Application Of LDPC Codes

Low-Density Parity-Check (LDPC) codes are a class of capacity approaching error-correcting codes. By using low complexity belief propagation algorithm, LDPC codes are able to get near Shannon limit decoding performance with almost all errors detectable. For long code lengths, LDPC codes can even outperform Turbo codes. Due to the advantages of LDPC codes, their applications in reliable communications have received great interests and have become one of the most attractive fields in channel coding community. Now, the application of LDPC codes has been put on the agenda. LDPC codes are regarded as a key technique in the 4G.This thesis investigates some aspects of LDPC codes with emphasis on message passing algorithms and girths of LDPC codes. Another part of the paper touches on GLD codes. The main contents and results are as follows.1. Based on Tanner graph, the representation and construction of LDPC codes are introduced and two decoding algorithms for LDPC codes, i.e., bit-flipping algorithm and sum-product algorithm are discussed.2. Several factors influencing LDPC codes are talked about, emphasis on methods for large girth construction.3. The efficient encoding problem of LDPC codes is mentioned and an improved scheme about concatenated LDPC and convolutional codes is proposed. Several codes can be encoded and decoded at the same time in the scheme. The realization of this scheme has low complexity and short delay. The scheme also has excellent performance.4. The theory about GLD codes is introduced. The results of simulations show the performance of these codes is outstanding.Several good Concatenated schemes about LDPC codes have been put forward, but in realization, selecting proper LDPC codes must be seriously considered. Although LDPC codes are superior to Turbo codes, it is not the case for short LDPC codes. Performance of GLD codes is between them in short code lengths. GLD decoder has a regular and parallel structure which makes it very suitable for practical integrated circuit (IC) implementations.