KR20080004650A - Apparatus and method for transmission in mimo system - Google Patents

Abstract

An apparatus and a method for transmission in an MIMO system are provided to consider channel and coding techniques in determining a cyclic delay time by using CDD(Cyclic Delay Diversity) techniques and to easily apply to all of OFDM systems regardless of kinds of method such as MIMO-OFDM system and duplexing system, thereby realizing optimal performance. An apparatus for transmission in an MIMO(Multiple Input Multiple Output) system comprises a first determiner(316), a second determiner(318), a generator(300,302,304), plural variable delayers(306-2~306Nt) and plural RF(Radio Frequency) processors(310-1~310-Nt). The first determiner determines a coding rate by using channel information. The second determiner determines a cyclic delay time to be applied to each of plural antennas(312-1~312-Nt) by using the coding rate from the first determiner and the channel information. The generator generates baseband sample data. The plural variable delayers shift sample data from the generator as much as a corresponding cyclic delay time under the control of the second determiner and outputs the sample data. The plural RF processors process each of the sample data from the variable delayers and transmit the sample data through a corresponding antenna.

Description

Transmission apparatus and method in a multi-antenna system {APPARATUS AND METHOD FOR TRANSMISSION IN MIMO SYSTEM}

1 is a diagram illustrating channel characteristics according to CDD application in a multi-antenna system.

2 is a diagram illustrating a configuration of a transmitter in a MIMO-OFDM system to which a CDD according to the prior art is applied.

3 is a diagram illustrating a configuration of a transmitter in a MIMO-OFDM system to which a CDD is applied according to an embodiment of the present invention.

4 is a diagram illustrating a transmission procedure of a transmitter in a MIMO-OFDM system employing a CDD according to an embodiment of the present invention.

5 to 8 are graphs comparing FER performance.

The present invention relates to a transmission apparatus and a method in a multi-antenna system, and in particular, to provide an apparatus and method for varying the cyclic delay time for each antenna in a multi-antenna system using a cyclic delay diversity (CDD) technique. have.

Recently, multiple-input multiple-output (MIMO) -orthogonal frequency division multiplexing (OFDM) technology is a powerful feature of next-generation communications in that spatial diversity gain and multi-path gain can be achieved with a simple receiver structure. It is emerging as a candidate.

In addition, an error control coding technique is used together to maximize the multipath gain in the MIMO-OFDM system. That is, the greater the delay spread, the greater the frequency selectivity can be obtained using coding. However, if the channel has a small delay spread, multipath gain cannot be obtained efficiently. Thus, a CDD technique has been proposed to provide sufficient multipath gain.

The CDD technique is a method of increasing diversity gain by providing a predetermined delay time for each antenna. This cyclic delay in the time domain causes phase rotation between subcarriers in the frequency domain, thereby reducing the correlation between subcarriers. This reduction in correlation can increase frequency selectivity, and consequently, improve error performance, as shown in FIG.

개 (

는 송신 안 테나 수)의 연속된 부반송파들간의 상관성만이 0이 된다는 단점이 있다. An important point in the CDD technology is the selection of delay time. In the past, a method of selecting a delay time such that the frequency correlation between adjacent subcarriers becomes zero has been proposed. However, this method is simple

Dog (

Has a disadvantage that only correlation between successive subcarriers of the number of transmission antennas is zero.

2 illustrates a configuration of a transmitter in a MIMO-OFDM system employing a CDD according to the prior art.

As shown, the transmitter includes an encoder 200, a modulator 202, an IFFT operator 204, a plurality of delayers 206-2 to 206-N _t , a plurality of guard interval inserters 208-. 1 to 208-N _t ) and a plurality of antennas 210-1 to 210 -N _t .

Referring to FIG. 2, first, the encoder 200 encodes transmission data at a given code rate and outputs code symbols. Here, the encoder 200 is a trellis encoder. The modulator 202 modulates the data from the encoder 200 according to a given modulation scheme and outputs modulation symbols.

An IFFT operator 204 outputs sample data by inverse fast Fourier transforming of the data from the modulator 202. The sample data thus output is provided to the first guard interval inserter 208-1 and the plurality of delayers 206-2 to 206-N _t . Each of the plurality of delayers 206-2 to 206-Nt cyclically delays and outputs input sample data according to the determined delay time.

The first guard interval inserter 208-1 inserts and outputs a guard interval (GI) in the sample data from the IFFT operator 204. In addition, each of the remaining guard interval inserters 208-2 to 208 -N _t inserts and outputs a guard interval in sample data from a corresponding delayer. In this way, each of the sample data output from the guard interval inserters 208-1 to 208-N _t is transmitted through a corresponding antenna.

와 같다. 또한,

은 서로 독립적이고,

을 만족하는 전력 분포를 가지며,

의 통계치(statistic)는 각 송신 안테나별로 동일하다고 가정한다. 그러면,

채널 벡터

의 상관 행렬 은 평균이 '0'인 복소 가우시안이 된다.For example, assume a frequency selective Rayleigh fading channel, and assume block fading in which the channel is static in one OFDM symbol period and the channel changes independently for each symbol. Here, if L is the number of channel taps, the discrete time baseband channel impulse response vector is

Same as Also,

Are independent of each other,

Has a power distribution that satisfies

The statistics of are assumed to be the same for each transmit antenna. then,

Channel vector

Correlation matrix Is a complex Gaussian with an average of zero.

Assuming that the receiver fully knows the effective channel transfer function considering the effects of delay time, after removing the guard interval and performing the FFT, the received signal at the p-th subcarrier is expressed as in Equation 1 below. Can be.

는 다음 <수학식 2>와 같이 나타낼 수 있다.Here, w (p) becomes iid (independent and identically distributed) complex Gaussian noise with an average of 0 and variance N ₀ . And efficient channels

Can be expressed as Equation 2 below.

는 채널 임펄스 응답의 전달함수가 된다. 상기 <수학식 2>에서 알 수 있듯이, 순환 지연 시간은 전달함수에서의 위상 회전을 야기한다. At this time,

Becomes the transfer function of the channel impulse response. As can be seen from Equation 2, the cyclic delay time causes the phase rotation in the transfer function.

는 다음 <수학식 3>과 같이 정리될 수 있다.Meanwhile, the efficient channel

Can be summarized as Equation 3 below.

Therefore, Equation 1 may be summarized as Equation 4 below.

는 SF(space-frequency) 코드의 심볼로 해석될 수 있고,

를 브랜치(branch)에서의 심볼로 정의하면 비터비 복호기는

와 같이 브랜치 매트릭을 계산할수 있다.From Equation 4

Can be interpreted as a symbol in space-frequency (SF) code,

Is defined as a symbol in the branch, the Viterbi decoder

You can calculate branch metrics like this:

번째 안테나에서의 지연 시간은 다음 <수학식 5>와 같이 나타낼 수 있다.In the system model as shown in FIG. 2, the delay time used in the delayers 206-2 to 206-N _t is designed to zero-forcing the correlation between adjacent subcarriers.

The delay time at the first antenna may be expressed as Equation 5 below.

는 부반송파 개수(FFT 사이즈)를 나타내고,

는 송신 안테나의 개수를 나타낸다.here,

Represents the number of subcarriers (FFT size),

Denotes the number of transmit antennas.

개의 인접한 부반송파들 사이의 상관값은 '0'이 되는 반면,

부반송파만큼 떨어진 거리에서의 상관값은 '0'이 되지 않는다. 뿐만 아니라,

거리를 주기로 상관 패턴이 반복되는 특징을 갖는다. 2개의 송신 안테나를 갖는 시스템을 예로 들면, 홀수번째와 짝수번째 부반송파 간의 상관값은 '0'이 되지만, 홀수번째들 혹은 짝수번째들 사이의 상관값은 '0'이 되지 않는다. When the delay time is determined as in Equation 5,

The correlation between the two adjacent subcarriers is '0',

The correlation value at a distance separated by the subcarrier does not become '0'. As well as,

The correlation pattern is repeated with a distance. In the example of a system having two transmitting antennas, the correlation value between odd and even subcarriers is '0', but the correlation value between odd or even numbers is not '0'.

As described above, the prior art considers only the selectivity of the frequency domain, and does not consider the coding used to obtain diversity. However, since coding is an important part in determining the performance of the CDD, it is preferable to consider coding in determining the delay time. In other words, when considering channel characteristics and coding schemes, the prior art has a problem that it does not guarantee the optimal delay time.

Accordingly, an object of the present invention is to provide an apparatus and method for optimizing delay time for each antenna in a multi-antenna system using a CDD technique.

Another object of the present invention is to provide an apparatus and method for varying antenna delay time in a multi-antenna system using a CDD technique.

Another object of the present invention is to provide an apparatus and method for determining delay time for each antenna in consideration of PEP in a multi-antenna system using a CDD technique.

Another object of the present invention is to provide an apparatus and method for determining antenna delay time according to signal to noise ratio (SNR) and coding rate in a multiple antenna system using a CDD technique.

According to an aspect of the present invention for achieving the above object, a transmission apparatus in a multi-antenna system using a cyclic delay diversity scheme, comprising: a first determiner for determining a code rate using channel information, and the first determiner And a second determiner for determining a cyclic delay time to be applied to each of the plurality of antennas using the code rate and the channel information.

According to another aspect of the present invention, in a multi-antenna system using a cyclic delay diversity scheme, a step of determining a code rate using channel information, and a plurality of using the determined code rate and the channel information And determining a cyclic delay time to be applied to each of the antennas.

Hereinafter, the operating principle of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

Hereinafter, a scheme for varying a cyclic delay for each antenna in a multiple antenna system using a CDD scheme will be described. Hereinafter, an embodiment of the present invention describes a case in which a cyclic delay time is determined by using PEP (Pairwise Error Probability), but in another embodiment, a cyclic delay time is determined using a frame error rate (FER) related to channel coding. It may be.

First, a process of inducing the PEP will be described.

대신

을 선택할 확률인 조건부 PEP는 다음 <수학식 6>과 같이 나타낼 수 있다. The length N _e of the error event in the convolutional code (or trellis code) is defined as the number of trellis intervals until the error path diverges from the transmission path and merges back into the transmission path. In this case, assuming that the error event started on the p-th subcarrier, the transmission path in the transfer function of a given efficient channel (see Equation 3)

instead

The conditional PEP, which is a probability of selecting, may be expressed as in Equation 6 below.

와

사이의 유클리드 거리를 나타내는

는 다음 <수학식 7>과 같이 나타낼 수 있다.At this time,

Wow

Representing the Euclidean distance between

Can be expressed as Equation 7 below.

Equations 6 and 7 refer to G. Bauch, "Capacity optimization of cyclic delay diversity," in Proc. IEEE VTC 2004-Fall, vol. 3, pp. 1820-1824, Sept. 2004. The detailed description thereof will be omitted here.

의 요소들은 유사한 전력을 갖지 않기 때문에 채널 벡터를 백색화하기 위해서 상기 <수학식 7>을 다시 정리하면 다음 <수학식 8>와 같 이 나타낼 수 있다.Generally, channel vector

Since the elements of do not have similar powers, in order to whiten the channel vector, Equation 7 may be rearranged as in Equation 8 below.

,

는

(

)의 제곱근(square root)이다.here,

,

Is

(

Square root.

는 다음 <수학식 9>와 같이 나타낼 수 있다.therefore,

Can be expressed as Equation 9 below.

는 <수학식 10>과 같다.therefore,

Is shown in Equation 10.

와

는 상기 수학식 3에 설명된 바와 같다.As described in Equation 10 above

Wow

Is as described in Equation 3 above.

Therefore, using Equation 8 and averaging channel values, Equation 6 is derived from Equation 11 below.

는

의 0이 아닌 고유값(eigenvalue)이 된다. 또한,

개의 수신 안테나들에 대해 상기 <수학식 11>의 오른쪽은

의 지수승으로 표현된다.here,

Is

Is a nonzero eigenvalue of. Also,

The right side of Equation 11 for the two receiving antennas

Is expressed as the power of.

As shown in Equation 11, although the subcarrier p is expressed in a form that is dependent, since the effective channel transfer function of the subcarriers is similar, the PEP may be represented independently of the subcarrier p. Thus, p = 0 can be assumed without generalization error.

Therefore, Equation 11 is summarized as Equation 12 below.

Next, a process of selecting a cyclic delay time for each antenna by using the PEP derived as described above will be described.

임을 확인한다. 즉, 지연 시간

은

과 동일한 것으로 간주할 수 있다. 따라서,

로 검색(search) 범위를 한정시킬 수 있다. first,

Check that it is. Ie delay time

silver

Can be considered equal. therefore,

You can limit the scope of your search.

임을 확인한다. 따라서, PEP는 지연 시간 차이에만 의존하고, 일반화의 오류 없이

을 '0'으로 가정할수 있다.The second,

Check that it is. Therefore, PEP relies only on the difference in latency, without the error of generalization

Can be assumed to be '0'.

In conclusion, for a given SNR and coding scheme, a delay time for minimizing the maximum PEP may be selected as shown in Equation 13 below.

개의 송신 안테나들에 대해

개의 지연 시간들이 최적화되어야 한다. 주어진 SNR 및 코딩 기법에 대해 공간

에서의 전체 검색(exhaustive search)을 수행하여 지연시간들(

)을 최적화한다. 이렇게 구해진 각 (SNR, 코딩 기법)에 대응하는 지연 시간 집합(set)은 룩업테이블 형태로 저장된다. 따라서, 송신기는 수신기로부터 피드백된 SNR을 가지고 코딩 기법(부호율)을 결정하고, 상기 SNR와 상기 코딩 기법에 대응하는 지연 시간 집합에 근거해서 신호를 송신한다.Meanwhile,

For 4 transmit antennas

Delays should be optimized. Space for a given SNR and Coding Technique

By performing an exhaustive search on

). The set of delay times corresponding to the angles (SNR, coding scheme) thus obtained are stored in the form of a lookup table. Thus, the transmitter determines a coding scheme (code rate) with the SNR fed back from the receiver, and transmits a signal based on the SNR and a set of delay times corresponding to the coding scheme.

Hereinafter, the specific operation of the present invention will be described in detail.

3 illustrates a configuration of a transmitter in a MIMO-OFDM system employing a CDD according to an embodiment of the present invention.

As shown, the transmitter includes an encoder 300, a modulator 302, an IFFT operator 304, a plurality of variable delayers 306-2 to 306-N _t , a plurality of guard interval inserters 308 -1 to 308-N _t), a plurality of RF processors (s 310-1 to 310-N _t), a plurality of antennas (312-1 through 312- N _t), the feedback receiving unit 314, a coding scheme determiner ( 316 and a delay time determiner 318.

Referring to FIG. 3, first, the feedback receiver 314 receives channel information (SNR, SINR, CINR, etc.) fed back from a receiver, and uses the coding technique determiner 316 and the delay time determiner 318 to receive the received SNR information. To provide. Then, the coding technique determiner 316 determines the modulation and coding scheme (MCS) level to be applied to the transmission data by using the SNR information, and provides the determined coding rate to the delay time determiner 318. do. Meanwhile, the determined MCS level is used to control the coding rate of the encoder 300 and the modulation order of the modulator 302.

The encoder 300 encodes the transmission data at a code rate according to the MCS level and outputs code symbols. For example, the encoder 300 may include a convolutional encoder, a turbo encoder, a low density parity check (LDPC) encoder, and the like.

The modulator 302 maps the symbols from the encoder 300 to a signal point by using a modulation scheme according to the MCS level (number of variations) and outputs complex symbols. For example, the modulation scheme includes binary phase shift keying (BPSK), which maps one bit (s = 1) to one signal point (complex symbol), and two bits (s = 2) to one complex symbol. Quadrature Phase Shift Keying (QPSK), 8-ary Phase Shift Keying (8PSK), which maps 3 bits (s = 3) to one complex symbol, and 4 bits (s = 4), one complex symbol 16QAM which maps to, 64QAM which maps 6 bits (s = 6) to one complex symbol.

An IFFT operator 304 outputs sample data by inverse fast Fourier transforming of the data from the modulator 302. The sample data thus output is provided to the guard interval inserter 308-1 and the plurality of delayers 306-2 to 306-N _t .

)에 근거해서 상기 복수의 가변 지연기들(306-2 내지 306-N_t)의 순환지연시간을 조정한다.The delay determiner 318 includes a delay lookup table that stores a mapping relationship between the (SNR, coding scheme) and the delay set, and includes a code rate from the coding technique determiner 316 and the feedback receiver 314. The delay lookup table is accessed with the SNR information from &lt; RTI ID = 0.0 &gt; In addition, the delay time determiner 318 obtains the obtained delay time set (

Circulating delay time of the plurality of variable delay units 306-2 to 306-N _t ) is adjusted.

Each of the plurality of variable delayers 306-2 to 306-Nt cyclically shifts the input sample data by a corresponding cyclic delay time under the control of the delay time determiner 318.

)은 '0'이다. 또한, 나머지 보호구간 삽입기들(308-2 내지 308-N_t) 각각은 대응되는 가변 지연기로부터의 샘플데이터에 보호구간을 삽입하여 출력한다.The first guard interval inserter 308-1 inserts and outputs a guard interval (GI) in the sample data from the IFFT operator 304. That is, the cyclic delay time of the baseband sample data corresponding to the first antenna

) Is '0'. In addition, each of the remaining guard interval inserters 308-2 to 308 -N _t inserts and outputs a guard interval in sample data from the corresponding variable delay unit.

Each of the RF processors 310-1 to 310 -N _t converts the sample data from the corresponding guard interval inserter into a baseband analog signal, and converts the baseband signal into a radio frequency (RF) signal to correspond to the corresponding antenna. Send via

4 illustrates a transmission procedure of a transmitter in a MIMO-OFDM system employing a CDD according to an embodiment of the present invention.

Referring to FIG. 4, first, the transmitter receives channel information (SNR or SINR or CINR) information fed back from the receiver in step 401. When the SNR information is received, the transmitter determines the MCS level to be applied to the transmission data using the received SNR information in step 403. That is, the coding rate of the encoder 300 and the modulation order of the modulator 302 are determined.

)을 획득한다. Next, the transmitter accesses the delay time lookup table with the determined code rate and the received SNR information in step 405 and applies the delay time set to the transmission data.

).

In operation 407, the transmitter adjusts the cyclic delay time for each antenna according to the obtained delay time set. That is, a cyclic delay time is set for each of the variable delayers 306-2 to 306-N _t .

In step 400, the transmitter cyclically shifts the transmission baseband sample signal corresponding to each antenna by the adjusted cyclic delay time and transmits it through the corresponding antenna. Specifically, the transmission data is coded and modulated according to the MCS level, and the modulated data is converted into baseband sample data through an IFFT operation. The sample data generated as described above is copied by the number of antennas, and the plurality of antenna signals generated through the copying are cyclically shifted by a corresponding cyclic delay time and transmitted through the corresponding antenna.

In order to help better understanding of the present invention, a practical application example will be described.

에 대한 검색 복잡도를 줄이기 위해 송신 코드워드(codeword)는 all-zero 수열을 가정하였다.The simulation environment is a CDD-MIMO-OFDM system with two transmit antennas. In addition, an exponential decay delay power distribution with a channel tap number (L) of 3 and rms delay spread of 0.3 samples was considered. The number of subcarriers (N _c ) is 32 and 64, and two coding techniques are used. One QPSK rate-1 / 2 16-state convolutional code (hereinafter referred to as "Code I") and the other 8-PSK rate-2 / 3 16-state convolutional code (hereinafter referred to as "Code II") . Optimal latency

In order to reduce the search complexity for, the transmit codeword is assumed to be an all-zero sequence.

At this time, the search results for SNR = [0 5 10 15 20 25 30] dB are shown in Table 1 below.

Code / N _c 32 64 Code I [12 12 16 16 16 16 16] [23 23 23 32 32 32 32] Code II [8 8 8 7 7 7 7] [16 16 16 14 14 14 13]

)은 '7'이 된다. 또한, 부반송파 개수가 64이고, 피드백된 SNR 값이 25이며, 코드 Ⅰ이 사용되었다면, 두 번째 안테나의 지연시간(

)은 '32'가 된다.Referring to Table 1, if the number of subcarriers is 32, the feedback SNR value is 15, and code II is used, the delay time of the second antenna (

) Becomes '7'. In addition, if the number of subcarriers is 64, the feedback SNR value is 25, and code I is used, the delay time of the second antenna (

) Becomes '32'.

)에 대하여 부반송파 p1=N_c/2+k와 부반송파 p2=N_c/2-k가 유사한 PEP를 가짐을 실험을 통해서 확인할 수 있었다. 즉, 동일한 지연 시간에 대하여 PEP는 N_c/2에 대해 대칭적(even symmetric)인 특성을 갖는다.Also, the same delay time (

For subcarriers p1 = N _c / 2 + k and subcarriers p2 = N _c / 2-k have similar PEP. That is, for the same delay time, the PEP has a characteristic of being symmetric with respect to N _c / 2.

Hereinafter, a comparison result of the performance between the present invention and the prior art will be described.

5 to 8, the prior art method (see Equation 5) is denoted as "Witrisal", and the method of the present invention is denoted as "PEP".

FIG. 5 is a graph of FER (Frame Error Rate) performance when code I is used, and FIG. 6 is a graph of FER performance when code II is used.

는 Witrisal 방법에서 구한

와 일치하고 있다. 하지만, 도 6에 도시된 바와 같이, 코드Ⅱ의 경우 PEP 기반 기법은 FER=10^-2에서 N_c가 32일 때 3dB, N_c가 64일 때 5dB의 성능 이득을 나타내고 있다. 이와 같이, PEP 기반 기법의 성능 이득은 코딩 기법에 의존함을 확인할 수 있다.As shown in FIG. 5, in the case of Code I, the PEP-based technique has no gain over the Witrisal method. PEP-based from part of N _c

Obtained from the Witrisal Way

Is consistent with However, as shown in FIG. 6, in the case of Code II, the PEP-based scheme shows a performance gain of 3 dB when N _c is 32 and 5 dB when N _c is 64 at FER = 10 ⁻² . As such, it can be seen that the performance gain of the PEP-based scheme depends on the coding scheme.

7 and 8 show simulation results in a channel environment having an exponential decay delay power distribution in which L = 3 and rms delay spreads are 0.9 samples. FIG. 7 is a graph of FER (Frame Error Rate) performance when code I is used, and FIG. 8 is a graph of FER performance when code II is used. Referring to FIGS. 7 and 8, it can be seen that the PEP-based scheme shows a performance gain over the conventional method even in a real channel environment.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. For example, although embodiments of the present invention have been described using an OFDM system as an example, the present invention is also easy for a single carrier system (eg, a single carrier FDMA system) using frequency-domain equalization in addition to OFDM. Can be applied. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

As described above, since the present invention considers the channel and the coding scheme in determining the cyclic delay time of the CDD scheme, there is an advantage that the optimal performance (FER performance) can be exhibited. That is, the present invention exhibits performance similar to that of space-time block code (STBC) with low transmit / receive complexity. In addition, the present invention can be easily applied to all OFDM systems regardless of the general MIMO-OFDM system and duplexing scheme.

Claims (14)

A transmission apparatus in a multi-antenna system using a cyclic delay diversity scheme, A first determiner for determining a code rate using channel information; And a second determiner for determining a cyclic delay time to be applied to each of the plurality of antennas using the code rate from the first determiner and the channel information. The method of claim 1, A generation unit for generating baseband sample data; A plurality of variable delayers for cyclically shifting and outputting sample data from the generation unit by a corresponding cyclic delay time under the control of the second determiner; And a plurality of RF processors for RF-processing each of the sample data from the variable delayers to be transmitted through a corresponding antenna. The method of claim 2, wherein the generation unit, An encoder for encoding and outputting transmission data at the code rate; A modulator for modulating and outputting data from the encoder in a determined modulation scheme; And an inverse fast Fourier transform of the data from the modulator to produce the sample data. The method of claim 2, And a cyclic delay time of the variable delay unit corresponding to the first transmission antenna is '0'. The method of claim 1, The channel information may be any one of Signal to Noise Ratio (SNR), Signal to Interference plus Noise Ratio (SINR), and Carrier to Interference plus Noise Ratio (CINR). The method of claim 1, And the second determiner includes a lookup table that stores a mapping relationship between a pair of channel information and a code rate and a cyclic delay time set. The method of claim 6, And the lookup table is prepared based on Pairwise Error Probability (PEP) criteria. A transmission apparatus in a multi-antenna system using a cyclic delay diversity scheme, Determining a code rate using channel information; And determining a cyclic delay time to be applied to each of a plurality of antennas by using the determined code rate and the channel information. The method of claim 8, Generating baseband sample data for transmission; Copying the sample data by the number of antennas and cyclically shifting each sample data by the determined cyclic delay time; And RF-processing each of the cyclically shifted sample data through a corresponding antenna. The method of claim 9, wherein the generating process, Encoding the transmission data at the code rate; Modulating the encoded data by the determined modulation scheme; And generating the sample data by inverse fast Fourier transforming the modulated data. The method of claim 8, The cyclic delay time corresponding to the first transmission antenna is characterized in that '0'. The method of claim 8, The channel information may be any one of Signal to Noise Ratio (SNR), Signal to Interference plus Noise Ratio (SINR), and Carrier to Interference plus Noise Ratio (CINR). The method of claim 8, wherein the determining of the cyclic delay time comprises: And a lookup table for storing a mapping relationship between a pair of channel information and a code rate and a set of cyclic delay times, and accessing the lookup table to determine a cyclic delay time to be applied to each antenna. The method of claim 13, Wherein the lookup table is prepared based on Pairwise Error Probability (PEP) criteria;

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