LDPC Codes And Their Applications In Compressed Image Transmission

LDPC is a class of linear block codes which can be defined by the sparse check matrix or bipartite graph,it was first invented by Dr.Gallager in the year of 1962,but its importance was not realized until the end of the last century. LDPC codes have the performance which is near Shannon limit,with advantages of high encoding gain, low decoding complexity and flexible codes, etc.Their applications in reliable communications have received great interests and have become one of the most atractive fields in channel coding community.In this thesis, the development of channel coding theory is introduced briefly. After the definition of LDPC code and several code design methods, The typical BP decoding algorithms,and several simplified BP algorithms are presented and deeply analyzed.SPECK is a good embedded image coding based on wavelet transform.This paper presents a joint source-channel coding scheme based on SPECK and improved LDPC codes according to the unequal error protection for the compressed data according to the importance for reconstruction.The experimental results show that this sheme gives excellent performance for compressed image transmission over noisy channels,improving the performance of the whole system.Finally,this paper construct the LDPC-COFDM simplified baseband signal processing model for 4G mobile communication system,combining with the technologies of WOFDM,simulate the performance of LDPC codes over the channel model.Some useful conclusions are drawn based the simulation results,the application foreground is discussed for 4G.