KR20080052900A - Method and system for data transmission in communication system - Google Patents

Abstract

The present invention relates to a data transmission method and system in a multiple-input multiple-output (MIMO) communication system. To this end, the present invention provides a method for transmitting data in a communication system, when a receiver receives data from a transmitter, after checking the subcarriers transmitting the data, grouping the identified subcarriers into subcarrier groups; Selecting precoding matrices corresponding to the subcarrier group, calculating an error of the selected precoding matrices, and detecting a precoding matrix having a minimum error, and detecting the precoding matrix. And transmitting feedback information including information corresponding to a matrix to the transmitter.

Description

METHOD AND SYSTEM FOR TRANSMITTING DATA IN COMMUNICATION SYSTEM}

1 schematically illustrates the structure of a communication system according to an embodiment of the invention.

2 is a diagram for explaining an operation of a receiver detecting an optimal precoding matrix in a communication system according to an exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system, and more particularly, to a communication system of a multiple input multiple output (MIMO) type (hereinafter referred to as 'MIMO') method (hereinafter referred to as a 'MIMO communication system'). The present invention relates to a data transmission method and system.

In the next generation communication system, active researches are being conducted to provide users with services having high speed and quality of service (hereinafter referred to as 'QoS'). In particular, in the current generation communication system, a wireless local area network (WLAN) system and a wireless metropolitan area network (WMAN) will be referred to as "WMAN". Researches are being actively conducted to support high-speed services in a form of guaranteeing mobility and QoS in a broadband wireless access communication system such as a system, and a representative communication system is IEEE (Institute of Electrical and Electronics Engineers). 802.16a / d communication system and IEEE 802.16e communication system.

The IEEE 802.16a / d communication system and the IEEE 802.16e communication system are orthogonal frequency division multiplexing (OFDM) for supporting a broadband transmission network on a physical channel of the wireless MAN system. A communication system employing a " OFDM " / orthogonal frequency division multiple access (OFDMA) scheme. The IEEE 802.16a / d communication system currently considers only a single cell structure and a state in which a subscriber station (SS) (hereinafter referred to as SS) is fixed, i.e., does not consider SS mobility at all. System. In contrast, the IEEE 802.16e communication system is a system that considers the mobility of the SS in the IEEE 802.16a communication system, and the SS having the mobility is referred to as a mobile terminal (MS). do.

On the other hand, unlike the wired channel environment, the wireless channel environment existing in the next-generation communication system is multi-path interference, shadowing, propagation attenuation, time-varying noise, interference, and fading. Factors cause errors in data transmission and loss of information. In order to reduce such information loss, various error-control techniques are used depending on the characteristics of the channel. In addition, a diversity scheme is used to remove communication instability due to the fading phenomenon, and the diversity scheme includes a time diversity scheme, a frequency diversity scheme, and an antenna. Diversity can be divided into antenna diversity schemes.

The antenna diversity scheme uses a multiple antenna, and the antenna diversity scheme includes a reception antenna diversity scheme including a plurality of reception antennas and a transmission antenna including a plurality of transmission antennas. It is classified into a diversity scheme and a MIMO scheme including a plurality of receive antennas and a plurality of transmit antennas.

The MIMO communication system can obtain a high transmission gain due to a transmit antenna diversity scheme or a spatial multiplexing diversity scheme. In the transmission antenna diversity scheme and the spatial multiple diversity scheme, the transmission gains are different depending on the state of a channel to be actually applied, and the weight of the transmission antenna is transmitted when the transmitter transmits a signal through a plurality of transmission antennas. The transmission gains differ depending on whether the path is open or closed loop.

Meanwhile, in a multi-user environment, the closed loop MIMO communication system uses channel quality information (CQI) fed back from each user, for example, each receiver, of each data stream of a precoding matrix of each user. Multi-user diversity gain can be obtained corresponding to a signal to interference and noise ratio (SINR), for example. That is, the receiver calculates an SINR for each channel and feeds back a CQI to the transmitter according to the calculated SINR. That is, when the receiver feeds back the CQI to the transmitter, not only can the multi-user diversity gain be sufficiently obtained and the overhead is reduced in the CQI feedback, but also the number of users, i.e., the number of receivers, is increased. As described above, there is a need for a data transmission scheme that guarantees multi-user diversity and prevents increased overhead.

In addition, as described above, the closed loop MIMO communication system transmits and receives data between the BS and the MS in accordance with a channel environment formed between a transmitter such as a base station (BS) and a receiver, such as an MS. Let this be done. In other words, in the MIMO communication system, the MS measures the environment of the channel formed with the BS, that is, the state of the channel, and transmits the CQI corresponding to the measurement result to the BS, and the BS corresponds to the CQI received from the MS. Send and receive data with the MS. In this case, when the MS receives data from a transmitter through subcarriers as described above, the MS measures a state of a channel formed corresponding to the subcarriers and transmits a CQI to the transmitter, and as the number of subcarriers increases. The amount of CQI to send to the transmitter is increased. As the CQI increases according to the number of subcarriers, the amount of feedback information to be transmitted by the receiver increases to the transmitter, thereby increasing overhead in transmitting and receiving data, thereby degrading the performance of the system.

Accordingly, an object of the present invention is to provide a data transmission method and system in a communication system.

The present invention also provides a data transmission method and system in a MIMO communication system.

In addition, the present invention is to provide a data transmission method and system that can reduce the overhead when a receiver transmits feedback information to a transmitter in a MIMO communication system.

In accordance with an aspect of the present invention, a method for transmitting data in a communication system includes receiving data from a transmitter, checking subcarriers that transmit the data, and then receiving the identified subcarriers. Grouping into carrier groups, selecting precoding matrices corresponding to the subcarrier group, calculating an error of the selected precoding matrices, and detecting a precoding matrix having a minimum error And transmitting feedback information including information corresponding to the detected precoding matrix to the transmitter.

According to another aspect of the present invention, there is provided a method of transmitting data in a communication system, the method comprising: receiving feedback information from a receiver by a transmitter;

Identifying a codebook index included in the feedback information, selecting precoding matrices corresponding to the identified codebook index, and mapping data to be transmitted to the receiver to the selected precoding matrices. Afterwards, a process of transmitting to the receiver by performing an Inverse Fast Fourier Transform (IFFT).

A system of the present invention for achieving the above objects, in a system for transmitting data in a communication system, when receiving data from a transmitter, after confirming the subcarriers transmitting the data, the identified subcarriers group The precoding matrices corresponding to the subcarrier group, calculate the errors of the selected precoding matrices, and detect the precoding matrix having the minimum error, and detect the precoding matrices. A receiver that transmits feedback information including information corresponding to a coding matrix to the transmitter, and when receiving feedback information from the receiver, checks the codebook index included in the feedback information, and checks the codebook index included in the checked codebook index. Corresponding precoding matrices Selection, and then mapped to the selected precoding matrix to the data to be transmitted to the receiver, an inverse fast Fourier transform: and (IFFT Inverse Fast Fourier Transform) and a transmitter for transmitting to the receiver.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

The present invention proposes a data transmission method and system in an IEEE 802.16 communication system, which is a communication system, for example, a broadband wireless access (BWA) communication system. do. In an embodiment of the present invention to be described later, an IEEE 802.16 communication system (hereinafter referred to as a 'MIMO communication system') using a multiple-input multiple output (MIMO) method. Proposes a data transmission method and system. Here, in the embodiment of the present invention to be described later, the MIMO communication system is described as an example, but the data transmission method and system proposed by the present invention can be applied to other communication systems.

 In addition, the present invention provides a communication service provided by a transmitter including a plurality of transmit antennas, for example, a base station (BS) (hereinafter, referred to as a BS) and a receiver including a plurality of receive antennas. A mobile station (hereinafter referred to as MS) is proposed a method and system for transmitting feedback information, for example, precoding matrix information, to the receiver.

Here, in an embodiment of the present invention to be described later, a transmitter comprising a plurality of transmit antennas to the receiver including a plurality of receive antennas using the data transmission transmission coding matrix for spatial multiplexing and rate adaptation (rate adaptation) Upon transmission, the receiver selects precoding matrices corresponding to the subcarriers included in the channel between the transmitter and the receiver. Then, the receiver detects a predetermined precoding matrix among the selected precoding matrices, and then transmits feedback information including the precoding matrix information corresponding to the detection to the transmitter. Here, the precoding matrix is preset as a codebook between the transmitter and the receiver according to a communication environment and a communication system, and the receiver includes the codebook index of the detected precoding matrix as precoding matrix information. Send feedback information to the transmitter.

In addition, in a communication system according to an embodiment of the present invention to be described later, when a receiver receives data from transmitters, adjacent receivers among the subcarriers that transmit the data are grouped into predetermined subcarrier groups, and Selects precoding matrices corresponding to carrier groups, detects a predetermined precoding matrix among the selected precoding matrices, and transmits feedback information including the precoding matrix information corresponding to the detection to the transmitter . In this case, the receiver calculates a mean square error (MSE) of precoding metrics corresponding to the subcarrier groups, and then becomes the minimum of the calculated MSEs. That is, feedback information including an optimal precoding matrix having a minimum mean square error (MMSE: hereinafter referred to as 'MMSE') and a codebook index of a precoding matrix corresponding to the detection are detected. Send to the transmitter. Next, the structure of the communication system according to an exemplary embodiment of the present invention will be described in more detail with reference to FIG. 1.

1 is a view schematically showing the structure of a communication system according to an embodiment of the present invention. Here, for convenience of description, it is assumed that the communication system shown in FIG. 1 includes a transmitter having N transmit antennas, a receiver having N receive antennas, and N subcarriers.

Referring to FIG. 1, the transmitter 100 transmits data to the receiver 150 using transmission precoding matrices for spatial multiplexing and rate adaptation. That is, the receiver 100 modulates an input bit stream of data to be transmitted to the receiver 150 in accordance with a predetermined modulation scheme, and the data streams modulated through the modulator 110. As described above, inverse fast Fourier transform (IFFT) converts a precoding unit 120 that maps to a corresponding precoding matrix for spatial multiplexing and rate adaptation, and a data stream precoded through the precoding unit 120. N N-point IFFT units for transmitting Fourier Transform (hereinafter referred to as 'FFT') and then transmitting the IFFT data through the N transmit antennas (Tx 1, Tx 2, Tx n) to the receiver 150. (130-1,130-2,130-n).

In addition, when the receiver 150 receives the data transmitted by the transmitter 100 through the N reception antennas RX 1 and Rx n, it is referred to as a Fast Fourier Transform (FFT). The N-point FFT units 160-1-160-n and the data stream FFT through the FFT units 160-1 and 160-n, and estimate the channel. After selecting a precoding matrix corresponding to the included subcarriers, detecting an optimal precoding matrix having MMSE among the selected precoding matrices, the feedback information including the precoding matrix information corresponding to the detection is obtained. And a precoding matrix selection and detection unit 170 for transmitting to the transmitter 100 and outputting an output bit stream received from the transmitter 100.

In this case, the precoding selector / detector 170 groups subcarriers of a channel formed between the transmitter 100 and the receiver 150 into predetermined subcarrier groups for data transmission, and corresponds to the subcarrier groups. Select the precoding matrices to Then, the MSEs of the selected precoding matrices are respectively calculated to detect an optimal precoding matrix having an MMSE, and the codebook index of the precoding matrix having the MMSE is included in feedback information and transmitted to the transmitter 100. do. Then, the precoding unit 120 of the transmitter 100 checks the codebook index of the precoding matrix included in the feedback information, and then modulates the data streams modulated by the modulator 110 to correspond to the codebook index. The precoding is performed by mapping to a precoding matrix, and the precoded data stream is transmitted to the IFFT units 130-1, 130-2, and 130-n.

More specifically, when the transmitter 100 generates data to be transmitted to the receiver 150, the transmitter 100 receives the receiver 150 through N transmit antennas Tx 1, Tx 2, and Tx n. When the input bit stream of the data to be transmitted to the receiver, that is, the data to be transmitted to the receiver 150 is input, the modulator 110, the precoding matrix unit 120, and the IFFT units 130-1, 130-2, 130 as described above. Data transmitted to the receiver 150 through the N transmit antennas Tx 1, Tx 2, and Tx n through -n) may be represented by Equation 1 below.

In Equation 1, Z _n denotes data transmitted by the transmitter 100 to the receiver 150 through an arbitrary nth subcarrier, and N _stream denotes data by N subcarriers. Ε _s means the power of data symbols, W _n means the precoding matrix mapped to any n th subcarrier, and x _n means transmission on any n th subcarrier It means the data input to the transmitter 100 so as to.

When the transmitter 100 transmits data to the receiver 150 in this way, the data received by the receiver 150 through the N reception antennas RX 1 and Rx n may be represented by Equation 2 below.

In Equation 2, r _n denotes data received by the receiver 150 from the transmitter 100 through an arbitrary nth subcarrier, and H _n denotes N transmit antennas Tx 1, Tx 2, and Tx n. N denotes a channel matrix by an arbitrary nth subcarrier between the transmitter 100 including the receiver 100 and the receiver 150 including the N reception antennas Rx 1 and Rx n, where _{n n} represents an arbitrary nth subcarrier. Means noise included in the carrier.

When the receiver 150 receives data as shown in Equation 2, the received data is FFTed by the FFT units 160-1-160-n and then input to the precoding matrix selection and detection unit 170. do. Then, the precoding matrix selection and detection unit 170 calculates the MSE of the precoding mattresses corresponding to the subcarriers as shown in Equation 3 below.

은 임의의 n번밴 서브캐리어에 상 응하는 프리코딩 매트릭스의 MSE를 의미하고,

은 임의의 n번째 서브캐리어를 통해 전송되도록 상기 송신기(100)로 입력된 데이터(x_n)와 상기 입력된 데이터(x_n)의 에르미트(Hermitia)(x_n ^H) 간의 항등원을 의미하고, N₀는 잡음을 의미하며,

는 트렐리스 구조(trellis structure) 연산을 의미한다. 여기서, 상기 트렐리스 구조 연산

은 도 2에서 보다 구체적으로 설명할 것이므로 여기서는 그에 관한 구체적인 설명을 생략하기로 한다.In Equation 3

Denotes the MSE of the precoding matrix corresponding to any van subcarrier,

Denotes an identity between the data (x _n ) input to the transmitter (100) and Hermitia (x _n ^H ) of the input data (x _n ) to be transmitted on any nth subcarrier, N ₀ means noise,

Denotes a trellis structure operation. Here, the trellis structure operation

Since it will be described in more detail in FIG. 2, a detailed description thereof will be omitted herein.

As shown in Equation 3, the precoding matrix selection and detection unit 170 that calculates MSE of precoding matrices corresponding to subcarriers corresponds to a subcarrier having MMSE as shown in Equation 4 below. Detect the optimal precoding matrix.

In Equation 4, W ^* _n means an optimal precoding matrix corresponding to any nth subcarrier having MMSE, and C _W means all codebooks of the precoding matrix corresponding to the nth subcarrier. That is, W ^* _n is the average of the MMSE in all codebooks of the precoding matrix corresponding to the nth subcarrier.

At this time, the precoding matrix selection and detection unit 170 of the receiver 150 selects the precoding matrix corresponding to all subcarriers, and then calculates the MSE of the selected precoding matrix as shown in Equation 3 above. Detecting an optimal precoding matrix having MMSE among the calculated MSEs increases the complexity of the receiver 150 and the amount of computation for MSE calculation, thereby degrading the performance of the system. Accordingly, as described above, in the communication system according to the embodiment of the present invention, the receiver 150, that is, the precoding matrix selection and detection unit 170 groups the subcarriers into a predetermined number of subcarrier groups, After selecting the precoding matrices corresponding to the carrier group, the MSE of the selected precoding metrics is calculated as shown in Equation 5 below. Here, the precoding matrix selection and detection unit 170 groups N subcarriers by the number of groups by grouping a predetermined number of adjacent subcarriers into one group.

는 임의의 i_j번째 서브캐리어 그룹에 상응하는 프리코딩 매트릭스의 MSE를 의미하고, S_G는 서브태리어 그룹의 총 개수를 의미 하며, j는 j번째 서브캐리어 그룹을 의미하고, i_j는 j번째 서브캐리어 그룹에 상응하는 i번째 프리코딩 매트릭스를 의미하한다. 여기서, 상기 j는

가 되며, i_j는

가 되며, S_c는 코드북으로부터 총 서브캐리어 그룹(S_G)에 상응하는 프리코딩 매트릭스의 총 개수를 의미한다.In Equation 5

Is the MSE of the precoding matrix corresponding to any i _j th subcarrier group, S _G is the total number of subcarrier groups, j is the j th subcarrier group, and i _j is j I-th precoding matrix corresponding to the first subcarrier group. Where j is

I _j is

S _c denotes the total number of precoding matrices corresponding to the total subcarrier group S _G from the codebook.

As shown in Equation 5, the precoding matrix selection and detection unit 170 that calculates the MSE of the precoding matrices is an optimal precoding matrix corresponding to the subcarrier group having the MMSE as shown in Equation 6 below. Detect.

는 MMSE를 갖는 j번째 서브캐리어 그룹에 상응하는 최적의 i번째 프리코딩 매트릭스를 의미하고,

와 같이

는 C_W에 포함되며,

는 이전 서브캐리어 그룹(j-1), 즉 인접한 서브캐리어 그룹에 상응하는 i번째 프리코딩 매트리스에 포함된다. 그러면 여기서, 도 2를 참조하여 본 발명의 실시예에 따른 통신 시스템에서 수신기가 MMSE를 갖는 최적의 프리코딩 매트릭스를 검출하는 동작을 보다 구체적으로 설명하기로 한다.In Equation 6

Denotes the optimal i th precoding matrix corresponding to the j th subcarrier group with MMSE,

together with

Is included in C _W ,

Is included in the previous subcarrier group j-1, i.e., the i-th precoding mattress corresponding to the adjacent subcarrier group. Next, the operation of detecting the optimal precoding matrix having the MMSE by the receiver in the communication system according to the embodiment of the present invention will be described in more detail with reference to FIG. 2.

2 is a diagram for describing an operation of detecting a precoding matrix by a receiver in a communication system according to an exemplary embodiment of the present invention. Here, FIG. 2 illustrates that the receiver calculates MSEs of precoding matrices corresponding to subcarrier groups as shown in Equation 5 in a communication system according to an embodiment of the present invention, and then performs a trellis structure operation. As shown in Equation 6, the optimal precoding matrix detection corresponding to the subcarrier group having the MMSE is shown.

Referring to FIG. 2, a trellis structure in which the x-axis represents each subcarrier group as a virtual time axis and the y-axis represents a precoding matrix corresponding to a subcarrier group from a codebook as a state axis Through operation, the receiver detects an optimal precoding matrix corresponding to the subcarrier group having MMSE as shown in Equation 6. Then, the codebook index of the detected precoding matrix is included in the feedback information and transmitted to the transmitter. In this case, since the detected codebook index is smaller than the entire codebook index, feedback information is reduced, and since the transmitter has the codebook of the same precoding matrix and the trellis structure shown in FIG. Detect and perform precoding.

서브캐리어 그룹(

)까지 동일한 과정을 수행하여, 추가된 MSE의 최소 경로를 선택함으로써 MMSE를 갖는 서브캐리어 그룹에 상응하는 최적의 프리코딩 매트릭스 검출한다.In more detail, the receiver has a state corresponding to an initialization of the first subcarrier group t = 1, and the first precoding matrix W (1) and the (k-1) precoding state. In the case of the matrix W (k-1) and the S _c precoding matrix W (S _c ), a state corresponding to the next subcarrier group t = 2, that is, the first precoding matrix (W (1)), first and then the receiver compares the MSE of the precoding matrix corresponding to an adjacent group on the k precoding matrix (W (k), the S _c precoding matrix (W (S _c)), Select the minimum MSE and add it to the state corresponding to the second subcarrier group (t = 2).

Subcarrier groups (

The same process is performed to determine the optimal precoding matrix corresponding to the subcarrier group with MMSE by selecting the minimum path of the added MSE.

In the prior art without using the trellis scheme, since all possible codebook indices can be selected for each subcarrier group, feedback information of N / S_G x log2 (Sc) bits is required. However, as shown in FIG. 2, in the communication system according to the embodiment of the present invention, all possible codebook indices of the subcarrier group corresponding to t = 1 may be selected, and in the subcarrier group from t = 2, Since only a predetermined number of codebook indices (M, M < Sc) can be selected in the release structure, only N / S_G x log2 (M) bits need to be fed back, thereby reducing the amount of information to be fit back. The receiver that detects the precoding matrix includes the codebook index corresponding to the precoding matrix in the feedback information and transmits it to the transmitter.

As such, when a receiver receives data from subcarriers from a transmitter in a communication system according to an embodiment of the present invention, the subcarriers are grouped into predetermined subcarrier groups and a precoding matrix corresponding to the subcarrier groups. After selecting to calculate the MSE, the optimal precoding matrix corresponding to the subcarrier group having the MSSE among the calculated MSEs is detected. The receiver that detects the precoding matrix includes the codebook index corresponding to the precoding matrix in the feedback information and transmits it to the transmitter. That is, the present invention reduces the amount of feedback information by calculating the MSE of the precoding matrix corresponding to the subcarrier group and then detects the optimal precoding matrix, and reduces the complexity of the receiver 150 and the calculation amount for calculating the MSE. do.

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 defined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, the present invention reduces the amount of feedback information by calculating the MSE of the precoding matrix corresponding to the subcarrier group in the MIMO communication system, and then detects the optimal precoding matrix, and reduces the complexity of the receiver and the MSE. The amount of calculation for calculation can be reduced, which can improve the performance of the system.

Claims (21)

In a method for transmitting data in a communication system, When the receiver receives data from the transmitter, identifying the subcarriers that transmitted the data, and then grouping the identified subcarriers into subcarrier groups; Selecting precoding matrices corresponding to the subcarrier group, calculating an error of the selected precoding matrices, and detecting a precoding matrix having a minimum error; And transmitting feedback information including information corresponding to the detected precoding matrix to the transmitter. The method of claim 1, The transmitting of the feedback information may include transmitting the feedback information including a codebook index of the detected precoding matrix. The method of claim 1, And the codebook is preset between the transmitter and the receiver according to the precoding matrices. The method of claim 1, The grouping of the subcarrier groups may include grouping a predetermined number of adjacent subcarriers from the identified subcarriers into one group. The method of claim 1, The calculating of each error of the selected precoding matrices may include calculating a mean square error (MSE) of precoding matrices corresponding to the subcarrier groups, respectively. The method of claim 5, The detecting of the precoding matrix having the minimum error may include detecting an optimal precoding matrix corresponding to a subcarrier group having a minimum mean square error (MMSE). The method of claim 6, The detecting of the optimal precoding matrix may include comparing the mean square error of the precoding matrix corresponding to the adjacent subcarrier group, and then detecting the precoding matrix having the minimum mean square error as a result of the comparison. Data transmission method. The method of claim 1, The detecting of the precoding matrix having the minimum error is performed by performing a trellis structure operation. The method of claim 8, The trellis structure is preset between the transmitter and the receiver according to the precoding matrices. In a method for transmitting data in a communication system, Receiving, by the transmitter, feedback information from the receiver; Identifying a codebook codebook index included in the feedback information and selecting precoding matrices corresponding to the identified codebook index; Mapping data to be transmitted to the receiver to the selected precoding matrices, and then performing an Inverse Fast Fourier Transform (IFFT) to transmit the data to the receiver. The method of claim 10, The codebook index included in the feedback information is a codebook index of a precoding matrix corresponding to a group of subcarriers to transmit data to the receiver. The method of claim 10, And the codebook is preset between the transmitter and the receiver according to the precoding matrices. In a system for transmitting data in a communication system, Upon receiving data from the transmitter, after confirming the subcarriers that transmitted the data, group the identified subcarriers into subcarrier groups, select precoding matrices corresponding to the subcarrier group, and select the selected subcarriers. A receiver configured to calculate an error of the precoding matrices, and then detect a precoding matrix having a minimum error, and transmit feedback information including information corresponding to the detected precoding matrix to the transmitter; When receiving feedback information from the receiver, the codebook index included in the feedback information is checked, precoding matrices corresponding to the identified codebook codebook index are selected, and data to be transmitted to the receiver is determined. And a transmitter for mapping to selected precoding matrices and then transmitting to the receiver by performing an Inverse Fast Fourier Transform (IFFT). The method of claim 13, And the receiver transmits the feedback information including the codebook index of the detected precoding matrix. The method of claim 13, And the codebook is preset between the transmitter and the receiver corresponding to the precoding matrices. The method of claim 13, And the receiver groups a predetermined number of adjacent subcarriers among the identified subcarriers into one group. The method of claim 13, And the receiver calculates a mean square error (MSE) of precoding metrics corresponding to the subcarrier groups, respectively. The method of claim 17, And the receiver detects an optimal precoding matrix corresponding to a subcarrier group having a minimum mean square error (MMSE). The method of claim 18, And the receiver compares the mean square error of the precoding matrix corresponding to the adjacent subcarrier groups, respectively, and detects the precoding matrix having the minimum mean square error as a result of the comparison. The method of claim 13, And the receiver performs a trellis structure operation to detect a precoding matrix having a minimum error. The method of claim 20, The trellis structure is preset between the transmitter and the receiver according to the precoding matrices.

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