Study And Implementation Of LDPC Code Encoding And Decoding Algorithm

In 1962 R.G.Gallager proposed liner group code based on sparse parity check matrix,namely Low-Density Parity-Check Code. Later, findings revealed that LDPC code is anadvanced code near Shannon limit and shows good performance in the circumstance of lowsignal to noise ratio. Thus LDPC code is generally accepted as a channel encoding schemewhich meets the demand of the fourth mobile communication system for great capacity andhigh speed data transmission.Firstly, this paper presents several encoding and decoding algorithms, deduces thedecoding error probability and density evolution process, and discusses the threshold effect ofchannel parameter. Secondly, this paper probes into the four-side cycles in Tanner graph ofLDPC codes and lodges an eliminating four-side cycle formation algorithm of LDPC codesparity check matrix, realizes its program design in amalgamation program fashion of Matlaband VC++. This algorithm generates parity check matrix of LDPC code in binary system fieldand in GF (q)field if amended. It avoids the repeated iteration in the decoding process ofLDPC codes and noticeably improves the bit error ratio capability of short frame LDPC codes.Moreover, it analyzes different parameters for the performance of LDPC codes and drawssome conclusions. Last, this paper realizes the whole LDPC encoder using VHDL languagebased on CPLD. Besides, it presents integral construct of LDPC decoder, according to theLLR-BP decoding algorithm, labors its each module.