KR20070009366A - Method of transmitting preamble and apparatus for transmitting data in mimo-ofdm system - Google Patents

Abstract

A method for transmitting a preamble and an apparatus for transmitting data in an MIMO-OFDMA(Multi Input Multi Output-Orthogonal Frequency Division Multiple Access) system are provided to estimate an independent channel variation generated between a transmitter and a receiver of each antenna by transmitting a preamble to each antenna. A method of transmitting a preamble in an MIMO-OFDMA system includes the steps of: creating a plurality of preambles by encoding certain preamble by using an orthogonal code; adding each preamble generated to a data symbol line allocated to each transmitting antenna; data processing each added symbol line in an orthogonal frequency division transmitting way; and transmitting the symbol line through a transmitting antenna.

Description

Method of transmitting precode and data transmitting apparatus in MIMO-OPEM system {Method of transmitting preamble and apparatus for transmitting data in MIMO-OFDM system}

1 shows an example of allocating one training symbol per three subcarriers.

Figure 2 is a block diagram of a preferred embodiment of a data transmission apparatus of a multi-input orthogonal frequency division multiple access system according to the present invention.

3 to 6 are diagrams for explaining a method of generating and adding a transposition code according to a first embodiment of the present invention.

7 to 15 are diagrams for explaining a method of generating and adding a prefix according to a second embodiment of the present invention.

The present invention relates to a wireless communication system of multiple input-output-orthogonal frequency division transmission. More specifically, the present invention relates to a method and a data transmission apparatus for transmitting a precode in all transmission antennas in order to perform efficient synchronization and channel estimation in a multi-input orthogonal frequency division transmission system.

The present invention relates to a precoding for synchronization and channel estimation in a wireless communication system using a multiple input-output-orthogonal frequency division transmission scheme. Orthogonal Frequency Division Multiplexing (OFDM) uses a multi-carrier modulation scheme. Orthogonal frequency division transmission scheme uses a CP (Cyclic prefix) that duplicates the signal of the last part of the OFDM symbol and attaches it in front of the OFDM symbol to compensate for the multipath when the signal is transmitted. Due to these characteristics, it has attracted attention as a high speed mobile communication transmission method because it has excellent performance in multipath and mobile reception environments.

In a wireless communication system environment, multipath fading occurs due to multipath time delay. The process of restoring a transmission signal by compensating for distortion of a signal caused by a sudden change of environment due to fading at the receiving side is called channel estimation. In general, a training symbol known to a transmitter and a receiver is used for channel estimation.

In a wireless communication system using an orthogonal frequency division transmission method, a training symbol is allocated to all subcarriers and a method is allocated between data subcarriers. The method of allocating subcarriers is a method of allocating a training symbol without allocating data over all subcarriers, as in the case of a preamble symbol, and the method of allocating data subcarriers is assigned to subcarriers between data subcarriers. This is a method of assigning training symbols.

The method of allocating the training symbols between data subcarriers can increase the amount of data transmission, but the degradation of the channel estimation performance occurs because the density of the training symbols decreases. In the single input / output transmission method, both the transmitting side and the receiving side are known, and in general, the precoding with a high density of training symbols is used for channel estimation.

Since the receiver knows the information of the training symbol, the receiver can estimate the channel by dividing it in the received signal, and can accurately estimate the data sent from the transmitter by compensating the estimated channel value.

, 훈련 심볼이 전송 중에 겪게 되는 채널 정보를

, 수신기에서 발생하는 열 잡음을

, 수신기에서 수신된 신호를

라고 하면

는 다음의 수학식 1에 의해 나타낼 수 있다. More specifically, the training symbol sent from the transmitter

The channel information experienced by the training symbol during transmission

To reduce thermal noise

, The signal received from the receiver

Say

Can be represented by Equation 1 below.

는 수신기가 이미 알고 있기 때문에 이를 이용하여 다음의 수학식 2와 같이 채널 정보(

)를 추정할 수 있다. Training symbol

Since the receiver already knows the channel information by using the channel information (

) Can be estimated.

를 이용하여 추정한 채널 추정값

는

값에 따라서 그 정확도가 결정되게 된다. 따라서, 정확한

값의 추정을 위해서는

이 0에 수렴해야만 하고, 이를 위해서는 많은 개수의 훈련 심볼을 이용하여 채널을 추정하여

의 영향을 최소화해야 한다.Training symbol

Channel Estimation Estimated Using

Is

The accuracy depends on the value. Thus, accurate

To estimate the value

It must converge to zero, and this requires a large number of training symbols to estimate the channel

Minimize the impact.

Looking at the prefix used in the IEEE 802.16 OFDMA system, one of 128, 512, 1024, and 2048 is used as the number of subcarriers of frequency. Some of both subcarriers are used as guard intervals, and the remaining area is used as a training symbol for every three subcarriers as follows. 1 shows an example of allocating one training symbol per three subcarriers.

PreambleCarrierSet _n  = n  + 3 k

PreambleCarrierSet _n : All subcarriers assigned to a specific prefix

n : number of exponentialized prefix carrier sets 0 ... 2,

k : Continuous index of the presigned subcarrier 0 ... 283

Segment 0: Use Presigned Carrier Set 0 ( PreambleCarrierSet ₀ )

Segment 1: Using Presigned Carrier Set 1 ( PreambleCarrierSet ₁ )

Segment 2: Using Presigned Carrier Set 2 ( PreambleCarrierSet ₂ )

The PN sequences transmitted in the prefix are listed in Table 1 below. The PN sequence used is determined by the segment number and IDcell parameter value. Each defined PN sequence is mapped to a presigned subcarrier in ascending order. In Table 1, PN sequences are expressed in hexadecimal format. To get the corresponding PN code value, convert the presented hexadecimal sequence to binary sequence W _k and then map W _k from MSB to LSB. (Maps 0 to +1 and 1 to -1. For example, in the 0th segment with index 0, W _k is 110000010010 ..., so the converted PN code value is -1 -1 +1 +1. +1 +1 +1 -1 +1 +1 -1 +1 ...)

The prefix is a signal used for synchronizing the transmission timing between two or more systems and estimating a time-varying channel in a wireless communication. In order to synchronize the transmission timing, the preamble having this role places the training symbol to have a symmetric signal in time as in the IEEE 802.16 system. However, the prior art transcoding method has a problem in that restoration is not easy when the same transposition signal is transmitted in a multi-input / output system.

That is, in the conventional single-input-orthogonal frequency divisional transmission system, the pre-signal can be used for channel estimation by transmitting a pre-signal. However, in the multiple input-output-orthogonal frequency divisional transmission system, it is not easy to use the pre-signal for each antenna. There is a problem. In detail, when each antenna transmits a preamble at the same time, interference exists between training symbols of a transmitted precode, so that a receiver cannot perform independent channel estimation on a channel path at a transmitting and receiving end and different transmission antennas. This signal causes a noise component to degrade the performance of the synchronization unit such as channel estimation, signal detection, and frequency offset estimation.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art as described above, and an object of the present invention is to provide a method and apparatus for efficiently performing synchronization and channel estimation in a wireless communication system of a multi-input orthogonal frequency division transmission scheme. To provide.

Another object of the present invention is to transmit the pre-code for each antenna in the wireless communication system of the multi-input orthogonal frequency division transmission method, and to estimate the independent channel change generated between the transmitting and receiving sides in each antenna by using the training symbol of the transmitted pre-code It is to provide a method and an apparatus capable of this.

In the multi-input-orthogonal frequency divisional transmission scheme, a pre-signal is transmitted through one antenna to be used for the detection of a signal, and after the reception of the received signal, the multi-input-orthogonal frequency division transmission scheme is used. However, in the present invention, in the existing multi-input-orthogonal frequency division transmission scheme, the preambles are transmitted through a plurality of antennas from the beginning, and the receiving side detects the received signal by using the precodes received for each antenna and performs channel estimation. It is characterized by making it possible to use.

In one aspect of the present invention, a method of transmitting a precode in a MIMO-OFDMA system according to the present invention includes a multi-input multi-output (MIMO) orthogonal frequency division multiple access (OFDMA) system. Adding a precode generated by encoding using an orthogonal code for a specific precode to a data symbol string allocated to each transmit antenna; And transmitting data through each transmission antenna by processing each data symbol string to which the precode is added.

According to another aspect of the present invention, a method of transmitting a precode in a MIMO-OFDMA system according to the present invention includes a plurality of preambles by performing encoding using orthogonal codes on specific precodes in a multi-input orthogonal frequency division multiple access system. Generating a call; Adding each generated precode to a data symbol string allocated to each transmit antenna; And transmitting data through each transmission antenna by processing each data symbol string to which the precode is added.

In still another aspect of the present invention, a data transmission apparatus of a multi-input orthogonal frequency division multiple access system according to the present invention is a data transmission apparatus for transmitting data processed by an orthogonal frequency division transmission scheme through a plurality of antennas. A multi-antenna encoder module for performing a multi-antenna encoding on the input data symbol string to generate a data symbol string allocated to each transmit antenna; A precode adding module for adding each precode generated by performing encoding using an orthogonal code with respect to a specific precode to a data symbol string allocated to each of the transmitting antennas; And an OFDM data processing module which performs data processing by an orthogonal frequency division transmission method for each data symbol string to which each prefix is added.

The construction, operation and other features of the present invention will be readily understood by the preferred embodiments of the present invention described below with reference to the accompanying drawings. 2 is a block diagram of a preferred embodiment of a data transmission apparatus of a multi-input orthogonal frequency division multiple access system according to the present invention.

In FIG. 2 the input data stream is channel coded by the channel coding module 21. Channel coding is to add parity bits to system bits so that the receiver can correct errors that occur while data is being transmitted over the channel. As the channel coding method, a convolutional coding, a turbo coding, or a low density parity check (LDPC) coding method may be used, but is not limited thereto. The binary data channel coded by the channel coding module 21 is mapped to the QPSK or QAM signal by the modulation module 22. The data symbols output from the modulation module 23 are input to the MIMO encoding module 23 to perform multi-antenna encoding.

Multi-antenna encoding processes data by a promised method for the data symbols to increase the capacity, throughput, coverage, etc. of the system in transmitting data symbols over multiple transmit antennas. To do. Multi-antenna encoding methods include spatial division multiplexing (SDM) and space time coding (STC). The SDM technique maximizes the transmission rate by sending independent data to each antenna at the transmitting side, while the STC technique applies antenna diversity gain and coding by coding at the symbol level over the antenna, that is, the spatial domain and the time domain. It is a technique that gains and improves link level performance. A good combination and generalization of both SDM and STC techniques is Linear Dispersion Coding (LDC). All multi-antenna techniques can be represented by LDC matrices used for multi-antenna encoding and decoding. By multi-antenna encoding, data symbols to be transmitted through each transmit antenna may be distinguished.

The multi-antenna encoding is performed by the MIMO encoding module 23, and the pre-coding is added by the pre-coding module 24 to each data symbol string allocated to each transmitting antenna. The method of adding a precode to the data symbol string allocated to each transmit antenna by the precoding module can be roughly divided into two methods. First, a method of generating a plurality of prefixes corresponding to the number of data symbol strings, that is, the number of transmit antennas, is added to each data symbol string whenever each data symbol string is input. Secondly, a plurality of precodes corresponding to the number of transmission antennas generated in advance by a specific method are stored and added when a data symbol string is input.

Hereinafter, some embodiments of a method of generating a prefix and adding it to each data symbol string will be described.

Example  One

The first embodiment relates to a method of generating two prefixes by performing encoding using an orthogonal code based on one prefix in case of two transmitting antennas. That is, by multiplying the transposition code by the orthogonal code so that each of the two antennas can transmit. As the orthogonal code, an alamuti code or a hardmard code may be used, but is not limited thereto.

3 and 4 illustrate a method of generating a transposition code according to a first embodiment. As shown in Figures 3 and 4, the first embodiment is based on a specific prefix (e.g., each prefix in Table 1) in terms of two antennas and two subcarriers (2x2). In this method, two prefixes generated by frequency-axis encoding using an alamouti code are used as a prefix sequence for each transmit antenna. In Fig. 3 and Fig. 4, since the number of transmitting antennas is two, a 2x2 orthogonal code is used. Therefore, when using an orthogonal code of 3x3 or more, it is also applicable to a multi-antenna system having three or more transmit antennas.

The signal encoded and transmitted in the above manner is received by the receiver in the form of Equation 3 below.

)을 이용하여 각 안테나로부터의 채널값(

)을 다음의 수학식 4와 같이 추정할 수 있다.The received signal as shown in Equation 3 is a training symbol known to the receiver (

Channel value from each antenna using

) Can be estimated as in Equation 4 below.

와

번째 부반송파에 해당하는

번째 송신 안테나로부터의 채널

는 동일한 값이라 가정할 수 있고, 이와 같은 방법으로 채널추정은 각각의 수신 안테나에 동일하게 적용함으로써 가능하다.At this time

Wow

Corresponding to the first subcarrier

Channel from the first transmit antenna

Can be assumed to be the same value, and in this way, channel estimation is possible by applying the same to each receiving antenna.

In the multi-input / output transmission scheme, in order to estimate the channel using the precoding, the precoding sequence of the first antenna is generated by multiplying the orthogonal code by the precoding sequence used in the 0th antenna as in the first embodiment. This method not only enables channel estimation, but also shows the auto-correlation and cross-correlation of the precoding sequence of the 0th antenna. This can be maintained in the precoding sequence, allowing synchronization across multiple antennas.

FIG. 6 shows the results of a performance test when the precodes are transmitted through the two antennas in the channel environment as shown in Table 2 below, based on the pedestrian having a speed of 10 km / h. Except for perfect conditions (bottom curve in Fig. 6), the transposition code according to the method of Example 1 (second curve from bottom to bottom in Fig. 6) shows the best performance compared to other schemes. Able to know.

Tap Ped-b Relative delay (ns) Average power (dB) One 0 0 2 200 -0.9 3 800 -4.9 4 1200 -8.0 5 2300 -7.8 6 3700 -23.9

Example  2

Embodiment 2 is a method of performing encoding using an orthogonal code on a specific prefix and transmitting it for two time symbol intervals through a plurality of antennas. The nth symbol of the specific prefix that is the basis for generating a plurality of prefixes is generated. When x _n (n = 0, 1, 2, 3, ...), the 0th time symbol of the 2m and (2m + 1) th antennas (m = 0, 1, 2, 3, ...) And the n th symbol of the prefix assigned to the first time symbol are x _n , x _n ^* , x _n, and −x _n ^* , respectively.

In this case, it is preferable that the interval between symbols of the prefixes allocated to the 0 th time symbol of an arbitrary antenna is twice the interval between symbols of the specific prefix. Further, each symbol of the precode assigned to the first time symbol of the arbitrary antenna is preferably allocated between the symbols of the precode assigned to the 0th time symbol of the arbitrary antenna on the frequency axis.

When the number of transmitting antennas is four or more, the prefixes assigned to the 0th time symbol and the 1st time symbol of 2 (m + 1) and 2 (m + 1) + 1th antennas are 2m and 2m +, respectively. Preferably, the precodes assigned to the 0th time symbol and the 1st time symbol of the first antenna are allocated to the subcarriers shifted by one subcarrier interval on the frequency axis.

7 and 8 show a more specific embodiment when using two transmit antennas. In FIG. 7 and FIG. 8, unlike the precode of the first embodiment, the training symbol is increased to four subcarrier intervals (4 k ) and the precode transmitted in one OFDM symbol interval is transmitted during two OFDM symbol intervals. . In addition, as shown in FIG. 7, the sequence of the precode transmitted in the second OFDM symbol period is located in the 4k + 2th subcarrier by pushing the sequence of the precode transmitted in the first OFDM symbol period by two subcarrier intervals. Will be mapped in the form of an intersection. That is, in Embodiment 1, orthogonal code encoding is performed on a frequency (3 k th subcarrier, 3 ( k +1) th subcarrier) -space (0 th antenna, 1 st antenna), whereas Example 2 performs time ( 0-th symbol, the first symbol) - frequency (sub-carrier k 4, k 4 +2 sub-carrier) by performing on the area (0-th antenna, a first antenna) to reduce the distance between the frequency of the training symbols by a product of the orthogonal codes This eliminates the possibility of the same presymbol sequence as other cells. In addition, it is possible to prevent the peak-to-average power ratio (PAPR) from increasing in the same manner as in the second embodiment. On the other hand, according to the second embodiment, it is possible to make the pattern of the precode located in the 0th time symbol of each transmitting antenna to be the same, thereby maintaining autocorrelation and cross-correlation characteristics.

Transmitting the prefix over two OFDM symbols reduces the amount of data transmission of one OFDM symbol in time when compared to the first embodiment. Therefore, in order to compensate for this, it is preferable to perform the procedure described below and then transmit. 9 and 10 are diagrams for explaining this.

FIG. 9 illustrates a case where IFFT of the precode is transmitted and the CP is added to each time symbol in order to transmit the precoded encoding using the orthogonal code for two time symbol intervals, and then only a part of the repeated signals are transmitted. It is a figure.

More specifically described as follows. That is, as shown in FIG. 7, the presignal code in which the subcarrier spacing is increased to four intervals in one time symbol is represented by four identical signals repeated ( Ts − Tg ) on the time axis. Therefore, instead of transmitting all four identical signals repeated, as shown in FIG. 9, only two of four transmits in a time interval of ( Ts - Tg ) / 2, and the receiving side receives two received in time. The repeated signal is copied and restored to four identical signals during the ( Ts - Tg ) period and then passed through an OFDM receiver. Through the above process, the loss of the transmission amount in time can be reduced by one Tg, which is a CP section. In FIG. 10, if the OFDM symbol transmission interval is Ts and the CP transmission interval is Tg, the precode transmission interval Tp modified according to the method of FIG. 9 becomes Equation 5 below.

Tp = (Ts-Tg) / 2 + Tg

Fig. 11 shows another embodiment for reducing the time taken to transmit a transposition code. The method described in FIG. 9 takes 2 Tp = 2 {( Ts - Tg ) / 2 + Tg } to transmit the prefix during the 0th and 1st time symbols. This is Tg rather than Ts , which is the time taken to transmit the prefix in Example 1 It takes more time. In order to reduce such a time loss, the embodiment of FIG. 11 transmits the first precode time symbol without adding a CP.

The first precode symbol has a shape in which zero, one or two subcarriers are shifted depending on the antenna on the frequency axis. If an antenna having a shape in which one or two subcarriers are shifted is transmitted without adding a CP to the first prefix symbol on the time axis, performance degradation due to time delay may occur because there is no CP to prevent time delay. However, since the influence is insignificant in a channel having a low time delay and a high frequency selectivity, transmission without CP addition is possible. Fig. 12 is a graph showing a simulation result comparing performances with and without CP added to the first precode time symbol. Simulation results show that the deterioration that can be caused by not adding CP is not much greater than when adding CP, so it is possible to transmit without adding CP to the first precode time symbol.

FIG. 13 shows a change in time when the first precoded time symbol is transmitted without adding CP. FIG. Tp, which means the modified precode transmission interval for the 0 th time symbol, is expressed by Equation 5 above. Tp 'which means the transposed precode transmission interval without adding CP to the first time symbol is expressed by Equation 6 below.

Tp '= (Ts-Tg) / 2

When both sides of Equation 5 and Equation 6 are added, Tp + Tp '= Ts. Therefore, when transmitting without adding CP to the 0th precoding time symbol, two OFDM symbols for precoding of multiple antennas are transmitted in one symbol interval. In the same way, transmission is possible in time.

14 and 15 illustrate embodiments in which the number of transmit antennas is extended to eight by extending the embodiment of FIG. 7. In the embodiment of Fig. 14, the prefixes assigned to the 0th time symbol and the 1st time symbol of the 2 (m + 1) and 2 (m + 1) + 1th antennas are 0th of the 2m and 2m + 1th antennas, respectively. In this example, the prefixes allocated to the time symbol and the first time symbol are allocated to the subcarriers shifted downward by one subcarrier interval on the frequency axis.

In the embodiment of FIG. 15, the preamble assigned to the 0 th time symbol of the 2 (m + 1) th antenna is assigned to the same subcarrier as the precode assigned to the 0 th time symbol of the 2 m th antenna, and 2 (m +). 1) The prefix assigned to the first time symbol of the +1 th antenna is an example of shifting the prefix assigned to the first time symbol of the 2m + 1 th antenna by one subcarrier on the frequency axis. The embodiment of FIG. 15 has an effect of reducing synchronization complexity due to phase rotation with respect to the 0 th time symbol as compared with the embodiment of FIG.

Referring to FIG. 2 again, each data symbol string to which a pre-code is added is subjected to data processing for orthogonal frequency division transmission by each OFDM data processing module 25a to 25m, thereby performing each transmission antenna 26a to 26m. Is sent via. Here, the data processing for the orthogonal frequency division transmission means a data processing process generally required for transmitting data by the OFDM scheme, and includes serial-to-parallel conversion and IFFT (Inverse). Fast Fourier Transform), protection interval (CP) addition, and so on. Since the data processing method using the OFDM method is already known, a detailed description thereof will be omitted.

It is apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit and essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

According to the present invention, it is possible to perform efficient synchronization and channel estimation in a wireless communication system of a multi-input orthogonal frequency division transmission scheme.

In addition, in a wireless communication system of a multi-input orthogonal frequency division transmission method, it is possible to transmit a precode for each antenna and to estimate an independent channel change occurring between the transmitting and receiving sides in each antenna by using the training symbol of the transmitted precode. It can be effective.

Claims (31)

In the Multi Input Multi Output (MIMO) Orthogonal Frequency Division Multiple Access (OFDMA) system, Adding a precode generated by encoding using an orthogonal code for a specific precode to a data symbol string assigned to each transmit antenna; And And transmitting each data symbol string to which the pre-code is added through each transmit antenna through a data processing process using an orthogonal frequency division transmission method. In a multi-input orthogonal frequency division multiple access system, Generating a plurality of prefixes by performing encoding using an orthogonal code with respect to a specific prefix; Adding each generated precode to a data symbol string allocated to each transmit antenna; And And transmitting each data symbol string to which the pre-code is added through each transmit antenna through a data processing process using an orthogonal frequency division transmission method. The method according to claim 1 or 2, The encoding using the orthogonal code is performed by a product of an orthogonal code in frequency-space. The method according to claim 1 or 2, The encoding method using the orthogonal code is performed by a product of orthogonal codes in time, frequency, and space. The method of claim 3, The orthogonal code is an Alamouti code, a transposition code transmission method in a MIMO-OFDMA system, characterized in that. The method of claim 4, wherein When the nth symbol of the specific prefix is x _n (n = 0, 1, 2, 3, ...), the prefix of the preamble assigned to the 0th time symbol and the 1st time symbol of the 0th and 1st antennas. n-th symbol is x _n , x _n ^* , x _n and -x _n ^{* respectively} . The method of claim 6, The inter-symbol transmission method in the MIMO-OFDMA system, characterized in that the interval between the symbols of the prefix is assigned to the 0th time symbol of any antenna. The method of claim 7, wherein Preambles in the MIMO-OFDMA system, wherein each symbol of the precode assigned to the first time symbol of the arbitrary antenna is allocated between the symbols of the precode assigned to the 0th time symbol of the arbitrary antenna on the frequency axis. Call transfer method. The method of claim 7, wherein The prefixes assigned to the 0th time symbol and the 1st time symbol of 2 (m + 1) and 2 (m + 1) + 1th antennas are the 0th time symbol and 1st time of 2m and 2m + 1th antennas, respectively. A precode transmission method in a MIMO-OFDMA system, characterized in that the precode assigned to a symbol is assigned to a subcarrier shifted by one subcarrier interval on the frequency axis. The method of claim 7, wherein The prefix assigned to the 0 th time symbol of the 2 (m + 1) th antenna is assigned to the same subcarrier as the prefix assigned to the 0 th time symbol of the 2 m th antenna. Transmission method. The method of claim 10, Each symbol of the precode assigned to the first time symbol of the 0th antenna and the 1st antenna is allocated between the precoded symbols assigned to the 0th time symbol and the 0th time symbol of the 1st antenna, respectively, on the frequency axis. Pre-transmission method in MIMO-OFDMA system. The method of claim 11, The prefix assigned to the first time symbol of the 2 (m + 1) + 1th antennas is assigned by shifting the prefix assigned to the first time symbol of the 2m + 1th antenna by one subcarrier on the frequency axis. A precode transmission method in a MIMO-OFDMA system. The data processing of claim 6, wherein Converting the precode to a signal in a time domain; And inserting a guard interval (CP) into the precode converted into the signal in the time domain. The method of claim 13, And transmitting a portion of the time domain signal through each of the transmitting antennas when there is a overlapped portion of the time domain signal into which the guard interval is inserted. The method of claim 13, And a step of inserting a guard interval in both the 0th time symbol and the 1st time symbol in the step of inserting the guard interval. The method of claim 13, And a step of inserting the guard interval in the step of inserting the guard interval, inserting the guard interval only in the zeroth time symbol. A data transmission device for transmitting data processed by an orthogonal frequency division transmission method through a plurality of antennas, A multi-antenna encoder module for performing multi-antenna encoding on the input data symbol string to generate a data symbol string allocated to each transmit antenna; A precode adding module for adding each precode generated by performing encoding using an orthogonal code with respect to a specific precode to a data symbol string allocated to each of the transmit antennas; And And an OFDM data processing module for performing data processing according to an orthogonal frequency division transmission method for each data symbol string to which each prefix is added. The method of claim 17, And a precode generation module configured to generate a plurality of precodes by performing encoding using an orthogonal code on the specific precode. The method of claim 17, And a memory module for storing each prefix generated by encoding using an orthogonal code with respect to the specific prefix. The method of claim 17, The orthogonal code is an Alamouti code. The method of claim 17, When the nth symbol of the specific prefix is x _n (n = 0, 1, 2, 3, ...), the prefix of the preamble assigned to the 0th time symbol and the 1st time symbol of the 0th and 1st antennas. and the n th symbol is x _n , x _n ^* , x _n and -x _n ^* , respectively. The method of claim 21, And an interval between symbols of a precode assigned to a zeroth time symbol of an arbitrary antenna is twice the interval between symbols of the specific prefix. The method of claim 22, And each symbol of the precode assigned to the first time symbol of the arbitrary antenna is allocated between the symbols of the precode assigned to the 0th time symbol of the arbitrary antenna on the frequency axis. The method of claim 22, The prefixes assigned to the 0th time symbol and the 1st time symbol of 2 (m + 1) and 2 (m + 1) + 1th antennas are the 0th time symbol and 1st time of 2m and 2m + 1th antennas, respectively. And a precode assigned to a symbol is assigned to a subcarrier shifted by one subcarrier interval on a frequency axis. The method of claim 22, And a precode assigned to the 0 th time symbol of the 2 (m + 1) th antenna is assigned to the same subcarrier as the precode assigned to the 0 th time symbol of the 2 m th antenna. The method of claim 25, Each symbol of the precode assigned to the first time symbol of the 0th antenna and the 1st antenna is allocated between the precoded symbols assigned to the 0th time symbol and the 0th time symbol of the 1st antenna, respectively, on the frequency axis. Data transmission device. The method of claim 26, The prefix assigned to the first time symbol of the 2 (m + 1) + 1th antennas is assigned by shifting the prefix assigned to the first time symbol of the 2m + 1th antenna by one subcarrier on the frequency axis. Data transmission apparatus. The method of claim 21, wherein the OFDM data processing module, An IFFT converting unit converting the precode into a signal in a time domain; And a CP insertion unit for inserting a guard interval (CP) into the precode converted into the signal in the time domain. The method of claim 28, And a part of the time domain signal is transmitted through the plurality of transmit antennas when there is a overlapped portion of the time domain signal in which the guard interval is inserted. The method of claim 28, The CP insertion unit inserts a guard interval in both the 0 th time symbol and the 1 st time symbol. The method of claim 28, The CP insertion unit inserts a guard interval only in the 0 th time symbol.

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