Research On Low-Density Parity-Check Codes And Their Applications In Parallel Concatenation Structure

Channel code is one of the key technologies in the future wide-band wireless communication system. As a class of error-correcting codes that has performance approaching Shannon limit, low-density parity-check (LDPC) codes is a hot topic in the research area of channel code. This dissertation investigates the LDPC codes. The dissertation includes eight chapters. Chapter one introduces the background and the main contribution of this dissertation. Chapter two introduces the basic knowledge of the LDPC codes, includes the bipartite graph, the code construction and several decoding algorithms.In chapter three, base on the theory analysis of mean magnitude of the LLR message output from the LDPC decoder, a low complexity stopping criterion, named Convergence of Mean Magnitude (CMM) method hereafter, is proposed for the LDPC decoder. Compared with other existing criteria, the CMM criterion has low computation complexity and the least storage requirement. Simulation results prove that the CMM method can reduce the average iteration number of the LDPC decoder efficiently. Hence the complexity and the delay of the decoder can be reduced. The simulation results also show that the optimal parameters of the CMM method are insensitive to the code length, the code rate, the channel SNR and the character of the channel. Thus the CMM criterion has perfect foreground in the engineering application.In chapter four, the sensitivity of the LDPC decoder to the Signal-to-Noise Ratio (SNR) mismatch in Rayleigh fading channel or high order modulated system is analyzed. Then two SNR estimation algorithms are proposed based on the idea of the on-line SNR estimator when the channel is Rayleigh fading or the system is high order modulated respectively. The simulation results proved that the proposed algorithms have good performance in the LDPC decoder.Based on the ideas from Gallager's LDPC codes and the parallel concatenation code structure in Turbo code, a new class of concatenated codes based on component...