Research On Structured Construcion Of LDPC Code And Application In CMMB

Low density parity-check (LDPC) code is one kind of sparse parity-check matrix based linear block error-correcting codes which could highly approach the Shannon limit with iterative decoding. LDPC codes have lots of advantages such as high encoding gain, low decoding complexity and flexible code rate and their parallel operation of decoding is easy for hardware implementation。Now the research about LDPC is one of the most amazing highlights in the area of channel coding.Compared with the traditional way of construction of LDPC codes, the random construction, which is complex with long searching time, structured construction of LDPC codes based on finite geometries or block design can reduce the complexity and insure the performance, which have great potential in application.In this paper, we firstly study on structured construction of LDPC codes, including those based on Euclidean geometry space-EG (Euclidean Geometries) method, and those based on the block design-BIBD (Balanced Incomplete Block Design). In the structured construction of LDPC code based on decomposition of Euclidean geometry, we proposed to use masking matrix to reduce the number of 6-loops in parity check matrix, and to lower the column and row weight to make them similar to the code which is random structured. Another way of structured construction of LDPC codes is through block design, we get the base incidence vectors by computer search, and the remainder incidence vectors are gotten by cyclically shifting these base incidence vectors. This kind of parity-check matrix has quasi-cyclic structure.We introduce methods of finding generator matrix of a structured construction of LDPC code which has quasi-cyclic (QC) structure from its parity-check matrix and its corresponding encoding schemes in this paper.These QC-LDPC codes can not only reduce the storage of LDPC generator matrix, but also decrease the encoding complexity efficiently, which is of great significant for application.We study on both hard-decision and soft-decision decoding algorithm of LDPC codes, and we focus on the most commonly used decoding algorithm called Belief Propagation algorithm. We simulated the performance of structured LDPC in the AWGN channel, BPSK Modulation, simulation results show that the performance of rational designed structured LDPC codes can meet or even be better than that of random structured LDPC codes.In the last part of this paper, we study on the latest applications of LDPC codes in China Mobile Multimedia Broadcasting (CMBB).One kind of construction of highly-structured LDPC code was discussed, and initialization of BP decoding algorithm using M-ary modulation in wireless fading channel (Rayleigh and Rice Channel) is introduced. Finally, we simulated the performance of CMMB-LDPC codes, results show that these highly-structured LDPC code have good capacity of resisting fading interference.