Block Coding Of Space-time Wireless Communication

Because of its extraordinary capacity and diversity, MIMO system has become the main future developing direction of wireless communication. Space-Time Coding is one of the key techniques of MIMO systems, which can fully explore space diversity and coding gain.This paper mainly investigates Space-Time Block Codes, including the research on Orthogonal Space-Time Block Codes (OSTBC), Quasi-Orthogonal Space-Time Block Codes (QOSTBC) ,the combination of OFDM and STBC in wideband wireless channel. The main content of the paper is as follows:a). Focus on the design and decoding of OSTBC. By simulation in Rayleigh channel, we can conclude that OSTBC can obviously improve the performance of the system. For example, under the condition of 1 bit/(s.Hz) transmitting rate and one receive antenna, at the BER 10^-3 the OSTBC G₄₄₈ system with 4 transmit antennas and QPSK modulation, is approximately 3.5dB better than the Alamouti scheme with 2 transmit antennas and BPSK modulation, and approximately 14 dB better than the uncoded system with 1 transmit antenna and BPSK modulation.b). Emphasis on the study of QOSTBC. Great attention is paid on the comparison of the Double Maximum Likelihood (DML) decoding algorithm, the Fast Maximum Likelihood (FML) decoding algorithm and the Low Complexity MMSE-QRD-based Maximum-Likelihood (LCML) decoding algorithm. By simulation, we can draw the following conclusions: DML is the best performance among three algorithms but the complexity is so high that it is an exponential function as the number constellation signals; FML owns the lowest complexity but the worst performance; LCML approximately achieves the same BER performance as DML with lower complexity than DML.c). Focus on the study of two combinations of OFDM and STBC: STBC-OFDM and SFBC-OFDM. By simulation in slow fading wideband wireless channel, we can find: a) The BER performace of SFBC-OFDM can be easily influenced by the number of subcarriers; b) STBC-OFDM is not sensitive to the number of subcarriers; C) STBC-OFDM outperforms SFBC-OFDM.