JP2009272942A - Receiver, radio communication system, quantization method of channel vector, and transmission method of multistream - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver capable of obtaining high transmission characteristics and transmission efficiency. <P>SOLUTION: The receiver includes: an antenna candidate-selecting part which selects a set of reception antennas of M(2≤M≤N-1) units from among reception antennas of N(N≥3) units, and then selects all sets formed of different K(K≥2) sets; a synthesizing/quantizing part which calculates K units of quantized vectors corresponding to each set by synthesizing/quantizing M units of channel vectors corresponding to M units of reception antennas; an angular difference calculating part for calculating, for each set, angular difference of K units of quantized vectors; an orthogonal quantization vector-selecting part which detects a set whose angular difference calculated by the angular difference calculating part is closest to right angle and selects K units of quantized vectors corresponding to the set; and a reception SINR calculating part which calculates reception SINR using K units of quantized vectors selected by the orthogonal quantization vector-selecting part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a receiving apparatus, a wireless communication system, a channel vector quantization method, and a multi-stream transmission method. In particular, the present invention relates to a receiving apparatus, a radio communication system, a channel vector quantization method, and a multi-stream transmission method according to a multi-user MIMO (Multiple-Input and Multiple-Output) scheme 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 contrivance is required to accurately remove the influence of noise added in the transmission path and interference generated between substreams and reproduce the transmission signal with accuracy 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 a 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 user is required. As a technique related to this, for example, the following Non-Patent Document 1 discloses a technique for calculating a beamforming matrix by performing singular value decomposition on a subchannel matrix fed back from each receiving apparatus.

  Further, a technique is known in which channel information estimated on the reception side is fed back to the transmission side, and a combination of users whose throughput is improved on the transmission side is selected. At this time, each channel vector is quantized to reduce the amount of feedback information of the channel information. At this time, a technique for combining and quantizing a plurality of channel vectors is known in order to reduce the quantization error. As an example of this synthetic quantization technique, Non-Patent Document 2 below discloses a technique called maximum ratio transmission channel vector quantization. By using such a method, it is possible to reduce the amount of feedback information when channel information is fed back.

Q. H. Spencer et al, “Zero-forcing methods for downlink multi-multiplexing in MIMO MIMO channels”, IEEE Trans. Signal Processing, vol. 52, no. 2, pp. 461-471, Feb 2004 D. Love, R.A. Heath and T.W. Strommer, “Grassmanian beamforming for multiple-input multiple-output wireless systems”, IEEE Trans. on Information Theory, vol. 49, no. 10, pp. 2735-2747, October 2003

  However, in the system described in Non-Patent Document 2, the quantized channel vector is calculated for each user using channel vectors corresponding to all receiving antennas, and therefore, only one stream can be transmitted for each user. Therefore, when the number of users is smaller than the number of transmission antennas, there is a problem that throughput characteristics are degraded. Further, there is a problem that even if a certain user requests high-speed data transmission, the number of streams cannot be increased to increase the speed.

  Further, in the system described in Non-Patent Document 1, it is possible to transmit a plurality of streams per user. However, transmission beamforming is performed using a beamforming matrix block-diagonalized for each user. Therefore, each user cannot know the MIMO channel information of other users. Therefore, it is impossible to predict the beamforming weight directed to the user. As a result, the signal quality information used when selecting a combination of users whose throughput is improved on the transmission side cannot be calculated for each user, and the throughput characteristics are reduced as compared with the case where the user is selected using the signal quality information. There is a problem of end.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved receiving apparatus and wireless communication system capable of improving transmission efficiency and transmission characteristics. And providing a wireless communication method.

  In order to solve the above-described problem, according to an aspect of the present invention, a combination of M (2 ≦ M ≦ N−1) receiving antennas is selected from N (N ≧ 3) receiving antennas and is different from each other. Corresponding to each set by combining and quantizing an antenna candidate selection unit that selects all sets formed by K combinations (K ≧ 2) and M channel vectors corresponding to the M reception antennas A synthetic quantization unit that calculates K quantization vectors to be performed, an angle difference calculation unit that calculates an angle difference between the K quantization vectors for each set, and an angle difference calculated by the angle difference calculation unit Detects the set closest to the right angle and selects the K quantized vector corresponding to the set, and the K quantized vectors selected by the orthogonal quantized vector selecting unit Receive SI using vector A reception SINR calculation unit that calculates R, and transmits the codebook index of the K quantization vectors selected by the orthogonal quantization vector selection unit and the reception SINR calculated by the reception SINR calculation unit A receiving device is provided that returns to the side.

  As described above, the above-described receiving apparatus selects a combination of M (2 ≦ M ≦ N−1) receiving antennas from N (N ≧ 3) receiving antennas by using the antenna candidate selection unit, and is different from each other. A plurality of sets formed by the combinations (K ≧ 2) are selected. There are a plurality of combinations of M (2 ≦ M ≦ N−1) receiving antennas that can be selected from N (N ≧ 3) receiving antennas. Therefore, it is possible to select K combinations that are different from each other and select a combination. The antenna candidate selection unit selects all such “groups”.

  Further, in the reception apparatus, the composite quantization unit performs composite quantization on the M channel vectors corresponding to the M reception antennas to calculate K quantization vectors corresponding to the sets. As described above, there are K “combinations of M reception antennas” for each “group”. A channel matrix can be generated from signals received by M receiving antennas. A channel vector corresponding to each receiving antenna can be extracted. That is, “M channel vectors” are obtained for each set. Thus, the synthetic quantization unit performs synthetic quantization on the M channel vectors to generate one quantization vector. As a result, K quantization vectors corresponding to each set are obtained.

  Further, in the receiving device, the angle difference calculation unit calculates the angle difference of the K quantization vectors for each set. Then, the orthogonal quantization vector selection unit detects a set in which the angle difference calculated by the angle difference calculation unit is closest to the right angle, and selects the K quantization vectors corresponding to the set. The closer this angle difference is to a right angle, the easier the substreams are separated in receive beamforming. In the receiving apparatus, the reception SINR calculation unit calculates the reception SINR using the K quantization vectors selected by the orthogonal quantization vector selection unit, together with the codebook index of each quantization vector. Return to the sender.

  As described above, a set of quantization vectors whose angle difference is close to a right angle is selected, and their codebook index and received SINR are fed back. On the transmission side, the quantization vector can be reproduced from the codebook index. Therefore, on the transmission side, it becomes possible to generate a transmission beamforming matrix (weight matrix) that can eliminate inter-user interference using the quantization vector. Further, on the transmission side, it is possible to select a combination of receiving apparatuses that improve the throughput characteristics using the received SINR. As a result, it is possible to improve throughput characteristics in the MIMO channel.

  In addition, the reception apparatus receives a signal subjected to transmission beamforming by a transmission beamforming matrix generated from the codebook index, and N channels corresponding to the N reception antennas from the received signal A beamforming channel estimation unit for estimating a vector, and reception for generating K received beamforming vectors for separating each substream using the N channel vectors estimated by the beamforming channel estimation unit A beamforming vector generation unit and a post-beamforming reception SINR calculation unit that calculates a reception SINR after beamforming using the K reception beamforming vectors may be further provided.

  In this case, the receiving apparatus is configured to feed back the received SINR after beamforming calculated by the received SINR calculating unit after beamforming to the transmission side. In addition, the receiving apparatus receives a signal that has been subjected to channel coding and modulation mapping according to a coding scheme determined based on the received SINR after beamforming and a modulation scheme, and receives the signal from the received signal. A reception beamforming unit that separates K substreams using K reception beamforming vectors may be further provided.

  In this manner, a signal subjected to transmission beamforming is received, a reception beamforming vector is generated using a channel vector estimated from the received signal, and a reception SINR is calculated from the reception beamforming vector. This reception SINR takes transmission beam forming and reception beam forming into consideration. This received SINR is fed back to the transmission side and is referred to when the combination of the encoding method and the modulation method is determined, so that a combination with higher transmission efficiency is selected, which contributes to improvement of throughput characteristics.

  In addition, the channel vector estimation process using the signal subjected to transmission beamforming corresponds to a process for estimating the effect of residual user interference. Therefore, as described above, by performing reception beam forming on the received signal to separate the substreams, it is possible to remove the residual inter-user interference.

  In order to solve the above problems, according to another aspect of the present invention, there is provided the following wireless communication system including a transmission device and a plurality of reception devices.

  Each of the receiving devices included in the wireless communication system selects a combination of M (2 ≦ M ≦ N−1) receiving antennas from N (N ≧ 3) receiving antennas, and K different ( An antenna candidate selection unit that selects all pairs formed by the combination of K ≧ 2), and K channels corresponding to the pairs by combining and quantizing M channel vectors corresponding to the M reception antennas. A combined quantization unit that calculates a quantization vector of the first, an angle difference calculation unit that calculates an angle difference of the K quantization vectors for each group, and an angle difference calculated by the angle difference calculation unit is the rightmost angle An orthogonal quantization vector selection unit that detects a set close to, and selects the K quantization vectors corresponding to the set, and uses the K quantization vectors selected by the orthogonal quantization vector selection unit Receive SIN A reception SINR calculation unit for calculating the code, the codebook index of the K quantization vectors selected by the orthogonal quantization vector selection unit, and the reception SINR calculated by the reception SINR calculation unit to the transmission apparatus. A codebook index / reception SINR feedback unit for feedback.

  In addition, the transmission device included in the wireless communication system is fed back from the plurality of reception devices and a quantization vector reproduction unit that reproduces a quantization vector based on a codebook index fed back from each reception device. A user selection unit that selects a combination of the reception devices whose throughput characteristics are improved based on the received SINR, and a combination of the quantization vectors corresponding to the combination of the reception devices selected by the user selection unit. A transmission beamforming matrix generation unit that generates a transmission beamforming matrix that prevents streams transmitted to the reception device from interfering with each other, and a signal transmitted to each reception device selected by the user selection unit is transmitted to K sub-bands. Distributed to the stream and using the transmit beamforming matrix, Comprising a transmitting beam forming process unit for performing transmission beam forming to the stream, and a transmission unit for transmitting a signal the transmission beam forming is performed by a plurality of antennas.

  Each of the reception devices included in the wireless communication system receives the signal subjected to the transmission beamforming, and estimates N channel vectors corresponding to the N reception antennas from the received signal. Beam forming channel estimation unit and reception beam forming vector generation for generating K reception beam forming vectors for separating each sub-stream using the N channel vectors estimated by the beam forming channel estimation unit , A post-beamforming received SINR calculator that calculates a received SINR after beamforming using the K received beamforming vectors, and a received SINR after beamforming calculated by the received SINR calculator after beamforming Return to the sender And after beamforming reception SINR feedback unit which may further comprise a.

  In this case, the transmitter included in the wireless communication system determines a combination of a coding scheme and a modulation scheme that improve throughput characteristics based on the received SINR after beamforming fed back from each receiver. And a channel coding & modulation mapping unit that performs channel coding and modulation mapping for each substream using a combination of the coding method and the modulation method, and the transmission beamforming processing unit includes the channel coding and modulation. A signal subjected to channel coding and modulation mapping by the mapping unit is configured to perform transmission beam forming using the transmission beam forming matrix.

  Each of the reception devices included in the wireless communication system receives a signal subjected to channel coding and modulation mapping based on a reception SINR after beamforming by the transmission device, and receives the signal from the received signal. A reception beamforming unit that separates K substreams using K reception beamforming vectors may be further provided.

  With the above configuration, multi-stream transmission for each receiving apparatus is realized. In addition, when selecting a user to whom a signal is transmitted simultaneously, the received SINR fed back from each receiving apparatus is referred to, so a combination of users with good throughput characteristics is selected. Furthermore, reception beam forming is performed in each reception apparatus, and residual inter-user interference is removed. At this time, since the angle formed by a plurality of quantization vectors fed back from each receiving apparatus is close to a right angle, substreams can be easily separated by receiving beam forming in each receiving apparatus. Since the encoding scheme and the modulation scheme are selected with reference to the received SINR taking transmission beamforming and reception beamforming into consideration, the throughput characteristics are further improved. From such an operation, the transmission efficiency and the transmission quality can be significantly improved.

  In order to solve the above problem, according to another aspect of the present invention, a combination of M (2 ≦ M ≦ N−1) receiving antennas is selected from N (N ≧ 3) receiving antennas. Antenna candidate selection step in which all sets formed by K combinations (K ≧ 2) different from each other are selected, and M channel vectors corresponding to the M reception antennas are combined and quantized, A synthetic quantization step in which K quantization vectors corresponding to each set are calculated, an angle difference calculation step in which an angle difference between the K quantization vectors is calculated for each set, and the angle difference calculation A set having the angle difference calculated in the step closest to the right angle is detected, and an orthogonal quantization vector selection step in which the K quantization vectors corresponding to the set are selected; and the orthogonal quantization vector selection step. A received SINR calculation step in which a received SINR is calculated using the K quantization vectors selected in Step 1, a codebook index of the K quantization vectors selected in the orthogonal quantization vector selection step, and There is provided a channel vector quantization method including the step of feeding back the received SINR calculated in the received SINR calculating step to the transmission side.

  In order to solve the above-described problem, according to another aspect of the present invention, there is provided the following multi-stream transmission method in a wireless communication system including a transmission device and a plurality of reception devices.

  In the multi-stream transmission method described above, a combination of M (2 ≦ M ≦ N−1) receiving antennas is selected from N (N ≧ 3) receiving antennas by the receiving devices, and K different from each other. Antenna candidate selection step in which all pairs formed by the combinations (K ≧ 2) are selected, and M channel vectors corresponding to the M reception antennas are combined and quantized, A combined quantization step in which corresponding K quantization vectors are calculated, an angle difference calculation step in which an angle difference between the K quantization vectors is calculated for each set, and an angle difference calculation step. An orthogonal quantization vector selection step in which a set having the closest angular difference is detected and the K quantization vectors corresponding to the set are selected; and the orthogonal quantization vector selection step. A reception SINR calculation step in which reception SINR is calculated using the K quantization vectors selected in a group; a codebook index of the K quantization vectors selected in the orthogonal quantization vector selection step; A codebook index / reception SINR feedback step in which the reception SINR calculated by the reception SINR calculation unit is fed back to the transmission apparatus.

  Further, the multi-stream transmission method includes a quantization vector reproduction step in which a quantization vector is reproduced based on a codebook index fed back from each reception device by the transmission device, and the plurality of reception devices. A user selection step in which a combination of the reception devices whose throughput characteristics are improved based on the received SINR fed back from the user is selected, and a combination of the quantization vectors corresponding to the combination of the reception devices selected in the user selection step. And a transmission beamforming matrix generation step for generating a transmission beamforming matrix for preventing the streams transmitted to the respective reception devices from interfering with each other, and transmission to each of the reception devices selected in the user selection step. K substreams And a transmission beamforming processing step in which transmission beamforming is performed on all substreams using the transmission beamforming matrix, and a transmission step in which signals subjected to the transmission beamforming are transmitted by a plurality of antennas. And are included.

  As described above, according to the present invention, it is possible to perform multi-stream transmission and to select a combination of users whose throughput characteristics are improved based on signal quality information for each user. Transmission characteristics can be improved.

  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.

<Organization of issues>
Prior to describing a preferred embodiment of the present invention, a configuration example of a multi-user MIMO system using beamforming will be briefly described in order to clarify the difference between the technology according to the embodiment and the conventional technology. explain.

  Specifically, zero-forcing beamforming (ZFBF) and block-diagonalizing beamforming (BDBF) will be described. In this section, we will point out the problems that these technologies have.

[Configuration of Communication System S1]
First, the configuration of a communication system S1 related to a multiuser MIMO system using ZFBF will be described with reference to FIG. FIG. 1 is an explanatory diagram showing a configuration example of a communication system S1 related to a multi-user MIMO system using ZFBF.

As illustrated in FIG. 1, the communication system S1 includes a transmission device 10 and a plurality of reception devices 24 (# 1, # 2, # 3, and # 4). The number of transmission antennas _NT of the transmission device 10 is four. Each receiving device 24 (# 1, # 2, # 3, # 4) has four receiving antennas N _R. In the following description, it is assumed that all the receiving devices 24 (# 1, # 2, # 3, # 4) have the same functional configuration. The receiving device 24 may be called a user.

  The communication system S1 shown in FIG. 1 is configured to quantize a channel vector and feed back a codebook index when channel information is fed back from the receiving device 24 to the transmitting device 10. The communication system S1 is configured to use CQI (Channel Quality Indicator) when the transmission apparatus 10 performs user selection processing, channel coding processing, and modulation mapping processing. Hereinafter, individual functional configurations of the reception device 24 and the transmission device 10 will be described.

(Functional configuration of receiving device 24)
First, the functional configuration of the receiving device 24 will be described. As described above, since the number of transmission antennas N _T = 4 of the transmission apparatus 10 and the number of reception antennas N _R = 4 of the reception apparatus 24, the channel matrix H estimated in any reception apparatus 24 is expressed by the following equation (1). ).

…（１）

... (1)

  The receiving device 24 included in the communication system S1 has a function of estimating the channel matrix H expressed by the above equation (1). When the channel matrix H is estimated, the receiving device 24 uses the estimated channel matrix H to calculate a quantized channel vector h ′ based on the following equation (2). The quantization channel vector calculation method expressed by the following equation (2) is called maximum ratio transmission channel vector quantization.

…（２）

... (2)

However, in the above equation (2), h ′ and _cm are vector quantities. Superscript H represents Hermitian conjugate. The vector _cm is an _NT- dimensional unit norm vector included in the quantization codebook. B is the number of quantization bits.

  As described above, the receiving device 24 calculates one quantized channel vector h ′ based on the channel matrix H estimated from the signals received by the four receiving antennas. After estimating the quantized channel vector h ′, the receiving device 24 feeds back the codebook index corresponding to the estimated quantized channel vector h ′ to the transmitting device 10. The returned codebook index is transmitted to the quantized vector reproduction unit 12 of the transmission apparatus 10 to be described later.

  Further, the reception device 24 calculates a temporary CQI used for the user selection process in the transmission device 10 using the quantized channel vector h ′. The provisional CQI is calculated as follows.

Assuming that the quantized channel vector h ′ ^* is used as a transmission beam weight, and using a virtual transmission signal vector s and a virtual noise vector n, the virtual reception signal vector x is expressed by the following formula ( It can be expressed as 3). However, the superscript * represents a complex conjugate.

…（３）

... (3)

  When reception beamforming is performed on the virtual reception signal vector x expressed by the above equation (3), the normalized maximum ratio combined reception beam vector v shown in the following equation (4) is used. Thus, the received beamforming output signal y is expressed as the following equation (5). However, in the following formula (5), the superscript T represents transposition.

…（４）

…（５）

(4)

... (5)

Therefore, assuming that the quantized channel vector h ′ ^* is used as a transmission beam weight, the received SINR (ρ) is | s | ² = 1 / N _T , ‖v ‖ ² = 1, and noise variance σ ^2. Is expressed as the following equation (6). Therefore, the receiving device 24 calculates the received SINR (ρ) based on the following equation (6). Further, the reception device 24 feeds back the calculated reception SINR to the transmission device 10 as a temporary CQI. At this time, the temporary CQI is fed back to the transmitter 10 together with the codebook index. The returned temporary CQI is transmitted to the user selection unit 14 of the transmission apparatus 10 to be described later.

…（６）

(6)

  As described above, the codebook index calculated by the receiving device 24 and the temporary CQI are fed back to the transmitting device 10. Then, the transmitting apparatus 10 reproduces the quantized channel vector based on the fed back codebook index, and selects a combination of users whose throughput is improved based on the quantized channel vector and the fed back provisional CQI. Is done. Thereafter, a signal subjected to transmission beamforming is transmitted to the selected combination of users. Receiving this signal, the receiving device 24 calculates CQI in consideration of transmission beam forming and reception beam forming. Hereinafter, this calculation process will be described.

  As described above, the transmission apparatus 10 performs transmission beamforming on the transmission signal in accordance with the selected combination of users. At this time, the transmission apparatus 10 collects the quantized channel vectors of the selected user from the quantized channel vectors reproduced based on the codebook index, and forms a channel matrix. Then, the transmission apparatus 10 performs transmission beamforming on the transmission signal using the ZFBF beamforming weight matrix calculated based on the channel matrix.

  Thus, since transmission beamforming is performed based on channel information fed back from each receiving device 24, the influence of inter-user interference should be removed. However, the influence of inter-user interference remains due to the error between the channel vector estimated by each receiving device 24 and the quantized channel vector. For this reason, the receiving apparatus 24 performs reception beamforming for removing the residual inter-user interference. For this reason, calculation of CQI in consideration of transmission beamforming performed by the transmission apparatus 10 and reception beamforming performed by the reception apparatus 24 is required.

  When receiving the signal subjected to the transmission beam forming, the receiving device 24 estimates the channel vector from each beam using the individual pilot signal added to the transmission signal for each beam. This estimation process corresponds to the above estimation of residual inter-user interference. Then, the reception device 24 calculates a reception beamforming vector for removing residual inter-user interference using the estimated channel vector. Further, the receiving device 24 calculates CQI using this received beamforming vector and feeds back to the transmitting device 10.

  The fed back CQI is transmitted to the channel coding & modulation mapping unit 18 of the transmission apparatus 10 and used for selection of MCS (Modulation and Coding Set). When receiving a signal transmitted based on the selected MCS, the receiving device 24 extracts the stream by superimposing the received beamforming vector on the received signal.

  The functional configuration of the receiving device 24 has been described above. As described above, the receiving device 24 of the communication system S1 calculates a quantization vector and a temporary CQI based on the estimated channel information and feeds back to the transmitting device 10. Furthermore, the reception device 24 calculates a reception beamforming vector for removing the residual inter-user interference, and feeds back the CQI calculated using the reception beamforming vector to the transmission device 10. As a result, the transmission apparatus 10 can select a combination of users that can obtain a high throughput and an MCS.

(Functional configuration of transmitting apparatus 10)
Next, a functional configuration of the transmission device 10 will be briefly described. In the above description regarding the receiving device 24, the flow of processing executed by the transmitting device 10 in a series of processing executed by the communication system S1 has already been described. Therefore, in the following description, specific functions of the components included in the transmission device 10 will be described in more detail.

  As shown in FIG. 1, the transmission apparatus 10 mainly includes a quantized vector reproduction unit 12, a user selection unit 14, a ZFBF matrix generation unit 16, a channel coding & modulation mapping unit 18, and a ZFBF processing unit 20. And a plurality of transmission antennas 22.

(Quantized vector reproduction unit 12)
The quantization vector reproducing unit 12 refers to the quantization code book, and reproduces a quantized channel vector corresponding to the channel vector estimated by each receiving device 24 based on the codebook index fed back from each receiving device 24. . Information on the quantized channel vector reproduced by the quantized vector reproducing unit 12 is input to the user selecting unit 14.

(User selection unit 14)
Based on the quantized channel vector of each receiving device 24 input from the quantized vector reproducing unit 12 and the provisional CQI fed back from the receiving device 24, the user selecting unit 14 transmits when a transmission signal is transmitted simultaneously. A combination of users that increases the channel capacity after beam forming and increases the throughput is selected. Then, the user selection unit 14 transmits the selected combination of users to the ZFBF matrix generation unit 16. At this time, a combination of user indexes corresponding to each receiving device 24 is transmitted to the ZFBF matrix generation unit 16.

Further, when a combination of the receiving devices 24 is selected by the user selection unit 14, data assigned to each stream according to the combination (data u ₁ for user # ₁ , data u ₂ for user # ₂ , user # 3) data u ₃ to _the data u ₄ to user # ₄₎ is determined and input to the channel coding & modulation mapping unit 18.

(ZFBF matrix generation unit 16)
When the combination of user indexes is transmitted from the user selection unit 14, the ZFBF matrix generation unit 16 calculates the beamforming matrix W corresponding to the combination as follows. However, in the following description, the quantized channel vector corresponding to the codebook index fed back from the receiving device 24 (#k) (k = 1 to 4) is expressed as h ′ _{# k} . Further, the quantized channel vector h ′ _{# k} is expressed as the following equations (7) to (10).

…（７）

…（８）

…（９）

…（１０）

... (7)

(8)

... (9)

(10)

First, as shown in the following formula (11), the ZFBF matrix generation unit 16 uses the quantized channel vector h ′ _{# k} of the selected user expressed by the above (7) to (10) to perform multiuser MIMO. A channel matrix H of the channel is generated.

…（１１）

... (11)

  Next, the ZFBF matrix generation unit 16 calculates a transmission beamforming matrix W by performing an inverse matrix operation on the channel matrix expressed by the above (11) as shown in the following equation (12). This transmission beamforming matrix W is for removing interference components between users for users belonging to the selected combination. The transmission beamforming matrix W calculated in this way is input to the ZFBF processing unit 20.

…（１２）

(12)

(Channel coding & modulation mapping unit 18)
The channel encoding & modulation mapping unit 18 performs channel encoding on the input data for each stream. Further, the channel coding & modulation mapping unit 18 performs modulation mapping of channel-coded data for each stream with a predetermined modulation scheme and modulation order, and determines a transmission symbol for each stream. When the CQI is fed back from the receiving device 24, the channel coding & modulation mapping unit 18 determines the combination of MCSs that improve the throughput in consideration of the CQI. The transmission symbol for each stream determined by the channel coding & modulation mapping unit 18 is input to the ZFBF processing unit 20.

(ZFBF processing unit 20)
As described above, the transmission beamforming matrix W is input from the ZFBF matrix generation unit 16 to the ZFBF processing unit 20, and the transmission symbols for each stream are input from the channel coding & modulation mapping unit 18. Therefore, the ZFBF processing unit 20 integrates the transmission beamforming matrix W with respect to the transmission symbol vector composed of the input transmission symbols.

For example, if a transmission symbol transmitted to the receiving device 24 (#k) (k = 1 to 4) is expressed as s _#k , a transmission symbol vector transmitted from the transmitting device 10 is s = [s _{# 1} , s _{#. 2} , s _{# 3} , s _{# 4} ] ^T. Similarly, when a received symbol received by the receiving device 24 (#k) (k = 1 to 4) is expressed as r _{# k} , a received symbol vector in the communication system S1 is r = [r _{# 1} , r _{# 2} ,. r _{# 3} , r _{# 4} ] ^T.

  When these notations are used, the relationship between the transmission symbol vector s and the reception symbol vector r is expressed by the following equation (13) using the transmission beamforming matrix W and the channel matrix H. As is clear from the following equation (13), the effective channel matrix HW after the transmission beamforming is performed is a diagonal matrix from which all off-diagonal elements indicating inter-user interference are removed.

…（１３）

... (13)

  Thus, the ZFBF processing unit 20 removes inter-user interference by applying the transmission beamforming matrix W to the transmission symbol vector. The transmission signal subjected to the transmission beamforming by the ZFBF processing unit 20 is transmitted to the reception device 24 via the antenna 22.

  The configuration of the communication system S1 has been described above. As described above, by adopting a configuration in which the channel vector is quantized and the codebook index is fed back, the amount of data to be fed back is reduced, and the communication load related to feedback is reduced. Further, since the provisional CQI is fed back, it becomes possible to select a combination of users in consideration of information on the size of the channel vector estimated by each user. Furthermore, since CQI taking into account transmission beam forming and reception beam forming for removing residual user interference is fed back, MCS can be determined in consideration of residual user interference.

(Problem of communication system S1)
As described above, the effect of improving the throughput can be obtained by applying the configuration of the communication system S1. However, although the receiving device 24 of the communication system S1 has a plurality of receiving antennas, the quantizing channel vector is calculated using channel matrices corresponding to all the receiving antennas. Therefore, the receiving device 24 returns only the codebook index of one quantization channel vector to the transmitting device 10. As a result, the transmission device 10 cannot simultaneously transmit a plurality of streams to the same reception device 24.

Therefore, as shown in FIG. 2, when the number of users is smaller than the number of transmission antennas _NT , the following problem occurs. FIG. 2 shows a case where the number of users is 2 (<N _T = 4) in the communication system S1. (Problem 1) When the number of users is smaller than the number of transmission antennas _NT , the maximum throughput rate of MCS is fixed, so the overall throughput characteristics are degraded. (Problem 2) When a specific user requests high-speed data transmission, the user cannot cope with the multi-stream transmission. In the embodiments of the present invention described later, means for solving such problems are proposed.

[Configuration of Communication System S2]
Next, the configuration of the communication system S2 related to the multiuser MIMO system using BDBF will be described with reference to FIG. FIG. 3 is an explanatory diagram showing a configuration example of the communication system S2 related to the multiuser MIMO system using the BDBF.

As illustrated in FIG. 3, the communication system S2 includes a transmission device 30 and a plurality of reception devices 44 (# 1, # 2). The number of transmission antennas _NT of the transmission device 30 is four. Each receiving device 44 (# 1, # 2) number of reception antennas _{N R} of is four. In the following description, it is assumed that all receiving apparatuses 44 (# 1, # 2) have the same functional configuration. The receiving device 44 may be called a user.

  The communication system S2 shown in FIG. 3 is configured to quantize a channel vector and feed back a codebook index when channel information is fed back from the receiving device 44 to the transmitting device 30. The communication system S2 is configured to use CQI (Channel Quality Indicator) when the transmission apparatus 30 performs channel coding processing and modulation mapping processing. Further, unlike the communication system S1 described above, the number of transmission streams transmitted to each user is two. Hereinafter, individual functional configurations of the reception device 44 and the transmission device 30 will be described.

(Functional configuration of receiving device 44)
First, the functional configuration of the receiving device 44 will be described. As described above, since the number of transmission antennas N _T = 4 of the transmission device 30 and the number of reception antennas N _R = 4 of the reception device 44, the channel matrix (H ₁ ) estimated in the reception devices 24 (# 1, # 2). , H ₂ ) is expressed as in the following formulas (14) and (15).

…（１４）

…（１５）

... (14)

... (15)

Further, when the channel matrices H ₁ and H ₂ expressed by the above formulas (14) and (15) are divided for every two receiving antennas, 4 expressed by the following formulas (16) to (19) 4 It is divided into two subchannel matrices H ₁₁ , H ₁₂ , H ₂₁ and H ₂₂ .

…（１６）

…（１７）

…（１８）

…（１９）

... (16)

... (17)

... (18)

... (19)

  The receiving device 44 quantizes the channel vector based on the subchannel matrix. For example, the receiving device 44 (#k) (k = 1, 2) calculates a quantized channel vector based on the following equation (20). Here, k is a user index. i is an index of the divided subchannel matrix. In the examples of the above formulas (16) to (19), i = 1, 2. Note that the division number of the channel matrix corresponds to the number of transmission streams per user.

…（２０）

... (20)

However, in the above equation (20), h ′ _ki and _cm are vector quantities. The vector _cm is an _NT- dimensional unit norm vector included in the quantization codebook. B is the number of quantization bits. When the quantized channel vector is calculated based on the above equation (20), the receiving device 44 feeds back the codebook index corresponding to the quantized channel vector to the transmitting device 30.

  As described above, the receiving device 44 of the communication system S2 divides the channel matrix by the number of streams to generate a subchannel matrix, and calculates a quantized channel vector. Therefore, channel vectors corresponding to all reception antennas are not used for calculation of the quantized channel vector. As a result, a plurality of streams can be transmitted simultaneously from the transmission device 30 toward the same reception device 44.

(Functional configuration of transmitting device 30)
Next, the functional configuration of the transmission device 30 will be described. Unlike the transmission apparatus 10 included in the communication system S1, the transmission apparatus 30 is configured to perform BDBF on a transmission signal to remove inter-user interference. Further, the transmission device 30 transmits a plurality of streams simultaneously to the same reception device 44.

  As illustrated in FIG. 3, the transmission apparatus 30 mainly includes a quantization vector reproduction unit 32, a BDBF matrix generation unit 34, an S / P conversion unit 36, a channel coding & modulation mapping unit 38, and a BDBF process. The unit 40 includes a plurality of transmission antennas 42.

(Quantized vector reproduction unit 32)
The quantization vector reproduction unit 32 refers to the quantization code book and reproduces a quantization channel vector corresponding to the channel vector estimated by each reception device 44 based on the codebook index fed back from each reception device 44. . Information on the quantized channel vector reproduced by the quantized vector reproducing unit 32 is input to the BDBF matrix generating unit 34.

For example, when the quantized channel matrices h ′ _k1 and h ′ _k2 corresponding to the subchannel matrices H _k1 and H _k2 are _{fed back} from the receiving device 44 (#k) (k = 1, 2), the quantized vector reproduction unit 32 reproduces the channel matrix H ′ _k corresponding to the receiving device 44 (#k) as shown in the following equations (21) and (22). The channel matrices H ′ ₁ and H ′ ₂ are input to the BDBF matrix generation unit 34.

…（２１）

…（２２）

... (21)

... (22)

(BDBF matrix generation unit 34)
As shown in the following equation (23), the BDBF matrix generation unit 34 performs singular value decomposition on the subchannel matrix H ′ ₂ of the reception device 44 (# 2) input from the quantization vector reproduction unit 32, and performs singular value decomposition. Vectors V ₂ ⁽¹⁾ and V ₂ ⁽⁰⁾ are calculated. Among them, the right singular value vector V ₂ ⁽⁰⁾ corresponds to the singular value 0 and gives a null space vector for the subchannel matrix H ′ ₁ .

Similarly, the BDBF matrix generation unit 34 performs singular value decomposition on the subchannel matrix H ′ ₁ of the reception device 44 (# 1) input from the quantization vector reproduction unit 32 as shown in the following equation (24). The singular value vectors V ₁ ⁽¹⁾ and V ₁ ⁽⁰⁾ are calculated. Among these, the right singular value vector V ₁ ⁽⁰⁾ corresponds to the singular value 0 and gives a null space vector for the subchannel matrix H ′ ₂ .

…（２３）

…（２４）

... (23)

... (24)

Therefore, the BDBF matrix generation unit 34 uses the right singular value vector V ₂ ⁽⁰⁾ as a beamforming matrix component for the receiving device 44 (# 1). Further, the right singular value vector V ₁ ⁽⁰⁾ is used as a beamforming matrix component for the receiving device 44 (# 2). That is, the BDBF matrix generation unit 34 generates the transmission beamforming matrix W = [V ₂ ⁽⁰⁾ , V ₁ ⁽⁰⁾ ] using the right singular value vectors V ₁ ⁽⁰⁾ , V ₂ ^(0). To do. The transmission beamforming matrix W generated in this way is input to the BDBF processing unit 40, and is calculated into a transmission symbol vector input from the channel coding & modulation mapping unit 38.

(S / P converter 36, channel coding & modulation mapping unit 38)
Data to be transmitted to each user is input to the S / P converter 36. The S / P converter 36 performs serial / parallel conversion on the input data and distributes the data to a plurality of substreams. The data distributed to each substream is input to the channel coding & modulation mapping unit 38.

  The channel encoding & modulation mapping unit 38 performs channel encoding on the input data for each substream. Further, the channel coding & modulation mapping unit 38 performs modulation mapping of channel-coded data for each substream with a predetermined modulation scheme and modulation order, and determines a transmission symbol for each substream. When the CQI is fed back from the receiving device 44, the channel coding & modulation mapping unit 38 determines the combination of MCS that improves the throughput in consideration of the CQI. The transmission symbol for each stream determined by the channel coding & modulation mapping unit 38 is input to the BDBF processing unit 40.

(BDBF processing unit 40)
As described above, the BDBF processing unit 40 receives the transmission beamforming matrix W from the BDBF matrix generation unit 34 and receives the transmission symbols for each substream from the channel coding & modulation mapping unit 38. Therefore, the BDBF processing unit 40 calculates a transmission beamforming matrix W with respect to a transmission symbol vector composed of the input transmission symbols. Then, the transmission signal subjected to the transmission beamforming is transmitted to the reception device 44 via the plurality of transmission antennas 42.

For example, the BDBF processing unit 40 applies the input transmission beamforming matrix W to the transmission symbol vector s. If the transmission symbol vector is expressed as s = [s ₁ , s ₂ , s ₃ , s ₄ ] ^T , the reception symbol vector r is expressed as the following equation (25). As is clear from the following equation (25), the effective channel matrix HW after the transmission beamforming is performed is a block diagonal matrix from which all off-diagonal elements corresponding to inter-user interference are removed. . This is because the null space vector of the MIMO channel matrix of another user is used when generating the beamforming matrix W. For this reason, the inter-user interference is eliminated.

…（２５）

... (25)

  Since the interference component between users is removed as in the above equation (25), each receiving device 44 estimates a MIMO subchannel for the device itself, and performs signal detection by MMSE detection, MLD detection, or the like. It becomes possible. If the quantization error due to channel vector quantization is sufficiently small, the transmission apparatus 30 can simultaneously transmit a plurality of streams using the transmission beamforming matrix W so as not to cause interference between users. .

(Problem of communication system S2)
As described above, the communication system S2 can simultaneously transmit a plurality of streams to the same receiving device 44 if the quantization error of the channel vector is small. Therefore, when the number of users is smaller than the number of transmission antennas _NT of the transmission device 30, the number of streams allocated to each reception device 44 can be increased to improve the throughput.

  However, if the transmission beam forming matrix W is used, the transmission beam is transmitted toward the null space of the MIMO channel of another user. Therefore, a user who has received transmission data beamformed by this transmission beamforming matrix W cannot obtain information on the MIMO channels of other users. As a result, there is a problem in that the beamforming weight directed to itself cannot be predicted, and the provisional CQI cannot be calculated in the receiving apparatus 44.

  As shown in FIG. 4, when the user selection unit 33 is provided in the transmission device 30 and a signal is transmitted to the selected combination of users, the user selection unit 33 only uses the angle information included in the quantization channel vector. Based on this, the user combination is selected. That is, signal quality information cannot be used when selecting a combination of users. As a result, there arises a problem that the throughput is reduced as compared with the case of user selection in consideration of signal quality. In the embodiments of the present invention described later, means for solving such problems are proposed.

<Embodiment>
Hereinafter, an embodiment of the present invention will be described. The present embodiment relates to a channel vector quantization method capable of multi-stream transmission for the same user and capable of generating a CQI used for user selection.

[Configuration of Communication System 1]
First, the configuration of the communication system 1 according to the present embodiment will be described with reference to FIG. FIG. 5 is an explanatory diagram illustrating a configuration example of the communication system 1 according to the present embodiment.

As illustrated in FIG. 5, the communication system 1 includes a transmission device 100 and a plurality of reception devices 200 (# 1, # 2). The number of transmission antennas _NT of the transmission device 100 is four. Each receiving apparatus 200 (# 1, # 2) has four receiving antennas N _R. In the following description, for the convenience of description, it is assumed that all receiving apparatuses 200 (# 1, # 2) have the same functional configuration. In addition, the receiving device 200 may be referred to as a user. Of course, the number of transmitting antennas, the number of receiving antennas, the number of users, etc. are not limited to this.

  The communication system 1 shown in FIG. 5 is configured to quantize a channel vector and feed back a codebook index when channel information is fed back from the receiving device 200 to the transmitting device 100. Further, the communication system 1 is configured to use CQI when the transmission apparatus 100 performs user selection processing, channel coding processing, and modulation mapping processing. Further, unlike the communication system S1 described above, a plurality of streams can be transmitted to the same user. Hereinafter, individual functional configurations of the reception device 200 and the transmission device 100 will be described.

(Functional configuration of transmitting apparatus 100)
First, the functional configuration of the transmission device 100 will be described. The transmission apparatus 100 is configured to perform transmission by applying ZFBF to a transmission signal. However, unlike the transmission device 10 included in the communication system S1, the data transmitted to each user is divided into a plurality of substreams, and the plurality of substreams are transmitted to the same user. Also, it is assumed that the codebook index, temporary CQI, and CQI are fed back from each receiving apparatus 200 to the transmitting apparatus 100 as in the case of the transmitting apparatus 10 described above.

  Hereinafter, each component of the transmission device 100 will be described in more detail. However, detailed description of components that are substantially the same as those of the transmission device 10 is omitted.

  As illustrated in FIG. 5, the transmission apparatus 100 mainly includes a quantization vector reproduction unit 102, a user selection unit 104, a ZFBF matrix generation unit 106, an S / P conversion unit 108, a channel coding & modulation mapping. Unit 110, ZFBF processing unit 112, and a plurality of transmission antennas 114.

(Quantized vector reproduction unit 102)
The quantization vector reproducing unit 102 reproduces a quantization channel vector corresponding to the channel vector estimated by each receiving apparatus 200 based on the codebook index fed back from each receiving apparatus 200 with reference to the quantization code book To do. Information on the quantized channel vector reproduced by the quantized vector reproducing unit 102 is input to the user selecting unit 104.

(User selection unit 104)
Based on the quantized channel vector of each receiving device 200 input from the quantized vector reproducing unit 102 and the provisional CQI fed back from the receiving device 200, the user selecting unit 104 transmits when transmission signals are transmitted simultaneously. A combination of users that increases the channel capacity after beam forming and increases the throughput is selected. Then, the user selection unit 104 inputs the selected user combination to the ZFBF matrix generation unit 106.

Further, when a combination of the receiving apparatuses 200 is selected by the user selection unit 104, data (data u ₁ to the user # 1, data u 2 to the user # ₂ ) to be assigned for each stream is determined according to the combination. , Input to the S / P converter 108.

(ZFBF matrix generation unit 106)
When a combination of user indexes is transmitted from the user selection unit 104, the ZFBF matrix generation unit 106 calculates a beamforming matrix W corresponding to the combination.

  First, the ZFBF matrix generation unit 106 generates a channel matrix H of a multiuser MIMO channel using the quantization channel vector of the selected user. Next, the ZFBF matrix generation unit 106 performs an inverse matrix operation on the channel matrix to calculate a transmission beamforming matrix W as shown in the above equation (12). The transmission beamforming matrix W calculated in this way is input to the ZFBF processing unit 112 and is calculated as a transmission symbol vector input from the channel coding & modulation mapping unit 110.

(S / P converter 108, channel coding & modulation mapping unit 110)
Data transmitted to each user is input to the S / P converter 108. The S / P converter 108 performs serial / parallel conversion on the input data and distributes it to a plurality of substreams. Data distributed to each substream is input to channel coding & modulation mapping section 110.

  The channel coding & modulation mapping unit 110 channel codes the input data for each stream. Further, the channel coding & modulation mapping unit 110 performs modulation mapping of channel-coded data for each stream with a predetermined modulation scheme and modulation order, and determines a transmission symbol for each stream. When CQI is fed back from receiving apparatus 200, channel coding & modulation mapping section 110 determines a combination of MCS that improves throughput in consideration of CQI. The transmission symbol for each stream determined by the channel coding & modulation mapping unit 110 is input to the ZFBF processing unit 112.

(ZFBF processor 112)
As described above, the ZFBF processing unit 112 receives the transmission beamforming matrix W from the ZFBF matrix generation unit 106 and the transmission symbol for each stream from the channel coding & modulation mapping unit 110. Therefore, the ZFBF processing unit 112 integrates the transmission beamforming matrix W with respect to the transmission symbol vector configured by the input transmission symbols. The transmission signal subjected to the transmission beam forming by the ZFBF processing unit 112 in this way is transmitted to the reception apparatus 200 via the transmission antenna 114.

  Heretofore, the functional configuration of the transmission device 100 according to the present embodiment has been described. As described above, the transmission apparatus 100 is configured to perform transmission beamforming on a transmission signal by ZFBF using inverse matrix calculation and transmit the transmission signal. Furthermore, in the user selection process, the temporary CQI fed back from the receiving apparatus 200 is used to select a combination of users whose throughput is improved.

  Further, the MCS is selected based on the CQI fed back from the receiving apparatus 200. Then, data transmitted to each user is distributed for each substream, and a plurality of streams are transmitted to the same user. The configuration of these transmission apparatuses 100 is realized by a characteristic configuration of the reception apparatus 200 described later. Therefore, with the functional configuration of the transmission apparatus 100 described above in mind, the functional configuration of the reception apparatus 200 according to the present embodiment will be described in detail below.

(Functional configuration of receiving apparatus 200)
Here, the functional configuration of the receiving apparatus 200 according to the present embodiment will be described with reference to FIG. FIG. 6 is an explanatory diagram illustrating a functional configuration of the receiving device 200 according to the present embodiment.

  As illustrated in FIG. 6, the reception apparatus 200 relates to a calculation process of a quantized channel vector and provisional CQI, and includes a channel estimation unit 204, an antenna candidate selection unit 206, a random vector quantization unit 208, and an angle difference calculation unit 210. And an orthogonal quantization vector index detection unit 212 and a provisional CQI calculation unit 214.

  Furthermore, the reception apparatus 200 includes a BF channel estimation unit 216, a reception beamforming vector calculation unit 218, and a CQI calculation unit 220 regarding CQI calculation processing and the like in consideration of transmission beamforming and reception beamforming. Reception apparatus 200 includes a plurality of reception antennas 202, a reception beamforming unit 222, an LLR calculation unit 224, and an error correction decoding unit 226.

(Calculation of quantization channel vector and provisional CQI)
First, a functional configuration related to a calculation process of a quantization channel vector and a provisional CQI among functional configurations included in the receiving apparatus 200 will be described.

  In the receiving device 24 included in the communication system S1, the quantized channel vector is calculated using all channel vectors obtained from signals received by the four receiving antennas. However, the receiving apparatus 200 according to the present embodiment calculates a quantized channel vector using a smaller number of receiving antennas 202 than the total number of receiving antennas. At that time, the receiving apparatus 200 according to the present embodiment is configured so that a combination of channel vectors used for calculation of a quantized channel vector can be suitably selected. This will be described in detail below, focusing on this structural feature point.

(Channel estimation unit 204)
Channel estimation section 204 estimates channel matrix H based on signals received from a plurality of reception antennas 202. For example, the channel estimation unit 204 estimates a channel vector h ₁ having a component corresponding to each transmission antenna 114 included in the transmission device 100 based on the signal received from the first reception antenna 202 (# 1). Similarly, the channel estimation unit 204 estimates a channel vector h _k having a component corresponding to each transmission antenna 114 based on a signal received from the k-th (k = 2 to 4) reception antenna 202. At this time, the channel matrix H is expressed as the following Expression (26).

…（２６）

... (26)

Each channel vector h _k (k = 1 to 4) estimated by the channel estimation unit 204 is input to the antenna candidate selection unit 206.

(Antenna candidate selection unit 206)
The antenna candidate selection unit 206 selects a combination of channel vectors used for calculating a quantized channel vector. Each channel vector is estimated from a signal received by each receiving antenna 202 as described above, and therefore corresponds to each receiving antenna 202. Therefore, the antenna candidate selection unit 206 selects a combination of the reception antennas 202 used for calculation of the quantization channel vector.

  For example, assume that three channel vectors are combined and quantized to calculate one quantized channel vector, and two different sets of receiving antennas 202 are selected to calculate two quantized channel vectors. That is, the antenna candidate selection unit 206 selects two combinations of the reception antennas 202 including the three reception antennas 202 from the four reception antennas 202 so as not to overlap each other.

  There are six such combinations as shown in Chart 1 in FIG. In FIG. 10, a combination number is assigned to each combination, and the first combination (# 1) and the second combination (# 2) are arranged side by side. In Table 1, the k-th (k = 1 to 4) receiving antenna 202 is represented by a number k, and for example, a combination of the first, second, and third receiving antennas 202 is represented by (1,2 , 3). The antenna candidate selection unit 206 can select, for example, a combination of the reception antennas 202 as described in FIG.

  However, the antenna candidate selection unit 206 can select a combination of channel vectors under various conditions other than the above example. For example, it is possible to cope with the condition of calculating two quantized channel vectors by combining and quantizing two channel vectors to calculate one quantized channel vector. That is, the antenna candidate selection unit 206 selects two combinations of the reception antennas 202 including the two reception antennas 202 from the four reception antennas 202 so as not to overlap each other.

  At this time, the antenna candidate selection unit 206 can also select the combination of the receiving antennas 202 so that the elements do not completely overlap each other. In this case, there are three combinations of the reception antennas 202 selected by the antenna candidate selection unit 206 as shown in Chart 2 of FIG. As is apparent from Chart 2, the elements of the two selected sets of receive antennas 202 do not completely overlap each other.

  As described above, the antenna candidate selection unit 206 can select a plurality of sets of channel vector combinations used for calculating the quantized channel vectors so as not to overlap each other. The combination information of the receiving antennas 202 selected by the antenna candidate selection unit 206 is input to the random vector quantization unit 208.

(Random vector quantization unit 208)
Random vector quantization section 208 performs synthetic quantization on a plurality of channel vectors estimated by channel estimation section 204 based on channel vector combination information selected by antenna candidate selection section 206.

First, as shown in the following equation (27), the random vector quantization unit 208 uses the reception antenna selection matrix P _{j, i} to calculate the i-th channel matrix H _{j, i} corresponding to each combination number j. calculate. However, the receiving antenna selection matrix P _{j, i} is set in advance corresponding to each combination number j as shown in FIG. 12, for example.

…（２７）

... (27)

The example of Chart 3 shown in FIG. 12 corresponds to each combination of Chart 1 shown in FIG. In the example of Chart 3, j = 1 to 6 and i = 1,2. That is, this is a case where one quantized channel vector is calculated from channel vectors corresponding to the three receiving antennas 202, and two quantized channel vectors are calculated. The reason why the two quantized channel vectors are calculated is to support 2-stream transmission. In this case, as shown in Chart 3, each receiving antenna selection matrix is 3 rows by 4 columns. In the case of the example shown in FIG. 3, for example, the channel matrix H _{1, i} (i = 1, 2) corresponding to the combination number 1 is expressed as the following Expression (28) and Expression (29).

…（２８）

…（２９）

... (28)

... (29)

After calculating the channel matrix H _{j, i} corresponding to each combination number in this way, the random vector quantization unit 208 performs maximum ratio transmission channel vector quantization based on the following equation (30), Quantization channel vectors h ′ _{j, i} corresponding to the combinations are calculated.

…（３０）

... (30)

However, in the above equation (30), h ′ _{j, i} and _cm are vector quantities. The vector _cm is an _NT- dimensional unit norm vector included in the quantization codebook. B is the number of quantization bits.

The quantized channel vector h ′ _{j, i} calculated by the random vector quantizing unit 208 in this way is input to the angle difference calculating unit 210.

(Angle difference calculation unit 210)
The angle difference calculation unit 210 calculates an angle difference between the quantized channel vectors h ′ _{j, i} input from the random vector quantization unit 208. For example, the angle difference calculation unit 210 calculates the angle difference between the quantization channel vectors h ′ _{j, 1} , h ′ _{j, 2} of the combination number j. This angle difference θ _j is calculated based on the following equation (31).

…（３１）

... (31)

  The angle difference calculated by the angle difference calculation unit 210 in this way is input to the orthogonal quantization vector index detection unit 212.

(Orthogonal quantization vector index detection unit 212)
The orthogonal quantization vector index detection unit 212 refers to the angle difference for each combination input from the angle difference calculation unit 210 and detects a combination in which the angle at which the quantization channel vectors intersect is closest to the orthogonality. That is, the orthogonal quantization vector index detection unit 212 detects the number j _max of combinations in which the angle difference is close to orthogonal based on the following equation (32). However, in the following equation (32), L is the maximum combination number. Further, ‖h ′ _{j, 1} ‖ = ‖h ′ _{j, 2} ‖ = 1.

…（３２）

... (32)

After detecting the number j _max of combinations in which the angle difference is close to orthogonal in this way, the orthogonal quantization vector index detection unit 212 detects the quantized channel vectors h ′ _{jmax, 1} , h ′ _jmax corresponding to the number of combinations j _{max. , 2} are returned to the transmitting apparatus 100. These quantized channel vectors h ′ _{jmax, 1} and h ′ _{jmax, 2} are input to the temporary CQI calculation unit 214.

(Temporary CQI calculation unit 214)
The temporary CQI calculation unit 214 calculates a temporary CQI used for user selection using the quantized channel vectors h ′ _{jmax, 1} , h ′ _{jmax, 2} input from the orthogonal quantization vector index detection unit 212. The provisional CQI is calculated as follows.

_{Assuming that the} quantized channel vectors h ′ ^* _{jmax, 1} and h ′ ^* _{jmax, 2} are used as transmission beam weights, the virtual transmission signal vectors s ₁ and s ₂ and the virtual noise vector n are used. The virtual received signal vectors x ₁ and x ₂ can be expressed as the following equations (33) and (34).

…（３３）

…（３４）

... (33)

... (34)

Further, when reception beamforming is performed on the virtual reception signal vectors x ₁ and x ₂ expressed by the above equations (33) and (34), the normalization shown in the following equation (35) is performed. Using the maximum ratio combined received beam vector v _i (i = 1, 2), the received beamforming output signals y ₁ and y ₂ are expressed by the following equations (36) and (37).

…（３５）

…（３６）

…（３７）

... (35)

... (36)

... (37)

Accordingly, assuming that the quantized channel vectors h ′ ^* _{jmax, 1} and h ′ ^* _{jmax, 2} are used as transmission beam weights, the received SINR (ρ) is | s ₁ | ² = | s ₂ | ² = 1 / N _T , ‖v _i ‖ ² = 1, and noise variance σ ² are used to express the following equation (38).

…（３８）

... (38)

  Therefore, provisional CQI calculation section 214 calculates reception SINR (ρ) based on the above equation (38), and returns this reception SINR to transmission apparatus 100 as provisional CQI. As described above, the provisional CQI that has been fed back is transmitted to the user selection unit 104 of the transmission apparatus 100, and is used when selecting a combination of users whose throughput is improved.

  Heretofore, among the functional configuration of the receiving apparatus 200 according to the present embodiment, the components related to the quantization channel vector and provisional CQI calculation processing, and the processing flow have been described. As described above, in the quantization channel vector calculation method according to the present embodiment, combinations of receiving antennas 202 that do not overlap each other are selected, and an angular difference regarding the quantization channel vector calculated for each combination is calculated. A combination of quantization channel vectors whose angle difference is close to a right angle is selected.

  With this configuration, it is possible to calculate a highly accurate quantized channel vector using a plurality of channel vectors, and simultaneously select a plurality of quantized channel vectors corresponding to a plurality of streams. Furthermore, since the relationship between the selected quantization channel vectors is nearly orthogonal to each other, signal separation by reception beam forming is facilitated.

(About CQI calculation processing considering transmission / reception beamforming)
As described above, when the codebook index and the provisional CQI are fed back to the transmission apparatus 100, the transmission apparatus 100 reproduces the quantization channel vector based on the fed back codebook index, and the throughput is based on the provisional CQI. Select user combinations to improve. Then, a signal subjected to transmission beamforming is transmitted to the selected user. When transmission beamforming is performed on the transmission signal in this way, the influence of interference between users is sufficiently removed if the quantization error is sufficiently small.

  However, when the quantization error cannot be ignored, reception beam forming is performed in the receiving apparatus 200, and the residual inter-user interference caused by the quantization error is removed. The receiving apparatus 200 according to the present embodiment is configured to be able to calculate CQI in consideration of transmission beamforming and reception beamforming even when a plurality of streams are transmitted. In addition, there is provided means for individually extracting a multi-stream by performing reception beam forming on a signal transmitted based on the MCS selected in consideration of the CQI.

  Hereinafter, a functional configuration of the receiving apparatus 200 related to CQI calculation in consideration of transmission beam forming and reception beam forming, and a series of processing flows will be described. It is assumed that the transmission apparatus 100 transmits a signal subjected to transmission beamforming after user selection based on the returned codebook index and provisional CQI.

(BF channel estimation unit 216)
The BF channel estimation unit 216 receives a signal from each of the reception antennas 202 and estimates a channel vector corresponding to each reception antenna 202 using an individual pilot signal added to the transmission signal for each beam. This estimation process corresponds to estimation of residual inter-user interference. The channel vector estimated by the BF channel estimation unit 216 is input to the reception beamforming vector calculation unit 218.

(Receiving beamforming vector calculation unit 218)
Reception beamforming vector calculation unit 218 calculates a reception beamforming vector based on the channel vector estimated by BF channel estimation unit 216. Note that reception beamforming is performed on signals received from all reception antennas 202. Therefore, the reception beamforming vector is calculated using channel vectors corresponding to all reception antennas 202. The reception beamforming vector calculated by reception beamforming vector calculation unit 218 is input to CQI calculation unit 220 and reception beamforming unit 222.

(CQI calculation unit 220)
The CQI calculation unit 220 calculates a reception SINR based on the reception beamforming vector input from the reception beamforming vector calculation unit 218. The received SINR calculated by CQI calculating section 220 is fed back to transmitting apparatus 100 as CQI.

  As described above, the returned CQI is used for the selection of MCS in transmitting apparatus 100. In transmitting apparatus 100, when MCS is selected based on the fed back CQI, channel coding and modulation mapping are performed based on the selected MCS, and further, transmission beamforming is performed and a signal is transmitted. This transmission signal is received by receiving apparatus 200 and input to reception beam forming section 222.

(Receiving beam forming unit 222)
The reception beamforming unit 222 accumulates the reception beamforming vectors input from the reception beamforming vector calculation unit 218 on the reception signals received via the reception antennas 202 and transmits the received signals to the user. The streams are extracted individually. Each stream extracted by the reception beamforming unit 222 is input to the LLR calculation unit 224.

(LLR calculation unit 224, error correction decoding unit 226)
The LLR calculation unit 224 calculates a log likelihood ratio (LLR) of each stream separated by the reception beamforming unit 222. The log likelihood ratio for each stream calculated by the LLR calculation unit 224 is input to the error correction decoding unit 226. The error correction decoding unit 226 performs error correction decoding processing on each stream using the log likelihood ratio calculated by the LLR calculation unit 224, and outputs decoded data.

  Heretofore, the functional configuration of the receiving device 200 according to the present embodiment has been described. Further, the quantization channel vector selection method, the provisional CQI calculation method used for user selection, and the CQI calculation method considering transmission beamforming and reception beamforming have been described. As described above, the receiving apparatus 200 according to the present embodiment selects a combination of the receiving antennas 202, calculates a quantization channel vector for each combination, and then selects a combination having an angle difference close to orthogonal to each other. Then, a temporary CQI is calculated using the selected quantization channel vector.

  In particular, receiving apparatus 200 divides a plurality of receiving antennas 202 into two sets of subsets that do not overlap each other and performs channel vector quantization. Then, a combination of quantized channel vectors in which the two quantized channel vectors are close to orthogonal is selected. Therefore, even when multi-streams are transmitted to the same user, a channel state can be formed in which streams can be easily separated by reception beam forming. Further, the provisional CQI is fed back together with the codebook index, so that a combination of users whose throughput is improved can be selected. As a result, it is possible to improve transmission characteristics and transmission efficiency within the framework of ZFBF.

[Application example]
Next, a configuration of a communication system 2 is shown as an application example of the communication system 1 according to the present embodiment with reference to FIGS. FIG. 7 is an explanatory diagram showing the configuration of the communication system 2 according to this application example. FIG. 8 is an explanatory diagram showing a functional configuration of the receiving apparatus 400 according to this application example. Note that a detailed description of the functional configuration substantially the same as the constituent elements of the transmission device 100 or the reception device 200 included in the communication system 1 is omitted.

  As illustrated in FIG. 7, the communication system 2 is an example of a multi-user MIMO system using ZFBF, and includes a transmission device 300 and a plurality of reception devices 400.

  As illustrated in FIG. 7, the transmission apparatus 300 includes a quantization vector reproduction unit 302, a user selection unit 304, a ZFBF matrix generation unit 306, an S / P conversion unit 308, a turbo coding & modulation mapping unit 310, , An individual pilot multiplexing unit 311, a ZFBF processing unit 312, a common pilot multiplexing unit 313, and a plurality of transmission antennas 314.

  The main structural differences from the above-described transmission apparatus 100 are the turbo coding & modulation mapping unit 310, the individual pilot multiplexing unit 311, and the common pilot multiplexing unit 313. That is, the point that the turbo code is used when data is encoded is different from the point that the process of multiplexing the individual pilot signal and the common pilot signal is explicitly shown.

  On the other hand, as shown in FIG. 8, the receiving apparatus 400 includes a plurality of receiving antennas 402, a channel estimation unit 404, an antenna candidate selection unit 406, a random vector quantization unit 408, an angle difference calculation unit 410, and an orthogonality. Quantization vector index detection unit 412, provisional CQI calculation unit 414, BF channel estimation unit 416, reception MMSE beamforming vector calculation unit 418, CQI calculation unit 420, reception MMSE beamforming unit 422, and LLR calculation unit 424 and a turbo decoding unit 426.

  The main structural differences from the receiving apparatus 200 described above lie in the reception MMSE beamforming vector calculation unit 418, the reception MMSE beamforming unit 422, and the turbo decoding unit 426. That is, the difference is that the MMSE detection method is used at the time of reception beamforming and the turbo decoding is performed when data is decoded corresponding to the transmission apparatus 300.

  Based on the above differences regarding the transmission apparatus 300 and the reception apparatus 400, a series of processing flows regarding the multi-stream transmission / reception method in the communication system 2 will be described below.

  First, the transmission apparatus 300 adds a common pilot signal to the frame signal by the common pilot multiplexing unit 313, and then transmits a plurality of streams to each reception apparatus 400 via the plurality of transmission antennas 314. Next, receiving apparatus 400 uses channel estimation section 404 to estimate the channel matrix using the common pilot signal added to the frame signal. The estimated channel matrix is input to the antenna candidate selection unit 406.

  The antenna candidate selection unit 406 divides the input channel matrix into two sets of channel matrices, for example, based on the chart 1 shown in FIG. The channel matrix divided by the antenna candidate selection unit 406 is input to the random vector quantization unit 408. Then, the input channel matrix is quantized by the random vector quantization unit 408. The plurality of sets of quantized channel vectors calculated in this way are input to the angle difference calculation unit 410.

  The angle difference calculation unit 410 calculates an angle difference for each set of input quantized channel vectors. The angle difference for each set calculated by the angle difference calculation unit 410 is input to the orthogonal quantization vector index detection unit 412. Then, the orthogonal quantization vector index detection unit 412 calculates a metric corresponding to the angle difference based on the above equation (32). Further, the orthogonal quantization vector index detection unit 412 selects the combination of the receiving antennas 402 having the smallest metric from the number of combinations shown in Table 1.

  Furthermore, the corresponding codebook index is determined for the set of quantized channel vectors that is the minimum metric. In addition, provisional CQI calculation section 414 calculates provisional CQI corresponding to this set of quantized channel vectors. Thereafter, these codebook index and provisional CQI are fed back to the transmitting apparatus 300.

  Next, in the transmission apparatus 300, the quantization channel reproduction unit 302 reproduces the quantization channel vector based on the codebook index fed back from the reception apparatus 400. The quantized channel vector reproduced by the quantized vector reproducing unit 302 is input to the user selecting unit 304. Next, the transmission apparatus 300 refers to the provisional CQI fed back from the reception apparatus 400 by the user selection unit 304, selects a combination of users whose throughput is improved, and transmits data to be transmitted to each user to the S / P conversion unit 308. To enter.

  Furthermore, the transmission apparatus 300 reproduces a channel matrix by collecting the quantized channel vectors corresponding to the selected user by the ZFBF matrix generation unit 306, and based on the inverse matrix operation, the ZFBF transmission beamforming is performed from the channel matrix. A matrix W is calculated. The calculated transmission beamforming matrix W is input to the ZFBF processing unit 312. The ZFBF processing unit 312 receives a signal obtained by multiplexing the dedicated pilot signal by the dedicated pilot multiplexing unit 311 and performs transmission beam forming. Then, the dedicated pilot signal after the transmission beamforming is transmitted toward the receiving apparatus 400 corresponding to the selected user.

  In receiving apparatus 400 that has received the dedicated pilot signal, BF channel estimation section 416 estimates a channel matrix including the effect of transmission beamforming. That is, the interference effect by the beam for other users included due to the quantization error is estimated. The estimated channel matrix is input to reception MMSE beamforming vector calculation unit 418. Reception MMSE beamforming vector calculation unit 418 uses the input channel matrix to calculate two sets of MMSE reception beamforming vectors for removing inter-user interference and extracting a substream for the own user.

  This MMSE receive beamforming vector is input to CQI calculation section 420. Then, reception SINR is calculated by CQI calculation section 420 based on the MMSE reception beamforming vector and the channel matrix. The calculated received SINR is fed back to transmitting apparatus 300 as CQI.

  Upon receiving the CQI fed back from each receiving device 400, the transmitting device 300 selects an optimum MCS. Then, the transmission apparatus 300 performs turbo encoding and modulation mapping for multiple streams based on the selected MCS by the turbo encoding & modulation mapping unit 310. Further, the transmission signal after being subjected to turbo coding and modulation mapping is subjected to transmission beamforming by the ZFBF processing unit 312 and transmitted to each receiving apparatus 400 via the transmission antenna 314.

  In each receiving apparatus 400, a reception MMSE beamforming unit 422 extracts a substream using the previously calculated MMSE reception beamforming vector. Specifically, the MMSE reception beamforming vector is superimposed on the reception signal vector. Instead of the previously calculated MMSE receive beamforming vector, a newly calculated MMSE receive beamforming vector using an individual pilot signal may be used. The extracted received beamforming signal for each substream is input to the LLR calculator 424, and a log likelihood ratio is calculated. Then, turbo decoding is performed by the turbo decoding unit 426 using the calculated log likelihood ratio, and decoded data is reproduced.

  The specific system configuration using the turbo code and the MMSE detection method and the flow of a series of processes have been described above as an application example according to the present embodiment. Also in this application example, similarly to the communication system 1 described above, even when multi-streams are transmitted to the same user, it is possible to form a channel state in which streams can be easily separated by reception beamforming. In addition, the provisional CQI is fed back together with the codebook index, so that a combination of users whose throughput is improved can be selected. And it becomes possible to improve transmission characteristics and transmission efficiency within the framework of ZFBF.

[effect]
Finally, specific effects obtained when the technique according to the present embodiment is applied will be described with reference to FIG. FIG. 9 is an explanatory diagram illustrating a simulation result when the technique according to the present embodiment is applied. This simulation result is calculated assuming that the number of transmitting antennas is 4 and the number of receiving antennas is 4. For MCS, there are 15 coding rates: 1/3, 1/2, 2/3, 3/4, 4/5, and modulation schemes of QPSK, 16QAM, and 64QAM.

(About the solid line (square) graph)
In FIG. 9, a graph indicated by a solid line (square) indicates throughput characteristics when the number of users is 4, and channel vectors are quantized from channel matrices corresponding to all reception antennas for each user. That is, each user calculates one quantized channel vector from channel vectors corresponding to all receiving antennas and feeds back to the transmitting side. On the transmission side, one stream is transmitted to each user by applying ZFBF.

  In this case, since four streams are transmitted from the transmission side, in the high SNR region (30 dB), the upper limit of the MCS rate is 4.8 bits / s / Hz (coding rate 4/5, modulation scheme 64QAM). It turns out that it is asymptotic to 19.2 bits / s / Hz corresponding to 4 times.

(Dotted line (triangle) graph)
In FIG. 9, a graph indicated by a dotted line (triangle) indicates throughput characteristics when the number of users is 2 and channel vectors are quantized from channel matrices corresponding to all reception antennas for each user. That is, each user calculates one quantized channel vector from channel vectors corresponding to all receiving antennas and feeds back to the transmitting side. On the transmission side, one stream is transmitted to each user by applying ZFBF.

  In this case, since the number of users is 2, only two streams are transmitted from the transmission side, and in the high SNR region, the upper limit of the MCS rate is 9.6 bits corresponding to twice 4.8 bits / s / Hz. It can be seen that it remains at / s / Hz.

(About the dotted line (circle) graph)
In FIG. 9, a graph indicated by a chain line (circle) shows throughput characteristics when the configuration of the present embodiment is applied when the number of users is two. As is apparent from this graph, the throughput characteristics of the present embodiment are asymptotic to when the number of users is 4 (solid line (square)) even though the number of users is 2. The reason why the throughput characteristics are slightly reduced as compared with the case of four users is that the maximum ratio transmission channel vector quantization is performed from three reception antennas. This is because the received power decreases compared to the case where quantization is performed. However, when the number of users is the same (dotted line (triangle)), it can be seen that the throughput characteristics can be greatly improved when the reception SNR is 10 dB or more.

  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.

  For example, in the above description, the number of transmission antennas is 4 and the number of reception antennas is 4. However, the present invention is not limited to this. Moreover, although the case where the number of users was 2 was demonstrated, the number of users may be 3 or more. Furthermore, the encoding method and the modulation method can be freely changed.

It is explanatory drawing which shows the structural example of the multiuser MIMO system using ZFBF. It is explanatory drawing which shows the problem of the multiuser MIMO system using ZFBF. It is explanatory drawing which shows the structural example of the multiuser MIMO system using BDBF. It is explanatory drawing which shows the problem of the multiuser MIMO system using BDBF. It is explanatory drawing which shows an example of the system configuration | structure of the communication system which concerns on one Embodiment of this invention, and the function structure of a transmitter. It is explanatory drawing which shows an example of a function structure of the receiver which concerns on this embodiment. It is explanatory drawing which shows the system configuration | structure of the communication system which concerns on one application example of this embodiment, and the function structure of a transmitter. It is explanatory drawing which shows the function structure of the receiver which concerns on one application example of this embodiment. It is explanatory drawing for demonstrating the improvement effect of the throughput characteristic obtained when the communication system which concerns on this embodiment is used. It is explanatory drawing which shows the example of a combination of the receiving antenna for channel vector synthetic | combination quantization which concerns on this embodiment. It is explanatory drawing which shows the example of a combination of the receiving antenna for channel vector synthetic | combination quantization which concerns on this embodiment. It is explanatory drawing which shows an example of the selection matrix of the receiving antenna which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Communication system 100, 300 Transmitter 102, 302 Quantization vector reproduction part 104, 304 User selection part 106, 306 ZFBF matrix generation part 108, 308 S / P conversion part 110 Channel coding & modulation mapping part 112, 312 ZFBF processor 114, 314 Transmit antenna 200, 400 Receiver 202, 402 Receive antenna 204, 404 Channel estimator 206, 406 Antenna candidate selector 208, 408 Random vector quantizer 210, 410 Angle difference calculator 212, 412 Orthogonal Quantized vector index detection unit 214, 414 Temporary CQI calculation unit 216, 416 BF channel estimation unit 218 Reception beamforming vector calculation unit 220, 420 CQI calculation unit 222 Reception beamforming unit 224, 24 LLR calculation unit 226 error correction decoder 310 turbo coding & modulation mapping unit 311 individually Pilot multiplexing unit 313 common Pilot multiplexing unit 418 receives MMSE beamforming vector calculating unit 422 receives MMSE beamforming unit 426 turbo decoder

Claims (8)

All combinations formed by selecting a combination of M (2 ≦ M ≦ N−1) reception antennas from N (N ≧ 3) reception antennas and K combinations (K ≧ 2) different from each other. An antenna candidate selector for selecting
A combined quantization unit for combining and quantizing M channel vectors corresponding to the M receiving antennas to calculate K quantized vectors corresponding to the sets;
An angle difference calculation unit for calculating an angle difference between the K quantization vectors for each set;
An orthogonal quantization vector selection unit that detects a set in which the angle difference calculated by the angle difference calculation unit is closest to a right angle and selects the K quantization vectors corresponding to the set;
A received SINR calculator that calculates a received SINR using the K quantized vectors selected by the orthogonal quantized vector selector;
With
A receiving apparatus that feeds back the codebook index of the K quantized vectors selected by the orthogonal quantized vector selecting unit and the received SINR calculated by the received SINR calculating unit to the transmitting side. Beamforming channel estimation for receiving a signal subjected to transmission beamforming by a transmission beamforming matrix generated from the codebook index and estimating N channel vectors corresponding to the N receiving antennas from the received signal And
A reception beamforming vector generation unit that generates K reception beamforming vectors for separating each substream using the N channel vectors estimated by the beamforming channel estimation unit;
A post-beamforming received SINR calculator that calculates a received SINR after beamforming using the K received beamforming vectors;
Further comprising
The receiving apparatus according to claim 1, wherein the reception SINR after beamforming calculated by the reception SINR calculation unit after beamforming is fed back to the transmission side.   A signal that has been subjected to channel coding and modulation mapping by a coding method determined based on the received SINR after the beamforming and a modulation method is received, and the K received beamforming vectors are received from the received signal. The receiving apparatus according to claim 2, further comprising: a receiving beamforming unit that uses and separates K substreams. A wireless communication system including a transmission device and a plurality of reception devices,
Each of the receiving devices is
All combinations formed by selecting a combination of M (2 ≦ M ≦ N−1) reception antennas from N (N ≧ 3) reception antennas and K combinations (K ≧ 2) different from each other. An antenna candidate selector for selecting
A combined quantization unit for combining and quantizing M channel vectors corresponding to the M receiving antennas to calculate K quantized vectors corresponding to the sets;
An angle difference calculation unit for calculating an angle difference between the K quantization vectors for each set;
An orthogonal quantization vector selection unit that detects a set in which the angle difference calculated by the angle difference calculation unit is closest to a right angle and selects the K quantization vectors corresponding to the set;
A received SINR calculator that calculates a received SINR using the K quantized vectors selected by the orthogonal quantized vector selector;
Codebook index / received SINR feedback for feeding back the codebook index of the K quantized vectors selected by the orthogonal quantized vector selecting unit and the received SINR calculated by the received SINR calculating unit to the transmitting apparatus And
With
The transmitter is
A quantization vector reproducing unit that reproduces a quantization vector based on the codebook index fed back from each of the receiving devices;
A user selection unit that selects a combination of the reception devices that improve throughput characteristics based on reception SINRs fed back from the plurality of reception devices;
Transmit beamforming for generating a transmit beamforming matrix that prevents streams transmitted to the respective receivers from interfering with each other using the combination of the quantization vectors corresponding to the combination of the receivers selected by the user selection unit A matrix generator;
A transmission beamforming processing unit that distributes a signal to be transmitted to each receiving apparatus selected by the user selection unit to K substreams, and performs transmission beamforming on all substreams using the transmission beamforming matrix; ,
A transmission unit for transmitting the signal subjected to the transmission beamforming with a plurality of antennas;
A wireless communication system. Each of the receiving devices is
A beamforming channel estimation unit that receives the signal subjected to the transmission beamforming and estimates N channel vectors corresponding to the N reception antennas from the received signal;
A reception beamforming vector generation unit that generates K reception beamforming vectors for separating each substream using the N channel vectors estimated by the beamforming channel estimation unit;
A post-beamforming received SINR calculator that calculates a received SINR after beamforming using the K received beamforming vectors;
A post-beamforming received SINR feedback unit that feeds back a received SINR after beamforming calculated by the post-beamforming received SINR calculating unit;
Further comprising
The transmitter is
A combination of a coding scheme and a modulation scheme that improve throughput characteristics is determined based on the received SINR after beamforming fed back from each receiving apparatus, and each substream is determined using the combination of the coding scheme and the modulation scheme. Further comprises a channel coding and modulation mapping unit for channel coding and modulation mapping,
The transmission beamforming processing unit according to claim 4, wherein the transmission beamforming processing unit performs transmission beamforming on the signal subjected to channel coding and modulation mapping by the channel coding & modulation mapping unit using the transmission beamforming matrix. Wireless communication system. Each of the receiving devices is
The transmitter receives a signal that has been subjected to channel coding and modulation mapping based on the received SINR after beamforming by the transmitter, and uses the received K beamforming vectors to generate K substreams from the received signal. The receiving apparatus according to claim 5, further comprising a receiving beam forming unit for separation. A combination of M (2 ≦ M ≦ N−1) reception antennas is selected from N (N ≧ 3) reception antennas, and all combinations formed by K combinations (K ≧ 2) different from each other. Antenna candidate selection step in which is selected,
A combined quantization step in which M channel vectors corresponding to the M reception antennas are combined and quantized, and K quantization vectors corresponding to the sets are calculated;
An angular difference calculating step in which an angular difference between the K quantization vectors is calculated for each set;
A set of orthogonal quantization vectors in which the set of angle differences calculated in the step of calculating the angle difference is detected at a right angle and the K quantization vectors corresponding to the set are selected;
A reception SINR calculation step in which a reception SINR is calculated using the K quantization vectors selected in the orthogonal quantization vector selection step;
A step of feeding back the codebook index of the K quantization vectors selected in the orthogonal quantization vector selection step and the reception SINR calculated in the reception SINR calculation step to the transmission side;
A method of quantizing a channel vector, including: A multi-stream transmission method in a wireless communication system including a transmission device and a plurality of reception devices,
By each receiving device,
A combination of M (2 ≦ M ≦ N−1) reception antennas is selected from N (N ≧ 3) reception antennas, and all combinations formed by K combinations (K ≧ 2) different from each other. Antenna candidate selection step in which is selected,
A combined quantization step in which M channel vectors corresponding to the M reception antennas are combined and quantized, and K quantization vectors corresponding to the sets are calculated;
An angular difference calculating step in which an angular difference between the K quantization vectors is calculated for each set;
A set of orthogonal quantization vectors in which the set of angle differences calculated in the step of calculating the angle difference is detected at a right angle and the K quantization vectors corresponding to the set are selected;
A reception SINR calculation step in which a reception SINR is calculated using the K quantization vectors selected in the orthogonal quantization vector selection step;
The codebook index / received SINR in which the codebook index of the K quantized vectors selected in the orthogonal quantized vector selecting step and the received SINR calculated by the received SINR calculating unit are fed back to the transmitting apparatus. A return step,
By the transmission device,
A quantization vector reproduction step in which a quantization vector is reproduced based on a codebook index fed back from each receiving device;
A user selection step in which a combination of the receiving devices that improve throughput characteristics is selected based on the received SINRs fed back from the plurality of receiving devices;
A transmission beamforming matrix is generated to prevent the streams transmitted to each receiving apparatus from interfering with each other using the combination of the quantization vectors corresponding to the combination of receiving apparatuses selected in the user selection step. A transmit beamforming matrix generation step;
A transmission beamforming process in which a signal transmitted to each receiving apparatus selected in the user selection step is distributed to K substreams, and transmission beamforming is performed on all substreams using the transmission beamforming matrix. Steps,
A transmission step in which signals subjected to the transmission beamforming are transmitted by a plurality of antennas;
Including a multi-stream transmission method.

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