RU2404515C2 - Method and device for correcting errors in multiple subcarrier communication system using multiple antennae - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: method involves determining a phase shift based precoding matrix which is phase shifted by a predetermined phase angle, initially transmitting each subcarrier symbol to a receiver in a packet unit by using the phase shift based precoding matrix, reconstructing the phase shift based precoding matrix to reduce a spatial multiplexing rate if a negative reception acknowledgement (NACK) is received from the receiver, and retransmitting the initially transmitted subcarrier symbol by using the reconstructed phase shift based precoding matrix or by changing the phase shift based precoding matrix using offset information fed back from the receiver or random offset information.

EFFECT: efficient error correction.

12 cl, 27 dwg, 2 tbl

Description

FIELD OF THE INVENTION

The present invention relates to a method for error correction in a multiple antenna system based on multiple subcarriers for performing an automatic repeat request circuit and a transmitting and receiving device supporting it.

BACKGROUND

Recently, as information transmission services have become popular, a number of multimedia services have appeared and high-quality services have appeared, the need for a wireless communication service is rapidly growing. In order to actively cope with this trend, it is necessary to increase the throughput of the communication system and increase the reliability of data transmission. A method for increasing throughput in a wireless communication environment may include a method for finding a new available frequency band, as well as a method for increasing the efficiency of a limited resource. As the latter method, special attention is paid to and multi-element antenna transmission / reception technologies are being developed, consisting of installing multiple antennas in a transceiver to further provide space for resource utilization, thereby gaining diversity gain or transmitting data through each of the antennas in parallel to increase bandwidth.

Among the multi-antenna transmission / reception technologies, the overall structure of a multi-input and output (MIMO) system based on orthogonal frequency division multiplexing (OFDM) will now be described with reference to FIG.

At the transmitter, the channel encoder 101 adds redundancy bits to the transmission information bits to reduce the influence of the channel or noise, the converter 103 converts the information bit into information from the data symbols, the serial-parallel converter 105 converts the data symbols into parallel data symbols for transport in multiple subcarriers, and a multi-antenna encoder 107 converts parallel data symbols into space-time signals. The multi-antenna decoder 109, the parallel-serial converter 111, the inverse converter 113, and the channel decoder 115, which are included in the receiver, perform the inverse functions of the multi-antenna encoder 107, the serial / parallel converter 105, the converter 103, and the channel encoder 101, respectively.

A multi-antenna OFDM system requires a number of technologies to increase reliability in data transmission. Examples of technologies include time-space code (STC), cyclic delay diversity (CDD), antenna selection (AS), hopping antenna (AH), spatial multiplexing (SM), beamforming (BF), and precoding. Below, the main technologies will be described in more detail.

An STC is a circuit for benefiting from spatial diversity by sequentially transmitting the same signals through different antennas under multiple antennas. The following determinant is the main space-time symbol used in a system having two transmitting antennas.

In the above qualifier, the row represents the antennas, and the column represents the time intervals.

The cyclic delay diversity (CDD) is intended to take advantage of the frequency diversity in the receiver by allowing all antennas to transmit OFDM signals with different delay values or different sizes when a system having multiple transmit antennas transmits OFDM signals. 2 illustrates a multi-antenna system transmitter that utilizes a cyclic delay diversity (CDD) scheme.

After the OFDM symbols are separately transmitted to each of the antennas through a serial-parallel converter and a multi-antenna encoder, they are summed with a cyclic prefix (CP) to prevent inter-channel interference and then transmitted to the receiver. At the same time, the data sequence transmitted to the first antenna is transmitted to the receiver as is, but the data sequence transmitted to the next antenna is cyclically delayed by a certain bit and then transmitted to the receiver.

Meanwhile, if the aforementioned cyclic delay diversity scheme is implemented in the frequency domain, then the cyclic delay can be expressed as a product of a phase sequence. In other words, as shown in FIG. 3, data sequences in the frequency domain are multiplied by predetermined other phase sequences (from a sequence of 1 phases to a sequence of M phases), which are set differently according to the antennas, and undergo an inverse fast Fourier transform (IFFT ) and thereby transmitted to the receiver. This is called a phase shift diversity pattern.

According to the phase shift diversity scheme, a uniform fading channel can be replaced by a frequency selective channel, and frequency diversity gain or frequency planning gain can be achieved by channel coding. In other words, as shown in FIG. 4, if the phase sequence is generated using a cyclic delay with a large value in the phase shift diversity scheme, then due to the short frequency selective period, the frequency selectivity becomes high, and as a result, the gain from frequency diversity can be obtained by channel coding. It is mainly used in an open system.

Also, if the phase sequence is generated using a cyclic delay with a small value in the phase shift diversity scheme, then because of the long frequency-selective period, the closed-loop system allocates the resource of the best channel region in order to gain from frequency planning. In other words, as shown in FIG. 4, if the phase sequence is generated using a cyclic delay with a small value in the phase shift diversity scheme, a certain subcarrier region in a uniformly fading channel has a significant channel size, and the remaining subcarrier regions have a small channel size. In this case, if an orthogonal frequency division multiple access (OFDMA) system that allows a plurality of users to transmit a signal through a subcarrier occupying a significant channel section for each user, the signal-to-noise ratio (SNR) may increase.

Meanwhile, the precoding scheme includes a codebook-based precoding scheme that is used when feedback information is limited in a closed system, and a circuit for quantizing and transmitting the channel information in a feedback manner. In the precoding scheme based on the codebook, the index of the precoding matrix, which is known to the transmitter / receiver in advance, is fed back to the transmitter to obtain an increase in SNR.

5 illustrates a transmitter / receiver configuration in a multi-antenna system that uses a codebook-based precoding scheme. The transmitter and receiver have finite precoding matrices P ₁ -P _L. The receiver feedbacks to the transmitter the optimum precoding matrix index l using channel information, and the transmitter applies the precoding matrix corresponding to the returned index to the transmission data X ₁ -X _Mt. Table 1 illustrates an example codebook that is used when 3-bit feedback information is used in an IEEE 802.16e system that supports a spatial multiplexing rate of 2 and has two transmit antennas.

Table 1 Matrix Index (binary) Column 1 Column 2 Matrix Index (binary) Column 1 Column 2 000 one 0 one hundred 0.7941 0.6038-j0.0689 0 one 0.6038 + j0.0689 -0.7941 001 0.7940 -0.5801-j0.1818 101 0.3239 0.6614-j0.6740 -0.5801 + j0.1818 -0.7940 0.6614 + j0.6740 -0.3289 010 0.7940 0.0576-j0.6051 110 0.5112 0.4754 + j0.7160 0.0576 + j0.6051 -0.7940 0.4754-j0.7160 -0.5112 011 0.7941 -0.2978 + j0.5298 111 0.3289 -0.8779 + j0.3481 -0.2978-j0.5298 -0.7941 -0.8779-j0.3481 -0.3289

Meanwhile, examples of improving reliability in data transmission in a wireless communication environment include an automatic repeat request (ARQ) scheme and a hybrid ARQ scheme (HARQ). These schemes will now be described in detail.

An orthogonal frequency division multiplexing (OFDM) system and a similar system define resource blocks defined in the time-frequency domain and use these resource blocks as one unit. In the downlink, the base station allocates at least one resource block to specific user equipment in accordance with a predetermined scheduling rule and transmits data using the corresponding resource block. Also in the uplink, if the base station selects a specific user equipment in accordance with a predetermined scheduling rule and allocates a resource block to the corresponding user equipment, then the corresponding user equipment transmits data to the base station using the allocated resource block. At the same time, if a frame is lost or damaged in the data transmitted in the downlink or uplink, then ARQ or HARQ is used to correct the corresponding errors.

Examples of the HARQ scheme include a HARQ channel adaptive / HARQ channel non-adaptive HARQ channel and a trackable combining scheme / incremental redundancy scheme. In a HARQ channel non-adaptive, frame modulation or the number of available resource blocks for retransmission is performed as determined during the initial transmission. Channel adaptive HARQ changes the above parameters depending on the current state of the channel. For example, according to the HARQ channel non-adaptive, if the transmitting side transmits data using eight resource blocks in case of initial transmission, then the transmitting side retransmits data using eight resource blocks even in case of retransmission. According to the channel adaptive HARQ, even if the transmitting side transmits data using eight resource blocks in the case of initial transmission, the transmitting side retransmits data using resource blocks larger than or less than eight resource blocks, depending on the state of the channel.

In addition, the HARQ scheme can be classified into a trackable combining scheme and an increasing redundancy scheme, depending on which packet is transmitted during retransmission. According to the monitored combining scheme shown in FIG. 6, the transmitting side retransmits a packet having the same format as used for the initial transmission, or the same data symbols in different formats during the second or third transmission, if errors occur in packet used for initial transmission. The HARQ scheme is similar to the ARQ scheme in that the receiving side transmits an NCK message to the transmitting side if the receiving side cannot demodulate the packet. However, the HARQ scheme differs from the ARQ scheme in that the receiving side stores the frame that was previously received in the buffer for a period of time, and if the corresponding frame is retransmitted, combines the retransmitted frame with the previously received frame to increase the success rate of reception. The incremental redundancy scheme is different from the monitored association scheme in that a packet having a different format from a packet format used for initial transmission can be retransmitted. In other words, as shown in FIG. 7, the even even portion of the channel code is retransmitted only during the second or third retransmission in order to reduce the channel coding rate, thereby correcting packet errors.

In addition, the HARQ scheme can be classified into synchronous HARQ and asynchronous HARQ depending on whether retransmission is performed in accordance with a given synchronization after failure of the transmission of initial data.

Since the aforementioned multi-antenna circuitry and ARQ-related circuitry are independently developed, the mutual amplification effect corresponding to the combination of circuitry has not been obtained. In this regard, the proposed HARQ based on the space-time symbol. A space-time symbol based HARQ is used in a multi-antenna system. According to HARQ, based on the space-time symbol shown in FIG. 8, the data rate is increased using the BLAST (Bell Labs layered space time) scheme during the initial transmission, and if errors occur in the S1 and S2 symbols of a particular time interval, then a space-time symbol is applied to the symbols of the corresponding time interval, and then retransmission is performed to increase transmission reliability.

However, the aforementioned spatiotemporal symbol HARQ has several problems. Firstly, the HARQ based on the space-time symbol has a limitation in that it is based on a channel with uniform fading, whose rate of change is relatively low. Secondly, if multiple codewords are used, it [HARQ] is inefficient in that retransmission of all codewords is mandatory, even if errors occur only in some codewords. Thirdly, flexibility is degraded in that the initial transmission should be performed using a spatial multiplexing scheme such as BLAST. Ultimately, since adaptive ARQ, such as incremental redundancy, cannot be used for space-time HARQ, effective error correction cannot be performed.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method for correcting errors in a multi-subcarrier-based multi-antenna system and a transmit / receive device supporting it, which substantially eliminate one or more problems due to limitations and disadvantages of the prior art.

An object of the present invention is to provide a method for correcting errors in a multi-subcarrier-based multi-antenna system and a transmit / receive device supporting it, in which a multi-antenna associated circuit is combined with an automatic repeat request circuit to simultaneously increase the speed and reliability of data transmission.

To solve these problems and achieve other advantages and in accordance with the purpose of the invention, which is implemented and outlined in this document, a method for error correction in a multi-antenna system based on multiple subcarriers includes determining a phase shift-based precoding matrix phase shifted by a predetermined phase angle, the initial transmission of each subcarrier symbol to the receiver in the packet using a phase shift-based precoding matrix , Reconstitution shift based precoding matrix phase to reduce a spatial multiplexing rate if the receiver received a negative acknowledgment (NACK), and retransmission initially transmitted sub-carrier symbol by using the reconstructed shift based precoding matrix phase. The method may further include applying offset information feedback from the receiver to the precoding matrix.

In another aspect of the present invention, a transmission and reception apparatus that supports a method for correcting errors in a multi-subcarrier-based multi-antenna system includes a precoding matrix determining module determining a precoding matrix phase-shifted by a predetermined phase angle, a module reconstructing the precoding matrix to recover the precoding matrix to reduce the spatial multiplexer rate if a negative acknowledgment of receipt (NACK) is received from the receiver, and a precoding unit precoding each subcarrier symbol using a precoding matrix. The transmitting and receiving device may further include an offset application module applying offset information fed back from the receiver to the precoding matrix.

In the aforementioned aspects, the number of columns corresponding to the reduced spatial multiplexing rate is selected from a certain phase shift-based precoding matrix, so that the precoding matrix is restored consisting of only selected columns.

In addition, if errors occur only in some initially transmitted packets, the retransmission step includes the retransmission of some packets where errors occur, but does not transmit a new packet until the retransmission is complete. Also, the retransmission step may include retransmission of some packets where errors occur, and transmits a new packet. In both cases, the retransmission step is performed using antennas other than those through which packets are transmitted where errors occur. Also, the retransmission step may include selecting antennas having an excellent channel condition.

In addition, the initial transmission step includes transmitting different subcarrier symbols to each antenna, and if errors occur in all initially transmitted packets, a retransmission step is performed to enable the subcarrier symbols of each antenna to obtain orthogonality.

In yet another aspect of the present invention, a method for correcting errors in a multi-subcarrier-based multi-antenna system includes determining a phase shift-based precoding matrix phase-shifted by a predetermined phase angle, initial transmission of each subcarrier symbol to the receiver in a packet with using a phase shift-based precoding matrix, applying predetermined offset information to the precoding matrix, if from the receiver receive are negative acknowledgment (NACK), and retransmission initially transmitted sub-carrier symbol by using shift based precoding matrix phase to which the offset information is applied.

In yet another aspect of the present invention, a transmission and reception apparatus that supports a method for correcting errors in a multi-subcarrier-based multi-antenna system includes a precoding matrix determining module determining a precoding matrix phase-shifted by a predetermined phase angle, a bias application module applying bias information fed back from the receiver to the precoding matrix and a pre-biasing module encoding pre-coding each symbol subcarrier with the precoding matrix.

The bias information includes at least one of the subcarrier index bias information and the phase magnitude bias information, or both of them. Also, the offset information is subcarrier index offset information applied to all subcarriers, and the subcarrier offset information is a constant value.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a block diagram illustrating an orthogonal frequency division multiplexing system having a plurality of transmit / receive antennas.

2 is a diagram illustrating a transmitter in a multi-antenna system based on the prior art cyclic delay diversity scheme.

3 is a diagram illustrating a transmitter in a multi-antenna system based on a prior art phase shift diversity scheme.

4 illustrates graphs of two examples of a phase shift diversity scheme of the prior art.

5 is a diagram illustrating a transmitter / receiver in a multi-antenna system based on a prior coding scheme of the prior art.

6 illustrates the concept of a HARQ traced combining scheme.

7 illustrates the concept of a scheme with increasing redundancy in HARQ.

8 illustrates the concept of a space-time symbol HARQ scheme.

FIG. 9 illustrates a procedure for performing a phase shift diversity scheme of the prior art in a system having four antennas and a spatial multiplexing rate of 2.

FIG. 10 illustrates a procedure for performing a phase shift precoding scheme according to the present invention in the system of FIG. 9.

11 is a precoding matrix used for a phase shift based precoding scheme according to the present invention in the system of FIG. 10.

12 illustrates precoding matrices for initial transmission and retransmission used when errors occur in all of a plurality of packets that are transmitted simultaneously in a multiple codeword (MCW) structure.

13 illustrates precoding matrices used in one embodiment of a phase shift diversity ARQ scheme for the case where errors occur in some of the plurality of packets that are transmitted simultaneously in the MCW structure.

FIG. 14 illustrates precoding matrices used in another embodiment of a phase shift diversity ARQ scheme for the case where errors occur in some of the plurality of packets that are transmitted simultaneously in the MCW structure.

FIG. 15 illustrates precoding matrices used in one embodiment of the hybrid ARQ scheme for the case where errors occur in some of the plurality of packets that are transmitted simultaneously in the MCW structure.

FIG. 16 illustrates precoding matrices used in one embodiment of an antenna hopping ARQ scheme for the case where errors occur in some of the plurality of packets that are transmitted simultaneously in the MCW structure.

17 illustrates precoding matrices used in another embodiment of a phase shift diversity ARQ scheme for the case where errors occur in some of the plurality of packets that are transmitted simultaneously in the MCW structure.

FIG. 18 is a block diagram illustrating a transmission / reception apparatus that supports a hybrid ARQ scheme based on a multi-antenna system according to the present invention.

FIG. 19 is a block diagram illustrating an OFDM SCW transmitter constituting the wireless communication module of FIG.

FIG. 20 is a block diagram illustrating an OFDM MCW transmitter constituting the wireless communication module of FIG.

21A and 21B illustrate the concept of a phase shift based precoding scheme in which the subcarrier index offset is feedback feedback in accordance with the present invention.

FIGS. 22A and 22B illustrate the concept of a phase shift precoding scheme in which a phase value offset is feedback feedback in accordance with the present invention; FIG. and

23A and 23B illustrate a concept of a phase shift based precoding scheme in which a subcarrier index offset and a phase magnitude offset are fed back in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Detailed reference will now be made to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

The present invention relates to a method for correcting errors in a multi-antenna system and its transmitting / receiving device, which can be applied to a frequency selective channel, whose change is frequent in addition to a channel with uniform fading, can be applied as a structure with one codeword, and to a structure with many codewords, and to which adaptive ARQ can be applied. To this end, the present invention uses a phase-shift precoding scheme that can restore or change the precoding matrix depending on the spatial multiplexing rate and various types of bias information, and if a NACK signal is received due to transmission errors from the receiver, the first a method of performing retransmission after restoration of the precoding matrix to reduce the spatial multiplexing rate and Ora method of performing retransmission after changing a precoding matrix by using predetermined offset information fed back from the receiver.

<First Embodiment>

As described above, cyclic delay diversity or phase diversity diversity is advantageous in that it can be applied to both an open system and a closed system depending on the value of the cyclic delay and can be easily implemented. However, a problem arises in that the data transfer rate is reduced due to the spatial multiplexing rate of 1. Also, although precoding based on a codebook is advantageous in that efficient data transmission can be performed using index feedback, problems arise in that codebook-based precoding is not suitable for a mobile environment in which channel change is frequent and memory usage is increased, since the codebook is should ensure that on both sides of the transmitter / receiver. Accordingly, the present invention provides a phase shift-based precoding method that can easily change precoding matrices as appropriate and has the advantages of phase-shift diversity and precoding, and a method for error correction that includes an ARQ scheme.

The phase shift precoding method and the ARQ scheme of the first method based on the phase shift precoding method will be described below. Subsequently, a transmission / reception apparatus that supports the ARQ scheme of the first method will be described.

Phase Shift Precoded Method

The phase shift-based precoding matrix P proposed in the present invention can be generalized and expressed as follows:

Equation 1

(i=1, …, N_t, j=1, …, R) обозначает комплексное взвешенное значение, определенное с помощью индекса k поднесущей, N_t обозначает количество передающих антенн или виртуальных антенн (значение, равное норме пространственного мультиплексирования, N_t=R) и R обозначает норму пространственного мультиплексирования. Комплексное взвешенное значение может изменяться в зависимости от символов OFDM, которые умножаются на антенны, и индекса соответствующей поднесущей.Where

(i = 1, ..., N _t , j = 1, ..., R) denotes the complex weighted value determined using the subcarrier index k, N _t denotes the number of transmitting antennas or virtual antennas (a value equal to the spatial multiplexing norm, N _t = R) and R denotes the rate of spatial multiplexing. The complex weighted value may vary depending on the OFDM symbols that are multiplied by the antennas and the index of the corresponding subcarrier.

Meanwhile, the precoding matrix P of equation 1 is preferably made using a unitary matrix in order to reduce the loss of channel capacity in a multi-antenna system. To verify the condition for configuring the unitary matrix, the channel capacity in a system with multiple antennas is expressed by equation 2

и N_r обозначает количество приемных антенн. Уравнение 3 получается путем применения основанной на сдвиге фаз матрицы Р предварительного кодирования к уравнению 2where H denotes a channel matrix with many antennas of size

and N _r denotes the number of receiving antennas. Equation 3 is obtained by applying the phase-shift precoding matrix P to equation 2

As can be seen from equation 3, in order to eliminate the loss of channel capacity, PP ^H should become a unit matrix. Accordingly, the phase shift-based precoding matrix P should satisfy equation 4

In order to allow the precoding matrix P based on the phase shift to become a unitary matrix, two types of conditions, i.e., an order restriction condition and an orthogonality restriction condition, must be satisfied simultaneously. The condition of the restriction of the order allows the level of each column of the matrix to become 1, and the condition of the restriction of orthogonality allows the corresponding columns of the matrix to have orthogonal characteristics. They are expressed respectively using equations 5 and 6

Equation 5

Equation 6

The following is an example of a generalized equation based on a phase shift matrix 2 × 2 precoding, and equations to satisfy two restrictive conditions are obtained as follows. Equation 7 shows a generalized equation of a phase shift-based precoding matrix when the number of transmit antennas is 2 and the spatial multiplex rate is 2

Equation 7

where α _i and β _i (i = 1, 2) are real numbers, θ _i (i = 1, 2, 3, 4) denotes the phase quantity and k denotes the subcarrier index of the OFDM signal. In order to implement the precoding matrix using the unitary matrix, the order restriction condition from equation 8 and the orthogonality restriction condition from equation 9 must be satisfied

Equation 8

Equation 9

where the sign * denotes a complex conjugate. An example of a phase-shift-based precoding matrix 2x2 that satisfies equations 7-9 is as follows:

Equation 10

where θ ₂ and θ ₃ have the ratio expressed by equation 11, according to the restriction of orthogonality

Equation 11

The precoding matrix may be stored in the memory of the transmitter and receiver in the form of a codebook, and the codebook may include a number of precoding matrices generated using different finite values θ ₂ . The values of θ ₂ can be set appropriately depending on the state of the channel and the availability of feedback information. If feedback information is used, then the values of θ ₂ are set to small values, and if feedback information is not used, then the values of θ ₂ are set to large values by which a large gain from frequency diversity can be obtained.

Meanwhile, the spatial multiplexing rate can be set to a smaller number of antennas, depending on the state of the channel, even if the phase shift-based precoding matrix is generated as shown in equation 7. In this case, the phase-shift-based precoding matrix can be re-created restored by selecting the number of specific columns corresponding to the current spatial multiplex rate (reduced spatial multi rate leksirovaniya) formed from shift based precoding matrix phase. In other words, a new precoding matrix applied to the corresponding system is not generated whenever the spatial multiplexing rate changes, but the original phase shift-based precoding matrix is used as is, in which a specific column of the corresponding precoding matrix is selected to restore the precoding matrix coding.

For example, the precoding matrix from equation 10 sets the spatial multiplex rate to 2 in a multi-antenna system having two transmit antennas. However, the spatial multiplex rate may be reduced to 1 for some reason. In this case, a specific column of the matrix shown in equation 10 may be selected to perform precoding. If a second column is selected, then the phase shift-based precoding matrix is equal to equation 12 below, which takes on the same format as the cyclic delay diversity scheme with two transmit antennas in accordance with the prior art.

Equation 12

Although an example of a system having two transmit antennas is described, the application of the present invention can be extended to a system having four transmit antennas. In other words, after a phase shift-based precoding matrix is generated in a system having four transmit antennas, a specific column may be selected to perform precoding depending on the variable spatial multiplex rate. For example, FIG. 9 illustrates that prior art spatial multiplexing and cyclic delay diversity are applied to a multi-antenna system having four transmit antennas and a spatial multiplex rate of 2, and FIG. 10 illustrates that a phase shift matrix the precoding from Equation 10 applies to the aforementioned multi-antenna system.

и вторая последовательность

, которые сдвинуты по фазе на заданный уровень, передаются второй антенне и четвертой антенне. Соответственно, отметим, что норма пространственного мультиплексирования становится равной 2.Referring to FIG. 9, a first sequence S ₁ and a second sequence S ₂ are transmitted to a first antenna and a third antenna, and a first sequence

and second sequence

which are phase shifted to a predetermined level are transmitted to the second antenna and the fourth antenna. Accordingly, we note that the norm of spatial multiplexing becomes equal to 2.

передается к первой антенне,

ко второй антенне

к третьей антенне, и

к четвертой антенне.In contrast, referring to FIG. 10,

transmitted to the first antenna,

to the second antenna

to the third antenna, and

to the fourth antenna.

Accordingly, since the system of FIG. 10 has the advantage of a cyclic delay diversity scheme along with the advantage of a precoding scheme, cyclic delay (or phase shift) is performed for four antennas using a single precoding matrix.

The above phase shift-based precoding matrix for each spatial multiplex rate for a two-antenna system and a four-antenna system is expressed as follows.

table 2 Dual antenna system Four Antenna System The spatial multiplex rate is 1 The spatial multiplex rate is 2 The spatial multiplex rate is 1 The spatial multiplex rate is 2

In Table 2, θ _i (i = 1, 2, 3) denotes the phase angle according to the cyclic delay value and K is the subcarrier index in OFDM. In Table 2, each of the four types of precoding matrices can be obtained using a specific part of the precoding matrix for a multi-antenna system having four transmit antennas and a spatial multiplex rate of 2, as shown in FIG. 11. Accordingly, since the codebook does not need each precoding matrix for the four types, the storage capacity of the transmitter and receiver can be saved. The aforementioned phase shift-based precoding matrix can be extended to a system having the number of M antennas (M is a natural number greater than 2) and the spatial multiplex rate is N (N is a natural number greater than 1) according to the same principle.

Although the procedure for configuring a phase-shift-based precoding matrix having four transmitting antennas and a spatial multiplexing rate of 2 is already described above, phase-shift-based precoding can be generalized by equation 13 below for a system having N _t antennas (N _t - a natural number greater than 2) and the spatial multiplexing rate equal to R (R is a natural number greater than 1). Hereinafter, generalized phase shift precoding will be referred to as phase shift generalized diversity (GPSD)

Equation 13

обозначает матрицу GPSD для k-й поднесущей сигнала MIMO-OFDM, имеющего N_t передающих антенн и норму пространственного мультиплексирования, равную R, и

- унитарная матрица (вторая матрица), которая удовлетворяет

и используется для предоставления возможности матрице со сдвигом фаз (первой матрице) стать унитарной матрицей. В уравнении 13 фазовый угол θ_i(t), i=1, …, N_t может быть получен следующим образом в соответствии со значением τ_i(t) задержки, i=1, …, N_t:Where

denotes a GPSD matrix for the kth subcarrier of a MIMO-OFDM signal having N _t transmit antennas and a spatial multiplex rate of R, and

- unitary matrix (second matrix), which satisfies

and is used to enable the phase shift matrix (first matrix) to become a unitary matrix. In equation 13, the phase angle θ _i (t), i = 1, ..., N _t can be obtained as follows in accordance with the delay value τ _i (t), i = 1, ..., N _t :

Equation 14

where N _fft denotes the number of subcarriers of the OFDM signal. An example of creating a GPSD matrix equation is as follows when the number of transmitting antennas is 2 and a 1-bit codebook is used:

Equation 15

In equation 15, since the value of β is easily determined if the value of α is determined, information about the value of α is obtained in such a way that two types of values of α are determined, and their information is fed back using the codebook index. For example, the value of α is predetermined between the transmitter and receiver that α is 0.2 if the returned index is 0, while α is 0.8 if the returned index is 1.

A predetermined precoding matrix to obtain an increase in SNR can be used as an example of a second matrix. When a Walsh code is used as the precoding matrix, the equation for creating the phase shift-based precoding matrix is as follows:

Equation 16

Equation 16 is based on a system having four transmit antennas and a spatial multiplex rate of 4. In this case, the second matrix is reconstructed properly to select a specific transmit antenna or adjust the spatial multiplex rate.

Equation 17 shows that the second matrix is reconstructed to select two antennas in a system having four transmit antennas.

Equation 17

Table 3 also shows a method for reconstructing a second matrix suitable for the spatial multiplexing norm, when the spatial multiplexing norm varies depending on the time or state of the channel:

Equation 18

Although Equation 18 shows that the first column, the first and second columns, and the first to fourth columns of the second matrix are selected depending on the multiplex rate, any of the first, second, third, and fourth columns can be selected if the multiplex rate equal to 1, while any two of the first, second, third and fourth columns can be selected if the multiplex rate is 2.

Meanwhile, a second matrix in the form of a codebook may be provided in the transmitter and receiver. In this case, the index information from the codebook is transmitted feedback from the receiver to the transmitter, and the transmitter selects the unitary matrix (the second half of the matrix) with the corresponding index from its codebook and then constructs a phase-shift-based precoding matrix using equation 13 above.

In addition, the second matrix may change periodically, so that the carriers transmitted in one time slot have different precoding matrices for each frequency band.

Meanwhile, the cyclic delay value for the precoding based on the phase shift could be a value previously determined at the transmitter and receiver, or a value transmitted from the receiver to the transmitter by feedback. Also, although the spatial multiplex rate R may be a value previously determined at the transmitter and the receiver, the receiver can calculate the spatial multiplex rate by checking the channel status and transmit the calculated value feedback to the transmitter. Alternatively, the transmitter can calculate and change the spatial multiplex rate using channel information feedback from the receiver.

An extended type of the above phase shift-based precoding may be expressed as follows:

Equation 19

и

обозначают унитарные матрицы.In equation 19 above, D _{1 is} used to change the channel, and D _{2 is} used to align the channel between the respective flows. Also

and

denote unitary matrices.

An ARQ execution procedure for error correction using the aforementioned phase shift precoding will now be described. It is assumed that the initial transmission is performed using a precoding matrix having two transmit antennas and a spatial multiplex rate of 2 in a multiple codeword (MCW) structure. However, as described above, a precoding matrix can be used for a system having M antennas (M is a natural number greater than 2) and a norm N of spatial multiplexing (N is a natural number greater than 1), and a structure with one codeword can be used ( SCW).

In a multiple codeword structure, multiple packets may be transmitted simultaneously using spatial multiplexing. Packet transmission can be performed in two types of cases. That is, the first case corresponds to the case where errors occur in all packets, even if i packets are transmitted (i is a natural number greater than 2), and the last case corresponds to the case where errors occur in j packets (j is a natural number less than i) even if i packets are transmitted. First, the first case will be described.

As shown in FIG. 12, a precoding matrix having a spatial multiplexing rate of 2 is used during initial transmission, and if a NACK signal is received from the receiver due to packet transmission errors, then the precoding matrix is restored so that the first column or second the column is selected from the precoding matrix during the initial transmission to obtain a spatial multiplex rate of 1. Then, ARQ is performed. If the rate of spatial multiplexing is reduced, then the transmission power can be increased, whereby transmission reliability can be improved. At the same time, the transmitting antennas used for retransmission can be selected as having an excellent channel condition, referring to the channel quality information transmitted from the receiver.

Then, if errors occur in some of the transmitted packets, as in the latter case, two types of ARQ schemes can be considered. In the case of the first type, only packets in which errors occur are retransmitted, and the spatial resource for normal packets is not used for retransmission. This type is called the blanking method. According to the cancellation method, a new packet is not transmitted until j packets in which errors occur are restored using ARQ. In the case of the second type, j packets are retransmitted, and at the same time a new packet is transmitted using the spatial resource for the remaining packets. This type is called non-blanking method.

Multiple Antenna Based ARQ Diagram

1. ARQ circuit with hopping antenna

For retransmission, antennas other than the transmit antennas used for the initial transmission are selected.

2. ARQ scheme with antenna selection

Transmitting antennas for retransmission are selected using information related to the transmitting antenna, transmitted feedback from the receiver. Alternatively, the transmit antennas are arbitrarily selected by direct channel estimation at the transmitter to perform retransmission.

3. Phase-shifted ARQ scheme

The spatial multiplexing scheme or phase shift diversity scheme is used during the initial transmission, and a phase shift precoding method having a spatial multiplexing rate corresponding to the number of packets in which errors occur is used during retransmission.

In other words, as shown in FIG. 13, a spatial multiplexing scheme having a spatial multiplexing rate of 2. is used during the initial transmission. If errors occur in the transmission packets, the retransmission is performed such that the first column or second column is selected from the phase shift precoding matrix in a system with two transmitting antennas to recover a precoding matrix having a spatial multiplex norm equal to 1. Also, as shown in FIG. 14, a phase shift diversity circuit having a spatial multiplexing rate of 2. is used during the initial transmission. If errors occur in transmission packets, the retransmission is performed such that the first column or the second column is selected from the phase shift-based precoding matrix in a system with two transmitting antennas to recover a precoding matrix having a spatial multiplexing rate Of 1. Alternatively, retransmission is performed by changing transmitting antennas even if a shift based precoding matrix phase.

4. Hybrid ARQ Scheme

If errors occur in j packets, then an ARQ scheme with hopping the antenna or an ARQ scheme with phase diversity diversity is used. If errors occur in all packets, then HARQ is used based on the space-time symbol of FIG. FIG. 15 illustrates a procedure for executing a phase shift diversity ARQ scheme when errors occur in some packets, and performing a space-time symbol HARQ when errors occur in all packets.

Multiple antenna based ARQ scheme in non-blanking method

1. ARQ circuit with hopping antenna

To perform retransmission, antennas other than the transmit antennas used for the initial transmission are selected. FIG. 16 illustrates a procedure for hopping antennas for retransmission when packets are transmitted by a phase shift diversity scheme.

2. Phase-shifted ARQ scheme

For the initial transmission, a spatial multiplexing scheme or a phase shift diversity scheme is used. A phase shift-based precoding method is used for retransmission in which the position of each column in the precoding matrix changes. FIG. 17 illustrates a permutation procedure of respective columns in a phase shift-based precoding matrix during retransmission when packets are transmitted using a phase shift diversity scheme.

3. Hybrid ARQ Scheme

If errors occur in j packets, then the non-blanking method uses an ARQ scheme with hopping an antenna or an ARQ scheme with phase diversity. If errors occur in all packets, then HARQ is used based on the space-time symbol of FIG.

At least one of any of a HARQ channel adaptive / HARQ channel non-adaptive, trackable combining / incremental redundancy and synchronous HARQ / asynchronous HARQ schemes may be used as the aforementioned ARQ scheme.

A transmission and reception device that supports the first method

Fig. 18 is a block diagram illustrating an internal configuration of a transmission and reception apparatus that supports the first method. The transmission and reception device includes an input module 1801 that selects the desired function or input information, a display module 1803 displaying various types of information for the operation of the transmission and reception device, a storage device module 1805 storing various programs required for the operation of the transmission and reception device, and data to be transmitted to the receiver, a wireless communication module 1807 that receives an external signal and transmits data to the receiver, an audio processor 1809 that converts the digital audio signal into analog Beep amplifying the signal and outputting the amplified signal through a speaker SP or amplifying the audio signal from the microphone MIC and converting the signal into a digital signal, and a controller 1811 controlling entire driving of the transmitting and receiving devices.

The configuration of the wireless communication module 1807 will be described in more detail. FIG. 19 illustrates a configuration of a single codeword (SCW) OFDM transmitter included in a wireless communication module 1807, and FIG. 20 illustrates a configuration of an MCW OFDM transmitter included in a wireless communication module 1807. Also, since the receiver corresponding to the transmitter includes modules having inverse functions of the respective transmitter modules, a detailed description thereof will be omitted.

In an OFDM transmitter with SCW, a channel encoder 1910 adds redundancy bits to transmission information bits to prevent distortion of transmission bits in a channel, and performs channel coding using an encoding code, such as an LDPC code. An interleaver 1920 performs interleaving by parsing code bits to minimize loss due to instantaneous noise in data transmission, and a converter 1930 converts the interleaved data bits into OFDM symbols. This symbol conversion can be performed by phase modulation, for example QPSK, or amplitude modulation, for example 16QAM, 8QAM and 4QAM. The OFDM symbols are then transferred to time-domain carriers using a pre-encoder 1940, a subchannel modulator (not shown), and an IFFT 1950 sequentially and then transmitted to the radio channel by a filter (not shown) and an analog converter 1960. Meanwhile, the OFDM transmitter with MCW has the same the configuration as the OFDM transmitter with SCW, except that OFDM symbols are placed in parallel for each channel and then transmitted to the channel encoder 2010 and the interleaver 2020.

The precoding matrix determination modules 1941 and 2041 determine the first precoding matrix for the subcarriers from the first index and phase shift the first precoding matrix to determine the precoding matrices for the remaining subcarriers. In the present invention, precoding is performed using a unitary matrix of size (number of transmitting antennas) x (spatial multiplexing rate), where a unitary matrix is provided for each subcarrier index. The unitary matrix for the first index is shifted in phase to obtain the unitary matrices of the remaining indices. This will be described in more detail.

In other words, the precoding matrix determination modules 1941 and 2041 select a random precoding matrix in a codebook previously stored in a memory (not shown), and the selected precoding matrix is determined as a precoding matrix (first precoding matrix) for the subcarrier from the first index. In this case, the first precoding matrix can also be selected depending on the specified policies, channel status, etc.

Then, the first precoding matrix is phase shifted by a predetermined size to form a second precoding matrix for the subcarrier from the second index. At the same time, the size of the shifted phase can be set depending on the current state of the channel and / or the presence of feedback information from the receiver. The second precoding matrix is phase shifted by a predetermined size to form a third precoding matrix for the subcarrier from the third index. In other words, the procedure for generating the second precoding matrix is repeated in the generating procedure from the third precoding matrix to the last precoding matrix.

The precoding matrix reconstruction modules 1942 and 2042 are pre-installed in the memory from each precoding matrix generated in the precoding matrix generation modules 1941 and 2041, or the precoding matrices are restored depending on the information reported from the controller 1811. In this case, the matrix restoration precoding may vary depending on the types of ARQ circuits supported by the transmit and receive device. In other words, the restoration of precoding matrices can be performed in such a way that a specific column of the precoding matrix is selected to reduce the spatial multiplexing rate or the position of each row or column of the precoding matrix is rearranged.

The precoding modules 1943 and 2043 perform precoding by replacing the OFDM sequence of the corresponding subcarrier with the reconstructed precoding matrix.

In addition, if the transmitting and receiving device supports any of the ARQ schemes with hopping antenna switching, ARQ schemes with antenna selection, ARQ schemes with phase diversity and hybrid ARQ circuitry in a blanking method, or any of the ARQ schemes with hopping antenna, the circuit Phase shift diversity and hybrid ARQ circuits in a non-blanking method, the transmit and receive device may further include any one or more spatial multiplexing modules (not shown), a shift diversity module th phase (not shown) and a time-space symbol module (not shown).

Controller 1811 reports various kinds of information for modifying or restoring the precoding matrix depending on the ARQ scheme supported by the transmitting and receiving apparatus, restoring the precoding matrix to modules 1942 and 2042, or updating the spatial multiplex rate information stored in the memory, so that modules 1942 and 2042, precoding matrix reconstruction are operated with access to updated information.

<Second Embodiment>

In the aforementioned first method, the corresponding precoding matrix is changed in such a way that the phase shift and / or subcarrier index offset information, which is transmitted feedback from the receiver or arbitrarily set in the transmitter, is applied to the phase shift-based precoding matrix before restoration, to reduce the rate of spatial multiplexing, whereby a pre-optimized matrix for retransmission can be obtained coding. Below, in accordance with embodiments, a procedure for changing a precoding matrix by allowing a system having four antennas and a spatial multiplexing rate of 2 to apply a phase shift and / or subcarrier index offset to a phase shift-based precoding matrix in Table 2 will be described in Table 2 In this case, it will be apparent to those skilled in the art to which the present invention relates that an improved method is preliminarily of the coding based on the phase shift of the present invention is not limited to the following embodiments and is applicable to a system having M antennas (M - natural number greater than 2) and a spatial multiplexing rate of N (N - natural number greater than 1).

<First feedback option>

In this embodiment, which is shown in FIG. 21A, the offset N _{offset of} the subcarrier index is fed back from the receiver and then applied to the phase shift based precoding matrix.

As shown in FIG. 21B, note that the channel region (the region allocated to the solid line sine wave) originally allocated to the subcarrier with index k is relatively insufficient compared to other regions. Accordingly, the receiver checks the channel status of the resource allocated by the corresponding subcarrier, sets the appropriate offset N _offset, and feeds the transmitter the set offset N _offset . The transmitter applies the returned offset N _offset to the existing phase shift-based precoding matrix so that the corresponding subcarrier moves to the optimized channel region (the region allocated to the dashed sinusoid). The equation of the phase shift-based precoding matrix to which the returned offset N _{offset of the} index is applied can be expressed as follows:

Equation 20

When equation 19 is applied to the generalized phase shift diversity scheme, the following equation 21 can be obtained:

Equation 21

Also, when equation 19 is applied to the extended phase shift diversity scheme, the following equation 22 can be obtained:

Equation 22

<Second feedback option>

In this embodiment, which is shown in FIG. 22A, either the proper phase value θ or the offset θ _{offset of the} phase value, which is equal to the difference between the previous returned phase value and the optimized phase value, is fed back from the receiver and then applied based on phase shift precoding matrix. Also, a previously determined value depending on the number of repetitions of the transmission can be used as the offset θ _{offset of the} phase quantity.

As shown in Figure 22B, note that the channel area (area allocated for a solid line sine wave with a) initially allocated to sub-carrier index k, having a phase θ _0, is relatively insufficient as compared with other areas. Accordingly, the receiver checks the channel status of the resource allocated by the corresponding subcarrier, sets the appropriate offset θ, compares the set offset θ with the returned phase value θ _0, and feeds back the transmitter the resulting offset θ _offset , which is the difference value. The transmitter applies the returned offset θ _offset to the existing phase shift-based precoding matrix so that the corresponding subcarrier moves to the channel region (the region allocated to the dashed sinusoid) that is relatively better than the previous region. The equation of the phase shift based precoding matrix to which the offset is applied returned θ _offset, can be expressed as follows:

Equation 23

Meanwhile, if the receiver checks the state of the channel allocated by the corresponding subcarrier, sets the optimized phase value θ and directly transmits the set value by feedback to the transmitter, the transmitter can re-form the phase shift-based precoding matrix based on the returned phase value.

When equation 23 is applied to the generalized phase shift diversity scheme, the following equation 24 can be obtained:

Equation 24

Also, when equation 23 is applied to an extended phase shift diversity scheme, the following equation 25 can be obtained:

Equation 25

The offset θ _offset from equations 24 and 25 can be transmitted in feedback from the receiver. Alternatively, the previously determined value may be used as the offset θ _offset depending on the number of repetitions of the transmission.

<Third embodiment of feedback>

In this embodiment, which is shown in FIG. 23A, the proper phase value θ and subcarrier index offset are fed back from the receiver. Alternatively, the offset θ _{offset of the} phase quantity, which is the difference between the previous returned phase quantity and the optimized phase quantity, and the offset N _{offset of} the subcarrier index are fed back from the receiver. Thus, the resulting values are applied to the phase shift-based precoding matrix.

As shown in Figure 23B, note that the channel area (area allocated for a solid line sine wave with a) initially allocated to sub-carrier index k, having a phase θ _0, is relatively insufficient as compared with other areas. Accordingly, the receiver checks the channel status of the resource allocated by the corresponding subcarrier, sets the phase value θ for the optimized state and the offset N _{offset of} the subcarrier index, feeds back the transmitter the _offset value θ _offset , which is equal to the difference between the phase value θ and the previous returned phase value θ ₀ , and index _offset N _{offset of the} subcarrier. The transmitter then adds the returned offsets θ _offset and N _offset to the existing phase shift-based precoding matrix so that the corresponding subcarrier moves to the optimized channel region (the area allocated to the dashed line sinusoid). The equation of the phase shift based precoding matrix to which the returned values applied displacement and θ _offset N _offset, can be expressed as follows:

Equation 26

When equation 26 is applied to the generalized phase shift diversity scheme, the following equation 27 can be obtained:

Equation 27

Also, when equation 28 is applied to an extended phase shift diversity scheme, the following equation 28 can be obtained:

Equation 28

<Fourth Feedback Embodiment>

In this embodiment, the subcarrier index of the phase shift-based precoding matrix is used as the offset N _{offset of} the subcarrier index feedback from the receiver.

The receiver checks the channel status of the resource allocated by an arbitrary subcarrier or a given subcarrier, sets the appropriate offset N _offset and transmits the set offset by feedback to the transmitter. The transmitter then applies the returned N _offset value to the existing phase shift-based precoding matrix for all subcarriers, regardless of subcarrier type (or subcarrier index), so that all subcarriers move to the optimized region of the channel (the area allocated to the dashed line sine wave). In other words, since the frequency domain having the largest channel size is equally applied to all subcarriers, system performance can be increased. The equation of the phase shift-based precoding matrix to which the returned offset N _{offset of the} index is applied can be expressed as follows:

Equation 29

In this case, the offset N _{offset of} the subcarrier index is a constant value and serves as information for the largest channel size in the receiver.

When equation 29 is applied to the generalized phase shift diversity scheme, the following equation 30 can be obtained:

Equation 30

Also, when equation 29 is applied to an extended phase shift diversity scheme, the following equation 31 can be obtained:

Equation 31

In the second method of the present invention, if the NACK signal is received from the receiver due to errors occurring in the transmission packets, the existing phase-shift-based precoding matrix is replaced with any of the first to fourth feedback matrices using various kinds of offset information transmitted feedback from the receiver, and then the packet is retransmitted using the modified precoding matrix. Below, a basic configuration of a transmission and reception apparatus that supports the second method will be described.

A transmission and reception device that supports the second method

In this transmission and reception device, an input module, a display module, a storage module, a wireless module, an SP speaker, a MIC microphone, a sound processor, a channel controller and encoder, an interleaver, a converter, a precoder, a subchannel modulator, IFFT, a filter and an analog converter that are included in the wireless module, and the module for determining the precoding matrix and the module for precoding, which are included in the precoder, are the same as in the devices transmission and reception, which supports the first method. Accordingly, an offset application module (not shown) provided in the precoder instead of the precoding matrix recovery module will now be described.

The bias application module applies phase-shift information obtained by feedback from the receiver and / or sub-carrier index offset information to the precoding matrix reconstructed by the precoding matrix recovery module to finally fill out any of the matrices 1 through 4 of the reverse communication if the transmission and reception device of the present invention is operated in a closed system. If the transmitting and receiving device of the present invention is operated in an open system, the bias application module uses phase offset information and / or subcarrier index offset information that are randomly provided from the transmitter.

Meanwhile, a personal digital assistant (PDA), a cell phone, a personal telephone service (PCS) telephone, a global mobile phone system (GSM), a broadband CDMA telephone (WCDMA) or a mobile broadband telephone (MBS) can be used as a transmission device and admission from the present invention.

According to the present invention, a multi-antenna coupled circuit is combined with an ARQ-coupled circuit to simultaneously increase the speed and reliability of data transmission. Also, the present invention can be applied to a frequency selective channel, allows error processing in a plurality of codewords, and can apply adaptive ARQ without limitation to a specific transmission method with multiple antennas.

Those skilled in the art will appreciate that the present invention may be embodied in other specific forms without departing from the spirit and essential characteristics of the invention. Thus, the aforementioned embodiments should be considered in all respects as explanatory and not restrictive. The scope of the invention should be determined by a reasonable interpretation of the appended claims, and all changes that fall within the equivalent scope of the invention are included in the scope of the invention.

Industrial applicability. The present invention can be applied to a wired communication system, for example, wireless Internet and a mobile communication system.

Claims (12)

1. A method of error correction in a system with multiple antennas using multiple subcarriers, comprising stages in which
determining a phase shift-based precoding matrix phase-shifted by a predetermined phase angle;
each subcarrier symbol is initially transmitted to the receiver in the packet using a phase shift-based precoding matrix;
recovering the phase shift-based precoding matrix to reduce the spatial multiplexing rate if a negative acknowledgment (NACK) is received from the receiver; and
retransmitting the initially transmitted subcarrier symbol using the reconstructed phase shift-based precoding matrix. 2. The method according to claim 1, wherein the step of restoring the precoding matrix includes the steps of:
selecting the number of columns corresponding to the reduced spatial multiplexing rate from a certain phase shift-based precoding matrix; and
restoring the precoding matrix to allow the precoding matrix to consist of only selected columns. 3. The method according to claim 1, in which, if errors occur only in some initially transmitted packets, the retransmission step includes the step of retransmitting some packets where errors occur, but do not transmit a new packet until it is completed retransmission. 4. The method according to claim 1, in which if errors occur only in some initially transmitted packets, the retransmission step includes the step of retransmitting some packets where errors occur and transmitting a new packet. 5. The method according to claim 3 or 4, in which the step of retransmission is performed using antennas other than those through which packets are transmitted where errors occur. 6. The method of claim 3, wherein the step of retransmitting is performed by some antennas having an excellent channel condition. 7. The method of claim 1, wherein the initial transmitting step includes transmitting different subcarrier symbols to each antenna, and if errors occur in all initially transmitted packets, a retransmission step is performed to allow the subcarrier symbols of each antenna have orthogonality. 8. A method for correcting errors in a multi-antenna system using multiple sub-carriers, comprising the steps of:
determining a phase shift-based precoding matrix phase-shifted by a predetermined phase angle;
each subcarrier symbol is initially transmitted to the receiver in the packet using a phase shift-based precoding matrix;
applying predetermined offset information to the precoding matrix if a negative acknowledgment (NACK) is received from the receiver; and
retransmit the originally transmitted subcarrier symbol using a phase shift-based precoding matrix to which the offset information is applied. 9. The method of claim 8, wherein the bias information is fed back from the receiver. 10. The method of claim 8, wherein the offset information is arbitrarily set at the transmitter. 11. The method according to claim 9 or 10, in which the offset information includes at least one of the subcarrier index offset information and the phase value offset information. 12. The method of claim 9 or 10, wherein the offset information is subcarrier index offset information applied to all subcarriers, and the subcarrier offset information is a constant value.

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