 has channel vectors h ₄ = [h ₄₁ , h ₄₂ , h ₄₃ , h having vector components corresponding to the respective antennas of the transmission device 100 based on the signal received from the antenna (4). ₄₄ ] ^T is estimated. Channel vectors h ₃ and h ₄ estimated by channel estimation units 222 and 224 are input to synthesis quantization unit 226.

(Synthetic quantization unit 226)
Next, the synthesis quantization unit 226 synthesizes the two channel vectors h ₃ and h ₄ estimated by the channel estimation units 224 and 226 to obtain the synthesis channel vector h ₂ ′ = a ₂ × h ₃ + b ₂ × h ₄ . Generate. However, a ₂ and b ₂ are synthesis coefficients. Further, synthesized quantization section 226 refers to the quantization codebook recorded in storage section 228, selects a quantization vector that matches synthesized channel vector h ₂ ′, and feeds back the index to transmitting apparatus 100. For example, the combined quantization unit 226 selects a quantized vector q ₂ = [q ₂₁ , q ₂₂ , q ₂₃ , q ₂₄ ] ^T that minimizes the angular difference with the combined channel vector h ₂ ′.

  As described above, a plurality of channel vectors estimated based on signals received from a plurality of antennas are combined and quantized into a plurality of sets. That is, the receiving apparatus 200 according to the present embodiment includes “multiple” means (synthetic quantization units 206 and 226) for performing synthetic quantization on a plurality of channel vectors. As a result, since a plurality of channel vectors are fed back to the transmission device 100, the transmission device 100 can transmit a plurality of streams based on these. Therefore, hereinafter, means relating to MIMO signal detection for separating a plurality of streams will be described.

(Synthesis coefficient acquisition unit 210, 230)
The synthesis coefficient acquisition unit 210 reduces the angle difference between the synthesis channel vector of the plurality of channel vectors h ₁ ′ and h ₂ ′ and the quantization vector q ₁ selected by the synthesis quantization unit 206. This is a means for obtaining synthesis coefficients a ₁ and b ₁ that are respectively multiplied by a plurality of channel vectors h ₁ ′ and h ₂ ′. The synthesis coefficient acquisition unit 210 may calculate the synthesis coefficients a ₁ and b ₁ based on the information on the plurality of channel vectors h ₁ ′ and h ₂ ′ and the information on the selected quantization vector q _1. Good. Then, the synthesis coefficient acquisition unit 210 inputs information on the acquired synthesis coefficients a ₁ and b ₁ to the signal synthesis unit 212.

Similarly, the synthesis coefficient acquisition unit 230 reduces the angle difference between the synthesis channel vectors of the plurality of channel vectors h ₃ ′ and h ₄ ′ and the quantization vector q ₂ selected by the synthesis quantization unit 226. In this way, it is a means for obtaining synthesis coefficients a ₂ and b ₂ that are respectively multiplied by a plurality of channel vectors h ₃ ′ and h ₄ ′. The synthesis coefficient acquisition unit 230 may calculate the synthesis coefficients a ₂ and b ₂ based on the information on the plurality of channel vectors h ₃ ′ and h ₄ ′ and the information on the selected quantization vector q _2. Good. Then, the synthesis coefficient acquisition unit 230 inputs information on the acquired synthesis coefficients a ₂ and b ₂ to the signal synthesis unit 232.

(Signal synthesis units 212 and 232)
The signal synthesis unit 212 synthesizes a plurality of reception signals (r ₁ , r ₂ ) received from the plurality of antennas (1) and (2) corresponding to the synthesis quantization unit 206. At this time, the signal synthesis unit 212 multiplies each received signal by the synthesis coefficients a ₁ and b ₁ input by the synthesis coefficient acquisition unit 210 and synthesizes them. For example, the signal synthesis unit 212 multiplies the reception signal r ₁ received from the antenna (1) by the synthesis coefficient a ₁ and multiplies the reception signal r ₂ received from the antenna (2) by the synthesis coefficient b ₁ . To do. Then, the signal synthesis unit 212 synthesizes the reception signals r ₁ and r ₂ multiplied by the synthesis coefficients a ₁ and b ₁ to generate a synthesis signal R ₁ = a ₁ × r ₁ + b ₁ × r ₂ .

Similarly, the signal synthesis unit 232 synthesizes a plurality of reception signals (r ₃ , r ₄ ) received from the plurality of antennas (3) and (4) corresponding to the synthesis quantization unit 226. At this time, the signal synthesis unit 232 multiplies each received signal by the synthesis coefficients a ₂ and b ₂ input by the synthesis coefficient acquisition unit 230 and synthesizes them. For example, the signal synthesis unit 232 multiplies the reception signal r ₃ received from the antenna (3) by the synthesis coefficient a ₂ and multiplies the reception signal r ₄ received from the antenna (4) by the synthesis coefficient b ₂ . To do. Then, the signal combining unit 232 generates the combined signal R ₂ = a ₂ × r ₃ + b ₂ × r ₄ by combining the received signals r ₃ and r ₄ multiplied by the combining coefficients a ₂ and b ₂ .

(Channel estimation unit 214, 234)
Based on the combined signal R ₁ generated by the signal combining unit 212, the channel estimation unit 214 has channel vectors h ₁ ′ = [h ₁₁ ′, h ₁₂ ′, having vector components corresponding to the respective antennas of the transmission device 100. h ₁₃ ', h ₁₄ '] ^T is estimated. Similarly, the channel estimation unit 234 has a channel vector h ₂ ′ = [h ₂₁ ′, h having vector components corresponding to each antenna of the transmission device 100 based on the combined signal R ₂ generated by the signal combining unit 232. _{22 ', h 23',} to estimate the _{h 24} ^{'] T.} Channel vectors h ₁ ′ and h ₂ ′ estimated by the channel estimators 214 and 234 are input to the MIMO signal detector 240.

(MIMO signal detector 240)
The MIMO signal detection unit 240 performs, for each stream, based on the combined signals R ₁ and R ₂ input from the plurality of signal combining units 212 and 232 and channel vectors h ₁ ′ and h ₂ ′ corresponding to the combined signals. The received signal is separated and the transmission symbol of each stream is reproduced. The MIMO signal detection unit 240 separates the received signal into a stream using various signal separation algorithms such as an MMSE detection method and an MLD detection method. Of course, as in this embodiment, when beamforming is performed on a transmission symbol vector using a beamforming matrix for block diagonalizing a channel matrix in units of users, MLD that can obtain better transmission characteristics It is preferable to apply the detection method or the QR decomposition MLD method.

  The functional configuration of the receiving device 200 has been described above. When the above configuration is applied, since a plurality of channel vectors are synthesized and quantized, the accuracy of channel vector quantization can be improved. In addition, since the transmission apparatus 100 has a plurality of synthetic quantization means, it is possible to transmit signals of a plurality of streams and to obtain a multiplex gain between the streams. Furthermore, by applying MLD detection to the MIMO signal detection unit 240, better transmission characteristics can be obtained.

  However, in the communication system 1000 described above, since the transmission apparatus 100 multiplies each stream to be transmitted by a weight vector and transmits it from all antennas, there is a problem in that substream allocation cannot be changed for each antenna. Therefore, when receiving a NACK and retransmitting a packet, only the same channel gain as the previous time can be obtained. As a result, there is a problem that even if hybrid ARQ is applied, the effect is not sufficiently exhibited.

  In view of such a problem, an embodiment of the present invention described below performs different channel gains at the time of packet retransmission by performing antenna switching on the reception side and changing the codebook index fed back to the transmission side. The technology which makes it possible to obtain is provided.

<One Embodiment of the Present Invention>
A configuration of a communication system 5000 according to an embodiment of the present invention will be described. As illustrated in FIG. 7, the communication system 5000 according to the present embodiment includes a transmission device 500 and a plurality of reception devices 600. Hereinafter, functional configurations of the transmission device 500 and the reception device 600 will be described in detail.

[Functional configuration of transmitting apparatus 500]
First, the functional configuration of the transmission apparatus 500 according to the present embodiment will be described with reference to FIG. FIG. 7 is an explanatory diagram illustrating a functional configuration of the transmission device 500 according to the present embodiment. However, components that are substantially the same as those of the transmission apparatus 100 included in the communication system 1000 described above are denoted by the same reference numerals in order to avoid redundant description, and detailed description thereof is omitted.

  As illustrated in FIG. 7, the transmission apparatus 500 mainly includes a quantization vector reproduction unit 102, a user selection unit 104, a subset matrix setting unit 106, an inverse matrix calculation unit 108, a beamforming matrix generation unit 110, and the like. The serial / parallel conversion unit 112, the retransmission control unit 502, the channel coding unit 114, the modulation mapping unit 116, the beamforming processing unit 118, and a plurality of antennas 120. The main difference from the transmission apparatus 100 described above is the configuration of the retransmission control unit 502. Therefore, the retransmission control unit 502 will be mainly described.

(Retransmission control unit 502)
The retransmission control unit 502 determines whether or not to perform retransmission control according to ACK or NACK fed back from each receiving apparatus 600, and performs retransmission control as necessary. For example, when receiving a NACK from receiving apparatus 600, retransmission control section 502 inputs transmission data corresponding to the retransmission data for which an error has been detected in receiving apparatus 600, to channel coding section 114 again. Conversely, when ACK is received from receiving apparatus 600, new transmission data input from serial / parallel converter 112 is input to channel encoder 114.

  Retransmission control is realized by the means described above. However, in the communication system 5000, every time an error is detected in the reproduction data by the receiving apparatus 600, a different codebook index is fed back to the transmitting apparatus 500. Therefore, transmission apparatus 500 generates a different beamforming matrix every time retransmission control is performed. As a result, it is possible to obtain different channel gains for retransmission packets and previously transmitted identical packets.

[Functional configuration of receiving apparatus 600]
Next, the functional configuration of the receiving apparatus 600 according to the present embodiment will be described with reference to FIG. FIG. 8 is an explanatory diagram illustrating a functional configuration of the receiving device 600 according to the present embodiment. However, components that are substantially the same as those of the receiving device 200 included in the communication system 1000 are denoted by the same reference numerals in order to avoid redundant description, and detailed description thereof is omitted.

  As shown in FIG. 8, the receiving apparatus 600 mainly includes an antenna switching unit 602, channel estimation units 202, 204, 214, 222, 224, 234, synthesis quantization units 206, 226, a storage unit 208, 228, synthesis coefficient acquisition units 210 and 230, signal synthesis units 212 and 232, MIMO signal detection unit 240, packet synthesis units 604 and 624, error correction decoding units 606 and 626, and error detection units 608 and 628 It consists of. The main differences from the receiving apparatus 200 described above lie in an antenna switching unit 602, packet combining units 604 and 624, error correction decoding units 606 and 626, and error detection units 608 and 628. Therefore, these configurations will be mainly described.

(Antenna switching unit 602)
The antenna switching unit 602 switches the combination of the antennas (1) to (4) according to the NACK notified from the error detection units 608 and 628. In the example of FIG. 8, signals received via the antenna (1) and the antenna (4) are input to the first synthesis quantization unit. On the other hand, signals received via the antenna (2) and the antenna (3) are input to the second synthesis quantization unit. The antenna switching unit 602 is means for switching the combination of antennas corresponding to each of these synthesized quantization units.

  When the number of receiving antennas is four and the number of combined quantization units is two, four to two combinations are made, so there are six switching patterns shown in FIGS. 9A to 9F. For example, the antenna switching unit 602 switches the connection between each reception antenna and the channel estimation units 202, 204, 222, and 224 so as to circulate through these six patterns. Of course, the order of circulation can be set arbitrarily. Further, even when the number of reception antennas is 4 or more and the number of combined quantization units is 2 or more, the antenna switching unit 602 can perform switching so as to circulate a switching pattern according to the number.

(Packet combiner 604, 624)
The packet combining unit 604 is a unit that combines the retransmission packet retransmitted in response to the NACK notified by the error detection unit 608 and the same packet transmitted before the retransmission. More specifically, the packet combining unit 604 converts the retransmission packet and the same packet transmitted before retransmission into a combined signal combined by the signal combining unit 212 and a channel vector estimated by the channel estimation unit 214. Based on this, the transmission signal for each stream detected by the MIMO signal detection unit 240 is synthesized. When retransmission control is repeatedly performed, a plurality of identical packets transmitted before retransmission are combined into a retransmission packet.

  Similarly, the packet combining unit 624 performs MIMO based on the combined signal combined by the signal combining unit 232 and the channel vector estimated by the channel estimation unit 234 for the retransmission packet and the same packet transmitted before retransmission. The transmission signals for each stream detected by the signal detection unit 240 are synthesized. Packet combining sections 604 and 624 then input the combined packets to error correction decoding sections 606 and 626, respectively.

(Error correction decoding units 606 and 626)
The error correction decoding unit 606 performs error correction decoding on the packet combined by the packet combining unit 604, and reproduces transmission data (hereinafter, a reproduction stream) for each stream. Similarly, the error correction decoding unit 626 performs error correction decoding on the packet combined by the packet combining unit 624 and reproduces transmission data for each stream. Then, error correction decoding sections 606 and 626 input transmission data for each stream to error detection sections 608 and 628, respectively.

(Error detection units 608 and 628)
The error detection unit 608 performs error detection on the playback stream decoded by the error correction decoding unit 606 based on the error detection code. Similarly, the error detection unit 628 performs error detection on the reproduced stream decoded by the error correction decoding unit 626 based on the error detection code. When an error is detected in the playback stream, error detection sections 608 and 628 return NACK to transmitting apparatus 500 and notify NACK to each of antenna switching section 602 and packet combining sections 604 and 624. To do. On the other hand, if no error is detected in the playback stream, error detection sections 608 and 628 return ACK to transmitting apparatus 500, and for each of antenna switching section 602 and packet combining sections 604 and 624. Notify ACK.

  As described above, when NACK is output, the antenna switching unit 602 switches the combination of the receiving antennas, and based on the retransmitted pilot signal, the channel estimation units 204 and 224 and the synthesis quantization units 206 and 226 newly A codebook index is selected. Then, this new codebook index is fed back to transmitting apparatus 500, and the transmission signal subjected to beamforming using the new beamforming matrix calculated based on the codebook index is retransmitted. FIG. 10 shows the feedback and transmission timings related to these automatic reproduction controls.

  As shown in FIG. 10, based on the pilot signal transmitted for the first time, receiving apparatus 600 estimates a channel vector for each stream and performs synthetic quantization (S102). Next, based on the codebook index fed back from the receiving device 600, the transmitting device 500 selects a combination of the receiving devices 600 that are transmission destinations so that the channel capacity after beamforming is increased (S104). Next, the transmitting apparatus 500 calculates a beamforming matrix (S106), and transmits the transmission signal after beamforming to the selected receiving apparatus 600 (S108).

  The receiving apparatus 600 reproduces transmission data for each stream (S110) and performs error detection. When an error is detected in the reproduced transmission data, receiving apparatus 600 returns NACK to transmitting apparatus 500. Then, receiving apparatus 600 switches the combination of reception antennas so that the combination of channel vectors to be combined and quantized is changed, and newly selects a codebook index (S112).

  At this time, transmitting apparatus 500 executes data retransmission control processing in response to NACK (S114). Further, transmitting apparatus 500 recalculates the beamforming matrix based on the codebook index fed back from receiving apparatus 600 (S116). Then, transmitting apparatus 500 retransmits the transmission signal subjected to beamforming based on the recalculated beamforming matrix to receiving apparatus 600 (S118).

  The receiving apparatus 600 receives the retransmitted transmission signal, combines the packets, and reproduces the transmission data for each stream (S120). When an error is detected again in the reproduced transmission data, the receiving apparatus 600 feeds back a NACK to the transmitting apparatus 500 and switches a combination of antennas to select a new codebook index (S122). Return. At this time, the transmission apparatus 500 performs retransmission control of transmission data (S124). Next, the transmitting apparatus 500 recalculates the beamforming matrix based on the codebook index fed back from the receiving apparatus 600 (S126), and retransmits the newly subjected transmission signal to the receiving apparatus 600. (S128). Then, the receiving apparatus 600 performs the transmission data reproduction process again (S130).

  As described above, when this embodiment is applied, in a multi-user MIMO system using zero forcing and beamforming, each receiving apparatus has four or more receiving antennas, while reducing the amount of feedback information, The maximum transmission rate for the receiving apparatus can be improved. Furthermore, since different channel gains can be obtained for the initial transmission stream and the retransmitted stream, a diversity effect by hybrid ARQ can be obtained. As a result, an improvement in transmission characteristics and an increase in maximum throughput for each receiving apparatus are realized.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  In the description of each of the above embodiments, the number of antennas of the transmission device and the reception device is four, but is not limited to this. In the above description, the example in which the antennas of the receiving apparatus are divided into the same number of antenna groups has been described. However, the antennas may be configured with different numbers of antennas for each group.

It is explanatory drawing which shows the MIMO system to which hybrid ARQ is applied. It is explanatory drawing for demonstrating hybrid ARQ. It is explanatory drawing which shows the structural example of the receiver which carries out synthetic | combination quantization of a channel vector. It is explanatory drawing which shows the synthetic | combination quantization method of a channel vector. It is explanatory drawing which shows the structure of the communication system to which the synthetic | combination quantization method is applied. It is explanatory drawing which shows the structure of the receiver which applied the synthetic | combination quantization method. It is explanatory drawing which shows the function structure of the transmitter which concerns on one Embodiment of this invention. It is explanatory drawing which shows the function structure of the receiver which concerns on the same embodiment. It is explanatory drawing which shows the antenna switching method which concerns on the same embodiment. It is explanatory drawing which shows the feedback and transmission timing which concern on the same embodiment.

Explanation of symbols

1000, 5000 Communication system 100 Transmitting device 102 Quantized vector reproduction unit 104 User selection unit 106 Subset matrix setting unit 108 Inverse matrix operation unit 110 Beamforming matrix generation unit 112 Serial / parallel conversion unit 114 Channel encoding unit 116 Modulation mapping unit 118 Beam forming processing unit 200 Receiver 202, 204, 214, 222, 224, 234 Channel estimation unit 206, 226 Synthetic quantization unit 208, 228 Storage unit (quantization codebook)
210, 230 Combining coefficient acquisition unit 212, 232 Signal combining unit 240 MIMO signal detecting unit 500 Transmitting device 502 Retransmission control unit 600 Receiving device 602 Switching unit 604, 624 Packet combining unit 606, 626 Error correction decoding unit 608, 628 Error detecting unit

Claims (5)

A receiving apparatus having N (N ≧ 4) antennas and capable of retransmission control,
A plurality of combined quanta for combining M channel vectors corresponding to the M (2 ≦ M ≦ N−2) antennas and selecting a predetermined quantization vector corresponding to the combined vector of the M channel vectors. And
A combination switching unit that switches the combination of the channel vectors synthesized by the synthesis quantization unit to the combination of the channel vectors corresponding to another combination of the antennas;
With
The receiving apparatus, wherein an index of the predetermined quantization vector selected by each of the combined quantization units is fed back to a transmitting apparatus. The combination switching unit switches the combination of the channel vectors when an error is detected in the reproduction data,
The synthetic quantization unit newly selects the predetermined quantization vector based on the combination of the channel vectors switched by the combination switching unit,
The receiving apparatus according to claim 1, wherein the receiving apparatus feeds back an index of the newly selected predetermined quantization vector to the transmitting apparatus. The receiving device receives a transmission signal subjected to beamforming based on a predetermined quantization vector corresponding to the index;
A signal synthesizer that synthesizes M received signals received via the M antennas corresponding to each of the synthesized quantizers and generates a synthesized signal corresponding to each of the synthesized quantizers;
A signal detection unit that detects a transmission signal for each stream based on a channel matrix estimated from a plurality of the combined signals corresponding to the plurality of combined quantization units;
The receiving apparatus according to claim 2, further comprising:   A received signal for each stream corresponding to the reproduction data in which an error is detected is combined with a received signal for each stream corresponding to a retransmission signal beamformed based on the newly selected predetermined quantization vector. The receiving apparatus according to claim 2, further comprising a detection signal synthesizing unit. The receiving device is a user terminal included in a multi-user MIMO system,
The transmitting device calculates a beamforming matrix for block diagonalizing the channel matrix for each user terminal based on the index of the predetermined quantization vector fed back from the receiving device, and a beam forming matrix is calculated by the beamforming matrix. The signal detection unit detects a transmission signal for each stream using a channel matrix estimated based on the combined signal when a formed transmission signal is transmitted. Or the receiving apparatus of 4.

Images