The Adaptability Between LDPC Codes And Modulation And Their Application

LDPC code is a type of error correcting block code with very sparse check matrix,which was put forward by Gallager in early 1962.Research results show that LDPC code's performance is better than Turbo code,and more approaching the Shannon limit.DVB-S2 is the next generation standard of the digital satellite broadcasting.DVB-S2 is the first standard of transmitting system which adopt LDPC codes,and it also means that the research of LDPC codes has transferred from theory into practice.In this paper shaping gains of LDPC Coded-QAM transmitting systems with non-uniform QAM constellation are presented over AWGN channel.The influences of code rate,frame length,the order of non-uniform QAM constellation and the finite fields GF(q) of LDPC codes on shaping gain are investigated through simulation experiment for the proposed system at the BER(bit error rate) level of 10^-6.It is found that shaping gain will be affected by these parameters mentioned above,and there is adoptability between the finite fields GF(q) of LDPC codes and the order of non-uniform QAM constellation.By using SPW,I design the DVB-S2 simulation system and finish the fixed-point simulation.The influences of the order of quantization and fix-point are investigated through simulation.And the result of simulation also shows that:performance of fixed-point system is no worse than float-point system when quantization of high order and suitable fix point are employed.As we don't have independent intellectual property rights of receiver based on DVB-S2,this work is of the far-reaching significance in hardware implementation of DVB-S2.