KR20100028859A - Apparatus and method for adaptive coloring codebook in a multiple input multiple output wireless communication system - Google Patents

Abstract

PURPOSE: In a MIMO(Multi-Input Multi-Output) wireless telecommunications system, an adaptive codebook coloring apparatus and method decompose a correlation matrix information of channel to the coefficient of correlation and phase. In that way, the beam forming is implemented in consideration of correlation between antennas. CONSTITUTION: A correlation matrix of channel calculates(303). If the feedback point of time of the long-term information comes, a feedback of a long-term information and one or more coefficient of correlation operates(305~311). One or more coefficient of correlation constitutes each element of the correlation matrix. Using channel and correlation matrix, the weighted value vector is selected. If the feedback point of time of the short-term information comes, the feedback of the short-term information operates(313~317). The short-term information shows the selection result of the weight vector.

Description

APPARATUS AND METHOD FOR ADAPTIVE COLORING CODEBOOK IN A MULTIPLE INPUT MULTIPLE OUTPUT WIRELESS COMMUNICATION SYSTEM

The present invention relates to a multiple input multiple output (MIMO) wireless communication system, and more particularly, to an apparatus and method for adaptively coloring codebooks in a multiple input and output wireless communication system.

Recently, as the demand for high-speed and high-quality data transmission has increased, a multiple input multiple output (MIMO) wireless communication system using a plurality of transmit / receive antennas has been attracting attention as one of techniques for satisfying this. The multiple input / output technology is a technology that can significantly improve channel capacity than when using a single antenna by performing communication using a plurality of streams through a plurality of antennas. For example, if both transmitter and receiver use M transmit and receive antennas, and the channels between the antennas are independent, and the bandwidth and the total transmit power are fixed, the average channel capacity is increased by M times compared to a single antenna. .

Spatial Multiplexing (SM) among the multiple input / output technologies forms a plurality of spatial subchannels between one transmitting end and one receiving end, and transmits data independently through each spatial subchannel so that each link To increase the data transfer capacity. In the spatial multiplexing scheme, a maximum transmission capacity is obtained by performing power allocation by spatial filling on spatial subchannels formed by singular vectors of a channel matrix between a transmitter and a receiver. In addition, Space Division Multiple Access (SDMA) is a method of increasing the transmission capacity of a system by simultaneously forming spatial subchannels in each of a plurality of receivers and transmitting data streams through each spatial subchannel. . In the spatial division multiple access scheme, ZF is formed to form a spatial subchannel to each link with a maximum singular vector of a downlink channel from a transmitter to each receiver, and to suppress interference between spatial subchannels of receivers simultaneously transmitted. By using zero-forcing or minimum-mean square error (MMSE) techniques, system transmission capacity is increased.

Therefore, the performance of the spatial multiplexing scheme and the spatial division multiple access scheme depends on how accurately the transmitting end knows the singular vector of the downlink channel of each receiving end. However, since a large amount of uplink feedback information is required to feed back the instantaneously changing downlink channel matrix information to a transmitter, methods using a vector codebook have been proposed. The vector codebook consists of G vectors representing singular vectors of each downlink channel, and the transmitter and the receiver must know the vector codebook in advance. Each receiving end selects a vector most similar to the singular vector of the estimated downlink channel from the codebook and delivers the index of the selected vector to the transmitting end. Therefore, only the number of bits of information as long as the log ₂ G is fed back. Accordingly, the transmitter regards the vector indicated by the feedback index as the singular vector of the corresponding downlink channel and performs signal processing for beamforming or spatial division multiple access.

As described above, by reducing the amount of feedback information by using a previously promised codebook, signal processing is performed for improving the performance of the multi-input / output technique with only a small amount of overhead. However, when using multiple transmit antennas or multiple receive antennas, there is correlation between the antennas. The correlation between the antennas varies depending on the arrangement of the antennas and the channel environment. In this case, the pre-defined formal codebook may not accurately represent the singular vector of the downlink channel of the receiver. Therefore, there is a need for an alternative for adaptively optimizing the codebook according to the arrangement of the antennas and the channel environment.

Accordingly, an object of the present invention is to provide an apparatus and method for adaptively optimizing a codebook according to an arrangement type and a channel environment of antennas in a multiple input multiple output (MIMO) wireless communication system.

Another object of the present invention is to provide an apparatus and method for feeding back correlation matrix information of a channel for coloring a codebook in a multiple input / output wireless communication system.

Another object of the present invention is to provide an apparatus and method for minimizing the amount of correlation matrix information of a channel in a multiple input / output wireless communication system.

Another object of the present invention is to provide an apparatus and method for expressing the correlation matrix by using the correlation coefficients and the phase constituting elements of the correlation matrix of the channel in a multiple input / output wireless communication system.

Another object of the present invention is to provide an apparatus and method for feeding back the correlation matrix information by using a quadratic function representing a distribution of correlation coefficients constituting elements of a channel correlation matrix in a multiple input / output wireless communication system.

According to a first aspect of the present invention for achieving the above object, the operation method of the receiver in a multiple input multiple output (MIMO) wireless communication system, the process of calculating the correlation matrix of the channel with the transmitter, and the long term when a time point for feeding back (long-term) information arrives, feeding back the long term information indicating at least one correlation coefficient and a phase constituting each element of the correlation matrix, and using the channel and the correlation matrix And selecting a weight vector, and feeding back the short term information indicating a result of selecting the weight vector when a time point for feeding back the short-term information arrives.

According to a second aspect of the present invention for achieving the above object, a method of operating a transmitter in a multiple input-output wireless communication system, the long term information indicating at least one correlation coefficient and phase constituting each element of the correlation matrix fed back from the receiver A process of reconstructing the correlation matrix using the at least one correlation coefficient and the phase, coloring a vector codebook using the correlation matrix, and among the weight vectors in the colored vector codebook. And identifying a weight vector for beam shaping the transmission signal to the receiver according to the short term information fed back from the receiver.

According to a third aspect of the present invention for achieving the above object, in a multiple input / output wireless communication system, a receiving end device includes a calculator for calculating a correlation matrix of a channel with a transmitting end, and when the time point for feeding back the long term information arrives, the correlation matrix A first generator for outputting the long term information representing at least one correlation coefficient and a phase constituting each element of the selector; a selector for selecting a weight vector using the channel and the correlation matrix; and a time point for feeding back the short term information The method may include a second generator configured to output the short term information indicating a result of selecting the weight vector.

According to a fourth aspect of the present invention for achieving the above object, in a multiple input-output wireless communication system, a transmitting end device confirms long term information indicating at least one correlation coefficient and phase constituting each element of a correlation matrix fed back from a receiving end. A decompressor for reconstructing the correlation matrix using the at least one correlation coefficient and the phase, a modifier for coloring a vector codebook using the correlation matrix, and a weight vector in the colored vector codebook, And a selector for identifying a weight vector for beamforming the transmission signal to the receiver according to the short term information fed back from the receiver.

Multiple Input Multiple Output (MIMO) In a wireless communication system, the correlation matrix information of a channel, which is information necessary for coloring a codebook, is decomposed into a correlation coefficient and a phase in consideration of the influence of the correlation between antennas, and the correlation coefficient and By feeding back the phase codebook index in a long term, beamforming in consideration of the correlation between antennas can be performed with only a small overhead.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that the specific description of the related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Hereinafter, a technology for optimizing codebooks according to environmental changes in a multiple input multiple output (MIMO) wireless communication system will be described. Hereinafter, the present invention will be described using an Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) scheme as an example. The same applies to other wireless communication systems.

The general codebook assumes that a singular vector of channels is uniformly distributed in space. For example, a Random Vector Quantization (RVQ) codebook such as a Grassmannian codebook corresponds to this. Codebooks composed of vectors with uniform distribution show optimal performance in an environment without spatial correlation. However. If spatial correlation exists, the singular vector of the actual channel may appear only in a specific range of space. In this case, using a codebook composed of vectors having the uniform distribution degrades performance. Accordingly, by modifying the vectors constituting the codebook to be concentrated within the specific range by reflecting the spatial correlation, a codebook suitable for a corresponding channel can be constructed, which is called coloring. The coloring may be expressed as Equation 1 below.

은 수신단k의 채널 특성에 따라 컬러링된 코드북의 m번째 가중치 벡터, 상기

는 수신단k의 상관 행렬, 상기

은 코드북의 m번째 가중치 벡터, 상기

는 코드북에 포함된 가중치 벡터의 개수를 의미한다.In Equation 1,

Is the m th weight vector of the codebook colored according to the channel characteristics of the receiving end k,

Is the correlation matrix of the receiving end k,

Is the m th weight vector of the codebook,

Denotes the number of weight vectors included in the codebook.

은 하기 <수학식 2>와 같이 산출된다.Correlation matrix in Equation 1

Is calculated as shown in Equation 2 below.

는 수신단k의 상관 행렬, 상기

는 수신단k의 채널 행렬을 의미한다.In Math 2,

Is the correlation matrix of the receiving end k,

Denotes a channel matrix of the receiving end k.

Through the coloring as shown in Equation 1, a colored codebook suitable for the correlation characteristic of the channel is generated. That is, when there are a plurality of receivers, a plurality of codebooks optimized for each receiver are generated.

The operation of the transmitter and the receiver for using the colored codebook will be described briefly as follows.

The receiving end estimates a downlink channel and calculates a correlation matrix as shown in Equation 2. The receiver feeds back the correlation matrix information to the transmitter. The transmitting end receiving the correlation matrix information checks a correlation matrix of a downlink channel and colors a codebook using the correlation matrix. The transmitter transmits the beam shaped signals using the colored vector.

Here, since the correlation matrix is calculated using the averaged channel, the correlation matrix information is preferably fed back at a long term as compared to a vector codebook index. Furthermore, since the correlation matrix information is a very large amount of information compared to the index, it is preferable to be fed back at a long interval. For example, the vector codebook index may be fed back every frame, and the correlation matrix information may be fed back at intervals of several hundred frames. Alternatively, the correlation matrix information may be fed back only when there is a large change in the correlation matrix.

In feeding back the correlation matrix information, directly feeding back the values of all elements of the correlation matrix can act as a very large overhead. Accordingly, the present invention proposes a method of configuring the correlation matrix information such that the feedback amount of the correlation matrix information is minimized.

The present invention assumes a system using four transmit antennas, and describes a method of configuring the correlation matrix information by taking two specific antenna structures as an example. In other words, the present invention will be described using a split linear antenna (SLA) antenna structure as shown in FIG. 1A and a uniform linear antenna (ULA) antenna structure as shown in FIG. 1B as an example.

First, the case of the SLA antenna structure is as follows.

The SLA antenna structure is a structure in which a plurality of antennas are arranged at two intervals, and according to an embodiment of the present invention, as shown in FIG. 1A, two pairs of four transmit antennas are formed. Consider the case where the antenna pairs are located far from each other in comparison with the distance between two antennas in each pair.

The narrower the spacing between the transmit antennas, the larger the capacity of the downlink spatial division multiple access system, but the wider the spacing between the receive antennas, the higher the uplink diversity gain. In general, due to the antenna installation space constraints of the base station, both transmit and receive antennas are used, and the SLA antenna structure as shown in FIG. 1A may be used to simultaneously satisfy the two opposing conditions described above. In FIG. 1A, d _T is preferably set to 0.5λ, that is, a length of half wavelength. In this case, the correlation matrix of the downlink channel of the receiver may be approximated as in Equation 3 below.

는 수신단k의 상관 행렬, 상기

는 수신단k의 상관 행렬의 상관 계수, 상기

는 수신단k의 상관 행렬의 위상을 의미한다.In Equation 3,

Is the correlation matrix of the receiving end k,

Is the correlation coefficient of the correlation matrix of the receiving end k,

Denotes the phase of the correlation matrix of the receiving end k.

및 위상

로 표현된다. 이는 인접한 안테나인 안테나 1과 안테나 2간, 그리고 안테나 3과 안테나 4간에만 상관도가 존재하고, 인접하지 않은 안테나인 안테나1과 안테나3, 안테나 1과 안테나 4, 안테나 2와 안테나 3, 안테나 2와 안테나 4 간의 상관도가 존재하지 않음을 의미한다. 따라서, 수신단은 상기 상관 계수

및 상기 위상

만을 피드백함으로써, 송신단으로 상관 행렬을 알릴 수 있다.Looking at the correlation matrix of Equation 3, (1,3), (1,4), (2,3), (2,4), (3,1), (3,2), (4 The elements at positions (1) and (4,2) are 0, and the elements at positions (1,2) and (2,1) (3,4) and (4,3) are correlation coefficients.

And phase

It is expressed as The correlation exists only between antenna 1 and antenna 2, which are adjacent antennas, and between antenna 3 and antenna 4, and antennas 1 and 3, antenna 1 and antenna 4, antenna 2 and antenna 3, and antenna 2 that are not adjacent antennas. Means that there is no correlation between and antenna 4. Therefore, the receiving end is the correlation coefficient

And the phase

By feeding back only, the correlation matrix can be informed to the transmitting end.

는 각 확산(angular spread)가 크더라도 약 0.97 정도의 큰 값을 갖기 때문에, 수신단은 각 링크에서 상기 상관 계수

를 피드백하지 않아도 된다. 그리고, 상기 위상

는 0 내지 2π의 범위에서 균일한 분포를 가진다. 따라서, 수신단 및 송신단은 0 내지 2π의 범위의 값들을 균일하게 양자화한 2^N개의 값들로 구성된 위상 코드북을 정의하고, 수신단은 상기 위상 코드북 내의 위상 값들을 나타내는 N비트의 인덱스를 이용하여 상기 위상

를 알린다.The correlation coefficient when the distance between two adjacent antennas is narrow

Since the angular spread has a large value of about 0.97 even though the angular spread is large, the receiving end has the correlation coefficient at each link.

You do not have to feed back. And the phase

Has a uniform distribution in the range of 0 to 2π. Accordingly, the receiving end and the transmitting end define a phase codebook consisting of 2 ^N values of uniformly quantized values in the range of 0 to 2π, and the receiving end uses the N-bit index representing the phase values in the phase codebook.

Inform.

를 N 비트의 롱텀(long-term) 정보로서 피드백하고, 송신단은 피드백된 위상

를 이용하여 상관 행렬을 구성한 후, 코드북을 컬러링할 수 있다.In summary, in the case of the SLA antenna structure, the receiving end is a phase constituting a correlation matrix

Is fed back as N bits of long-term information, and the transmitting end is fed back.

After constructing the correlation matrix by using the codebook can be colored.

Next, the case of the ULA antenna structure will be described.

The ULA antenna structure is a structure in which a plurality of antennas are arranged at equal intervals, and according to an embodiment of the present invention, as shown in FIG. 1B, four transmitting antennas are arranged at uniform intervals.

In the case of using a spatial division multiple access technique based on uplink beamforming such as uplink cospatial multiplexing (CSM), the narrower the antenna spacing of the transmit / receive array antenna, the better the performance. Therefore, the ULA antenna structure as shown in FIG. 1B is used. For example, when using a ULA antenna structure having a uniform interval of 0.5λ, the correlation matrix of the downlink channel of the receiver is expressed by Equation 4 below.

는 수신단k의 상관 행렬, 상기

는 m의 안테나 인덱스 차이를 갖는 두 송신 안테나들에 대한 수신단k의 상관 계수, 상기

는 수신단k의 상관 행렬의 위상을 의미한다.In Equation 3,

Is the correlation matrix of the receiving end k,

Is a correlation coefficient of the receiving end k for two transmitting antennas having an antenna index difference of m,

Denotes the phase of the correlation matrix of the receiving end k.

,

,

및 위상

를 송신단으로 피드백해야 한다.Looking at the correlation matrix of Equation 4, each antenna has a correlation with all other antennas. Accordingly, the receiver may use the correlation coefficient as correlation matrix information.

,

,

And phase

Should be fed back to the transmitter.

는 0 내지 2π의 범위에서 균일한 분포를 가진다. 따라서, 수신단 및 송신단은 0 내지 2π의 범위의 값들을 균일하게 양자화한 2^N개의 값들로 구성된 위상 코드북을 정의하고, 수신단은 상기 위상 코드북 내의 위상 값들을 나타내는 N비트의 인덱스를 이용하여 상기 위상

를 알린다. The phase

Has a uniform distribution in the range of 0 to 2π. Accordingly, the receiving end and the transmitting end define a phase codebook consisting of 2 ^N values of uniformly quantized values in the range of 0 to 2π, and the receiving end uses the N-bit index representing the phase values in the phase codebook.

Inform.

,

및

는 각 행 또는 각 열에서 순환적으로 반복되므로, 일부의 행 또는 열의 상관 계수들의 크기만이 근사되어 피드백된 다. 상관 행렬의 첫 번째 행 또는 첫 번째 열의 근사화된 상관 계수들은 1,

,

및

이다. 상기 상관 계수들 간 위치 차이는 안테나들 간 간격에 비례하므로, 상기 상관 계수들은 1에서 시작하여 점차 감소되는 경향을 보인다. 따라서, 상기 상관 계수들은 하기 <수학식 5>와 같은 2차 함수로 모델링될 수 있다.Meanwhile, the correlation coefficient

,

And

Since is repeated cyclically in each row or each column, only the magnitudes of the correlation coefficients of some rows or columns are approximated and fed back. Approximated correlation coefficients of the first row or first column of the correlation matrix are 1,

,

And

to be. Since the position difference between the correlation coefficients is proportional to the spacing between the antennas, the correlation coefficients tend to decrease gradually starting at one. Therefore, the correlation coefficients may be modeled as a quadratic function as shown in Equation 5 below.

은 수신단k의 상관 행렬의 근사화된 m번째 상관 계수, 상기

는 근사화된 이차항 계수, 상기

은 안테나 인덱스를 의미한다.In Equation 5,

Is an approximated m th correlation coefficient of the correlation matrix of the receiving end k,

Is an approximated quadratic coefficient,

Means antenna index.

만이 결정되면, 송신단은 모든 상관 계수들을 결정할 수 있다. 따라서, 수신단 및 송신단은 2^S개의

후보들을 정의하고, 수신단은 상관 행렬로부터 얻어진 상관 계수들 및 상기 2차 함수로부터 계산되는 상관 계수들 간 오차가 가장 적도록 상기 이차항 계수

후보들 중 하나를 선택하여 송신단으로 피드백한다. 이때, 상기 이차항 계수

는 S비트의 피드백 정보로 전송될 수 있다.Looking at the quadratic function of Equation 5, the quadratic coefficient

If only is determined, the transmitting end can determine all correlation coefficients. Therefore, the receiving end and the transmitting end have 2 ^S

Candidates are defined, and the receiving end selects the quadratic coefficient such that the error between the correlation coefficients obtained from the correlation matrix and the correlation coefficients calculated from the quadratic function is minimal.

One of the candidates is selected and fed back to the transmitter. In this case, the secondary term coefficient

May be transmitted as feedback information of S bits.

의 후보들을 0.0111 내지 0.0426 내의 균일 한 8개의 값들로 설정한 경우. 상기 이차항 계수

의 변화에 따라 상기 <수학식 5>로부터 산출되는 상관 계수들의 변화는 도 2에 도시된 바와 같다. 상기 이차항 계수

의 선택은 하기 <수학식 6>과 같이 수행된다.For example, the quadratic coefficient

The candidates of are set to eight uniform values within 0.0111 to 0.0426. The secondary term coefficient

The change of correlation coefficients calculated from Equation 5 according to the change of Equation 5 is as shown in FIG. 2. The secondary term coefficient

Is selected as in Equation 6 below.

는 근사화된 이차항 계수, 상기

는 이차항 계수, 상기

는 송신 안테나 개수, 상기

은 오차 함수, 상기

는 수신단k의 상관 행렬의 m번째 상관 계수, 상기

은 수신단k의 상관 행렬의 근사화된 m번째 상관 계수를 의미한다.In Equation 6,

Is an approximated quadratic coefficient,

Is the quadratic coefficient,

Is the number of transmit antennas, the

Is the error function,

Is the m th correlation coefficient of the correlation matrix of the receiving end k,

Denotes an approximate m th correlation coefficient of the correlation matrix of the receiving end k.

In Equation 6, the specific shape of the error function may be defined in various ways. For example, the error function may be defined as in Equation 7 below.

은 오차 함수를 의미한다.In Equation 7,

Is an error function.

및 이차항 계수

각각을 N 비트와 S 비트의 롱텀 정보로서 피드백하고, 송신단은 피드백된 위상

를 이용하여 상관 행렬을 구성한 후, 코드북을 컬러링한다.In summary, in the case of the ULA antenna structure, the receiver is configured to construct a correlation matrix.

And quadratic coefficients

Feed back each as long-term information of N bits and S bits, and the transmitting end feeds back the phase

After constructing the correlation matrix by using the color codebook.

The transmitter selects one of the SLA and the ULA according to the channel environment for operating the beam shaping and the spatial division multiple access system and the operation target of the wireless network. When the transmitting end uses the SLA antenna structure, the receiving end feeds back only N bits of long term information to the transmitting end, and when the transmitting end uses ULA antenna structure, the receiving end feeds back the long term information of N bits and S bits to the transmitting end. That is, the type and amount of information to be fed back may vary according to the arrangement of the transmitting antenna used by the transmitting end.

To this end, a procedure for negotiating the type and amount of information to be fed back according to the transmission array antenna arrangement of the transmitting end and the receiving end is necessary. This procedure is also required at the handoff when the receiving end moves to a cell of another transmitting end. Therefore, in the downtown environment where frequent handoffs occur, performance and capacity degradation may occur due to the above procedure. Accordingly, the transmitter and the receiver according to the present invention may use a feedback scheme that can be used without performing the above-described procedure.

에 대한 롱텀 피드백은 SLA 및 ULA에 공통적으로 요구되므로, 수신단은 상술한 바와 같이 N 비트의 롱텀 정보를 이용하여 피드백한다. 즉, 수신단은 0 내지 2π의 범위에서 균일하게 양자화된 2^N개의 값들로 구성된 위상 코드북 내에서 위상

와 가장 비슷한 값

를 선택하고, 선택된

을 나타내는 N 비트의 인덱스를 롱텀 정보로서 피드백한다. Phase of correlation matrix

Since long term feedback for is commonly required for SLA and ULA, the receiver feeds back using N bits of long term information as described above. That is, the receiving end phase in a phase codebook consisting of 2 ^N values quantized uniformly in the range of 0 to 2π.

Most similar to

Select the selected

The N-bit index indicating the feedback signal is fed back as long term information.

를 나타내는 정보의 형태 및 양은 달라진다. 따라서, 본 발명은 송신단의 모든 안테나 구조들에 대한 상관 계수

를 나타내는 정보들을 하나의 통합 계수 코드북으로 구성한다. 예를 들어, 상기 SLA 안테나 구조 및 ULA 안테나 구조에 대한 통합 계수 코드북은 하기 <표 1>과 같이 나타낼 수 있다.On the other hand, the correlation coefficient of the correlation matrix according to the structure of the transmission array antenna

The type and amount of information representing the different. Accordingly, the present invention provides a correlation coefficient for all antenna structures of the transmitting end.

Information representing a is composed of one integrated coefficient codebook. For example, an integrated coefficient codebook for the SLA antenna structure and the ULA antenna structure may be represented as shown in Table 1 below.

index

)Quadratic coefficient (

) ρ _{k, 1} ρ _{k, 2} ρ _{k, 3} One 0 0.97 0 0 2 0.0111 0.97 0.9 0.85 · · · · · · · · · · · · · · · 2 ^S -1 0.0336 0.95 0.85 0.65 2 ^S 0.0381 0.94 0.83 0.55

In the integrated coefficient codebook as shown in Table 1, the row of index 1 is a codeword for the SLA antenna structure, and the rows of index 2 to index 2 ^S are codewords for the ULA antenna structure.

의 값을 포함하지만, 피드백에 사용되는 인덱스 및 이차항 계수 값만을 포함하는 통합 계수 코드북도 가능하다.The integrated coefficient codebook of Table 1 is an example of an index, a quadratic coefficient value, and a correlation coefficient used for feedback.

An integrated coefficient codebook is also possible that includes the value of but includes only the index and quadratic coefficient values used for the feedback.

의 값만을 포함하는 통합 계수 코드북도 사용될 수 있다. 이 경우, 수신단은 2^S개의 코드워드들이 나타내는 근사화된 상관 계수

및 추정된 상관 계수

간 오차가 최소화되도록 하나의 코드워드를 선택한 후, 선택된 코드워드의 인덱스를 롱텀 정보로서 피드백한다. 또는, 인덱스 및 이차항 계수 값만으로 구성된 통합 계수 코드북이 사용되는 경우, 수신단은 상관 행렬로부터 상관 계수

를 나타내는 이차 함수의 이차항 계수

를 산출하고, 이차항 계수

와 가장 유사한

를 선택한 후, 선택된

의 인덱스를 롱텀 정보로서 피드백한다. 인덱스, 이차항 계수 값 및 상관 계수를 모두 포함하는 통합 계수 코드북이 사용되는 경우, 수신단은 상술한 방식들 중 하나에 따라 인덱스 선택한 후, 선택된 인덱스를 롱텀 정보로서 피드백한다.In addition, the index and correlation coefficient used for feedback

An integrated coefficient codebook containing only the value of may also be used. In this case, the receiving end approximates the correlation coefficients represented by the 2 ^S codewords.

And estimated correlation coefficient

After selecting one codeword to minimize the inter-error, the index of the selected codeword is fed back as long term information. Alternatively, when an integrated coefficient codebook consisting of only index and quadratic coefficient values is used, the receiver may determine the correlation coefficient from the correlation matrix.

Quadratic coefficient of the quadratic function

Yield the quadratic coefficient

Most similar to

Select, then select

The index of is fed back as long term information. When an integrated coefficient codebook including all indexes, quadratic coefficient values, and correlation coefficients is used, the receiving end selects an index according to one of the above-described schemes, and then feeds back the selected index as long term information.

Hereinafter, the present invention will be described in detail with reference to the drawings the operation procedure and configuration of the receiving end and the transmitting end performing the communication as described above.

3A and 3B illustrate an operation procedure of a receiver in a multiple input / output wireless communication system according to an exemplary embodiment of the present invention. 3A and 3B illustrate an operation procedure of a receiving end during one frame period. FIG. 3A illustrates an example of selecting a vector codebook index using a calculated correlation matrix directly, and FIG. 3B illustrates an example of selecting a vector codebook index using a quantized correlation matrix.

First, referring to FIG. 3A, the receiver estimates a downlink channel in step 301. That is, the receiver estimates a downlink channel using pilot signals received from the transmitter. In this case, the downlink channel is a matrix having the size of {the number of transmitting antennas of the transmitting end} × {the number of receiving antennas of the receiving end}.

After estimating the downlink channel, the receiver proceeds to step 303 to calculate a correlation matrix of the channel. The correlation matrix is a matrix representing correlation between transmission antennas of a transmitter and is calculated using an averaged channel. Here, the averaged channel is one of a channel averaged on the time axis, a channel averaged on the frequency axis, and a channel averaged on both the time axis and the frequency axis. For example, the receiver calculates the correlation matrix as shown in Equation 2.

After calculating the correlation matrix, the receiver proceeds to step 305 and determines whether it is time to feed back the long term information. The long term information refers to the correlation matrix, and is periodically transmitted at a predetermined interval or when a change amount of the correlation matrix is large. If the long term information is transmitted periodically, the transmission interval of the long term information is longer than the transmission interval of the short term information, for example, several hundred frames are transmitted.

If it is time to feed back the long term information, the receiver proceeds to step 307 to extract the correlation coefficient and phase of the correlation matrix. Here, the correlation coefficient may be one or two or more. In other words, the receiver extracts the minimum elements constituting the elements of the correlation matrix. For example, when the transmitting end has the SLA antenna structure as shown in FIG. 1A, the receiving end extracts one correlation coefficient and one phase. On the other hand, when the transmitter has the ULA antenna structure as shown in FIG. 1B, the receiver extracts three correlation coefficients and one phase.

After extracting the at least one correlation coefficient and phase, the receiver proceeds to step 309 to select a coefficient codebook index and a phase codebook index. In other words, the receiving end selects a quadratic coefficient index corresponding to the extracted correlation coefficient among the correlation coefficient codewords in the integrated coefficient codebook, and phase index of the phase value most similar to the extracted phase among the phase values in the phase codebook. Select. In this case, when the integrated coefficient codebook includes an index and a correlation coefficient value, the receiving end searches for one codeword to minimize an error between the approximated correlation coefficient and the estimated correlation coefficient represented by the codewords, and then selects the selected codeword. Select the index of. Alternatively, when the integrated coefficient codebook includes an index and a quadratic coefficient value, the receiving end calculates a quadratic coefficient of a quadratic function representing a correlation coefficient extracted from a correlation matrix, and the quadratic coefficient and the quadratic coefficient in the integrated coefficient codebook. Select the index of the most similar value.

In operation 311, the receiving end feeds back the coefficient codebook index and the phase codebook index. That is, the receiver feeds back the long term information. In this case, the long term information is fed back through a predetermined physical feedback channel, or fed back in the form of a media access control management message. When the physical feedback channel is used, the receiving end generates a physical signal corresponding to the content of the long term information and transmits the physical signal through the feedback channel. On the other hand, when the MAC management message is used, the receiving end configures a MAC management message including the content of the long term information, performs encoding and modulation, and then transmits the MAC management message.

In operation 313, the receiver determines whether it is time to feed back the short term information. The short term information means the vector codebook index and is periodically transmitted at a predetermined interval. For example, the short term information may be transmitted every one frame.

If it is time to feed back the short term information, the receiver proceeds to step 315 to select a vector codebook index. In other words, the receiving end selects an index of a weight vector to be used for beam shaping a transmission signal to itself among weight vectors included in a vector codebook. In detail, the receiver calculates the inverse of the square root of the correlation matrix and the product of the channel as shown in Equation 8 below, and selects a weight vector most similar to the result of the product. do.

는 하향링크 채널, 상기

는 상관 행렬을 의미한다.In Equation 8,

Is a downlink channel,

Denotes a correlation matrix.

After selecting the vector codebook index, the receiver proceeds to step 317 to feed back the vector codebook index. In this case, the vector codebook index is fed back through a predetermined physical feedback channel or in the form of a MAC management message. When the physical feedback channel is used, the receiving end generates a physical signal corresponding to the vector codebook index and transmits the physical signal through the feedback channel. On the other hand, when the MAC management message is used, the receiving end constructs a MAC management message including the vector codebook index, performs encoding and modulation, and then transmits the MAC management message.

Next, referring to FIG. 3B, the receiver estimates a downlink channel in step 351. That is, the receiver estimates a downlink channel using pilot signals received from the transmitter. In this case, the downlink channel is a matrix having the size of {the number of transmitting antennas of the transmitting end} × {the number of receiving antennas of the receiving end}.

After estimating the downlink channel, the receiver proceeds to step 353 to calculate a correlation matrix of the channel and updates the correlation matrix previously calculated. That is, since the correlation matrix is continuously averaged during the feedback interval of the long term information, the receiver calculates a correlation matrix for each channel estimation and updates the previously calculated correlation matrix by using the newly calculated correlation matrix.

After calculating the correlation matrix, the receiver proceeds to step 355 and determines whether it is time to feed back the long term information. The long term information refers to the correlation matrix, and is periodically transmitted at a predetermined interval or when a change amount of the correlation matrix is large. If the long term information is transmitted periodically, the transmission interval of the long term information is longer than the transmission interval of the short term information, for example, several hundred frames are transmitted.

If it is time to feed back the long term information, the receiver proceeds to step 357 to extract the correlation coefficient and phase of the correlation matrix. Here, the correlation coefficient may be one or two or more. In other words, the receiver extracts the minimum elements constituting the elements of the correlation matrix. For example, when the transmitting end has the SLA antenna structure as shown in FIG. 1A, the receiving end extracts one correlation coefficient and one phase. On the other hand, when the transmitter has the ULA antenna structure as shown in FIG. 1B, the receiver extracts three correlation coefficients and one phase.

After extracting the at least one correlation coefficient and phase, the receiver proceeds to step 359 to select a coefficient codebook index and a phase codebook index. In other words, the receiver selects a quadratic coefficient index corresponding to the extracted correlation coefficient among the correlation coefficient codewords in the integrated coefficient codebook, and phase of the phase value most similar to the extracted phase among the phase values in the phase codebook. Select an index. In this case, when the integrated coefficient codebook includes an index and a correlation coefficient value, the receiving end searches for one codeword to minimize an error between the approximated correlation coefficient and the estimated correlation coefficient represented by the codewords, and then selects the selected codeword. Select the index of. Alternatively, when the integrated coefficient codebook includes an index and a quadratic coefficient value, the receiving end calculates a quadratic coefficient of a quadratic function representing a correlation coefficient extracted from a correlation matrix, and the quadratic coefficient and the quadratic coefficient in the integrated coefficient codebook. Select the index of the most similar value.

In operation 361, the receiving end feeds back the coefficient codebook index and the phase codebook index. That is, the receiver feeds back the long term information. In this case, the long term information is fed back through a predetermined physical feedback channel or in the form of a MAC management message. When the physical feedback channel is used, the receiving end generates a physical signal corresponding to the content of the long term information and transmits the physical signal through the feedback channel. On the other hand, when the MAC management message is used, the receiving end configures a MAC management message including the content of the long term information, performs encoding and modulation, and then transmits the MAC management message.

After feeding back the long term information, the receiver proceeds to step 363 to generate a quantized correlation matrix using the coefficient codebook index and the phase codebook index, and then updates the quantized correlation matrix. Since the coefficient codebook index and the phase codebook index cannot represent an accurate correlation coefficient and an accurate phase, the correlation matrix reconstructed using the long term information at the transmitting end is the same as the correlation matrix calculated and updated in step 353. Not. Accordingly, the receiver generates a quantized correlation matrix using the coefficient codebook index and the phase codebook index to use the same correlation matrix as the correlation matrix reconstructed by the transmitter in selecting the weight vector of the receiver. The receiver updates the previously generated quantized correlation matrix using the newly generated quantized correlation matrix. Accordingly, until the next long term information feedback point, the receiver selects a weight vector using the quantized correlation matrix.

In operation 365, the receiver determines whether it is time to feed back the short term information. The short term information means the vector codebook index and is periodically transmitted at a predetermined interval. For example, the short term information may be transmitted every one frame.

If it is time to feed back the short term information, the receiver proceeds to step 367 to select a vector codebook index. In other words, the receiving end selects an index of a weight vector to be used for beam shaping a transmission signal to itself among weight vectors included in a vector codebook. In this case, the receiver uses the channel estimated in step 351 and the quantized correlation matrix generated in step 363. In detail, the receiver calculates the inverse of the square root of the quantized correlation matrix and the product of the channels, and selects the weight vector most similar to the result of the product.

After selecting the vector codebook index, the receiver proceeds to step 369 to feed back the vector codebook index. In this case, the vector codebook index is fed back through a predetermined physical feedback channel or in the form of a MAC management message. When the physical feedback channel is used, the receiving end generates a physical signal corresponding to the vector codebook index and transmits the physical signal through the feedback channel. On the other hand, when the MAC management message is used, the receiving end constructs a MAC management message including the vector codebook index, performs encoding and modulation, and then transmits the MAC management message.

4 is a flowchart illustrating an operation procedure of a transmitter in a multiple input / output wireless communication system according to an exemplary embodiment of the present invention. 4 illustrates an operation procedure of a transmitter during one frame period. 4 illustrates only an operation procedure for one receiver, and when communicating with multiple receivers at the same time, the procedure shown in FIG. 4 is independently performed by the number of receivers.

Referring to FIG. 4, the transmitter determines whether long term information is received from the receiver in step 401. The long term information includes the coefficient codebook index and the phase codebook index representing the correlation matrix of the receiver, and is periodically transmitted at a predetermined interval or transmitted by the receiver. For example, the long term information is transmitted every few hundred frames. In this case, the long term information is received through a predetermined physical feedback channel or in the form of a MAC management message.

When the long term information is received, the transmitter proceeds to step 403 to restore the correlation matrix of the receiver using the long term information, that is, the coefficient codebook index and the phase codebook index. In detail, the transmitter determines at least one correlation coefficient value through the coefficient codebook index, and determines a phase value using the phase codebook index. The transmitter restores the elements of the correlation matrix by combining the at least one correlation coefficient value and the phase value, and restores the correlation matrix by arranging the elements according to the shape of the correlation matrix. In this case, the shape of the correlation matrix depends on the structure of the transmit array antenna of the transmitter. For example, in the case of the SLA antenna structure, the correlation matrix has the form as shown in Equation 3, and in the case of the ULA antenna structure, the correlation matrix has the form as shown in Equation 4. Here, the checking of the at least one correlation coefficient value depends on the form of the integrated coefficient codebook included in the transmitter. For example, when the integrated coefficient codebook includes an index and a correlation coefficient value, the transmitter checks correlation coefficient values included in a codeword corresponding to the coefficient codebook index. On the other hand, when the integrated coefficient codebook includes an index and a quadratic coefficient value, the transmitter checks a value indicated by the coefficient codebook index, substitutes the value into a quadratic function, and then uses the quadratic function to perform the At least one correlation coefficient value is calculated.

After restoring the correlation matrix, the transmitter proceeds to step 405 to color the vector codebook. In other words, the transmitter modifies the vector codebook composed of the vectors having a uniform distribution to suit the receiver. That is, the transmitter generates a colored vector codebook by multiplying the square root of the correlation matrix by each vector of the vector codebook. For example, the coloring is performed as in Equation 1 above.

In step 407, the transmitter determines whether short term information is received. The short term information includes a vector codebook index of the receiver and is periodically received at a predetermined interval. For example, the short term information is transmitted every one frame. In this case, the short term information is received through a predetermined physical feedback channel or in the form of a MAC management message.

When the short term information is received, the transmitter determines the short term information, ie, the vector corresponding to the vector codebook index, among the vectors included in the colored vector codebook in step 409. In other words, the transmitter checks the weight vector for beam shaping the signal transmitted to the receiver.

After checking the beam format vector, the transmitter proceeds to step 411 to process a signal transmitted to the receiver using the identified weight vector, and then transmits the signal through a plurality of transmit antennas. In other words, the transmitter performs beamforming by multiplying the signal transmitted to the receiver by the weight vector, and then transmits each element of the beamformed signal sequence through a corresponding transmit antenna.

5A and 5B illustrate a block configuration of a receiving end in a multiple input / output wireless communication system according to an embodiment of the present invention.

As shown in FIG. 5A, the receiver includes a radio frequency (RF) receiver 502, an OFDM demodulator 504, a subcarrier demapper 506, a signal detector 508, a channel estimator 510, and a correlation matrix. Calculator 512, vector selector 514, long term information generator 516, short term information generator 518, feedback controller 520, subcarrier mapper 522, OFDM modulator 524, RF transmitter 526 It is configured to include.

The RF receiver 502 converts an RF band signal received through an antenna into a baseband signal. The OFDM demodulator 504 divides the baseband signal into OFDM symbol units, removes a cyclic prefix (CP), and restores signals in a frequency domain through a fast fourier transform (FFT) operation. The subcarrier demapper 506 divides the signals in the frequency domain into data signals and pilot signals, provides the data signals to the signal signal detector 508, and provides the pilot signals to the channel estimator 510. ) The signal detector 510 detects a transmission signal from the data signals. The channel estimator 510 estimates a channel with a transmitter using the pilot signals. That is, the channel estimator 510 estimates a downlink channel using the pilot signals. In this case, the downlink channel is a matrix having the size of {the number of transmitting antennas of the transmitting end} × {the number of receiving antennas of the receiving end}.

The correlation matrix calculator 512 calculates a correlation matrix by using the channel estimated by the channel estimator 510. The correlation matrix is a matrix representing correlation between transmission antennas of a transmitter and is calculated using an averaged channel. Here, the averaged channel is one of a channel averaged on the time axis, a channel averaged on the frequency axis, and a channel averaged on both the time axis and the frequency axis. For example, the correlation matrix calculator 512 calculates the correlation matrix as shown in Equation 2 above.

The vector selector 514 selects a vector codebook index. In other words, the vector selector 514 selects an index of the weight vector to be used for beam shaping a transmission signal to itself among the weight vectors included in the vector codebook. In detail, the vector selector 514 multiplies the channel estimated by the channel estimator 510 with the inverse of the square root of the correlation matrix and the channel, as shown in Equation 8, Choose the most similar weight vector. In this case, in order to prevent performance degradation due to an error between the correlation matrix reconstructed at the transmitting end and the correlation matrix calculated by the correlation matrix calculator 512, the vector selector 514 is configured by the long term information generator 516. The generated quantized correlation matrix may be generated using the generated coefficient codebook index and the phase codebook index, and the quantized correlation matrix may be used in place of the correlation matrix calculated by the correlation matrix calculator 512.

The long term information generator 516 generates long term information for informing the correlation matrix calculated by the correlation matrix calculator 512. To this end, the long term information generator 516 extracts the minimum elements constituting the elements of the correlation matrix and generates long term information using the minimum elements. The detailed configuration of the long term information generator 516 is as follows.

As shown in FIG. 5B, the long term information generator 516 uses a coefficient extractor 552, a coefficient index selector 554, a phase extractor 556, a phase index selector 558, and a signal generator 560. It is configured to include.

The coefficient extractor 552 extracts at least one correlation coefficient from the correlation matrix calculated by the correlation matrix calculator 512. For example, when the transmitting end has the SLA antenna structure as shown in FIG. 1A, the coefficient extractor 552 extracts one correlation coefficient, and when the transmitting end has the ULA antenna structure as shown in FIG. 1B, the coefficient extractor Extracts three correlation coefficients.

The coefficient index selector 554 selects a coefficient index representing the at least one correlation coefficient. In other words, the coefficient index selector 554 selects a quadratic coefficient index corresponding to the extracted correlation coefficient among the correlation coefficient codewords in the integrated coefficient codebook. In this case, when the integrated coefficient codebook includes index and correlation coefficient values, the coefficient index selector 554 searches one codeword to minimize an error between the approximated correlation coefficients and the estimated correlation coefficients represented by the codewords. Then, the index of the selected codeword is selected. Alternatively, when the integrated coefficient codebook includes an index and a quadratic coefficient value, the coefficient index selector 554 calculates a quadratic coefficient of a quadratic function that represents the correlation coefficient extracted from the correlation matrix, and in the integrated coefficient codebook The index of the value most similar to the quadratic coefficient is selected.

The phase extractor 556 extracts a phase from the correlation matrix calculated by the correlation matrix calculator 512. The phase index selector 558 selects a phase codebook index. In other words, the phase index selector 558 selects a phase index of the phase value most similar to the extracted phase among the phase values in the phase codebook. The signal generator 560 generates a signal of long term information including a coefficient codebook index selected by the coefficient index selector 554 and a phase codebook index selected by the phase index selector 558. In this case, the long term information is fed back through a predetermined physical feedback channel or in the form of a MAC management message. When the physical feedback channel is used, the signal generator 560 generates a physical signal corresponding to the content of the long term information. On the other hand, when the MAC management message is used, the signal generator 560 constructs a MAC management message including the content of the long term information, and performs encoding and modulation.

The short term information generator 518 generates short term information for informing the vector codebook index selected by the vector selector 514. Here, the short term information is fed back through a predetermined physical feedback channel or fed back in the form of a MAC management message. When the physical feedback channel is used, the short term information generator 518 generates a physical signal corresponding to the vector codebook index. On the other hand, when the MAC management message is used, the short term information generator 518 constructs a MAC management message including the vector codebook index, and performs encoding and modulation.

The feedback controller 520 controls a feedback starting point of the long term information and the short term information. That is, the feedback controller 520 determines whether the transmission time of the long term information and the transmission time of the short term information arrive, and the operation of the long term information generator 516 and the short term information generator 518 according to the determination result. Trigger In this case, the long term information is transmitted periodically at a predetermined interval or when a change amount of the correlation matrix is large. If the long term information is transmitted periodically, the transmission interval of the long term information is longer than the transmission interval of the short term information, for example, several hundred frames are transmitted. In this case, the feedback controller 520 triggers the operation of the long term information generator 516 once every few hundred frames. On the other hand, when the long term information is transmitted when the change amount of the correlation matrix is large, the feedback controller 520 monitors the change of the correlation matrix, and when the change amount of the correlation matrix exceeds a threshold, the long term information generator ( 516 triggers the operation. The short term information means the vector codebook index and is periodically transmitted at a predetermined interval. For example, the short term information is transmitted every one frame. In this case, the feedback controller 520 triggers the operation of the short term information generator 518 once every frame.

The subcarrier mapper 522 maps the long term information and the short term information to a physical feedback channel or an allocated uplink resource. The OFDM modulator 524 converts the signals in the frequency domain provided from the subcarrier mapper 522 into a time domain signal through an inverse fast fourier transform (IFFT) operation, and constructs OFDM symbols by inserting a CP. The RF transmitter 526 upconverts the OFDM symbols into an RF band signal and then transmits them through an antenna.

In the configuration of the receiver shown in FIG. 5A, the receiver has one transmit / receive antenna. However, the receiving end may be provided with a plurality of transmit and receive antennas, in which case, a plurality of RF receivers, a plurality of OFDM demodulators, a plurality of subcarrier demappers, a plurality of subcarrier mappers, a plurality of OFDM modulators A plurality of RF transmitters are included.

6 is a block diagram of a transmitter in a multiple input / output wireless communication system according to an exemplary embodiment of the present invention.

As shown in FIG. 6, the transmitter includes a signal generator 602, a beam shaper 604, a plurality of subcarrier mappers 606-1 through 606-N, and a plurality of OFDM modulators 608-1 through 608-N), multiple RF transmitters 610-1 through 610-N, multiple RF receivers 612-1 through 612-N, multiple OFDM demodulators 614-1 through 614-N, A plurality of subcarrier mapperes 616-1 to 616-N, a feedback information interpreter 618, a correlation matrix restorer 620, a codebook modifier 622, and a vector selector 624 are configured.

The signal generator 602 generates a signal to be transmitted to the receiving end. That is, the signal generator 620 generates a transmission signal by encoding and modulating the transmission data. The beamformer 604 beamforms the transmission signal using the weight vector selected by the vector selector 624. In other words, the beamformer 640 performs beamforming by multiplying the transmission signal by the weight vector, and then provides each element of the beamformed signal sequence to a corresponding subcarrier mapper 606. Each of the plurality of subcarrier mappers 606-1 through 606 -N maps signals and pilot signals to be transmitted through a corresponding transmit antenna in a frequency domain. Each of the plurality of OFDM modulators 608-1 through 608 -N generates OFDM symbols to be transmitted via a corresponding transmit antenna. That is, each of the plurality of OFDM modulators 608-1 through 608 -N converts the signals of the frequency domain into a time domain signal through an IFFT operation, and then configures OFDM symbols by inserting a CP. Each of the plurality of RF transmitters 610-1 to 610 -N up-converts the OFDM symbols into an RF band signal and then transmits the signals through a responsible antenna.

Each of the plurality of RF receivers 612-1 through 612 -N down-converts an RF band signal received through a responsible antenna to a baseband signal. Each of the plurality of OFDM demodulators 614-1 to 614 -N divides the baseband signal into OFDM units, removes a CP, and restores signals in a frequency domain through an FFT operation. Each of the plurality of subcarrier dimappers 616-1 to 616 -N extracts a signal of feedback information among the signals of the frequency domain and provides a signal of the feedback information to the feedback information analyzer 618. .

The feedback information parser 618 confirms feedback information from the signal of the feedback information. That is, the feedback information interpreter 618 converts the signal of the feedback information into an information bit string, and distinguishes short term information and long term information. The feedback information interpreter 618 provides the short term information to the vector selector 624, and provides the long term information to the correlation matrix restorer 620. Here, the short term information is received through a predetermined physical feedback channel or in the form of a MAC management message. When the physical feedback channel is used, the feedback information parser 618 outputs a bit string corresponding to the physical signal received through the feedback channel. On the other hand, when the MAC management message is used, the feedback information analyzer 618 restores the MAC management message including the vector codebook index through demodulation and decoding, and extracts feedback information from the MAC management message.

The correlation matrix restorer 620 restores the correlation matrix of the receiver by using the long term information, that is, the coefficient codebook index and the phase codebook index. In detail, the correlation matrix restorer 620 determines at least one correlation coefficient value through the coefficient codebook index, and determines a phase value using the phase codebook index. Thereafter, the correlation matrix restorer 620 restores the elements of the correlation matrix by combining the at least one correlation coefficient value and the phase value, and arranges the correlation matrix by arranging the elements according to the shape of the correlation matrix. Restore In this case, the shape of the correlation matrix depends on the structure of the transmit array antenna of the transmitter. For example, in the case of the SLA antenna structure, the correlation matrix has the form as shown in Equation 3, and in the case of the ULA antenna structure, the correlation matrix has the form as shown in Equation 4. Here, the checking of the at least one correlation coefficient value depends on the form of the integrated coefficient codebook included in the transmitter. For example, when the integrated coefficient codebook includes an index and a correlation coefficient value, the correlation matrix restorer 620 checks correlation coefficient values included in a codeword corresponding to the coefficient codebook index. On the other hand, when the integrated coefficient codebook includes an index and a quadratic coefficient value, the correlation matrix restorer 620 checks the value indicated by the coefficient codebook index, assigns the value to a quadratic function, and then A quadratic function is used to calculate the at least one correlation coefficient value.

The codebook modifier 622 colors the vector codebook using the correlation matrix reconstructed by the correlation matrix restorer 620. In other words, the codebook modifier 622 transforms a vector codebook composed of vectors having a uniform distribution to suit the receiver. In other words, the codebook modifier 622 generates a colored vector codebook by multiplying the square root of the correlation matrix by each vector of the vector codebook. For example, the coloring is performed as in Equation 1 above.

The vector selector 624 is short weighted information provided from the feedback information interpreter 618 among the weight vectors in the vector codebook colored by the codebook modifier 622, that is, a weight vector corresponding to the vector codebook index. Check it. The vector selector 624 provides the identified weight vector to the beamformer 604.

In the embodiment of the present invention described with reference to FIGS. 3 to 6, a vector codebook including weight vectors is used for beamforming. Here, the weight has the form of a vector because it is assumed that there is one transmission stream to the receiving end. Therefore, when a plurality of transmission streams are allocated to one receiver, the number of weight vectors increases in proportion to the number of streams. In this case, the weights have the form of a matrix rather than a vector. In other words, the weight vector is replaced with a weight matrix. Therefore, even when the matrix codebook and the weight matrix are used, the above-described present invention can be equally applied.

7A and 7B illustrate the performance of a multiple input / output wireless communication system according to the present invention. 7A and 7B illustrate spectral efficiency according to an increase in the number of users of a system to which the present invention is applied in an environment in which the number of transmit antennas is 4, the number of receive antennas is 2, and the average signal to noise ratio (SNR) of the channel is 5 dB. graphs showing efficiency). However, it is assumed that there is no correlation between receiving antennas. Here, FIG. 7A is a graph showing the result of the experiment when the transmission array antenna structure is SLA, and FIG. 7B is a graph of the result of the experiment when the transmission array antenna structure is ULA.

In the simulations of FIGS. 7A and 7B, it is assumed that a transmitter using a Zero-Forcing Maximum Eigenmode Transmission (ZF-MET) technique. The ZF-MET technique uses a ZF weight to recognize a transmission channel of each downlink as a maximum singular vector of a downlink channel from a transmitter to each receiver, and to suppress interference between channels of each receiver. The codebook used is a 6-bit codebook of Institute of Electrical and Electronics Engineers (IEEE) 802.16e, and the transmission angle spread is set to 20 degrees.

를 양자화하기 위한 비트 수 N이 2에서 4로 증가할수록, 양자화되지 않은 완전한 상관 행렬을 사용하는 경우의 용량에 근접함이 확인된다. 특히, 상기 N이 3비트 이상일 경우, 위상

의 양자화에 의한 성능 열화가 미미함이 확인된다. 또한, 본 발명에 따른 적은 양의 롱텀 피드백을 사용하 는 컬러링된 코드북을 사용하는 기법은 기존의 RVQ 코드북 또는 DFT(Discrete Fourier Transform) 코드북과 같은 MAD(Maximum Angular Distance) 코드북을 사용하는 기법에 비하여 상당한 용량 이득을 제공함이 확인된다.Referring to FIG. 7A, the phase

As the number of bits N for quantizing increases from 2 to 4, it is confirmed that the capacity is closer to the case of using the unquantized complete correlation matrix. In particular, when N is 3 bits or more, phase

It is confirmed that performance degradation due to quantization is minimal. In addition, the technique of using a colored codebook using a small amount of long term feedback according to the present invention is compared with the technique using a maximum Angular Distance (MAD) codebook such as a conventional RVQ codebook or a Discrete Fourier Transform (DFT) codebook. It is confirmed that it provides a significant capacity gain.

를 양자화하기 위해 3비트를 사용하고, 상관 계수

를 근사화하기 위해 3비트를 사용하는 기법이 양자화 되지 않은 완전한 상관 행렬을 사용하는 경우의 용량에 근접함이 확인된다. 또한, 기존의 MAD 코드북을 사용하는 기법에 비해 용량 이득을 제공함이 확인된다.With reference to Figure 7b, the phase according to the present invention

Uses 3 bits to quantize

It is confirmed that the technique of using 3 bits to approximate the approximation of the capacity when using a non-quantized complete correlation matrix. In addition, it is confirmed that the present invention provides a capacity gain over the conventional MAD codebook.

In conclusion, the system according to the present invention additionally uses only 6 bits of long term feedback information, which is less than the existing RVQ codebook or MAD codebook, thereby providing a channel environment with various transmission array antenna structures such as SLA and ULA and spatial correlation. Provides an improvement in performance.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

1A and 1B illustrate an example of a transmission array antenna structure in a multiple input / output wireless communication system according to the present invention;

2 is a diagram illustrating an example of correlation coefficients according to quadratic coefficient change in a multiple input / output wireless communication system according to the present invention;

3A and 3B illustrate an operation procedure of a receiver in a multiple input / output wireless communication system according to an embodiment of the present invention;

4 is a diagram illustrating an operation procedure of a transmitting end in a multiple input / output wireless communication system according to an embodiment of the present invention;

5A and 5B are block diagrams of a receiving end in a multiple input / output wireless communication system according to an embodiment of the present invention;

6 is a block diagram of a transmitter in a multiple input / output wireless communication system according to an embodiment of the present invention;

7A and 7B illustrate the performance of a multiple input / output wireless communication system in accordance with the present invention.

Claims (26)

Multiple Input Multiple Output (MIMO) A method of operating a receiver in a wireless communication system, Calculating a correlation matrix of the channel with the transmitter; When a time point for feeding back long-term information arrives, feeding back the long-term information indicating at least one correlation coefficient and a phase constituting each element of the correlation matrix; Selecting a weight vector using the channel and the correlation matrix; And when the time point for feeding back short-term information arrives, feeding back the short-term information indicating a result of selecting a weight vector. The method of claim 1, The process of feeding back the long term information, Extracting the at least one correlation coefficient and phase from the correlation matrix; Selecting a phase codebook index indicating the phase; Selecting a coefficient codebook index indicating a quadratic coefficient of the quadratic function representing the distribution of the at least one correlation coefficient; And feeding back the long term information including the phase codebook index and the coefficient codebook index. The method of claim 2, The process of selecting the coefficient codebook index, Retrieving a codeword that minimizes an error with the at least one correlation coefficient among codewords in an integrated coefficient codebook including an index and a correlation coefficient value; And selecting an index of a codeword that minimizes the error. The method of claim 2, The process of selecting the coefficient codebook index, Calculating a quadratic coefficient of the quadratic function representing the at least one coefficient; Selecting an index of a value that minimizes an error with the secondary term coefficient among values in an integrated coefficient codebook comprising an index and a secondary term coefficient value. The method of claim 2, The quadratic function is a function of expressing a magnitude of correlation reduced with distance between antennas in proportion to a square of a ratio of distances between antennas. The method of claim 1, The process of selecting the weight vector, And among the weight vectors in the vector codebook, selecting a weight vector most similar to the inverse of the square root of the correlation matrix and the product of the channel. The method of claim 1, The short term information is periodically fed back at a predetermined interval, The long term information is periodically fed back according to a longer interval than the feedback interval of the short term information. The method of claim 1, The short term information is periodically fed back at a predetermined interval, The long term information is fed back when the amount of change in the correlation matrix exceeds a threshold. In the operation method of the transmitting end in a multiple input and output wireless communication system, Identifying long-term information indicating at least one correlation coefficient and a phase constituting each element of the correlation matrix fed back from the receiver; Restoring the correlation matrix using the at least one correlation coefficient and the phase; Coloring a vector codebook using the correlation matrix; And among the weight vectors in the colored vector codebook, identifying a weight vector for beam shaping the transmission signal to the receiver according to the short term information fed back from the receiver. The method of claim 9, Restoring the correlation matrix, Determining a phase value through a phase codebook index included in the long term information; Determining at least one correlation coefficient value through a coefficient codebook index included in the long term information; Restoring elements of the correlation matrix by combining the at least one correlation coefficient value and the phase value; Disposing the elements according to the shape of the correlation matrix. The method of claim 10, Determining the at least one correlation coefficient value, Determining at least one value included in a codeword corresponding to the coefficient codebook index as the at least one correlation coefficient value among codewords in an integrated coefficient codebook including an index and a correlation coefficient value. How to. The method of claim 11, Each of the codewords is composed of an approximated correlation coefficient value calculated using a quadratic function in which the magnitude of the correlation reduced with the distance between antennas is proportional to the square of the ratio of the distance between antennas. How to. The method of claim 10, Determining the at least one correlation coefficient value, Identifying a value corresponding to the coefficient codebook index among values in an integrated coefficient codebook including an index and a quadratic coefficient value; Constructing a quadratic function with the identified values as quadratic coefficients, Calculating the at least one correlation coefficient value using the quadratic function. In the receiving end device in a multiple input and output wireless communication system, A calculator for calculating a correlation matrix of channels with a transmitter, A first generator configured to output the long term information indicating at least one correlation coefficient and a phase constituting each element of the correlation matrix when a time point for feeding back the long term information arrives; A selector for selecting a weight vector using the channel and the correlation matrix; And a second generator for outputting the short term information indicating a result of selecting the weight vector when the time point for feeding back the short term information arrives. The method of claim 14, The first generator, An extractor for extracting the at least one correlation coefficient and a phase from the correlation matrix; A phase index selector for selecting a phase codebook index indicating the phase; A coefficient index selector for selecting a coefficient codebook index indicating a quadratic coefficient of the quadratic function representing the distribution of the at least one correlation coefficient; And a signal generator for generating a signal of the long term information including the phase codebook index and the coefficient codebook index. The method of claim 15, The coefficient index selector, Among codewords in an integrated coefficient codebook including an index and a correlation coefficient value, a codeword that minimizes an error with the at least one correlation coefficient is searched, and an index of a codeword that minimizes the error is selected. Device. The method of claim 15, The coefficient index selector, Calculating a quadratic coefficient of the quadratic function representing the at least one coefficient, and selecting an index of a value that minimizes an error with the quadratic coefficient among values in an integrated coefficient codebook comprising an index and a quadratic coefficient value; Characterized in that the device. The method of claim 17, The quadratic function is a function of expressing the magnitude of the correlation reduced with the distance between antennas in proportion to the square of the ratio of the distance between antennas. The method of claim 14, And the second selector selects, among the weight vectors in the vector codebook, a weight vector most similar to the inverse of the square root of the correlation matrix and the product of the channel. The method of claim 14, And controlling the short term information to be periodically fed back according to a preset interval, and controlling the long term information to be periodically fed back at a longer interval than the feedback interval of the short term information. The method of claim 14, And controlling the short term information to be periodically fed back according to a predetermined interval, and controlling the long term information to be fed back when the variation amount of the correlation matrix exceeds a threshold. In the transmitting end device in a multiple input / output wireless communication system, An analyzer for identifying long-term information indicating at least one correlation coefficient and a phase constituting each element of the correlation matrix fed back from the receiver; A reconstructor for reconstructing the correlation matrix using the at least one correlation coefficient and the phase; A transformer for coloring a vector codebook using the correlation matrix; And a selector for identifying among the weight vectors in the colored vector codebook a weight vector for beam shaping a transmission signal to the receiver according to the short term information fed back from the receiver. The method of claim 22, The restorer, Determine a phase value through a phase codebook index included in the long term information, determine at least one correlation coefficient value through a coefficient codebook index included in the long term information, and determine the at least one correlation coefficient value and the phase value. Combining to restore the elements of the correlation matrix and to arrange the elements according to the shape of the correlation matrix. The method of claim 23, wherein The restorer, And determining at least one value included in a codeword corresponding to the coefficient codebook index as the at least one correlation coefficient value among codewords in an integrated coefficient codebook including an index and a correlation coefficient value. The method of claim 24, Each of the codewords is composed of an approximated correlation coefficient value calculated using a quadratic function in which the magnitude of the correlation reduced with the distance between antennas is proportional to the square of the ratio of the distance between antennas. Device. The method of claim 23, wherein The restorer, Among the values in an integrated coefficient codebook including an index and a quadratic coefficient value, a value corresponding to the coefficient codebook index is identified, a secondary function having the identified value as a secondary term coefficient is constructed, and the secondary function is used to determine the value. Calculating at least one correlation coefficient value.

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