KR20100107096A - Alamouti sfbc-ofdm system and communication method using partial response coding - Google Patents

Abstract

PURPOSE: An alamouti SFBC-OFDM system and a communicating method using a partial response coding are provided to encode a data stream to be transmitted by using a frequency-domain partial response coding. CONSTITUTION: A transmitter transmits data. A receiver receives the data. The transmitter includes a partial response coding unit for partial response encoding. A modulation unit(11) modulates an input data stream. A serial to parallel converter(12) converts a serial data stream to a parallel data stream. An alamouti SFBC-OFDM encoder(14) performs an alamouti encoding. A plurality of inverse fast Fourier transform units(15) performs an inverse fast Fourier transform for converting the data stream into the data of a time domain in a transmission process. A partial response coding unit is connected between the serial to parallel converter and the alamouti encoder.

Description

Alamouti SFBC-OFDM System and Communication Method Using Partial Response Coding

The present invention relates to an Alamouti SFBC-OFDM system and a communication method, and more particularly, to an Alamouti SFBC-OFDM system and a communication method using partial response coding to eliminate intercarrier interference.

Digitization of communications has brought many advantages to users or providers. Methods that are not available in analog systems, such as source compression, multiplexing, multiple access, error correction codes, and efficient digital modulation techniques, have been introduced into digital communication systems to provide various and reliable communication services at low cost. In particular, in the broadcasting field, technology has been developed through digitization and bidirectionalization, and the development of Orthogonal Frequency Division Multiplexing (OFDM) technology that digitalizes transmission methods in addition to video and audio signals and connects them to digital transmission lines at home and abroad It is actively underway.

OFDM is robust to frequency-selective fading, but sensitive to time-selective fading. The variation of the fading channel over time within one OFDM symbol destroys orthogonality between subcarriers and causes inter-carrier interference (ICI). This ICI causes an error floor if not corrected.

Antenna diversity is known to be effective in reducing the degrading effect of fading channels. Space-frequency block coding (SFBC) is a means of combining the advantages of transmit antenna diversity and OFDM. In the absence of ICI, a space-frequency block coded (SFBC) OFDM system exhibits much better symbol error rate (SER) performance than an OFDM system with one transmit antenna. However, ICI reduces the advantages of antenna diversity gain in the SFBC-OFDM system and causes an error floor.

The present invention to solve the above-mentioned problems of the prior art, by encoding a data stream to be transmitted through frequency-domain partial response coding (PRC) to remove inter-carrier interference (ICI) It is an object of the present invention to provide an Alamouti Spatial Frequency Block Coding (SFBC) -Orthogonal Frequency Division Multiplexing (OFDM) system and method capable of improving symbol error rate performance and lowering an error floor.

An Alamouti Spatial Frequency Block Coding (SFBC) -Orthogonal Frequency Division Multiplexing (OFDM) system according to an embodiment of the present invention for achieving the above object comprises a transmitter for transmitting data and a receiver for receiving the data; The transmitter may comprise a partial response coding unit for performing partial response encoding.

The Alamouti SFBC-OFDM communication method according to another aspect of the present invention includes a transmitting step of transmitting data and a receiving step of receiving the data, wherein the transmitting step includes encoding the data stream with partial response coding. Can be configured.

Using the Alamouti Spatial Frequency Block Coding (SFBC) -Orthogonal Frequency Division Multiplexing (OFDM) system and method according to the present invention, inter-carrier interference, Since the ICI) is reduced, the symbol error rate performance is improved and the error floor is reduced.

Hereinafter, with reference to the accompanying drawings looks at in detail with respect to the preferred embodiment of the present invention.

1 is a block diagram illustrating a transmitter of an Alamouti Spatial Frequency Block Coding (SFBC) -Orthogonal Frequency Division Multiplexing (OFDM) system according to an embodiment of the present invention. As shown, the transmitter comprises a modulation unit 11 for performing modulation on the input data stream, a serial-to-parallel converter 12 for converting a serially modulated data stream into a parallel data stream, and performing partial response encoding. Partial response coding (PRC) unit 13, Alamouti encoder 14 performing Alamouti encoding, performs Fast Fourier Inverse Transform (IFFT) to convert the data stream into data in time domain during transmission. And a plurality of fast Fourier inverse transform units 15 and a plurality of transmit antennas 16.

2 is a block diagram illustrating a receiver of an Alamouti Spatial Frequency Block Coding (SFBC) -Orthogonal Frequency Division Multiplexing (OFDM) system according to an embodiment of the present invention. As shown, the receiver comprises one receive antenna 21, a plurality of fast Fourier transform units 22 which perform fast Fourier transform (FFT) to convert the received data into a data stream in the frequency domain, the data An Alamouti decoder 23 for performing Alamouti decoding on the stream, a maximum-likelihood sequence detector (MLSD) 24 for restoring the decoded data stream, and a parallel recovered data stream in series. And a demodulation unit 26 for performing demodulation on an output data stream.

transmitter

3 is a flowchart illustrating an operation of a transmitter of the Alamouti SFBC-OFDM communication method according to an embodiment of the present invention. The intercarrier interference cancellation method according to the above embodiment starts with receiving an input data stream from a transmitter. The input data stream is modulated by the modulation unit 11 (S301), and thus the modulated data stream is serially converted into a parallel data stream through the serial-to-parallel converter 12 (S302). The converted data stream is encoded through the PRC unit 13 (S303), and the encoded sequence may be represented by Equation 1 below.

들은 송신될 심볼들이고,

이며,

들은 정규화된 PRC 가중치 계수들이다. 즉,

이다.here,

Are the symbols to be transmitted,

,

Are normalized PRC weighting coefficients. In other words,

to be.

는 알라모우티 인코더(14)에 의해 공간 및 주파수로 인코딩되고(S304), 고속 퓨리에 역변환 유닛(15)에 의한 고속 퓨리에 역변환을 통해 시간 영역의 데이터 스트림으로 전환된다(S305). 시간 영역의 송신된 신호는 다음과 같은 수학식들로 표현된다.sequence

Is encoded in spatial and frequency by the Alamouti encoder 14 (S304), and is transformed into a data stream in the time domain through fast Fourier inverse transform by the fast Fourier inverse transform unit 15 (S305). The transmitted signal in the time domain is represented by the following equation.

는 p번째 부반송파의 주파수이고,

는 부반송파 간격이며,

는 한 OFDM 심볼 주기이다. 여기서, 위 첨자

는 i번째 송신 안테나를 나타내고,

는 복소 켤레를 나타낸다.here,

Is the frequency of the p-th subcarrier,

Is the subcarrier spacing,

Is one OFDM symbol period. Where superscript

Denotes the i th transmit antenna,

Denotes a complex conjugate.

The signals in the time domain represented by the above equations are transmitted through the plurality of transmit antennas 16 (S306).

receiving set

4 is a flowchart illustrating an operation of a receiver of the Alamouti SFBC-OFDM communication method according to an embodiment of the present invention. The receiver receives a signal in a time domain transmitted from the transmitter through one receiving antenna 21 (S401).

The PRC weighting factor of the frequency-selective fading channel is applicable to the frequency-selective fading channel. This is because the path delay is usually very small compared to the OFDM symbol period. Therefore, we will assume a frequency-non-selective fading channel for easy mathematical analysis in obtaining meaningful PRC weighting coefficients. The received signal of the frequency-non-selective and time-selective fading channel is given by equation (4).

는 i번째 송신 안테나(16)로부터 수신 안테나로(21)의 채널 임펄스 응답이다.

및

는 독립적이고 동일한 통계적 특성을 갖는다고 가정한다. 또,

라고 가정한다.here

Is the channel impulse response from the i th transmit antenna 16 to the receive antenna 21.

And

Is assumed to be independent and have the same statistical properties. In addition,

Assume that

The received signal is subjected to a fast Fourier transform (FFT) in the fast Fourier transform unit 22 (S402). The fast Fourier transform result of the p th subcarrier is expressed by Equation 5 below.

After some manipulations, the result is as follows.

및

는 원하는 신호의 이득(gain)이고

는 i번째 송신 안테나로부터 비롯된 간섭신호의 합을 나타낸다. 여기서,

및

는 각각 다음의 수학식들과 같이 정의된다.here,

And

Is the gain of the desired signal

Denotes the sum of the interference signals originating from the i th transmit antenna. here,

And

Are each defined as the following equations.

는 다음과 같은 수학식들로 쓰여진다.And

Is written as the following equation.

는 간단한 알라모우티 디코더(23)에 의해 디코딩되어

들로부터 구할 수 있고(S403),

는 최대 우도 시퀀스 검출기(maximum-likelihood sequence detector (MLSD))(24)에 의해 복원될 수 있다(S404). ICI가 없는 경우,

및

은 각각 다음과 같은 수학식들로 구해진다.As shown in FIG. 1,

Is decoded by a simple Alamouti decoder 23

It is available from the field (S403),

May be restored by a maximum-likelihood sequence detector (MLSD) 24 (S404). If there is no ICI,

And

Are each obtained from the following equations.

Equations 14 and 15 above indicate that the Alamouti SFBC-OFDM system can obtain two diversity orders. Diversity order affects the slope of the SER, so the Alamouti SFBC-OFDM system has much better SER performance than an OFDM system with one transmit antenna when ICI is suppressed.

The data stream passing through the MLSD 24 is converted into a serial data stream through the parallel-to-serial converter 25 (S405), and demodulated into an output data stream by the demodulation unit 26 (S406) and output.

Alamouti SFBC - OFDM For PRC Weights

Here, the PRC weighting factors close to the optimum are calculated based on the formal expression of the ICI power in the SFBC-OFDM system using the PRC. The ICI total power in the P th subcarrier is defined as in Equation 16 below.

는 영평균(zero mean) 가우시안 랜덤 과정(Gaussian random process)으로 모델링될 수 있다.

및

가 독립적(independent)이므로,

및

는 독립적이고 무상관(uncorrelated)이다. 즉,

이다. 그 다음, 수학식 16은 다음 수학식 17과 같이 정리된다.Based on the central limit theorem,

May be modeled as a zero mean Gaussian random process.

And

Since is independent,

And

Is independent and uncorrelated. In other words,

to be. Then, Equation 16 is arranged as in Equation 17 below.

는 다음 수학식 18과 같이 얻어진다.Computed total ICI power,

Is obtained as shown in Equation 18 below.

는 다음 수학식 19와 같이 주어진다.here,

Is given by Equation 19 below.

는 다음 수학식 20과 같이 주어진다.And

Is given by Equation 20 below.

는

의 전력 스펙트럼 밀도(power spectral density)이고,

는 최대 도플러 주파수 편이(maximum Doppler frequency shift)이며,

는 가중치 계수 벡터이다.

Is

Power spectral density of

Is the maximum Doppler frequency shift,

Is a weighting coefficient vector.

를 최소화하는 최적의 가중치 계수 벡터

를 찾을 필요가 있다.

일 때,

이므로,

및

는 수학식 21 및 수학식 22에 주어진

및

로 각각 근사될 수 있다.To reduce ICI power, we

Optimal weighting factor vector to minimize

You need to find

when,

Because of,

And

Is given by Equations 21 and 22

And

Can be approximated respectively.

,

일 때,

임이 얻어지고, 행렬

및

는 다음과 같이 정의 된다.

,

when,

Is obtained, the matrix

And

Is defined as

및

And

가 대칭 행렬이므로,

는 실대칭(real symmetric)이고 에르미트(Hermitian)이다. 레일리-리쯔 비(Rayleigh-Ritz ratio)에 대한 정리를 이용하면, 다음의 수학식 23을 얻을 수 있다.

Since is a symmetric matrix,

Is a real symmetric and Hermitian. Using the theorem on the Rayleigh-Ritz ratio, the following equation 23 can be obtained.

및

는

의 최소 및 최대 고유값(eigen value)이다. 수학식 23의 왼쪽 등식은

가 최소 고유값

에 해당하는

의 정규화된 고유벡터(normalized eigenvector)일 때 성립한다.

And

Is

Is the minimum and maximum eigen value of. The left equation of Equation 23 is

Is the minimum eigenvalue

Equivalent to

Holds for the normalized eigenvector of.

는 양반정치(positive semidefinite)가 아니다. 왜냐하면,

의 모든 대각 성분(diagonal entry)들이 0이고,

는 대각적으로 우세(diagonally dominant)하지 않기 때문이다. 거기에는 음의 고유값들이 있을 것이고

은 음일 것이다. 즉, 최적의 PRC 가중치 계수 벡터

는 최소 고유값

에 해당하는

의 정규화된 고유벡터이며, 최적의 PRC 가중치 계수 벡터는

를 음으로 만들고 ICI 총 전력

를 줄여 준다는 것을 뜻한다.

Is not a positive semidefinite. because,

All the diagonal entries of are 0,

Is not diagonally dominant. There will be negative eigenvalues

Will be negative. In other words, the optimal PRC weighting factor vector

Is the minimum eigenvalue

Equivalent to

Is the normalized eigenvector of, and the optimal PRC weighting coefficient vector is

Negative and ICI total power

It means to reduce.

While specific embodiments of the present invention have been illustrated and described, the technical spirit of the present invention is not limited to the accompanying drawings and the above description, and various modifications can be made without departing from the spirit of the present invention. It will be apparent to those skilled in the art, and variations of this type will be regarded as belonging to the claims of the present invention without departing from the spirit of the present invention.

1 is a block diagram illustrating a transmitter of an Alamouti Spatial Frequency Block Coding (SFBC) -Orthogonal Frequency Division Multiplexing (OFDM) system according to an embodiment of the present invention.

2 is a block diagram showing the configuration of a receiver of the Alamouti SFBC-OFDM system according to an embodiment of the present invention.

3 is a flow chart showing operation in a transmitter of the Alamouti SFBC-OFDM communication method according to an embodiment of the present invention.

4 is a flowchart illustrating operation at a receiver of an Alamouti SFBC-OFDM communication method according to an embodiment of the present invention.

Claims (8)

A transmitter for transmitting data; And And a receiver for receiving the data, wherein the transmitter comprises a partial response coding unit for performing partial response encoding. 10. An Alamouti spatial frequency block coding (SFBC) -orthogonal frequency division multiplexing (OFDM) system. The method of claim 1, The transmitter, A modulation unit for performing modulation on the input data stream; A serial-to-parallel converter that converts a serially modulated data stream into a parallel data stream; An Alamouti encoder for performing Alamouti encoding; A plurality of fast Fourier inverse transform units for performing fast Fourier inverse transform (IFFT) to convert the data stream into data in the time domain at the time of transmission; And The Alamouti SFBC-OFDM system, further comprising a plurality of transmit antennas, wherein the partial response coding unit is connected between a parallel-parallel converter and an Alamouti encoder. The method of claim 1, The receiver, One receiving antenna; One fast Fourier transform unit for performing Fast Fourier Transform (FFT) to convert the received data into a data stream in the frequency domain; An Alamouti decoder for performing Alamouti decoding on the data stream; A maximum likelihood sequence detector to recover a decoded data stream; A parallel-to-parallel converter for converting the parallel recovered data streams into a serial data stream; And An Alamouti SFBC-OFDM system comprising a demodulation unit for performing demodulation on an output data stream. The method of claim 1, The partial response coding unit is a matrix

And

end

And

Is defined as

ego,

silver

Is the minimum eigenvalue of, and the PRC weighting factor vector

When we say

Selected by

Alamouti SFBC-OFDM system for performing partial response encoding according to. A transmitting step of transmitting data; And Alamouti Spatial Frequency Block Coding (SFBC) -Orthogonal Frequency Division Multiplexing (OFDM) communication, characterized in that it comprises a receiving step of receiving the data, the transmitting step comprising encoding the data stream with partial response coding. Way. The method of claim 5, The transmitting step, Modulating the input data stream; Converting the serially modulated data streams into parallel data streams; Encoding Alamouti; Performing a Fast Fourier Inverse Transform (IFFT) to convert the data stream into data in the time domain at the time of transmission; Transmitting through a plurality of transmit antennas; Further comprising the step of encoding with partial response coding following the step of converting to a parallel data stream. The method of claim 5, The receiving step, Receiving through one receiving antenna; Performing a Fast Fourier Transform (FFT) to convert the received data into a data stream in the frequency domain; Performing alamouti decoding; Restoring the decoded data stream: Converting the parallel recovered data streams into a serial data stream; Demodulating into an output data stream. The method of claim 5, Encoding with the partial response coding may comprise a matrix

And

end

And

Is defined as

ego,

silver

Is the minimum eigenvalue of, and the PRC weighting factor vector

When we say

Selected by

And performing partial response encoding according to the Alamouti SFBC-OFDM communication method.

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