JP2014179794A - Radio communication system and its method, transmitting device and its method, and receiving device and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress inter-layer interference in MIMO communication in cooperative transmission to a satisfactory extent while restraining the amount of feedback information.SOLUTION: In a radio communication system in which a plurality of transmitting stations including a plurality of transmission antennas and one receiving station including a plurality of reception antennas perform radio communication by multiple input multiple output (MIMO), the receiving station obtains a channel matrix between each of the plurality of transmitting stations and the receiving station, and feeds back to part of the plurality of transmitting stations information about the channel matrix between the part of the transmitting stations and the receiving station, and the part of the transmitting stations generate a transmission signal vector by precoding a transmission symbol on the basis of the information about the channel matrix, and transmit it from each of the plurality of transmission antennas. Transmission stations that did not get feedback regard a transmission symbol vector as a transmission signal vector, and transmits the transmission signal vector as it is from each of the plurality of transmission antennas.

Description

  The present invention relates to a wireless communication technology in which a plurality of transmitters cooperate to transmit a plurality of data streams simultaneously using multiple input multiple output (MIMO).

  A multi-input multi-output (MIMO) technique is known in which a transmitting / receiving station simultaneously transmits / receives a plurality of data streams using a plurality of antennas to increase the speed of data transmission / reception. In MIMO technology, signals output simultaneously from multiple transmitting antennas interfere with each other at the receiving antenna, so the technology that removes the interference (interlayer interference) at the receiving antenna ensures sufficient channel capacity. To be important. Note that the maximum channel capacity is achieved when the transmission side can receive all channel state information (CSI) for transmission paths between antennas without error (see Non-Patent Document 1). In addition, Tomlinson-Harashima precoding (see Non-Patent Document 2) and vector perturbation (see Vector Perturbation, Non-Patent Document 3) are used as signal transmission techniques for achieving channel capacity when the channel matrix between transmission and reception is known The method is known. Similarly, a technique is also known in which a transmission signal is multiplied by a channel inverse matrix or a generalized inverse matrix in advance using an inverse matrix of a channel matrix or a generalized inverse matrix (Non-Patent Document 4).

  When the transmission signal is transformed and transmitted in advance, for example, the transmission signal vector x ′ = Px is generated so that the transmission symbol vector x can be detected without error from the reception signal vector y. Note that x represents a transmission symbol vector of N rows and 1 column, x ′ represents a transmission signal vector of N rows and 1 column, P represents a precoding matrix of N rows and N columns, and z represents a noise vector of M rows and 1 column, respectively. . Here, y = Hx ′ + z, where H is an M × N channel matrix and y is an M × 1 received signal vector.

At this time, when M = N, by setting P = H ⁻¹ , y = x + z is obtained, and thereby it is possible to remove interference between layers (see Non-Patent Document 4). On the other hand, if the communication quality is not good in at least a part of the channel matrix, calculating the inverse matrix may significantly increase the norm of the inverse matrix and increase the transmission power significantly. In this case, the same effect can be obtained with a small transmission power by perturbing the channel matrix to obtain a generalized inverse matrix (see Non-Patent Document 4). Moreover, in order to reduce transmission power, a transmission vector can be perturbed before pre-encoding (refer nonpatent literature 3).

  By the way, in recent years, cooperative multi-point (CoMP) in which a plurality of transmitting stations cooperate to transmit a signal to one receiving station has been studied. In CoMP, one base station capable of performing MIMO communication can similarly perform communication using MIMO with respect to a user terminal (UE) existing at a cell edge of a cell deployed by the base station. Signals are transmitted in cooperation with other base stations. A schematic diagram of such a wireless communication network using CoMP is shown in FIG. In CoMP, as shown in FIG. 1, there is one serving cell (primary cell) that accommodates a UE and one or more neighboring cells (CoMP cell) that perform coordinated transmission. Then, when the primary base station and the CoMP base station that deploy each cell perform signal transmission in cooperation, the UE can receive signals at high speed, for example.

There are various modes in CoMP, and among them, there is a mode in which a primary base station and a CoMP base station simultaneously transmit one signal to a UE at the cell edge (see Non-Patent Document 5). In this case, the received signal vector y received at the UE is
_{y = (H P P + H} S S) x + z
It becomes. Here, H _P is a channel matrix of M rows and N columns representing the channel state between the primary base station and the UE, and H _S is M rows N representing the channel state between the CoMP base station and the UE. A channel matrix of columns. x is a transmission symbol vector of N rows and 1 column, and y is a reception signal vector of M rows and 1 column. P is a precoding matrix of N rows and N columns for the primary base station to linearly convert the transmission symbol vector x to the transmission signal vector Px. Similarly, S is a precoding matrix of N rows and N columns for the CoMP base station to linearly convert the transmission symbol vector x to the transmission signal vector Sx. Z is a noise vector of N rows and 1 column.

A. Goldsmith, S.M. Jafar, N .; Jindal and S.J. Vishwanath, “Capacity limits of MIMO channels,” IEEE Journal on Selected Areas in Communications, 2003, vol. 21, no. 5, pp. 684-702 R. F. H. Fischer, C.I. Windpassinger, A.M. Lampe, and J.A. B. Huber, “Tomlinson-Harashima Precoding In Space-Time Transmission For Low-Rate Backward Channel”, Proc. International Zurich Seminar on Broadband Communications (IZS), Switzerland, February 2002 Bertrand M.C. Hochwald, Christian B. Peel, and A.M. Lee Windlehurst, “Vector Perturbation Techniques for Near-Maximum Multi-Antenna Multi-User Communication: Part 1: Perturbation (Technique for near-capacitance multi-quantity multi-energy e-interaction)” 2005, vol. 53, no. 3, pp. 537-544 Christian B. Peel, Bertrand M.C. Hochwald, and A.H. Lee Swindlehurst, “Vector Perturbation Techniques for Nearly Maximum Multi-Antenna Multi-user Communication-Part 1: Channel-inversion and generalization-capacitance multi- directionality of multi- antenna communication ) ", IEEE Transactions on Communications, 2005, vol. 53, no. 3, pp. 537-544 R. Irmer, H.M. Droste, and P.M. Marsch et al., “Cooperative Multipoints: Concepts, Performance and Field Test Results (concepts, performances, and field trials results)”, IEEE Communications Magazine, 2011, vol. 49, no. 2, pp. 102-111 G. Ginis, and J.A. Cioffi, “Vectorized Transmission for Digital Line Systems”, IEEE Journal on Selected Areas in Communications, June 2002, v. 2002. Cioffi, “Vectorized Transmission for Digital Line Systems”, IEEE Journal on Selected Areas in Communications, June 2002. 20, no. 5, pp. 1085-1104

The primary base station and the CoMP base station need to receive feedback of the respective channel matrices H _P and H _S from the UE in order to generate the precoding matrices P and S to cope with inter-layer interference. Therefore, compared to the case where CoMP is not used, there is a problem that the amount of feedback information for suppressing inter-layer interference increases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for sufficiently suppressing inter-layer interference of MIMO communication in CoMP while suppressing the amount of feedback information.

  In order to achieve the above object, a wireless communication system according to the present invention includes a plurality of transmitting stations having a plurality of transmitting antennas and a single receiving station having a plurality of receiving antennas by wireless communication using multiple input multiple output (MIMO). In the wireless communication system, the receiving station has a channel between each of the plurality of transmitting antennas and each of the plurality of receiving antennas between each of the plurality of transmitting stations and the receiving station. And obtaining means for obtaining a channel matrix having a value indicating the state of the element as an element, and feeding back information on the channel matrix between the part of the transmitting station and the receiving station to a part of the plurality of transmitting stations. A transmission symbol vector having a transmission symbol as an element based on information on the channel matrix. A generation unit configured to generate a transmission signal vector by performing pre-encoding, and a part of the transmission station transmits each element of the transmission signal vector generated by the generation unit from each of the plurality of transmission antennas; The transmitting station that has not received feedback transmits each element of the transmission signal vector from each of the plurality of transmission antennas using the transmission symbol vector as the transmission signal vector, and the receiving station transmits the plurality of transmission signals. Based on the signal from the station, there is further provided restoring means for restoring the transmission symbol vector and the channel matrix between the transmitting station and the receiving station that did not receive the feedback.

  In addition, the transmission device according to the present invention is a wireless communication system in which a plurality of transmission devices having a plurality of transmission antennas and a single reception device having a plurality of reception antennas perform wireless communication by multiple input multiple output (MIMO). A transmission device, wherein a value indicating a state of a channel between each of the plurality of transmission antennas and each of the plurality of reception antennas between the transmission device and the reception device is received from the reception device as an element. When receiving feedback on information about a channel matrix to be transmitted, generation means for pre-encoding a transmission symbol vector having transmission symbols as elements based on the information on the channel matrix to generate a transmission signal vector, and receiving the feedback If the transmission signal vector element generated by the generating means is When transmitting from each of a plurality of transmission antennas and not receiving the feedback, the transmission symbol vector is used as the transmission signal vector, and each element of the transmission signal vector is transmitted from each of the plurality of transmission antennas. Means.

  A receiving apparatus according to the present invention is a wireless communication system in which a plurality of transmitting apparatuses having a plurality of transmitting antennas and a single receiving apparatus having a plurality of receiving antennas perform wireless communication by multiple input multiple output (MIMO). A receiving device, wherein each of the plurality of transmitting devices and the receiving device has a value indicating a channel state between each of the plurality of transmitting antennas and each of the plurality of receiving antennas as an element. An acquisition means for acquiring a channel matrix, feedback means for feeding back information on the channel matrix between a part of the transmission apparatus and the reception apparatus to a part of the plurality of transmission apparatuses, Some pre-encode a transmission symbol vector whose elements are transmission symbols based on information about the channel matrix. The transmission signal vector element transmitted from each of the plurality of transmission antennas and the transmission apparatus that did not receive feedback transmitted from each of the plurality of transmission antennas using the transmission symbol vector as the transmission signal vector. Based on the reception means for simultaneously receiving the elements of the transmission signal vector by the plurality of reception antennas, the received signal, and the channel matrix between the transmission device and the reception device that did not receive the feedback, Restoring means for restoring the transmission symbol vector.

  According to the present invention, it is possible to sufficiently suppress inter-layer interference of MIMO communication in CoMP while suppressing the amount of feedback information.

The figure which shows the structural example of the network which performs coordinated transmission. FIG. 3 is a sequence diagram illustrating a processing flow according to the first embodiment. Schematic diagram of a table holding the probability that the equivalent channel matrix is a diagonal dominant matrix and the corresponding value of λ.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  The configuration of the wireless communication system according to the present embodiment is assumed to be, for example, as shown in FIG. In the example of FIG. 1, an example in which a primary base station that deploys a serving cell that accommodates a user terminal (UE) and a CoMP base station that deploys an adjacent cell adjacent to the serving cell is shown. Although FIG. 1 shows an example in which one primary base station and one CoMP base station are included, a plurality of CoMP base stations may exist. However, in the following example, for simplicity, it is assumed that there is only one CoMP base station. The primary base station and the CoMP base station can communicate with each other via a higher-level control apparatus or the like in the network configuration, or can transmit the same data (transmission symbol) to one UE. And FIG. 1 shows an example in which a host control device is included in the network configuration, but such a device may not be provided, and in this case, the primary base station and the CoMP base station are directly connected to each other. Communicate.

となる。ここで、ｚは雑音ベクトルである。したがって、このような構成により、レイヤ間干渉を除去して通信を行うことができる。 Prior to detailed description, first, a method for suppressing inter-layer interference between the primary base station and the CoMP base station at the same time in coordinated transmission will be examined. As a simple technique, in order for both the primary base station and the CoMP base station to remove inter-layer interference, a technique of multiplying the transmission symbol vector x by the inverse matrix of the channel matrix in advance can be considered. That is, x ₁ ′ = H _P ⁻¹ x / 2 and x ₂ ′ = H _S ⁻¹ x / 2 are transmitted from the primary base station and the CoMP base station, respectively. Here, H _P and H _S is the channel matrix between each and the UE of the primary base station and CoMP base stations. According to this, the received signal vector y is

It becomes. Here, z is a noise vector. Therefore, with such a configuration, it is possible to perform communication while eliminating inter-layer interference.

  However, in order for each of a plurality of base stations (transmitting stations) to multiply the transmission symbol vector by the channel inverse matrix, information on each element of the channel matrix (or inverse matrix) is fed back from the UE (receiving station). There is a need. This is at least twice the amount of feedback information for the elimination of inter-layer interference in multiple-input multiple-output (MIMO) communication between a single base station and a single UE, and M CoMP base stations In some cases, this means that (M + 1) times the amount of information needs to be fed back.

を満足する行列である。例えば、

の場合、この行列Ａは対角優位行列である。１００＞５＋７、かつ３２＞１０＋２、かつ５４＞１５＋２．５だからである。 On the other hand, in the following embodiment, the inter-layer interference is not completely removed in advance, but the receiving apparatus controls the channel matrix to be a diagonal dominant matrix, and the receiving apparatus performs further signal detection. A method for performing processing and obtaining (almost) optimum interference removal performance will be described. As a result, the amount of information used by the transmission apparatus can be reduced, so that the amount of feedback information can be reduced. The diagonal dominant matrix is an integer i and j from 1 to N when the size of the matrix is N × N.

Is a matrix that satisfies For example,

In this case, the matrix A is a diagonal dominant matrix. This is because 100> 5 + 7, 32> 10 + 2, and 54> 15 + 2.5.

が成り立つ。 In addition, when a channel matrix is a diagonal dominant matrix, it is known that interference removal performance will become substantially optimal by performing the signal detection process called QR-DFE on the receiving side (refer nonpatent literature 6). . Here, QR-DFE is a signal detection technique that combines QR decomposition of a channel matrix and decision feedback equalization (DFE). The QR decomposition of the channel matrix H is a process of searching for the unitary matrix Q and the upper triangular matrix R so that H = QR. For such matrices Q and R, since Q is a unitary matrix, Q ^H Q = I (I is a unit matrix) holds, so by multiplying both sides of H = QR by Q ^H from the left , Q ^H H = R holds. Thus, for example, for a channel matrix of 3 rows and 3 columns:

Holds.

となる。 As a result, the signal y _i (the i-th element of the received signal vector) at the receiving antenna i after multiplying the unitary matrix Q from the left is

It becomes.

  Therefore, on the reception side, interference can be canceled for signals received by the nth antenna based on signals corresponding to the (n + 1) th to Nth antennas. In other words, the determination result of the signal corresponding to the Nth antenna can be fed back, and the interference component in the signal corresponding to the (N-1) th antenna can be canceled. The interference component of the signal to be canceled can be canceled.

  Further, when the channel matrix is a diagonal dominant matrix, the inter-layer interference component can be treated as noise and each element of the transmission symbol vector can be restored. In other words, since the channel matrix is a diagonal dominant matrix, the desired signal component is received stronger than the interference component, so that in some cases, the transmission symbol can be restored without performing interference cancellation. In addition, when the channel matrix is a diagonal dominant matrix, the receiving apparatus performs zero-forcing, that is, the received signal vector is multiplied by the inverse matrix of the channel matrix, thereby obtaining suboptimal interference. Removal can be performed.

<< Embodiment 1 >>
[Overview]
In this embodiment, only the primary base station generates and transmits a transmission signal vector by multiplying the transmission symbol vector by the channel inverse matrix, while the CoMP base station transmits the transmission symbol vector as it is as a transmission signal vector. . Thereby, the sum (equivalent channel matrix) of two channel matrices between the primary base station and the CoMP base station in the UE (receiving apparatus) is diagonally dominant.

[Process flow]
FIG. 2 is a diagram illustrating an example of processing executed between the primary base station, the CoMP base station, and the terminal (UE) according to the present embodiment. In addition, although this figure has shown the example which a primary base station and a CoMP base station communicate directly, for example, the control apparatus in a backbone network performs communication mediation and the start of cooperative transmission (CoMP). May be communicated to.

  In FIG. 2, first, the UE detects a state in which CoMP is to be performed, that is, exists at the cell edge, and notifies the primary base station (serving base station of the UE) of the state. Then, the primary base station starts CoMP processing and first starts transmission of a channel estimation signal. Here, the signal for channel estimation uses a pilot signal in FIG. 2, but it is a known signal on the receiving side (UE) such as a training sequence, and any other signal can be used as long as it can identify each transmitting antenna. It may be a signal. The UE estimates a channel state between each transmission antenna of the primary base station and each reception antenna of the UE by using, for example, correlation detection using a signal for channel estimation, and generates a channel matrix. Then, the UE feeds back each element of the channel matrix to the primary base station as channel information.

  Subsequently, when the start of CoMP is transmitted from the primary base station, the CoMP base station transmits a signal for channel estimation in the same manner as the primary base station. Then, the UE estimates a channel state between each transmission antenna of the CoMP base station and each reception antenna of the UE using the channel estimation signal, and generates a channel matrix. However, the UE does not feed back this channel matrix.

  The primary base station acquires a precoding matrix from the channel matrix received by feedback, for example, by using one of an inverse matrix, a generalized inverse matrix, and a vector perturbation technique. Thereafter, transmission data is acquired, and a transmission symbol vector x is acquired by performing processing such as modulation. Then, the primary base station transmits each element of the transmission signal vector obtained by multiplying the transmission symbol vector by the precoding matrix and the predetermined value (scalar) λ from each transmission antenna.

  On the other hand, since the CoMP base station has not received the feedback information, the transmission symbol vector x obtained by acquiring the same transmission data as the primary base station and transforming the transmission data by modulation or the like is used as it is as the transmission signal vector. As shown in FIG. In FIG. 2, it is described that the primary base station transfers the transmission data to the CoMP base station, but the present invention is not limited to this. For example, when a primary base station and a CoMP base station perform coordinated transmission, a higher-level device in the network may simultaneously transmit the same transmission data to these two base stations.

  The UE simultaneously receives a signal pre-encoded from the primary base station and multiplied by a predetermined value and a signal from the CoMP base station, and restores the transmitted symbol, that is, each element of the transmission symbol vector. .

のようになる。ここで、行列Ｉは単位行列である。この式から、ＵＥにおいて、受信信号ベクトルは、等価チャネル行列Ｈ_eq＝（λＩ＋Ｈ_S）が送信シンボルベクトルｘに乗じられた形式で受信される。したがって、所定値λを適切に選択することにより、この等価チャネル行列を対角優位行列とすることができる。したがって、適切に選択されたλを、プライマリ基地局がどのように取得するかが重要となる。以下では、プライマリ基地局がどのようにλを取得するかの手法について複数の例を挙げて説明する。 [Selection of predetermined value λ]
By the above processing, the received signal is

become that way. Here, the matrix I is a unit matrix. From this equation, at the UE, the received signal vector is received in a format in which the transmission channel vector x is multiplied by the equivalent channel matrix H _eq = (λI + H _S ). Therefore, by appropriately selecting the predetermined value λ, this equivalent channel matrix can be made a diagonal dominant matrix. Therefore, it is important how the primary base station obtains the appropriately selected λ. Hereinafter, a method of how the primary base station obtains λ will be described with a plurality of examples.

(Method 1. Selection of λ in UE)
In the first method, the UE selects λ and notifies the primary base station of λ determined together with feedback of channel information. Since the UE acquires the information of the channel matrix between the CoMP base station, if any λ is selected, it is the sum of the two channel matrices between the primary base station and the CoMP base station It can be seen whether the equivalent channel matrix is diagonally dominant. Therefore, the UE can select, for example, the minimum λ in which the equivalent channel matrix becomes a diagonal dominant matrix by calculation.

(Method 2. Selection of λ by empirical method)
In the second method, the primary base station holds a value of λ corresponding to the channel state in advance as a table, and determines the value of λ based on channel information fed back from the UE. The primary base station refers to the table using the value of the channel information (channel estimation value) fed back from the UE itself or a statistical value such as the average value of the channel estimation value, and specifies the corresponding λ value. . Note that the values held in the table are empirically obtained values, and the primary base station specifies λ that can make the equivalent channel matrix a diagonal dominant matrix for one channel state. And memorize it in a table. Note that an appropriate λ for each channel state needs to be specified in advance by learning. In this case, for example, the learning may be performed by receiving feedback of λ from the UE using the above-described method 1. Good.

(Method 3. Selection of λ by post-adjustment)
In the third method, the primary base station initially selects a small λ and transmits a signal, and then the UE determines whether the equivalent channel matrix is a diagonal dominant matrix and is not a diagonal dominant matrix. In this case, the primary base station is notified so as to increase the value of λ. When receiving the notification from the UE, the primary base station increases the value of λ by a predetermined amount, and thereafter generates a transmission signal vector using the λ. When the value of λ is not sufficient, the UE notifies the primary base station how much λ should be increased, and the primary base station may increase λ by the notified amount. In addition, when the UE determines that the signal reception is successful without changing the value of λ, the UE does not need to make a notification for increasing the value of λ.

(Method 4: Selection of λ by statistical method)
The fourth method is to select the optimal λ analytically (theoretical). This is based on the fact that the channel matrix between the CoMP base station and the UE follows a probability distribution. If each element of the channel matrix between the CoMP base station and the UE follows an independent and identical probability distribution (iid), λ can be selected as follows.

となる。なお、本数式の１段目から２段目への変形は確率分布の独立性により、２段目から３段目への変形は確率分布の同一性による。本数式から、チャネル行列のうち１つの行の確率のみについて、すなわち、以下の確率ｐ₀、

についてのみ検討すれば十分であることが分かる。この１つの行についての確率が１に近づけば、必然的にそのＮ乗も１に近づくからである。 First, as a generalized example, the probability that the matrix A of N rows and N columns is a diagonal dominant matrix is

It becomes. It should be noted that the transformation from the first stage to the second stage of the equation is based on the independence of the probability distribution, and the transformation from the second stage to the third stage is based on the identity of the probability distribution. From this equation, only the probability of one row of the channel matrix, ie, the probability p ₀ ,

It can be seen that it is sufficient to consider only. This is because if the probability for this one row is close to 1, the N-th power is necessarily close to 1.

とすると、確率ｐ₀は、

となる。ここで、Ｐｒ｛Ｘ＞Ｙ｝は、ＸがＹより大きい確率を表し、任意の値ｓを用いて、Ｐｒ｛Ｘ＞Ｙ｝＝Ｐｒ｛Ｘ＞ｓ，Ｙ≦ｓ｝と表すことができる。したがって、Ｐｒ｛Ｘ＞Ｙ｝は、

と書くことができる。ここで、ｆ_X(ｓ)はＸの確率密度関数（ｐｄｆ）であり、ｆ_Y(ｓ)はＹのｐｄｆである。Ｆ_Y(ｓ)はＹの累積分布関数（ＣＤＦ）である。 here,

Then the probability p ₀ is

It becomes. Here, Pr {X> Y} represents a probability that X is larger than Y, and can be expressed as Pr {X> Y} = Pr {X> s, Y ≦ s} using an arbitrary value s. . Therefore, Pr {X> Y} is

Can be written. Here, f _X (s) is a probability density function (pdf) of X, and f _Y (s) is a pdf of Y. F _Y (s) is a cumulative distribution function (CDF) of Y.

とすると、

となる。したがって、

であるため、λは、ｆ_X(ｓ)に対してのみ影響を与えることが分かる。このため、確率ｐ₀を、例えば、

のように書くことができる。 Here, the equivalent channel matrix H _eq , that is, the case where A = H _eq = λI + H _S is considered. Here, the equivalent channel matrix is obtained by adding a predetermined value λ to the diagonal component of the channel matrix between the CoMP base station and the UE. The channel matrix H _S between the CoMP base station and the UE is

Then,

It becomes. Therefore,

Therefore, it can be seen that λ affects only f _x (s). For this reason, the probability p ₀ is, for example,

Can be written as

Therefore, for example, the primary base station or the UE can statistically calculate λ so that the equivalent channel matrix becomes a diagonal dominant matrix with a predetermined probability. That is, the primary base station or the UE can calculate the minimum λ that satisfies the above-described p ₀ ^N with a predetermined probability. In other words, the minimum λ with which the probability p ₀ satisfies the Nth root of the predetermined probability is calculated. The predetermined probability may be specified according to the communication status. For example, when it is desired to reduce the transmission power, the predetermined probability may be set low, or the predetermined probability may be set high under the condition where the communication quality is most important.

  When the primary base station performs this calculation, the primary base station preliminarily calculates the average value and variance of the channel matrix between the CoMP base station and the UE, for example, when the channel follows a Gaussian distribution. Get from. The primary base station acquires from the UE not only the average and the variance, but the primary base station may acquire a parameter for specifying the distribution according to the distribution that the channel follows. In addition, when the channel follows one of a plurality of distribution candidates, the primary base station may also acquire information specifying the distribution followed by the channel matrix between the CoMP base station and the UE from the UE. Good. In the UE, λ can be easily obtained by the above-described method 1. However, when the channel fluctuation is fast, the probability that the equivalent channel matrix is a diagonal dominant matrix is increased even for the channel after the change. Therefore, λ may be calculated statistically by this method.

  The above method will be described below using a specific example.

であるものとする。ここで、ｈ₁₁も平均がゼロで、分散が１のガウス分布に従う（すなわち、ｈ₁₁〜Ｎ（０，１）である）ため、λ＋ｈ₁₁は、平均がλで分散が１の分布に従うこととなる。そして｜λ＋ｈ₁₁｜は、正の値のみを有するため、折り重ねられた正規分布Ｆｏｌｄｅｄ（λ，１）に従うこととなる。折り重ねられた正規分布Ｆｏｌｄｅｄ（λ，１）のｐｄｆは、

で与えられる。 Let the channel matrix between the CoMP base station and the UE follow a Gaussian distribution with a mean of zero and a variance of one. That is,

Suppose that Here, since h ₁₁ also has a Gaussian distribution with an average of zero and a variance of 1 (ie, h _{11 to} N (0,1)), λ + h ₁₁ follows a distribution with an average of λ and a variance of 1. It becomes. Since | λ + h ₁₁ | has only a positive value, it follows the folded normal distribution Folded (λ, 1). The pdf of the folded normal distribution Folded (λ, 1) is

Given in.

となる。ただし、パラメータｍ及びΩは、Ｅ｛・｝を期待値、Ｖａｒ｛・｝を分散とする場合に、

である。なお、仲上ｍ分布のＣＤＦは、

であることが知られている。なおΓ（・）はガンマ関数である。 On the other hand, for an arbitrary j, since h _{1j to} N (0, 1), Y follows the Nakagami m distribution. That is, when Nakagami m distribution with parameters m and Ω is expressed by Nakagami (m, Ω),

It becomes. However, when the parameters m and Ω are E {·} as an expected value and Var {·} as a variance,

It is. The CDF of Nakagami m distribution is

It is known that Note that Γ (·) is a gamma function.

のように得られる。したがって、例えば、０．９５（９５％）の確率で等価チャネル行列が対角優位行列であるには、数式

を解くことにより、λを算出することができる。 From the above, p ₀ is

Is obtained as follows. Thus, for example, if the equivalent channel matrix is a diagonal dominant matrix with a probability of 0.95 (95%)

Λ can be calculated by solving.

Note that λ can be specified in advance for each piece of information that specifies the probability that the equivalent channel matrix should be a diagonal dominant matrix and the distribution that the channel matrix between the CoMP base station and the UE follows. For example, as shown in FIG. 3, the primary base station determines λ for a plurality of probabilities p ₀ ^{N with} respect to information specifying a distribution that a channel matrix between one (one set) CoMP base station and the UE follows. May be held as a table. In this way, it is not necessary to perform the above calculation every time communication is performed.

であり、ＣｏＭＰ基地局とＵＥとの間のチャネル行列が、

であるものとする。このとき、チャネル行列Ｈ_Pの逆行列は、

である。ここで、λ＝２とする。このとき、プライマリ基地局は、送信シンボルベクトルｘに、λＨ_P ^-1を乗じて送信信号ベクトルｘ’を生成して、ＵＥへ向けて送信する。このとき、等価チャネル行列Ｈ_eqは、

となる。ＵＥにおいては、送信シンボルベクトルｘに、この等価チャネル行列Ｈ_eqが乗じられ、雑音ベクトルｚが加えられた受信されたように、各受信アンテナにおいて信号が観測される。ここで、等価チャネル行列Ｈ_eqの各要素の大きさは、

である。したがって、この行列の対角成分とその他の成分とを比較することにより、この等価チャネル行列は、対角優位行列であることが分かる。なお、等価チャネル行列Ｈ_eqの逆行列は、

である。 [Numeric example of sending and receiving]
Next, a transmission / reception operation when feedback is actually performed only to the primary base station will be described using numerical examples. In the following example, a case will be described in which the number of transmission antennas between the primary base station and the CoMP base station is four and the number of reception antennas at the UE is four. Here, the channel matrix between the primary base station and the UE is

And the channel matrix between the CoMP base station and the UE is

Suppose that At this time, the inverse matrix of the channel matrix H _P is

It is. Here, λ = 2. At this time, the primary base station generates a transmission signal vector x ′ by multiplying the transmission symbol vector x by λH _P ⁻¹ , and transmits the transmission signal vector x ′ to the UE. At this time, the equivalent channel matrix H _eq is

It becomes. In the UE, a signal is observed at each receiving antenna as if the transmission symbol vector x was multiplied by the equivalent channel matrix H _eq and the noise vector z was added. Here, the size of each element of the equivalent channel matrix H _eq is

It is. Therefore, by comparing the diagonal component of this matrix with other components, it can be seen that this equivalent channel matrix is a diagonal dominant matrix. The inverse matrix of the equivalent channel matrix H _eq is

It is.

Here, it is assumed that the transmission symbol vector is x = (1.0 + 1.0i−1.0 + 3.0i 1.0 + 3.0i−1.0−1.0i) ^T. Note that the superscript T represents transposition of a matrix. Further, the noise vector is assumed to be z = (− 0.3146−0.1454i 0.0963 + 0.0802i 0.1784-0.0275i−0.0619 + 0.1326i) ^T.

が得られる。この結果から、上述の処理によって得られるシンボルベクトルが、送信シンボルベクトルｘ＝（１．０＋１．０ｉ −１．０＋３．０ｉ １．０＋３．０ｉ −１．０−１．０ｉ）^Tとほぼ一致していることが分かる。なお、等価チャネル行列Ｈ_eqの逆行列は、ＵＥにおいて、ＣｏＭＰ基地局との間のチャネル行列Ｈ_Sとλとから算出することができる。なお、ここでは等価チャネル行列の逆行列を受信信号ベクトルに乗じるが、等価チャネル行列をＱＲ分解して、判定帰還型等化により、送信シンボルベクトルｘの各要素を復元してもよい。 At this time, when the reception signal vector y is multiplied by the inverse matrix of the above-described equivalent channel matrix H _eq to the reception signal,

Is obtained. From this result, the symbol vector obtained by the above-described processing almost coincides with the transmission symbol vector x = (1.0 + 1.0i−1.0 + 3.0i 1.0 + 3.0i−1.0−1.0i) ^T. I understand that Note that the inverse matrix of the equivalent channel matrix H _eq can be calculated from the channel matrix H _S and λ with the CoMP base station in the UE. Here, the reception signal vector is multiplied by the inverse matrix of the equivalent channel matrix, but each element of the transmission symbol vector x may be restored by QR decomposition of the equivalent channel matrix and decision feedback equalization.

  Thus, it can be seen that by converting the equivalent channel matrix into a diagonal dominant matrix, it is possible to perform accurate signal reception and transmission symbol recovery in the UE (receiving apparatus). At this time, since the UE feeds back channel information only to the primary base station and does not feed back to the CoMP base station, the amount of feedback information is larger than in the case of feeding back channel information to both base stations. Can be halved. Further, when k CoMP base stations exist, channel information is not fed back to these CoMP base stations, so the amount of feedback information is 1 as compared with the case where channel information is fed back to all CoMP base stations. / (K + 1). Furthermore, the CoMP base station does not need to perform processing specific to this coordinated transmission. For this reason, the processing amount of the CoMP base station can be suppressed to a low level, and as a result, the delay time is short, so that it is easy to ensure synchronization with the primary base station for cooperative transmission. Furthermore, since the CoMP base station transmits the transmission symbol vector as it is, the power of the transmission signal does not increase due to pre-encoding.

となる。ここで、ｔｒ{・}は行列のトレース（対角成分の和）を表し、上付きのＨは行列の共役転置を表す。ここで、上式の右辺第１項及び第２項は、常に正の値となる。また、右辺第３項は、平均値は０となる。したがって、上述の手法によれば、平均して、プライマリ基地局が単独で信号を送信する場合と比べて、上式の右辺第２項の分だけ受信電力を増やすことが可能となる。したがって、上述の手法によって、協調送信による効果を得ながら、フィードバック情報量を減らし、かつ、ＵＥにおいて正確な信号の受信を行うことが可能となる。 Moreover, the effect of the coordinated transmission that the reception power can be secured sufficiently high in the cell edge UE by transmitting the primary base station and the CoMP base station at the same time can be maintained as it is. That is, when the equivalent channel matrix is represented by λI + H _S , the expected value of this power is

It becomes. Here, tr {·} represents the trace of the matrix (sum of diagonal components), and the superscript H represents the conjugate transpose of the matrix. Here, the first term and the second term on the right side of the above formula are always positive values. The average value of the third term on the right side is 0. Therefore, according to the above-described method, on average, the received power can be increased by the amount of the second term on the right side of the above equation, compared to the case where the primary base station transmits a signal alone. Therefore, according to the above-described method, it is possible to reduce the amount of feedback information and obtain an accurate signal at the UE while obtaining the effect of coordinated transmission.

In the above equation, it has been explained that, on average, the effect of coordinated transmission can be obtained. However, in some cases, transmission from a CoMP base station is not performed in order to obtain sufficient communication quality at each transmission / reception ( Or the transmission power may be kept low. For example, when the trace of the channel matrix H _S between the UE and the CoMP base station has a negative value, the UE does not transmit a signal from the CoMP base station or decreases the transmission power to the primary base station. You can be notified. In addition to this, when tr {(H _S ) ² } <tr {λH _S + λH _S ^H } holds, the UE does not transmit a signal from the CoMP base station or lowers the transmission power. The primary base station may be notified. These cases correspond to the case where the signal from the CoMP base station can act as interference in the UE. In such a case, the coordinated transmission is not performed or the influence from the CoMP base station is minimized. The communication quality of the entire system can be further improved. Similarly, when there are a plurality of CoMP base stations, the primary base station may be notified not to transmit a signal from a CoMP base station that can be an interference source. In addition, when there are a plurality of CoMP base stations, channel information may be fed back to a part of the CoMP base stations, and feedback may not be performed for the remaining CoMP base stations. As a result, feedback to some CoMP base stations is performed to improve communication quality, and feedback to the remaining CoMP base stations is not performed, so that the amount of feedback information can be reduced.

Further, λI + H _S and λI + H _P are compared, and when the latter can perform communication with higher quality, feedback may be performed only to the CoMP base station. Alternatively, in such a case, the above method may be applied by handing over the UE to the CoMP base station and treating the CoMP base station as a primary base station. Thereby, communication quality can be made better.

<< Embodiment 2 >>
In the first embodiment, the configuration in which the channel information is notified to the primary base station has been described. However, in the present embodiment, not the channel information itself but the information on the resulting matrix after performing a predetermined process on the channel matrix. Notify the primary base station. Hereinafter, an example in which singular value decomposition is used as the predetermined process will be described.

のように、ユニタリ行列Ｕ_P及びＶ_Pと、対角行列Σ_Pとに分解する。ここで、Σ_Pの対角成分は、１行目からＮ行目に向けて順に小さくなる正の値をとる。そして、ＵＥは、チャネル行列ではなく、ユニタリ行列Ｖ_Pをプライマリ基地局へフィードバックする。なお、本実施形態においても、ＣｏＭＰ基地局へはフィードバックは行わない。 In the present embodiment, when the UE acquires a channel matrix with the primary base station, the UE subsequently performs singular value decomposition of the channel matrix. That is, the channel matrix H _P is

As shown, the unitary matrices U _P and V _P and the diagonal matrix Σ _P are decomposed. Here, the diagonal component of Σ _P takes a positive value that decreases in order from the first row to the Nth row. Then, the UE feeds back the unitary matrix V _P instead of the channel matrix to the primary base station. Also in this embodiment, feedback is not performed to the CoMP base station.

The primary base station multiplies the transmission symbol vector x by this unitary matrix V _P and a predetermined value λ to form a transmission signal vector x ′, and directs each element of the transmission signal vector x ′ = λV _P x to the UE. Transmit from each transmit antenna. Also in this embodiment, since there is no information fed back to the CoMP base station, the CoMP base station transmits the transmission symbol vector as it is.

となる。その後、ＵＥは、この受信信号ベクトルの左から、ユニタリ行列Ｕ_Pの共役転置行列Ｕ_P ^Hを乗じる。その結果、受信信号ベクトルｙは、

のように変形される。したがって、本実施形態においては、λΣ_P＋Ｕ_P ^HＨ_Sが等価チャネルベクトルＨ_eqとなる。Σ_Pが非負の値を対角要素とする対角行列であるため、十分な大きさのλに対して、等価チャネル行列を対角優位行列とすることが可能となる。その後の処理は、上述のように、等価チャネル行列の逆行列を変形後の受信信号ベクトルに乗じてもよいし、ＱＲ−ＤＦＥ手法を適用してもよい。 At this time, the received signal vector y representing the received signal at the UE is

It becomes. Thereafter, UE, from the left of the reception signal vector, multiplied by the conjugate transpose matrix U _P ^H of the unitary matrix U _P. As a result, the received signal vector y is

It is transformed as follows. Accordingly, in the present ^{_{embodiment, λΣ P + U P H H}} S is the equivalent channel vector H _eq. Since Σ _P is a diagonal matrix having a non-negative value as a diagonal element, the equivalent channel matrix can be a diagonal dominant matrix for a sufficiently large λ. In the subsequent processing, as described above, the transformed received signal vector may be multiplied by the inverse matrix of the equivalent channel matrix, or the QR-DFE method may be applied.

Since U _P ^H is a unitary matrix, noise is not excited even if U _P ^H is multiplied by noise vector z, and the noise vector is maintained at the same power.

The method for determining the predetermined value λ is the same as in the first embodiment. However, in this case, rather than λI + H _S, should define the λ for the purpose of λΣ _P + U _P ^{H H} _S is a diagonal dominant matrix, so that the selection procedure of λ is slightly changed. For example, according to the procedure 1 described above, since the value of the diagonal component of Σ _P is different for each row, the UE compares the size of the diagonal component with the sum of the sizes of the other components for each row, The minimum λ that becomes a diagonal dominant matrix is selected.

を満たすコードワードＷ_kをコードブックΩから探索し、コードワードＷ_kを特定する値“ｋ”を、プライマリ基地局へフィードバックする。これにより、１つの値を送るだけでフィードバックが完了するため、フィードバック情報量を大幅に削減することができる。 In this embodiment, the unitary matrix _VP is fed back. However, the unitary matrix itself may not be fed back. For example, the code book Ω = {W ₁ ,..., W _q } is shared between the UE and the primary base station, and the UE uses information identifying the code word W _k closest to the unitary matrix V _P. You may notify to a primary base station. That is, the UE

A code word W _k satisfying the above is searched from the code book Ω, and a value “k” specifying the code word W _k is fed back to the primary base station. Thereby, since feedback is completed only by sending one value, the amount of feedback information can be greatly reduced.

となる。したがって、この場合も、上述と同様に、ユニタリ行列Ｕ_Pの共役転置行列Ｕ_P ^Hを受信信号ベクトルの左から乗じることにより、チャネル行列を対角優位行列化することができる。その後の処理は上述の通りである。 In this case, the primary base station transmits the codeword W _k and the predetermined value λ by multiplying the transmission symbol vector x. That is, the primary base station transmits each element of the transmission signal vector x ′ = λW _k x from each transmission antenna. At this time, the received signal vector y at the UE is

It becomes. Therefore, in this case as well, the channel matrix can be converted into a diagonal dominant matrix by multiplying the conjugate transpose matrix U _P ^H of the unitary matrix U _P from the left of the received signal vector, as described above. The subsequent processing is as described above.

  Therefore, according to the coordinated transmission method of the present embodiment, the equivalent channel matrix in the UE becomes a diagonal dominant matrix, so high-quality communication can be performed by multiplying the inverse matrix of the equivalent channel matrix or using QR-DFE. Can be secured. Also, by specifying a unitary matrix to be fed back using a codebook shared by the UE and the primary base station, the amount of feedback information can be greatly reduced.

  In this embodiment, the singular value decomposition is performed. However, the present invention is not limited to this, and any method can be used as long as the channel matrix is represented by a matrix product of a diagonal matrix and a matrix multiplied from the left and right. There may be. In this case, the UE feeds back a matrix multiplied from the right of the diagonal matrix, and the primary base station can generate a transmission signal vector by multiplying the transmission symbol vector by the inverse matrix of the matrix. And UE can acquire the effect similar to the above-mentioned case by multiplying a received signal by the inverse matrix of the matrix multiplied from the left of a diagonal matrix from the left.

Similarly to the first embodiment, in some cases, a signal may not be transmitted from the CoMP base station. That is, the UE does not perform transmission (stops) from the CoMP base station or lowers transmission power when U _P ^H H _S that is a channel matrix component with the CoMP base station is considered to act as interference. As such, the primary base station may be notified. Similarly, when there are a plurality of CoMP base stations, it is possible to perform control so that transmission from a CoMP base station that can be an interference source is not performed or power is minimized. If the UE determines that the communication quality is better when the channel matrix with the CoMP base station is decomposed than when the channel matrix with the primary base station is decomposed, the CoMP The unitary matrix V obtained by decomposition may be transmitted to the base station. Thereby, communication quality can be further improved.

  Each process described above may be realized by dedicated hardware, or may be realized by software by causing a computer including a processor such as a CPU to execute a program that realizes the process.

  Further, the above-described processing can be applied when a plurality of transmitting stations cooperatively transmit signals to individual receiving stations, and the relationship between the transmitting station and the receiving station is limited to the relationship between the base station and the UE. It is not something.

Claims (19)

A wireless communication system in which a plurality of transmitting stations having a plurality of transmitting antennas and a single receiving station having a plurality of receiving antennas perform wireless communication by multiple input multiple output (MIMO),
The receiving station is
Obtaining a channel matrix having a value indicating a channel state between each of the plurality of transmitting antennas and each of the plurality of receiving antennas between each of the plurality of transmitting stations and the receiving station as an element; Acquisition means;
Feedback means for feeding back information on the channel matrix between the part of the transmitting station and the receiving station to a part of the plurality of transmitting stations;
Have
Some of the transmitting stations are
Based on information on the channel matrix, pre-encoding a transmission symbol vector having transmission symbols as elements to generate a transmission signal vector;
A part of the transmitting station transmits each element of the transmission signal vector generated by the generating means from each of the plurality of transmitting antennas;
The transmitting station that did not receive feedback transmits each element of the transmission signal vector from each of the plurality of transmission antennas, using the transmission symbol vector as the transmission signal vector.
The receiving station further includes a restoring means for restoring the transmission symbol vector based on signals from the plurality of transmitting stations and the channel matrix between the transmitting station that has not received the feedback and the receiving station. Have
A wireless communication system. The information on the channel matrix is information on each element of the channel matrix between a part of the transmitting station and the receiving station,
The generating means generates the transmission signal vector by multiplying the transmission symbol vector by an inverse matrix of the channel matrix.
The wireless communication system according to claim 1. The information about the channel matrix is obtained when the channel matrix between a part of the transmitting station and the receiving station is expressed by a matrix product of a diagonal matrix and a matrix multiplied from the left and right of the diagonal matrix. , Information of matrix elements to be multiplied from the right of the diagonal matrix,
The generating means generates the transmission signal vector by multiplying the transmission symbol vector from the left by an inverse matrix of the matrix multiplied from the right,
The restoration means is based on a vector obtained by multiplying a reception signal vector having elements received from signals received from the plurality of transmitting stations as an inverse matrix of a matrix multiplied from the left of the diagonal matrix in the matrix product, from the left. Recovering the transmitted symbol vector;
The wireless communication system according to claim 1. The receiving station further comprises holding means for holding a plurality of candidates of a matrix to be fed back;
The feedback means selects one matrix from the plurality of candidates that is closest to the matrix multiplied from the right of the diagonal matrix, and feeds back information that identifies one of the candidates to a part of the transmitting station. ,
The wireless communication system according to claim 3. When the receiving station receives only the signal transmitted by the part of the transmitting station that has received the feedback, the communication quality is the same as the signal transmitted by the part of the transmitting station that has received the feedback and the transmission that has not received the feedback. Notification that notifies the transmitting station that did not receive the feedback that the transmission from the transmitting station that did not receive the feedback is not performed if the communication quality is higher than the signal that is received simultaneously with the signal transmitted by the station Further having means,
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. The transmitting station is a base station, and the receiving station is a user terminal;
The feedback means feeds back information on the channel matrix between the base station and the user terminal to a base station that develops a serving cell that develops a cell accommodating the user terminal, and a channel matrix to other base stations. Do not provide feedback on
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. The transmitting station is a base station, and the receiving station is a user terminal;
The feedback means feeds back information on the channel matrix between the base station and the user terminal to a base station that develops a serving cell that develops a cell accommodating the user terminal, and a channel matrix to other base stations. Without feedback on information about
The notifying means notifies the other base station that the signal from the other base station is not transmitted via the base station that deploys the serving cell.
The wireless communication system according to claim 5. The generating means multiplies a vector obtained by pre-encoding the transmission symbol vector by a predetermined value to generate a transmission signal vector.
The wireless communication system according to claim 1, wherein the wireless communication system is a wireless communication system. The receiving station further includes a determining unit that determines the predetermined value based on the channel matrix with a transmitting station that does not receive feedback,
The feedback means feeds back the predetermined value determined by the determining means to a part of the transmitting station together with information on the channel matrix between the part of the transmitting station and the receiving station.
The wireless communication system according to claim 8. The part of the transmitting station uses the information about the channel matrix between the part of the transmitting station and the receiving station that are fed back, and the predetermined value corresponding to the information about the channel matrix and the information about the channel matrix And determining means for determining the predetermined value corresponding to the information related to the channel matrix by referring to a table holding
The wireless communication system according to claim 8. In the precoding, a precoding matrix is calculated by any one of a calculation of an inverse matrix of a channel matrix between a part of the transmitting station and the receiving station, a calculation of a generalized inverse matrix, or a vector perturbation method. , By multiplying the transmission symbol vector by the precoding matrix,
A part of the transmitting station or the receiving station has a matrix obtained by adding the predetermined value to a diagonal component of a channel matrix between the transmitting station and the receiving station that does not receive feedback. A table that holds the probability of becoming a diagonal dominant matrix and the predetermined value corresponding to the probability, the probability that the matrix should be a diagonal dominant matrix, and between the transmitting station that does not receive feedback and the receiving station And determining means for determining the predetermined value corresponding to the information related to the channel matrix by referring to the information related to the channel matrix.
The wireless communication system according to claim 8. The probability is determined based on a probability distribution followed by each element of a channel matrix between the transmitting station and the receiving station that do not receive feedback.
The wireless communication system according to claim 11. A transmission apparatus in a wireless communication system in which a plurality of transmission apparatuses having a plurality of transmission antennas and a single reception apparatus having a plurality of reception antennas perform wireless communication by multiple input multiple output (MIMO),
From the receiving device, information on a channel matrix having a value indicating a channel state between each of the plurality of transmitting antennas and each of the plurality of receiving antennas between the transmitting device and the receiving device. When receiving feedback, based on the information about the channel matrix, generation means for pre-encoding a transmission symbol vector having transmission symbols as elements to generate a transmission signal vector;
When receiving the feedback, each element of the transmission signal vector generated by the generating means is transmitted from each of the plurality of transmission antennas. When not receiving the feedback, the transmission symbol vector is transmitted by the transmission unit. Transmitting means for transmitting each of the elements of the transmission signal vector as a signal vector from each of the plurality of transmission antennas;
A transmission device comprising: The generating means multiplies a vector obtained by pre-encoding the transmission symbol vector by a predetermined value to generate a transmission signal vector.
The transmission apparatus according to claim 13. A plurality of transmission apparatuses having a plurality of transmission antennas and one reception apparatus having a plurality of reception antennas are reception apparatuses in a wireless communication system that performs wireless communication by multiple input multiple output (MIMO),
A channel matrix having a value indicating a state of a channel between each of the plurality of transmission antennas and each of the plurality of reception antennas between each of the plurality of transmission apparatuses and the reception apparatus is obtained. Acquisition means;
Feedback means for feeding back information on the channel matrix between the part of the transmitting apparatus and the receiving apparatus to a part of the plurality of transmitting apparatuses;
A part of the transmission apparatus generates a transmission symbol vector having transmission symbols as elements based on information on the channel matrix and generates transmission symbol vectors transmitted from each of the plurality of transmission antennas. Receiving means for simultaneously receiving, by the plurality of reception antennas, elements of the transmission signal vector transmitted from each of the plurality of transmission antennas by using the transmission symbol vector as the transmission signal vector; When,
Restoring means for restoring the transmission symbol vector based on the received signal and the channel matrix between the receiving device and the receiving device that did not receive the feedback;
A receiving apparatus comprising: Communication quality when only a signal transmitted by a part of the transmission apparatus that has received feedback is received, a signal transmitted by a part of the transmission apparatus that has received feedback, and a signal transmitted by a transmission apparatus that has not received feedback If the communication quality is higher than when receiving simultaneously, the signal transmission from the transmission device that did not receive the feedback is not performed, further comprising a notification means for notifying the transmission device that did not receive the feedback,
The receiving device according to claim 15. A communication method in a wireless communication system in which a plurality of transmitting stations having a plurality of transmitting antennas and a single receiving station having a plurality of receiving antennas perform wireless communication by multiple input multiple output (MIMO),
In the receiving station,
A channel whose element is a value indicating a state of a channel between each of the plurality of transmitting antennas and each of the plurality of receiving antennas between each of the plurality of transmitting stations and the receiving station; An acquisition step of acquiring a matrix;
A feedback step in which feedback means feeds back information on the channel matrix between a part of the transmitting station and the receiving station to a part of the plurality of transmitting stations;
Have
In some of the transmitting stations,
A generating step for generating a transmission signal vector by pre-encoding a transmission symbol vector having a transmission symbol as an element based on information on the channel matrix; and
A transmission step of transmitting each of the elements of the transmission signal vector generated in the generation step from each of the plurality of transmission antennas;
Have
At the transmitting station that did not receive feedback,
The transmission means includes the transmission step of transmitting each of the elements of the transmission signal vector from each of the plurality of transmission antennas using the transmission symbol vector as the transmission signal vector,
In the receiving station,
The restoration means further comprises a restoration step of restoring the transmission symbol vector based on signals from the plurality of transmitting stations and the channel matrix between the transmitting station and the receiving station that did not receive the feedback. ,
A communication method characterized by the above. A transmission method in a transmission apparatus of a wireless communication system in which a plurality of transmission apparatuses having a plurality of transmission antennas and a single reception apparatus having a plurality of reception antennas perform wireless communication by multiple input multiple output (MIMO),
A channel whose element is a value indicating a state of a channel between each of the plurality of transmission antennas and each of the plurality of reception antennas between the transmission device and the reception device; A generation step of generating a transmission signal vector by pre-encoding a transmission symbol vector having a transmission symbol as an element based on information on the channel matrix when receiving feedback of information on the matrix;
When the transmission means receives the feedback, each of the elements of the transmission signal vector generated in the generation step is transmitted from each of the plurality of transmission antennas. When the transmission means does not receive the feedback, the transmission symbol Transmitting the vector as the transmission signal vector, and transmitting each of the elements of the transmission signal vector from each of the plurality of transmission antennas;
A transmission method characterized by comprising: A reception method in a reception apparatus of a wireless communication system in which a plurality of transmission apparatuses having a plurality of transmission antennas and a single reception apparatus having a plurality of reception antennas perform wireless communication by multiple input multiple output (MIMO),
A channel whose element is a value indicating a state of a channel between each of the plurality of transmission antennas and each of the plurality of reception antennas between each of the plurality of transmission devices and the reception device. An acquisition step of acquiring a matrix;
A feedback step in which feedback means feeds back information about the channel matrix between a part of the transmission device and the reception device to a part of the plurality of transmission devices;
A transmission signal generated by a receiving unit, which is generated by a part of the transmission apparatus by pre-encoding a transmission symbol vector having transmission symbols as elements based on information on the channel matrix and transmitted from each of the plurality of transmission antennas A transmission apparatus that has not received feedback uses the transmission symbol vector as the transmission signal vector, and the transmission signal vector element transmitted from each of the plurality of transmission antennas is simultaneously transmitted by the plurality of reception antennas. A receiving process for receiving;
A restoring step for restoring the transmission symbol vector based on the received signal and the channel matrix between the transmitting device and the receiving device that did not receive the feedback;
A transmission device comprising:

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