KR100866195B1 - Stfbc coding/decoding apparatus and method in ofdm mobile communication - Google Patents

Abstract

The present invention modulates data input with a predetermined size into an Orthogonal Frequency Division Multiplexing (OFDM) symbol, and in the mobile communication system transmitting the OFDM symbol through at least two antennas, rotationally rotating the input data. Generate the first data and the second antenna signal by performing space-time block encoding on the input data and the copy data, and generating a first OFDM symbol by performing inverse fast Fourier transform on the first antenna signal. A first OFDM symbol is transmitted through a first antenna and at the same time, the second antenna signal is inversely fast Fourier-transformed to generate a second OFDM symbol, and the second OFDM symbol is transmitted through a second antenna to maximize transmission diversity effect. .

OFDM scheme, space-time block code, transmit diversity, cyclic rotation, channel estimation, cyclic rotation feedback

Description

Apparatus and method for spatio-temporal frequency-frequency coding / decoding in orthogonal frequency division multiplexing mobile communication system {STFBC CODING / DECODING APPARATUS AND METHOD IN OFDM MOBILE COMMUNICATION}

1 is a diagram illustrating a transmitter structure of a mobile communication system using a conventional orthogonal frequency division multiplexing scheme.

2 illustrates a receiver structure of a mobile communication system using a conventional orthogonal frequency division multiplexing scheme.

3 is a diagram illustrating a transmitter structure of a mobile communication system using an orthogonal frequency division multiplexing method according to an embodiment of the present invention.

4 is a diagram illustrating a receiver structure of a mobile communication system using an orthogonal frequency division multiplexing method according to an embodiment of the present invention.

5 shows a detailed configuration of the copy generator of FIG.

6 is a diagram showing a detailed configuration of the frequency diversity combiner of FIG.

7 is a diagram illustrating a control flow performed by a transmitter according to an embodiment of the present invention.

8 illustrates a control flow performed in a receiver according to an embodiment of the present invention.

9 is a diagram illustrating correlation between subcarriers with respect to a 0 th subcarrier according to an embodiment of the present invention.

10 is a diagram showing an example of a copy that can obtain the maximum frequency diversity according to an embodiment of the present invention.

11 is a diagram illustrating a receiver structure for performing decoding on N _R receiving antennas according to an embodiment of the present invention.

FIG. 12 is a diagram schematically illustrating a structure for feeding back a cyclic rotation amount according to a minimum cross-correlation of a transmission channel estimated by a receiver of a mobile communication system of an orthogonal frequency division multiplexing method according to an embodiment of the present invention.

FIG. 13 is a diagram illustrating a control flow performed in consideration of a cyclic rotation amount according to a mutual correlation fed back in a transmitter of a mobile communication system of an orthogonal frequency division multiplexing method according to an embodiment of the present invention.

FIG. 14 is a diagram illustrating a correlation between subcarriers with respect to a 0, 52, and 204th subcarrier according to an embodiment of the present invention. FIG.

The present invention relates to an apparatus and method for encoding / decoding in a mobile communication system using an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and more particularly to a space-time block coding transmission diversity ( STTD: Space Time block coding based Transmit Diversity, hereinafter referred to as "STTD") relates to a coding / decoding apparatus and method using.

Recently, the OFDM method, which is used as a useful method for high-speed data transmission in a wired / wireless channel, is a method of transmitting data using multi-carriers, and converts a symbol string serially input in parallel. Multi Carrier Modulation (MCM), which modulates each of the parallel-converted symbols into sub-carriers (Sub-Channels) having mutual orthogonality and transmits them, will be referred to as 'MCM'. It's a kind of way.

The system applying the MCM scheme was first applied to military high frequency radios in the late 1950s, and the OFDM scheme for superimposing a plurality of orthogonal subcarriers began to be developed since the 1970s, Since the implementation was a difficult problem, there was a limit to the actual system application. However, in 1971 Weinstein (SB Weinstein and PM Ebert, \ "Data transmission by frequency division multiplexing using the discrete Fourier transform, \" IEEE Trans. On Commun., Vol. 19, no. 4, pp. 628-675, Oct. 1971) et al. Announced that the modulation and demodulation using the OFDM scheme can be efficiently processed using a Discrete Fourier Transform (DFT). In addition, the use of guard intervals and the introduction of cyclic prefix guard intervals have further reduced the system's negative effects on multipath and delay spread. Thus, this OFDM scheme is used for digital audio broadcasting (DAB), digital television, wireless local area network (WLAN), wireless asynchronous transfer mode (WATM) or fixed broadband wireless access. It is widely applied to digital transmission technology such as fixed BWA. That is, the OFDM scheme is not widely used due to hardware complexity, but recently, a Fast Fourier Transform (FFT) and an Inverse Fast Fourier Transform (IFFT) are used. Various digital signal processing technologies including Transform, hereinafter referred to as " IFFT " The OFDM scheme is similar to the conventional Frequency Division Multiplexing (FDM) scheme, but above all, it is possible to obtain optimal transmission efficiency in high-speed data transmission by maintaining orthogonality among a plurality of subcarriers. In addition, since the frequency use efficiency is good and multi-path fading is strong, an optimum transmission efficiency can be obtained in high-speed data transmission. In addition, since the OFDM scheme uses a frequency spectrum superimposed, frequency use is efficient, strong for frequency selective fading, strong for multipath fading, and intersymbol interference using a guard interval (ISI). : It can reduce the effect of Inter Symbol Interference, and it is possible to design the equalizer structure simply by hardware, and it has the advantage that it is strong against impulsive noise. There is a trend.

Here, the operation of the transmitter and the receiver of the mobile communication system using the OFDM scheme will be briefly described as follows.                         

In the OFDM transmitter, input data is modulated into a subcarrier through a scrambler, a coder, and an interleaver. In this case, the transmitter may provide various variable data rates, and may have different coding rates, interleaving sizes, and modulation schemes according to the data rates. Typically, the coder uses coding rates such as 1/2, 3/4, etc., and the size of the interleaver to prevent burst errors is determined according to the number of coded bits per OFDM symbol (NCBPS). The modulation method uses Quadrature Phase Shift Keying (QPSK), Phase Shift Keying (8PSK), Quadrature Amplitude Modulation (16QAM), 64-ary Quadrature Amplitude Modulation (64QAM), etc., depending on the data rate. On the other hand, a signal modulated with a predetermined number of subcarriers by the above configurations is added with a predetermined number of pilots, which pass through an IFFT block to generate one OFDM symbol. After inserting a guard interval for eliminating intersymbol interference in a multi-path channel environment, a symbol waveform generator is called and finally inputted to a radio frequency (RF) unit to be transmitted through a channel.

In the receiver corresponding to the transmitter as described above, an inverse process occurs with respect to the process performed by the transmitter, and a synchronization process is added. First, a process of estimating a frequency offset and a symbol offset using a training symbol determined for the received OFDM symbol should be preceded. After that, the data symbols having the guard interval removed are recovered through a FFT block to a predetermined number of subcarriers to which a predetermined number of pilots are added. Also, in order to overcome the path delay phenomenon on the actual radio channel, the equalizer estimates the channel state of the received channel signal to remove the signal distortion on the actual radio channel from the received channel signal. The channel estimated data through the equalizer is converted into a bit string, passed through a de-interleaver, and then output as final data through a decoder and a de-scrambler for error correction. do.

Although the OFDM scheme as described above has a strong characteristic for frequency selective fading, its performance is limited. In order to overcome the limitations of the performance, the proposed performance improving devices are attracting much attention in the OFDM type mobile communication system using multiple antennas. However, since a receiver receiving a wireless data service is generally limited in size and power problems, it is a matter of implementation to provide the receiver with the multiple antennas. For this reason, transmission diversity (Tx diversity) technology has been developed that can improve performance deterioration due to fading while reducing complexity of the receiver by providing a plurality of transmit antennas in a transmitter having a more favorable environment than the receiver.

Among the many transmit diversity techniques developed to date, the STTD technique has a relatively small computational complexity and low complexity in implementation. In addition, the OFDM scheme is the most suitable communication scheme for applying the STTD technique, and overcomes the multipath phenomenon and simultaneously transmits a large amount of information without sacrificing a minimum frequency band.

Next, a transmitter structure of a mobile communication system using the OFDM scheme will be described with reference to FIG. 1.

1 is a diagram illustrating a transmitter structure of a mobile communication system using a conventional OFDM scheme. The structure of the transmitter shown in FIG. 1 is a structure of a transmitter in an OFDM mobile communication system incorporating the STTD technology.

Referring to FIG. 1, input data at a transmitter is encoded at a predetermined coding rate, and data 110 after encoding bits output by the encoding are interleaved is provided to the modulator 120. Here, although various methods have been proposed as the encoding method, a method of encoding using a turbo code, which is an error correction code, is typically used. In this case, coding rates such as 1/2 and 3/4 are used as the coding rates. The modulator 120 modulates the input data 110 by a predetermined modulation method and outputs modulation symbols. Here, the modulation schemes include 8PSK, 16QAM, 64QAM, QPSK, and the like, and each of the modulation schemes performs modulation by unique symbol mapping schemes. In FIG. 1, it is assumed that QPSK and QAM are used as modulation methods. The modulation symbols output from the modulator 120 are provided to the space-time block code encoder 130.

The space-time block code encoder 130 maps the modulation symbols to the space-time block code and outputs the modulation symbols encoded by the space-time block code. The signal output from the space-time block code encoder 130 is output through two paths for transmit diversity. The output signals from the space-time block code encoder 130 are provided to the first IFFT unit 140 and the second IFFT unit 150, respectively. Each of the first and second IFFT devices 140 and 150 performs an IFFT on subcarriers encoded by the space-time block code to output an OFDM symbol. OFDM symbols output from each of the first and second IFFT devices 140 and 150 are provided to corresponding first and second guard interval inserters 160 and 170, respectively. The first coded interval inserter 160 and the second guard interval inserter 170 may be guard intervals for each of the OFDM symbols output from the first IFFT 140 and the second IFFT 150. Insert Typically, the transmission of the OFDM symbol is processed in units of blocks, but is affected by the previous symbol while the OFDM symbol is transmitted through the multipath channel. In order to prevent such interference between OFDM symbols, the guard interval is inserted between consecutive blocks. OFDM symbols in which the guard intervals are inserted in the first and second guard interval inserters 160 and 170, respectively, may be formed through the first antenna ANT1 and the second antenna ANT2 through the first and second RF processors 180 and 190. It is sent on a multipath channel.

In FIG. 1, a transmitter structure of a mobile communication system using an OFDM scheme has been described. Next, a receiver structure corresponding to the transmitter structure will be described with reference to FIG.

2 is a diagram illustrating a receiver structure of a mobile communication system using a conventional OFDM scheme. The receiver structure shown in FIG. 2 is a receiver structure in a mobile communication system using an OFDM scheme incorporating the space-time block coding technique, and corresponds to the transmitter structure of FIG.

Referring to FIG. 2, a signal transmitted from a transmitter through a multipath channel is received by the first RF processor 210 and the second RF processor 220 through the first antenna ANT1 and the second antenna ANT2. Each of the first and second RF processors 210 and 220 down-converts a signal received through the first antenna ANT1 and the second antenna ANT2 to an intermediate frequency (IF) band and then converts the first and second RF processors 210 and 220 into the first and second RF processors 210 and 220. Output to each of the second guard interval remover (230,240). Each of the first guard interval remover 230 and the second guard interval remover 240 removes the guard interval inserted into the OFDM symbol output from the first RF processor 210 and the second RF processor 220. The OFDM symbol from which the guard interval is removed is provided to the corresponding first and second FFT units 250 and 260 to output a symbol encoded by a space-time block code through an FFT process. The symbol encoded by the space-time block code is provided to the space-time block code decoder 270 to perform decoding by the space-time block code. The modulation symbols decoded by the space-time block code are provided to a demodulator 280. The demodulator 280 demodulates the decoded modulation symbols in a demodulation scheme corresponding to a predetermined modulation scheme applied by the transmitter, and outputs coded bits, and the coded bits are deinterleaved and decoded to obtain original data 290. Is output. Here, the demodulator 280 sets the demodulation scheme to correspond to the QPSK and QAM scheme since the modulation scheme applied by the modulator 120 of the transmitter is the QPSK and QAM scheme.

In the structure of the transmitter and the receiver shown in FIG. 1 and FIG. 2, two antennas are used to apply the transmission diversity technique, but it will be apparent that two or more antennas can be used.

If N subcarriers are used in the OFDM-based mobile communication system, a signal passed through each of the first and second FFTs 250 and 260 in the receiver shown in FIG. 2 may be expressed as Equation 1 below. .

If Equation 1 is expressed as a determinant, Equation 2 is obtained.

In Equation 2, r denotes an N × 1 received symbol vector, x denotes an N × 1 transmission symbol vector, n denotes an N × 1 noise vector, and H denotes an N × N diagonal representing a frequency response of the channel. It is a matrix. In this case, the case where the receiver has one antenna and the case where the receiver has a plurality of antennas, for example N_R, will be described below.

(1) If the receiver has one antenna

When a signal transmitted by a space-time block code for two transmission antennas at a transmitter is received through one antenna at a receiver, a vector of signals received through the two transmission antennas is obtained by Equation 3 below. same.

의 허미시안(hermitian)을 곱하여 하기 <수학식 4>와 같이 얻어진다.In Equation 3, "*" represented by a superscript is an operator that complex conjugates each matrix component. H ₁ and H ₂ are frequency responses of respective channels, and x ₁ and x ₂ are vectors of transmission symbols. Therefore, the decoded signal is a channel matrix by the orthogonality of the space-time block code.

It is obtained by the following equation by multiplying the hermitian of:

Therefore, since the received signal after the decoding process of the space-time block code is obtained by multiplying the sum of the power of each channel, the second diversity gain is obtained.

(2) When the number of receiving antennas is N_R

When there are a plurality of antennas of the receiver, the received signals received through each of the plurality of antennas are decoded by a space-time block code decoding method and then decoded signals from each of the antennas are added. This may be represented by Equation 5 below.

In Equation 5, H _1m represents a channel frequency response between the first receiving antenna and the mth receiving antenna, and H _2m represents a channel frequency response between the second receiving antenna and the mth receiving antenna. Therefore, in case of having N _R reception antennas, the received signal after the decoding process of the space-time block code obtains a diversity gain of 2 N _R.

As described above, the mobile communication system using the OFDM scheme is a mobile communication system made to overcome interference between symbols by a wireless channel. However, it is not very strong in the signal attenuation effect caused by the multipath phenomenon of the wireless channel without other methods. In order to improve performance degradation due to the fading channel, an OFDM mobile communication system using STTD technology has been proposed. The proposed mobile communication system has the advantage of significantly reducing the complexity of the receiver when implementing the system by using multiple antennas in the transmitter. However, the performance of the OFDM communication system using the STTD technology is limited by the number of transmission antennas. That is, in the OFDM mobile communication system to which the STTD technology is applied, performance is determined by the number of transmission antennas, so it is inevitable to increase the number of transmission antennas in order to increase the performance of the system. For example, if the number of transmit antennas is increased to three or more to improve the performance of the system, the number of transmit antennas in the performance increases more than two. However, in the OFDM mobile communication system to which the STTD technology is applied, a large amount of calculation is largely increased in proportion to the number of transmitting antennas, and a decrease in transmission rate also occurs. Therefore, in the OFDM mobile communication system to which the STTD technology is applied, increasing the number of transmission antennas to three or more in order to improve performance may cause problems in terms of system complexity and transmission rate.

Accordingly, an object of the present invention to solve the above problems is to provide an apparatus and method for overcoming the distortion of the multipath fading phenomenon of the space-time block code using orthogonal frequency division multiplexing.

Another object of the present invention is to provide an apparatus and method for space-time-frequency block encoding / decoding that can efficiently use frequency diversity.

It is still another object of the present invention to provide an apparatus and method for obtaining a fourth diversity gain using only two transmit antennas and one receive antenna.

It is still another object of the present invention to provide an apparatus and method in which all processing processes are performed by linear operations in a mobile communication system using an orthogonal frequency division multiplexing method using a space-time block code.

The transmitting apparatus of the present invention for achieving the above objects; In a data transmission apparatus of an orthogonal frequency division multiplexing (OFDM) system, a first transmission antenna, a second transmission antenna, and input data are converted into a first OFDM symbol to be transmitted through the first transmission antenna. And an OFDM symbol generator for converting the input data into a second rotated OFDM symbol to be transmitted through the second transmit antenna.

According to an aspect of the present invention, there is provided a method of transmitting a data in an Orthogonal Frequency Division Multiplexing (OFDM) system, the method comprising: converting input data into a first OFDM symbol; Converting input data into a second OFDM symbol by rotating the input data; and mapping the first OFDM symbol to be transmitted through a first transmitting antenna and simultaneously mapping the second OFDM symbol to be transmitted through a second transmitting antenna. .

The receiving device of the present invention for achieving the above objects; An apparatus for receiving data in an orthogonal frequency division multiplexing (OFDM) system, the method comprising: a reception antenna for receiving a signal transmitted through transmission antennas and a signal received at the reception antenna for fast Fourier transform to generate an OFDM symbol A fast Fourier transformer, a decoder for space-time block decoding the OFDM symbol to generate a first transmit antenna signal and a second transmit antenna signal, and reversely rotate the first transmit antenna signal, and And a frequency diversity combiner for adding the second transmit antenna signal to demodulate the input data.

In accordance with another aspect of the present invention, there is provided a method of receiving a data in an orthogonal frequency division multiplexing (OFDM) system, which receives a signal transmitted through transmission antennas through a reception antenna. Generating a OFDM symbol by performing fast Fourier transform on the signal received through the receiving antenna, and generating a first transmit antenna signal and a second transmit antenna signal by space-time block decoding the OFDM symbol; Reverse-rotating the first transmit antenna signal, and adding the reverse-rotated signal and the second transmit antenna signal to demodulate the input data.

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

First, in the present invention, an Orthogonal Frequency Division Multiplexing (OFDM) scheme using two transmission antennas is called a space time block (STTD) in a mobile communication system. We propose an apparatus for encoding and decoding data using coding based Transmit Diversity (hereinafter, referred to as “STTD”) technology, which has two transmit antennas by simultaneously obtaining a spatial diversity gain and a frequency diversity gain. In this case, the same performance as that of using four transmission antennas is achieved, and the encoder using the STTD technology is divided into two parts.

이다. 그리고, 본 발명의 또 다른 실시예에서는 수신기에서 전송 채널들의 상호상관도(correlation)를 구하여 상호 상관도 값이 최소가 되는 부반송파의 위치를 상기 수신기에 상응하는 송신기의 순환 회전량 d로 설정한다. 여기서, 상기 수신기에서 전송 채널들의 상호상관도를 가지고서 순환 회전량 d를 설정하는 과정은 하기에서 설명할 것이므로 그 상세한 설명을 여기서는 생략하기로 한다. 다음으로 공간 다이버시티를 얻기 위해 복사본 발생기를 통해 만들어진 두 개의 OFDM 심벌들을 시공간 블록 부호에 맵핑시킨다.First, the encoder has one OFDM symbol made of N sub-carriers (Sub-Carriers, Sub-Channels) and generates two OFDM symbols made of N sub carriers to obtain frequency diversity. Generator). One of the two OFDM symbols is the same as the OFDM symbol originally input to the copy generator, the other is generated by rotating the input OFDM symbol by a certain amount. In the embodiment of the present invention, the degree of circular rotation of the OFDM symbol input from the copy generator is defined as a circular rotation amount “d”, and the circular rotation amount d is obtained based on statistical characteristics.

to be. In another embodiment of the present invention, the receiver obtains a correlation between the transmission channels and sets the position of the subcarrier whose cross-correlation value is minimum to the cyclic rotation amount d of the transmitter corresponding to the receiver. Here, since the process of setting the cyclic rotation amount d with the cross-correlation of the transmission channels in the receiver will be described below, a detailed description thereof will be omitted. Next, to obtain spatial diversity, two OFDM symbols generated by the copy generator are mapped to the space-time block code.

The transmitted signal is decoded through a reverse process of the process applied by the transmitter in the receiver. The decoder of the space-time block code can also be largely divided into two parts.

First, a first decoding process is performed by passing through a decoder of a space-time block code with a signal received over the air. The signal subjected to the first decoding process is output as two OFDM symbols. The two OFDM symbols output correspond to the OFDM symbols output from the copy generator of the transmitter. Therefore, the reception OFDM symbol corresponding to the transmission OFDM symbol cyclically rotated by the transmitter among the two OFDM symbols is again reversely rotated by the cyclic rotation amount d applied by the transmitter. Then, the inverse cyclically rotated OFDM symbol and another OFDM symbol are added. The decoding process is terminated by determining the combined OFDM symbol as the closest signal using the channel information.

By going through the above-described transmission and reception procedures, the space-time-frequency block code obtains a secondary spatial diversity gain and a secondary frequency diversity gain. In addition, since both encoding and decoding processes are performed only with linear processing, only simple operations are required. In addition, when the receiver obtains the cross-correlation of the transmission channels and sets the subcarrier position at which the cross-correlation is the minimum value as the cyclic rotation amount d to feed back to the transmitter corresponding to the receiver, the space-time-frequency Second-order spatial diversity gain and second-order frequency diversity gain for the block code are obtained. Determining the circulating rotation amount d using the cross-correlation diagram will be described below, and thus a detailed description thereof will be omitted. In addition, since both the encoding and decoding processes are performed only with linear processing, only a simple operation is required.

1. Covariance Matrix of Channels in OFDM Systems

The impulse response of a frequency selective fading channel with L multipaths is referred to as a finite impulse response (FIR) with L taps (FIR). Modeled as a filter. This may be represented by Equation 6 below.

In Equation 6, h (i) is the attenuation coefficient of the channel impulse response in the I-th path, and τ _i represents the delay time in the I-th path. Since τ is modeled with the FIR filter, τ _i is equal to the sample interval. Each channel coefficient, h (i), in a system using multiple antennas is modeled as an independent complex Gaussian random variable with zero mean. Therefore, the amplitude of each channel tap is Rayleigh distribution or Rician distribution and the phase is uniform distribution. It can also be assumed that the power delay profile of the channel is uniform or has an exponential distribution.

If the power delay profile of the channel is uniform, the frequency response of the channel corresponding to the kth subcarrier of the OFDM symbol passed through the FFT in the receiver due to the characteristics of the mobile communication system using the OFDM scheme is expressed by Equation 7 below. Can be expressed as:

In Equation 7, N is the total number of subcarriers of the OFDM symbol. In order to obtain the covariance matrix of the channel, a correlation value between the frequency response of the channel corresponding to the kth subcarrier and the frequency response of the channel corresponding to the (k + Δk) th subcarrier is obtained as shown in Equation 8 below.                     

은 i 번째 채널 탭 계수의 분산으로 채널의 i 번째 경로의 전력과 같다. 채널의 전력 지연 프로파일이 균일하기 때문에

이고,

은 경로들마다 서로 독립적이다. 그러므로, 상기 수학식 8은 하기 <수학식 9>로 유도된다.In Equation 8, a characteristic in which coefficients of each channel tap do not correlate with each other is used for developing the equation. In Equation 8

Is the variance of the i th channel tap coefficient, which is equal to the power of the i th path of the channel. Because the power delay profile of the channel is uniform

ego,

Are independent of each other in paths. Therefore, Equation 8 is derived from Equation 9 below.

In Equation 9, the channel vector H is defined as in Equation 10 below.                     

Therefore, the total covariance matrix C _H is obtained as shown in Equation 11 below.

In the matrix of Equation 11, ρ _Δk has the following characteristics by Equation 4.

First characteristic:

Second characteristic:

Third characteristic:

By the above first to third characteristics, the total covariance matrix C _H is represented by a cyclic Hermit matrix.

In the above description, the power delay profile of each of the channels is assumed to be uniform. However, when the power delay profiles of the channels are not the same, the covariance of the channels is not circulated by simulation verification. However, when the matrix is constructed based on the smallest cross-correlation, the cyclic characteristics of the above-described subcarriers are satisfied.

2. Optimal Subcarrier Selection for Maximum Frequency Diversity

The basic concept of diversity is to allow receivers to receive replicas of the same information over independent fading channels. Therefore, in order to obtain frequency diversity in a mobile communication system using an OFDM scheme, the same signal may be transmitted on different subcarriers. However, to get the maximum benefit from diversity, each copy must be received through an independent fading channel. Therefore, in order to maximize the frequency diversity gain in the mobile communication system using the OFDM scheme, the subcarriers having non-correlation with the copies must be searched for and transmitted through the retrieved subcarriers.

In addition, the complex Gaussian random variable does not change its characteristic even after passing through the FFT. This is because the FFT is a linear function. Therefore, H (k), the frequency response of the channel, is modeled as a complex Gaussian random variable with zero mean and single variance. Therefore, if two Gaussian random variables are uncorrelated due to the characteristics of the Gaussian distribution, the two random variables are independent. Therefore, the two channels to find a channel H (k ₂₎ for a k ₂ beonjjae sub-carriers do not have correlation to the channel H (k) for the k ₁ beonjjae sub-carriers is independent of each other.

Any value of the channel H (k ₁₎ and the channel H (k ₂₎ for any k ₂ beonjjae sub-carriers for any k ₁ beonjjae subcarrier is expressed as <Equation 12>.

인 조건을 만족해야 한다. 그러므로 상기 조건을 만족하기 위해서는 상기 수학식 12는 하기 <수학식 13>의 조건을 만족하면 된다.If there is no correlation between each other in Equation 12,

Condition must be met. Therefore, in order to satisfy the condition, Equation 12 may satisfy the condition of Equation 13 below.

이다. 단, 상기 <수학식 13>에서

이어야 한다. 상기 <수학식 13>에 나타낸 바와 같이 결국 서로 독립적인 채널은 두 개의 부 반송파들간 거리의 함수로 유도된다. 그러므로, 상기 <수학식 13>의 일반적인 해는 하기 <수학식 14>로 표현된다. In Equation 13

to be. However, in <Equation 13>

Should be As shown in Equation 13, channels independent of each other are derived as a function of the distance between two subcarriers. Therefore, the general solution of Equation 13 is expressed by Equation 14 below.

의 제한이 있으므로, 상기 m에도 역시 제한이 있게 된다. 그러나, 일반성을 잃지 않으면서서도 k₁=0으로 설정하는 것이 가능하다. 그러면,

이므로, 하기 <수학식 15>로 표현될 수 있다.In Equation 14, m is an integer other than 0. However, as shown in Equation 13,

Since m is limited, m is also limited. However, it is possible to set k ₁ = 0 without losing generality. then,

Therefore, it may be represented by Equation 15 below.

Applying Equation 15 to Equation 14, the Equation 15 is expressed as Equation 16 below.

"의 범위를 가진다.In the formula (16) m is an integer, L and N is a natural number, so m is "

Has a range of ".

Therefore, the number of subcarriers irrelevant to the 0 th subcarrier is L-1. Therefore, there are L subcarrier channels independent of each other including the 0 th subcarrier. According to the third characteristic of the covariance matrix of the channel described above, in the channel having L paths, the number of subcarriers independent of any k-th subcarrier and each other becomes L.

3. Space-time-frequency block code for maximum frequency diversity when using two transmit antennas

Matters to consider in proposing a space-time block code according to an embodiment of the present invention are as follows.

First, maximum frequency and spatial diversity gain

Second, keep the maximum distance for all subcarriers

Third, strong characteristics in channel correlation

In order to obtain the maximum frequency diversity gain, which is the first consideration, it is necessary to find a subcarrier that does not correlate the copies in the mobile communication system using the OFDM scheme and transmit the copies on the carrier. Next, a correlation between any one subcarrier and other subcarriers will be described with reference to FIG. 9.

9 is a diagram illustrating the correlation between subcarriers with respect to a 0 th subcarrier according to an embodiment of the present invention. In particular, when L = 4 and when N = 64, the 0 th subcarrier has the same power delay profile. It is a graph showing the magnitude component of the correlation between each subcarrier for.

Referring to FIG. 9, it can be seen that the correlation is reduced as the subcarrier index has a median value. On the other hand, if only the magnitude component of the correlation is seen, the second characteristic of the covariance matrix of the channel described above is symmetrical. Therefore, in order to have a strong characteristic on channel correlation, which is the third consideration mentioned above, a copy of a symbol should be transmitted on the lower side of the channel, that is, the middle subcarrier. In addition, since the covariance matrix of the channel becomes a circulant matrix due to the third characteristic of the covariance matrix of the channel, each row of the matrix is a circularly rotated form of the first row (which indicates correlation with the 0 th subcarrier). Therefore, channels independent of each other for each subcarrier are obtained in a cyclically rotated form. Therefore, the most ideal proposal for satisfying the third consideration mentioned above is to set the subcarrier position spaced apart by N / 2. This keeps the maximum distance because all subcarriers are all fairly equal to N / 2. Therefore, a subcarrier that satisfies the first while satisfying the second and the third of the above-mentioned considerations is the middle subcarrier among the subcarriers whose correlation is zero. Therefore, the subcarrier having no correlation divides the entire subcarriers into L equals by Equation 14, and Δk is an integer. Thus, the optimal Δk is given by Equation 17 below.

Since the correlation is cyclically rotated by the third characteristic of the above-described covariance matrix of the channel, the optimum subcarrier k 'with respect to the kth subcarrier is obtained as shown in Equation 18 below.

In Equation 18, mod denotes a modulo operation. Then, as an example, the position of the copy for obtaining the maximum frequency diversity when L = 4 and N = 8 will be described with reference to FIG. 10.

10 is a diagram showing an example of a copy position to obtain the maximum frequency diversity according to an embodiment of the present invention.

Referring to FIG. 10, as described above, all subcarriers are transmitted by carrying a copy on a subcarrier in a position spaced apart by N / 2. In FIG. 10, since the number of subcarriers is 8, that is, N = 8, a copy is carried at a subcarrier position of a position separated by 8/2, that is, a position separated by 4 subcarriers. That is, a copy of the first subcarrier is carried on a copy of the fifth subcarrier, a copy of the second subcarrier is carried on a copy of the sixth subcarrier, and so on, a copy of the eighth subcarrier is placed on a copy of the fourth subcarrier. Is sent.

Meanwhile, FIG. 9 illustrates the correlation between subcarriers for the 0 th subcarrier when the power delay profile of each channel is constant. Next, referring to FIG. 14, the power delay profile of each channel is not constant. In this case, correlation between subcarriers will be described.

14 is a diagram illustrating the correlation between subcarriers with respect to the 0, 52, and 204 th subcarriers according to an embodiment of the present invention.

Referring to FIG. 14, it can be seen that each channel has a minimum correlation because the power delay profile is not constant. The reason is that the power delay profile of each of the channels is not constant as described above, and the difference between the positions of the subcarriers having the minimum correlation with the 0 th subcarrier becomes the cyclic rotation amount d. Therefore, the position of the subcarrier having the minimum correlation with the corresponding subcarrier is set to the cyclic rotation amount d to transmit feedback to the transmitter, and the transmitter sets the cycle having the position of the subcarrier having the received minimum correlation. The spatiotemporal frequency diversity process is performed by rotating the copy symbol with the total amount d.

An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

(1) an apparatus for encoding space-time block codes

3 is a diagram illustrating a transmitter structure of a mobile communication system using an OFDM scheme according to an embodiment of the present invention.

Referring to FIG. 3, the space-time block code uses a space-time block code to obtain maximum space diversity with maximum frequency diversity gain. Therefore, the encoding process of space-time block code using two transmit antennas is as follows.

When the data 310 to be transmitted is input, the input data 310 is input to the modulator 312 to output one OFDM symbol s buffered by N subcarriers. The OFDM symbol s output from the modulator 312 is expressed by Equation 19 below.

Prior to applying the space-time block code, two OFDM symbols are generated using a replica generator 314 to obtain maximum frequency diversity. That is, the OFDM symbol s output from the modulator 312 is input to the copy generator 314, and the copy generator 314 outputs two different OFDM symbols. One OFDM symbol of the two OFDM symbols output from the copy generator 314 uses the original OFDM symbol s as it is, and the other OFDM symbol calculates the cyclic rotation amount d by Equation (17). By substituting Equation 18, the OFDM symbol s is rotated in rotation. That is, two OFDM symbols output from the copy generator 314 are X ₁ and X ₂ , and X ₁ and X ₂ are expressed as follows.

,

,

Next, a process of calculating the circulating rotation amount d will be described with reference to FIG. 7.

7 is a diagram illustrating a transmitter operation process according to an embodiment of the present invention. Referring to FIG. 7, in step 710, the transmitter calculates a cyclic rotation amount d for the OFDM symbol s and then proceeds to step 712. In step 712, the transmitter rotates a symbol vector by the calculated rotation amount d for the OFDM symbol s to generate a copy, and proceeds to step 714. Here, a detailed operation process and configuration of step 710 of determining the cyclic rotation amount d for the OFDM symbol s and step 712 of generating a copy of the OFDM symbol s with the determined cyclic rotation amount d are shown in FIG. 5. On the other hand, if the power delay profile for each of the channels is not constant, the cyclic rotation amount d is determined in a different manner from the method of determining in step 710, that is, based on the position of the subcarrier having the minimum correlation. In order to feed back the determined rotational rotation amount d to the transmitter, the rotational rotation amount determiner 516 determines the rotational rotation amount d. Thus, in the copy generator 314 of the transmitter, the OFDM s is cyclically rotated by the cyclic rotation amount d to generate a copy.

5 is a diagram illustrating a detailed configuration of the copy generator 314 of FIG. Referring to FIG. 5, the OFDM symbol s output from the modulator 312 is input to and stored in a buffer 512. Meanwhile, the OFDM symbol s stored in the buffer 512 is provided to the space-time block code encoder 316 as one output X ₁ of the copy generator 314. On the other hand, the OFDM symbol s stored in the buffer 512 is provided to the cyclic rotor 514. The cyclic rotator 514 rotates the OFDM symbol s by the cyclic rotation amount d determined by the cyclic rotation determiner 516 to the second output X ₂ of the copy generator 314 to the space-time block code encoder ( 316). In FIG. 5, the rotational rotation amount d determined by the rotational rotation amount determiner 516 is provided to a counter 518, and the counter 518 causes the rotational rotation amount d to be counted. I'm proposing. However, the counter 518 may not be an essential configuration. That is, it may be preferable to implement the cyclic rotation amount d determined by the cyclic rotation amount determiner 516 to cyclically rotate and output the OFDM symbol s stored in the buffer 512 provided to the circulator 514. will be.

Two OFDM symbols X ₁ and X ₂ generated through the copy generator 314 are input to the space-time block code encoder 316, and the space-time block code encoder 316 performs encoding by space-time block code. To perform. The process of encoding the space-time block code is performed in step 714 of FIG. 7. When the space-time block code is applied to two OFDM symbols X ₁ and X ₂ output from the copy generator 314, the two OFDM symbols are mapped as shown in Equation 20 below.

The two OFDM symbols mapped by Equation 20 are sent to each antenna through typical configurations of a transmitter using the OFDM scheme. That is, two OFDM symbols output from the space-time block code encoder 316 are respectively called a first inverse fast Fourier transform (IFFT) device 318 and a second IFTT device. Input 320. Each of the first IFFT unit 318 and the second IFFT unit 320 IFFT-processes the OFDM symbols output from the space-time block encoder 316, and then includes a first guard interval inserter 322 and a second protection unit. Output to section inserter 324. The first guard interval inserter 322 inserts a guard interval into the signal output from the first IFFT apparatus 318 and outputs the guard interval to the first RF processor 326, and the second guard interval inserter 324 is The guard period is inserted into the signal output from the second IFFT device 320 and output to the second RF processor 328. Each of the first RF processor 326 and the second RF processor 328 RF-processes the signals output from the first guard interval inserter 322 and the second guard interval inserter 324 to each antenna ANT1,. ANT2) to transmit to a wireless channel.

Meanwhile, in FIG. 5, a copy generator structure for generating a copy by determining a cyclic rotation amount d when each of the channels has a constant power delay profile has been described. However, as described above, when each of the channels does not have a constant power delay profile, the cyclic rotation amount d is not determined in the manner described with reference to FIG. 5. Therefore, a structure for feeding back the cyclic rotation amount d when each of the channels does not have a constant power delay profile will be described with reference to FIG. 12.

12 is a diagram schematically illustrating a structure for feeding back a minimum cross-correlation value of a transmission channel estimated by a receiver of a mobile communication system using an OFDM scheme to a transmitter.

Referring to FIG. 12, when the transmitter 1110 transmits two OFDM symbols of an original and a copy for two OFDM symbols s through two antennas, the receiver 1150 transmits the two antennas at the transmitter 1110. Receive two OFDM symbols transmitted. The received two OFDM symbols are input to a transmission channel correlation detector 1151, and the transmission channel correlation detector 1151 detects the correlation between subcarriers for transmission channels with the received two OFDM symbols. do. Here, the detected correlation between the subcarriers is input to the cyclic rotation amount determiner 1153, and the cyclic rotation amount determiner 1153 has a minimum cross-correlation value between the 0 th subcarrier between transmission channels and the cyclic rotation amount d. Decide on The circular rotation amount determiner 1153 feeds back the determined circular rotation amount d to the transmitter 1110.

Here, an operation process of the receiver 1150 illustrated in FIG. 12 will be described with reference to FIG. 13.

FIG. 13 is a diagram illustrating a control flow performed in consideration of a cyclic rotation amount d according to a cross-correlation feedback fed back by a transmitter of a mobile communication system using an OFDM scheme according to an embodiment of the present invention.

Referring to FIG. 13, first, in step 1210, the transmitter determines a cyclic rotation amount d fed back from a receiver, that is, a cyclic rotation amount d generated with a subcarrier position having a minimum cross correlation with a 0 th subcarrier between transmission channels. Proceed to step 1220. In step 1220, the transmitter cyclically rotates the symbol vector of the OFDM symbol input with the determined cyclic rotation amount d to generate a copy, and then proceeds to step 1230. In step 1230, the transmitter performs space-time block coding with the original OFDM symbol and the generated copy, and then proceeds to step 1240. In step 1240, the transmitter outputs the two space-time block-coded OFDM symbols to the IFFT unit of the corresponding antenna and ends. Here, the operation of the components according to the operation of the transmitter is also identical to the operation of the components described in FIG. 7 except that the cyclic rotation amount d is fed back from the receiver.

(2) Space-time-frequency block code decoding device

4 is a diagram illustrating a receiver structure of a mobile communication system using an OFDM scheme according to an embodiment of the present invention. Before describing FIG. 4, the following points should be noted. In FIG. 4, the receiver includes a plurality of antennas, for example, two antennas, that is, a first antenna ANT1 and a second antenna ANT2, and a signal received through the first antenna ANT1. A first RF processor 410 for RF processing and a second RF processor 412 for RF processing the signal received through the second antenna (ANT2). In addition, the receiver inputs the signal output from the first RF processor 410 to remove the guard interval, the first guard interval remover 414 and the signal output from the second RF processor 412 to input the guard interval. And a second guard interval eliminator 416 for removing the first guard interval eliminator 416 and performing FFT processing on the signal output from the first guard interval eliminator 414 and the second guard interval eliminator 416. And a second FFT unit 420 for performing FFT processing on the signal output from the. However, the receiver may be provided with only one antenna to perform the reception operation according to the present invention, and also may include the plurality of antennas to perform the reception operation according to the present invention. That is, the first antenna ANT1, the first RF processor 414, and the first FFT device 418 illustrated in FIG. 4 correspond to a structure when the receiver includes one antenna. A first antenna ANT1, a first RF processor 414, a first antenna 418, as well as a second antenna ANT2, a second RF processor 416, and a second FFT device 420 are provided together. If there is, it corresponds to the structure when the receiver is provided with two antennas.

Referring to FIG. 4, a signal passing through each of the FFT units 418 and 420 in a receiver of an OFDM mobile communication system having N subcarriers may be expressed in a matrix form as shown in Equation 21 below.

In Equation 21, r denotes an N × 1 received symbol vector, X denotes an N × 1 transmitted symbol vector, n denotes an N × 1 noise vector, and H denotes an N × N diagonal matrix indicating a frequency response of the channel. .

1) When there is one receiving antenna

As a characteristic of an OFDM mobile communication system, a received signal passing through the FFT devices 418 and 420 appears as a simple product of the frequency response of the channel and the transmission signal by Equation 21 even though the multipath fading channel is passed. . Therefore, the space-time block coded signal may be expressed as Equation 22 below.

In Equation 22, * denoted by superscript is an operator that complex conjugates each matrix component. H ₁ and H ₂ are diagonal matrices of the frequency response of the channel corresponding to each of the transmission antennas and the reception antennas, and X ₁ and X ₂ are transmission symbol vectors, respectively.

Meanwhile, the received signals output from the FFTs 418 and 420 are provided to the controller 601 of FIG. 6, and the received signals are divided into multipath channels and input to the respective buffers 603 and 605. The buffers 603 and 605 store received signals separated on the time axis, and output the received signals to the space-time block code encoder 422 when the received signals of a predetermined unit are stored. Received signals output from the buffers 603 and 605 are divided into r ₁ and r ₂ . An index for distinguishing the received signal, that is, a number indicated by a subscript in r ₁ and r ₂ corresponds to a time index. On the other hand, the r ₁ and r ₂ is the mixed signal is X ₁ and X ₂ which are separated from the transmitter by the use of space-time block code.

의 허미시안(hermitian)을 곱하여 하기 <수학식 23>과 같이 얻어진다.Accordingly, the signal decoded by performing the space-time block code decoder 422 of FIG. 8 by performing orthogonality of the space-time block code is performed in the channel matrix.

It is obtained by the following equation by multiplying the hermitian of:

와

에서 상기

는 상기

을 순환 회전시켜 발생시킨 것이므로, 도 6의 역순환 회전기(612)는 상기 도 8의 818단계에서 상기

를 상기 송신기에서 수행된 순환 회전의 역동작으로서 상기 순환 회전량 d만큼 역 순환 회전시킨다. 상기 역 순환 회전을 위해서는 역 순환 회전할 역 순환 회전량 d가 요구된다. 상기 역 순환 회전량 d는 순환 회전량 결정기(616)에 의해 결정된다. 상기 역 순환 회전량은 상기 도 8의 810단계에서 수행된다. 상기 역 순환 회전시켜 발생된 심벌

의 각 부 반송파는 하기 <수학식 24>와 같이 나타난다.The symbol vector decoded in Equation 23

Wow

From above

Above

Is generated by circular rotation, the reverse rotation rotator 612 of FIG.

Is reversely rotated by the circular rotation amount d as a reverse operation of the circular rotation performed in the transmitter. For the reverse rotation, the reverse rotation amount d to reverse rotation is required. The reverse circulation amount d is determined by the circulation amount determiner 616. The reverse rotation amount is performed in step 810 of FIG. 8. A symbol generated by the reverse rotation

Each subcarrier is represented by Equation 24 below.

는 역 순환 회전에 의해 하기 <수학식 25>와 같이 실제 전송된 OFDM 심벌 s로 표현할 수 있다.Therefore, the equation excluding the noise component by Equation 23

Can be expressed by the actual transmitted OFDM symbol s by Equation 25 by reverse rotation.

과 상기

가 똑같은 전송 심벌 벡터 s를 포함하고 있으므로, 상기 두 벡터를 더한 심벌 벡터

의 k 번째 부 반송파는 하기 <수학식 26>과 같이 표현된다. remind

And said

Contains the same transmission symbol vector s, so the two vectors plus the symbol vector

The kth subcarrier of is expressed by Equation 26 below.

이다.here,

to be.

과 상기

는 상기 도 6의 가산기(614)에 의해 가산되며, 상기 가산 과정은 상기 도 8의 820단계에서 수행된다.remind

And said

6 is added by the adder 614 of FIG. 6, and the adding process is performed in step 820 of FIG. 8.

과

도 서로 독립적이다. 또한, 상기 <수학식 17>에서 순환 회전량 d 값은 각 부 반송파들간 채널이 서로 독립이 되도록 정해졌으므로, H₁(k)와

도 서로 독립적이다. 그리고, H₂(k)와

도 서로 독립적이다. 그러므로 상기 <수학식 26>에서 전송 신호 s(k)는 2차의 공간 다이버시티 이득과 2차의 주파수 다이버시티 이득으로 전체 4차의 다이버시티 이득을 얻는다는 것을 보여준다.In general, in a mobile communication system using multiple antennas, channels between antennas are independent of each other. Therefore, H ₁ and H ₂ are independent of each other. Therefore, in Equation 26, H ₁ (k) and H ₂ (k) are independent of each other,

and

Are also independent of each other. In addition, in Equation 17, the cyclic rotation amount d is determined such that channels between subcarriers are independent of each other, so that H ₁ (k) and

Are also independent of each other. And H ₂ (k) and

Are also independent of each other. Therefore, in Equation 26, the transmission signal s (k) shows that the fourth-order diversity gain is obtained with the second-order spatial diversity gain and the second-order frequency diversity gain.

Therefore, the same performance as that of the OFDM communication system using the space-time block code using four transmission antennas with only two transmission antennas is achieved. After decoding the space-time block code by the space-time block code decoder 422 and completing the decoding process through the frequency diversity combiner 424, the signal is input to the demodulator 426 in step 822 of FIG. To provide a demodulation process. The demodulation process by the demodulator 426 may be performed by Equation 27 below.

가 결정된다.
Output data by Equation 27

Is determined.

2) When the receiving antenna is N _R

Similar to the case of the space-time block code, the received signals are decoded for each receiving antenna by the method of decoding the space-time block code, and then the decoded signals are summed for each antenna. This may be represented by Equation 28 below.

In Equation 28, H _1m and H _2m represent the frequency response of the channel between the first antenna and the m-th antenna, and the frequency response of the channel between the second and m-th antennas, respectively. Therefore, the signal encoded by the space-time block code in Equation 28 is obtained by adding N _R equations of Equation 23. Since the channels between the receiving antennas are independent of each other, the spatial diversity gain is 2N _R. Next, frequency diversity is combined in the same process as in the case of one reception antenna described above. Therefore, if the reception antenna is N _R , the space-time-frequency block code using two transmit antennas obtains a diversity gain of 2 × 2N _R.

In the case where the reception antenna is N _R, the configuration of the receiver according to the embodiment of the present invention is as shown in FIG. 11. FIG. 11 illustrates a receiver structure for decoding N _R reception antennas according to an embodiment of the present invention.

Referring to FIG. 11, the controller 1101 divides a symbol encoded by a space-time block code provided from the FFT units 418 and 420 shown in FIG. 4 by a multipath channel and a reception time axis. Each symbol is distributed to the corresponding buffers 1102. The symbols distributed from the controller 1101 are provided to the corresponding buffer 1102, and each buffer 1102 provides the corresponding space-time block code decoder 1103 when symbols of a predetermined size are stored. In this case, symbols output from the buffer are divided into r ₁₁ , r ₂₁ ,..., R _1m , and r _2m . In the representation of the symbols, the number before the subscript corresponds to the time index, and the number after the subscript indicates the multipath channel. Meanwhile, the space-time block code decoders 1103 are provided in the same number as M _R , which is the number of reception antennas. The modulation symbols output from the plurality of space-time block code decoders 1103 are provided to the complex summer 1104, summed into one modulation symbol, and output. Subsequent operations of processing the modulation symbol output by the complex summer 1104 are processed by the same process as in the case where there is only one reception antenna.

As described above, the apparatus and method for space-time encoding / decoding according to the present invention can achieve the same performance as using two or four transmission antennas with only one or two transmission antennas without a great increase in complexity. In the present invention, the diversity gain of the second or fourth order can be obtained using only one or two transmit antennas by a transmission diversity scheme that utilizes not only spatial diversity but also frequency diversity. Therefore, the linear performance such as simple circular rotation can improve the performance without increasing the complexity due to the increase of the transmit antenna. In addition, since it maintains perfect compatibility with the OFDM-based mobile communication system using a space-time block code, the performance can be improved while fully utilizing the existing mobile communication system. In addition, in the channel environment where the strong characteristics of the multipath fading channel and the antennas are highly correlated, the performance improvement is larger than that of the conventional mobile communication system. In addition, even if the power delay profile of each channel is not constant, the receiver estimates the cyclic rotation amount according to the correlation through the transmission channel estimation and feeds it back to the transmitter so that it is not an ideal environment. The same environment has the advantage of maximizing spatial diversity and frequency diversity effects. Therefore, the present invention will be used as a technique to be applied to the future mobile communication system to improve the performance of the system.

Claims (31)

A data transmission apparatus of an orthogonal frequency division multiplexing (OFDM) system, A first transmitting antenna, A second transmit antenna, An OFDM symbol generator converting input data into a first OFDM symbol and mapping the first data to be transmitted through the first transmission antenna, and converting the input data into a second rotated second OFDM symbol to be transmitted through the second transmission antenna. Data transmission device. The method of claim 1, wherein the OFDM symbol generator, An inverse fast Fourier transformer for converting an input frequency domain signal into a time domain signal; And a circulator for rotating the input data in a frequency domain in phase. The method of claim 1, wherein the OFDM symbol generator, And a circular rotator for rotating the input data in a frequency domain to generate the second OFDM symbol. The method of claim 3, wherein the OFDM symbol generator, And a cyclic rotation amount determiner for determining a cyclic rotation amount for phase rotation of the input data and outputting the determined cyclic rotation amount to the circulator. The apparatus of claim 4, wherein the circulating rotation amount determiner determines the circulating rotation amount using Equation (29). <Equation 29>

Here, d is a cyclic rotation amount, N is the total number of subcarriers included in any one OFDM symbol of the first OFDM symbol and the second OFDM symbol, L is the number of multipaths. The method of claim 4, wherein the OFDM symbol generator, And a counter for counting the determined cyclic rotation amount. The method of claim 4, wherein the circulating rotation amount determiner And a cyclic rotation amount is determined using a position value of a subcarrier having a minimum correlation with a first subcarrier among the subcarriers included in the first OFDM symbol or the second OFDM symbol. The method of claim 1, wherein the OFDM symbol generator, And a space-time block encoder that encodes each of the input data and the rotationally rotated input data. The method of claim 8, wherein the OFDM symbol generator, And an inverse fast Fourier transformer for converting the space-time block coded input data and the cyclically rotated input data into frequency domain signals, respectively. The method of claim 1, wherein the OFDM symbol generator, And an inverse fast Fourier transformer for converting each of the input data and the circularly rotated input data into a time domain signal. In the data transmission method of Orthogonal frequency Division Multiplexing (OFDM) system, Converting the input data into the first OFDM symbol; Converting the input data into a second OFDM symbol by rotating the input data; Mapping the first OFDM symbol to be transmitted through a first transmitting antenna, and mapping the second OFDM symbol to be transmitted through a second transmitting antenna. The method of claim 11, wherein the converting of the second OFDM symbol comprises: Phase rotating the input data in the frequency domain; And converting the phase rotated signal into an inverse fast Fourier transform into a time domain signal. The method of claim 12, wherein the phase rotation process, And determining a cyclic rotation amount for the phase rotation of the input data. The method of claim 13, wherein the phase rotation process, Using the following Equation 30 to determine the rotational rotation amount, And rotating the input data in phase according to the determined cyclic rotation amount. <Equation 30>

Here, d is a cyclic rotation amount, N is the total number of subcarriers included in any one OFDM symbol of the first OFDM or second OFDM symbol, L is the number of multipath. The method of claim 13, wherein the phase rotation of the input data on the frequency axis comprises: And counting the determined rotational rotation amount. According to claim 13, The circulating rotation amount, And determining the position value of the subcarrier having the minimum cross-correlation with the first subcarrier among the first OFDM symbol or the second OFDM symbol. The method of claim 12, wherein the phase rotation process, And space-time block encoding each of the input data and the cyclically rotated input data. The method of claim 11, wherein the converting of the first OFDM symbol comprises: And spatiotemporal block encoding the input data. The method of claim 18, wherein converting the first OFDM symbol comprises: And converting the space-time block coded input data into an inverse fast Fourier transform into a time-domain signal. In the data receiving apparatus of Orthogonal frequency Division Multiplexing (OFDM) system, A receiving antenna for receiving a signal transmitted through the transmitting antennas; A fast Fourier transformer for generating an OFDM symbol by performing fast Fourier transform on the signal received from the reception antenna; A decoder for generating a first transmit antenna signal and a second transmit antenna signal by space-time block decoding the OFDM symbol; And a frequency diversity combiner configured to reverse-rotate the first transmit antenna signal and to demodulate the input data by adding the reverse-rotated signal and the second transmit antenna signal. The method of claim 20, wherein the frequency diversity combiner, And a reverse circulation rotor configured to reversely rotate the first transmitting antenna signal by a preset rotational rotation amount. delete 22. The apparatus of claim 21, wherein the frequency diversity combiner; A circulation rotation amount determiner for determining the circulation rotation amount; And a counter for counting the determined cyclic rotation amount. The method of claim 23, wherein the circulating rotation amount determiner, A data receiving apparatus according to Equation (31) to determine a circulating rotation amount. <Equation 31>

Where d is a cyclic rotation amount, N is the total number of subcarriers of the OFDM symbol, and L is the number of multipaths. The method of claim 24, wherein the circulating rotation amount determiner, And feeding back the determined rotational rotation amount to a transmitter. In a data receiving method of an orthogonal frequency division multiplexing (OFDM) system, Receiving a signal transmitted through transmission antennas through a reception antenna, Generating an OFDM symbol by performing fast Fourier transform on a signal received through the receiving antenna; Generating a first transmit antenna signal and a second transmit antenna signal by space-time block decoding the OFDM symbol; And performing reverse cyclic rotation of the first transmitting antenna signal and adding the reverse cyclically rotated signal and the second transmitting antenna signal to demodulate the input data. The method of claim 26, Reverse rotation of the first transmission antenna signal, And reversely rotating the first transmitting antenna signal by a predetermined cyclic rotation amount. The method of claim 27, wherein the circulating rotation amount is And determining a location value of a subcarrier having a minimum cross-correlation with a first subcarrier among the subcarriers included in the OFDM symbol. The method of claim 27, wherein the rotational rotation amount, A method for receiving data, characterized in that determined using Equation 32. <Equation 32>

Where d is a cyclic rotation amount, N is the total number of subcarriers of the OFDM symbol, and L is the number of multipaths. The method of claim 27, And transmitting the determined cyclic rotation amount to a transmitter. The method of claim 23, wherein the circulating rotation amount determiner, And the cyclic rotation amount is determined using the first transmit antenna signal using a subcarrier position value having a minimum cross correlation with the first subcarrier among the subcarriers included in the OFDM symbol.

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