Research On LDPC Codes, Turbo Codes And Space-Time Codes In The Wireless Communication System

MIMO(Multiple-Input-Multiple-Output) link system can provide better performance and greater capacity compared with SISO system, which exactly meets the increasing demands of high speed and high quality communication of cellular mobile, Internet and multimedia services. Now it has been paid more and more attentions. Recently, space-time coding theories and efficient channel coding theories, such as LDPC codes and Turbo codes, have been rapidly developed and become hot spot in study. In this paper, some aspects of LDPC codes, Turbo codes and space-time modulation are studied including the LDPC coded USTM(Unitary Space-Time Modulation), LDPC coded DUSTM(Differential USTM) scheme and their corresponding combined iterative decoding algorithms. Furthermore, the performance of LDPCC-USTM system and the optimum LDPC codes design are deeply analysed based on Gaussian approximation and density evolution theories. Moreover, a fast Turbo codes decoding algorithm is studied in addition. Such works are summarized and listed below:1. Give the LDPC codes definition based on graph representation and describe the sum-product iterative decoding algorithm or belief propagation decoding algorithm in detail, and the corresponding concrete message update formulas over probability field and log domain are also given. In addition, LDPC codes over GF(q) (q>2) are studied. Moreover, we provide various simulation results of regular and irregular LDPC codes over GF(2~P) (p>=1). The reasons for the different performance of different codes are discussed.2. Propose concatenated LDPC coded USTM system and develop corresponding iterative decoding algorithm which gives considerable coding gains without CSI(Channel State Information). The concatenated USTM based on binary LDPC codes is extended to that based on GF(q)(q>2) in which the USTM is encoded according to the symbols over GF(q) for each unitary matrix and the sum-product decoding algorithm is performed as forward and backward message update. Simulation results show, for one hand, that our proposed schemes outperforms any other schemes such as trellis coded USTM, Turbo coded USTM etc., yielding almost 23dB coding gain over uncoded USTM system and about 5dB coding gain against Turbo coded USTM system. Moreover, full parallel...