LDPC-Coded Cooperation: Performance Studies And Codes Design

With the demand for wireless communications increasing gradually in the modern society, people pay more attention to the more reliable and efficient communication services. Advanced channel coding techniques can provide coding gain which enhances the transmission reliability. Cooperation techniques can achieve spatial diversity which improves the performance of communication systems. By combining low density parity check(LDPC) codes with cooperation techniques, LDPC-coded cooperation obtains both high coding gain and diversity gain. In this thesis, we investigate the performance and codes design of LDPC-coded cooperation. The main contributions of this thesis are summarized as follows:(1) For LDPC-coded cooperation, firstly, two coding schemes which employ regular LDPC codes and generator-matrix-based LDPC(G-LDPC) codes are proposed. From the viewpoint of the destination, the overall parity-check matrix corresponding to the coded cooperation system is deduced, and then the bilayer Tanner graph is introduced, based on which the joint belif propagation(BP) iterative decoding algorithm is proposed. The outage probability of the ideal coded cooperation system is analyzed. Secondly, for additive white gaussian noise(AWGN) channels, by introducing the notation of average signal-to-noise ratios(SNRs) in the destination, the Point-to-Point transmission model corresponding to the coded cooperation system is set up. Simulation results verify that the problems in the coded cooperation system may be transferred to the Point-to-Point transmission model for further investigation in some scenarios. Finally, the model of LDPC-coded nonideal cooperation is set up and analyzed.(2) Considering the scenarios where the source and relay as mobile devices can support only single antenna and the the destination as a base station can support multiple antennas, LDPC-coded cooperative multiple-input multiple-output(MIMO) where the source and relay have single antenna and the destination is equipped with multiple antennas is investigated. This system can achieve high coding gain, cooperation diversity gain and receive multi-antenna gain simultaneously. Firstly, a coding scheme based on repeat accumulate(RA) codes is proposed. Secondly, the outage probability of the coded cooperative MIMO over Rayleigh block fading channels is deduced and analyzed. Compared with the noncooperation scheme, theoretical analysis and numerical simulations show that the outage probability of the coded cooperative MIMO decreases sharply. Meanwhile, more attention is paid to the LDPC-coded cooperative MIMO with unkown channel state information(CSI) in the destination. In the unknown CSI scenario, the spatio-temporal recursive least squares(ST-RLS) and spatio-temporal least mean square(ST-LMS) adaptive detection algorithms are proposed. Simulation results verify the effectiveness of these two algorithms. Finally, because the the joint BP iterative decoding algorithm need acquire perfect CSI and its implementation complexity is high, it is not applicable to the LDPC-coded cooperative MIMO with unkown CSI. The joint “Min-Sum”(MS) iterative decoding algorithm is proposed.(3) Network-coding-based multisource multirelay LDPC-coded cooperative MIMO is investigated. Firstly, considering multiple sources, the network coding technique is adopted, and the network-coding-based multisource multirelay LDPC-coded cooperative MIMO is proposed. Secondly, from the viewpoint of the destination, the overall parity-check matrix corresponding to the proposed system is resulted, based on which the equivalent joint Tanner graph is introduced. Meanwhile, the outage probability of the network-coding-based coded cooperative MIMO over Rayleigh block fading channels is analyzed and deduced. In the scenario where the numbers of sources and relays are large enough, the closed-form expression of the instantaneous channel capacity is resulted based on the law of large number. Finally, the bit error rate(BER) performance of the system is studied by simulations.(4) Quasi-cyclic LDPC(QC-LDPC) codes joint design for coded cooperation system is investigated. Firstly, a kind of QC-LDPC codes constructed based on the base matrix and exponent matrix are introduced. A necessary and sufficient condition, which must be satisfied for avoiding girth-4 cycles in this kind of QC-LDPC codes, is proposed. Meanwhile, more attention is paid to the coded cooperation system employing this kind of QC-LDPC codes. There are two kinds of girth-4 cycels in the overall parity-check matrix, i.e. Type-I and Type-II girth-4 cycles. To cancel both of these two kinds of girth-4 cycels, joint design approach of QC-LDPC codes adopted by the source and relay is proposed. Furthermore, the proposed joint design approach is extended to the multirelay coded cooperation and cascade-based multisource coded cooperation systems.