연접부호를 적용한 시공간 OFDM 시스템의 성능 개선

서완우,정연호 한국정보통신학회 2004 한국정보통신학회논문지 Vol.8 No.3

시공간 부호(Space-Time Coding)는 송신부에서 전송신호를 시간영역과 공간영역으로 확장하여 전송하는 기법으로 다이버시티 이득과 부호화 이득을 동시에 얻을 수 있다. 본 논문에서는 SPW(Signal Processing Worksystem) 시뮬레이션 플랫포옴을 이용하여 고속 무선랜 관련 표준안인 IEEE 802.11a 시스템을 기초로 한 연접부호 시공간 OFDM 시스템의 성능 개선을 분석하였다. IEEE 802.11a에 포함된 구속장의 길이가 7인 콘볼루션 부호 대신에, 시공간 블록 부호를 이용한 시스템과 콘볼루션 부호와 시공간 블록 부호를 연접한 시스템을 SPW 시뮬레이션 플랫포옴에서 각각 구현하여 그 성능을 비교하였다. SPW 시뮬레이션 결과에 의하면 데이터율 6Mbps에서 두 부호를 연접한 시스템의 성능이 콘볼루션 부호기를 적용한 IEEE 802.11a 시스템보다 약 5dB 이상 우수한 성능을 보였고 데이터을 12Mbps에서는 6dB 이상의 성능 개선을 얻을 수 있었다. Space-Time Coding(STC) is a technique that utilizes joint correlation of transmitted signals in both time and space domains. Through this approach, diversity and coding gains can be simultaneously obtained. In this paper, we use SPW simulation tool to implement the IEEE 802.11a system. Based on this system, OFDM system with STC and convolutional coder concatenated is implemented. The system performance is analyzed and compared with the performance of the IEEE 802.11a system. The simulation results show that the performance with concatenated codes at a data rate of 6Mbps shows approximately a 5dB gain over the system with the convolutional code only. At a data rate of 12Mbps, the performance with concatenated codes is further improved by approximately 6dB.

차동 시공간 선 부호와 성상에 따른 성능 비교

정진곤 한국통신학회 2024 韓國通信學會論文誌 Vol.49 No.5

본 연구에서는 시변 채널 환경에서 무선통신을 위한 차동 시공간 선 부호(DSTLC: differential space-time line code)를 제안한다. 시불변 채널 환경에서 제안된 기존 시공간 선 부호 (STLC: space-time line code) 기법은 송신단에서 모든 시변 채널 정보가 있어야 하며, 이는 시변 채널 환경에서 동작하는 이동체 통신에 STLC 기술을 적용하는데 큰 제약이 된다. 반면, 제안한 DSTLC 기법은 시변 채널 정보를 쓰지 않고 변복조가 가능하다. 하지만, 설계한 DSTLC 기법은 변조 신호 진폭에 불확실성이 있어, 비상수 모듈러스 성상(NCMC: non-constant modulus constellation)에 동일한 위상이 존재한다면, 복조할 수 없으므로, 위상변조(PSK: phase-shift keying)와 같은 상수모듈러스 성상(CMC: constant modulus constellation)을 갖는 변조 기법을 써야 한다. 이를 해결하기 위해 동일한위상을 갖지 않는 다양한 크기-위상 편이 변조(APSK: amplitude and phase-shift keying)인 NCMC 성상을 제시하고, 이를 쓴 DSTLC 시스템의 성능을 검증한다. 그 결과 제안한 DSTLC 기법은 표준화 도플러 주파수(normalized Doppler frequency)가 0.01 이내인 시변 채널 환경에서, 모든 시변 채널 정보를 쓴 기존 STLC 시스템 대비 성능저하가 무시할 수 있는 정도임을 확인함으로써 제안한 DSTLC 기법이 이동체 통신에 적용할 수 있음을 보였다. This study proposes a differential space-time line code (DSTLC) for wireless communications in a time-varying channel environment. The existing space-time line code (STLC) technique proposed in a time-invariant channel environment requires full channel state information (CSI) at the transmitter, which is unsuitable for mobile communications operating in a time-varying channel environment. On the other hand, the proposed DSTLC system does not require CSI for the encoding and decoding. However, since the DSTLC techniques suffer ambiguity on the amplitude of the modulated signals, a non-constant modulus constellation (NCMC) like a quadrature amplitude modulation (QAM) probably having symbols with the identical phases cannot be used, and thus, a constant modulus constellation (CMC), such as phase-shift keying, must be used for the designed DSTLC systems. To resolve this issue, various amplitude and phase-shift keying methods with NCMC are designed, and using them, the feasibility of DSTLC is verified for mobile communications.

시공간 turbo 부호의 성능 분석과 효율적인 복호 알고리즘

신나나,이창우,Shin Na na,Lee Chang woo 한국통신학회 2005 韓國通信學會論文誌 Vol.30 No.4c

Space-time turbo codes have been studied extensively as a powerful and bandwidth efficient error correction code over the wireless communication environment. In this paper, the efficient algorithm for decoding space-time turbo codes is proposed. The proposed method reduces the computational complexity by approximating a prior information for a iterative decoder. The performance of space-time turbo codes is also analyzed by using the fixed point implementation and the efficient method for approximating the Log-MAP algorithm is proposed. It is shown that the BER performance of the proposed method is close to that of the Log-MAP algorithm. 최근 무선 이동통신에서 상대적으로 늘어난 다중 접속자들에 대해 대역폭을 효율적으로 사용하면서도 보다 빠른 데이터 전송률을 지원하기 위해 제안된 시공간 turbo 부호에 대한 연구가 많이 이루어지고 있다. 본 논문에서는 시공간 turbo 부호의 복호 시 요구되는 계산량을 줄이기 위해 사전 정보를 근사화하여 이 정보를 고정 소수점 연산 시 간단하게 구현할 수 있는 복호 알고리즘을 제안하였다. 또한 시공간 turbo 부호의 복호 알고리즘을 고정 소수점 연산을 이용하여 구현하였을 때 성능을 해석하였고 Log-MAP 알고리즘의 성능에 근사하는 효율적인 고정 소수점 구현 방법을 제안하였다. 이 방법을 Log-MAP 알고리즘에 적용하여 성능을 분석하였고 기존의 Log-MAP의 결과에 거의 근접한 성능을 보임을 확인하였다.

Differential Space Time Coding based on Different Unitary Matrices Sets

Kwang-Jae Lee,Chang-Joo Kim,Hyun-Seok Yoo,Sung-Hun Kim,Moon-Ho Lee 한국전자파학회JEES 2006 Journal of Electromagnetic Engineering and Science Vol.6 No.4

This paper investigates a distinct set of complex unitary matrices for QPSK differential space time coding. After properly selecting the initial transmission matrix and unitary matrices we find that the different combinations of them could lead different BER performance over slow/fast Rayleigh fading channels and antennas correlated channels. The numerical results show that the proper selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels.

New Design for Linear Complex Precoding over ABBA Quasi-Orthogonal Space-Time Block Codes

Ran Rong,안찬호,김동구,양장훈 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.12

codes, a class of quasi-orthognal space-time block codes (QoSTBC) proposed by Tirkkonen and others, allow full rate and a fast maximum likelihood (ML) decoding, but do not have full diversity. In this paper, a linear complex precoder is proposed for ABBA codes to achieve full rate and full diversity. Moreover, the same diversity produce as that of orthogonal space-time block code with linear complex precoder (OSTBC-LCP) is achieved. Meanwhile, the size of the linear complex precoder can be reduced by half without affecting performance, which means the same complexity of decoding as that of the conventional ABBA code is guaranteed.

Coding Advantage Optimization of Space-time-frequency Block Codes

Vahid Momenaei Kermani,Hossein Momenaee Kermani,Alireza Morsali 한국통신학회 2020 Journal of communications and networks Vol.22 No.2

In this article, we study the coding advantage of spacetime-frequency block codes (STFBCs). Since in MIMO-OFDMcoding there is the potential of exploiting space, time and frequencydiversities and as the frequency tones of OFDM modulation arerelatively substantial, the intricate structure of STFBCs makes italmost impossible to optimize the parameters of the code as thenumber of symbols increases in each block. Consequently, we investigatehow to optimize the code parameters independently toreduce the computational complexity. Furthermore, code permutationis an important part of the STFBCs. However, due to elaboratestructure of the STFBCs, it is very hard to calculate the optimumpermutation. Therefore, we put forth a technique to decompose thecoding advantage of the STFBCs. Using this technique, the permutationparameter can be easily introduced and optimized for STFBCs. We then design a novel STFBC based on any given STBC andapply the proposed scheme on the proposed STFBC to illustratethe application of this technique by designing the optimum permutationfor the code. Simulation results confirm that the proposedSTFBC outperforms the best existing STFBCs in the literature.

OFDM에서 트렐리스 부호화된 차동 시공간 변조의 다중 심벌 검파

유항열,한상필,김진용,김성열,김종일 한국융합신호처리학회 2004 융합신호처리학회 논문지 (JISPS) Vol.5 No.3

최근에 OFDM과 시공간 부호화(Space-Time Code, STC)는 차세대 이동 통신에서 고속의 신뢰성 있는 통신을 위해 각광받고 있다. 본 논문에서는 다중경로 페이딩 채널에서 고속의 데이터를 전송하고자 할 경우에 성능을 향상시키고자 트렐리스 부호화된(Trellis-Coded, TC) 차동 시공간 변조(Differential Space Time Modulation, DSTM)를 사용한 OFDM에서 다증 심벌 검파 시스템을 제안한다. 차동 시공간 부호화된 OFDM의 성능을 향상시키기 위해 DUSTM(differential unitary space-time modulation)을 이용하여 송신기를 설계하고 수신단에서 다중 심벌 검파를 수행하는 수신기와 디코딩 알고리듬을 개발하며, 이를 위한 새로운 가지 메트릭을 유도한다. Recently, OFDM and STC techniques have been considered to be candidate to support multimedia services in the next generation mobile radio communications and have been developed the many communications systems in order to achieve the high data rates. In this paper, we propose the Trellis-Coded Differential Space Time Modulation-OFDM system with multiple symbol detection. The Trellis-code performs the set partition with unitary group codes. The Viterbi decoder containing new branch metrics is introduced in order to improve the bit error rate (BER) in the differential detection of the unitary differential space time modulation. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbl decoder improves BER performance without sacrificing bandwidth and power efficiency.

Design and Performance of Space-Time Trellis Codes for Rapid Rayleigh Fading Channels

Zummo, Salam A.,Al-Semari, Saud A. The Korea Institute of Information and Commucation 2003 Journal of communications and networks Vol.5 No.2

Space-Time (ST) codes are known to provide high transmission rates, diversity and coding gains. In this paper, a tight upper bound on the error probability of ST codes over rapid fading channels is presented. Moreover, ST codes suitable for rapid fading channels are presented. These codes are designed using the QPSK and 16-QAM signal constellations. The proposed codes are based on two different encoding schemes. The first scheme uses a single trellis encoder, whereas the second scheme uses the I-Q encoding technique. Code design is achieved via partitioning the signal space such that the design criteria are maximized. As a solution for the decoding problem of I-Q ST codes, the paper introduces a low-complexity decoding algorithm. Results show that the I-Q ST codes using the proposed decoding algorithm outperform singleencoder ST codes with equal complexity. The proposed codes are tested over fading channels with different interleaving conditions, where it is shown that the new codes are robust under such imperfect interleaving conditions.

Error Control Coding and Space-Time MMSE Multiuser Detection in DS-CDMA Systems

Hamouda, Walaa,McLane, Peter J. The Korea Institute of Information and Commucation 2003 Journal of communications and networks Vol.5 No.3

We consider the use of error control coding in direct sequence-code-division multiple access (OS-COMA) systems that employ multiuser detection (MUO) and space diversity. The relative performance gain between Reed-Solomon (RS) code and convolutional code (CC) is well known in [1] for the single user, additive white Gaussian noise (AWGN) channel. In this case, RS codes outperform CC's at high signal-to-noise ratios. We find that this is not the case for the multiuser interference channel mentioned above. For useful error rates, we find that soft-decision CC's to be uniformly better than RS codes when used with DS-COMA modulation in multiuser space-time channels. In our development, we use the Gaussian approximation on the interference to determine performance error bounds for systems with low number of users. Then, we check their accuracy in error rate estimation via system's simulation. These performance bounds will in turn allow us to consider a large number of users where we can estimate the gain in user-capacity due to channel coding. Lastly, the use of turbo codes is considered where it is shown that they offer a coding gain of 2.5 dB relative to soft-decision CC.

An Efficient Scheme to Achieve Differential Unitary Space-Time Modulation on MIMO-OFDM Systems

shouyin Liu,정정화 한국전자통신연구원 2004 ETRI Journal Vol.26 No.6

Differential unitary space-time modulation (DUSTM) has emerged as a promising technique to obtain spatial diversity without intractable channel estimation. This paper presents a study of the application of DUSTM on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with frequency-selective fading channels. From the view of a correlation analysis between subcarriers of OFDM, we obtain the maximum achievable diversity of DUSTM on MIMO-OFDM systems. Moreover, an efficient implementation strategy based on subcarrier reconstruction is proposed, which transmits all the signals of one signal matrix in one OFDM transmission and performs differential processing between two adjacent OFDM blocks. The proposed method is capable of obtaining both spatial and multipath diversity while reducing the effect of time variation of channels to a minimum. The performance improvement is confirmed by simulation results.