Research Of Bit-interleaved Coded Modulation Technology Based On LDPC Code

Convolution coded BICM, BICM-ID coding and decoding schemes as well as lots of design rules are studied in this paper. Moreover, the infection of mapping, iterative times and interleave length are analyzed in theory and simulation. On this foundation, BICM and BICM-ID based on LDPC are investigated. The results show that most kinds of design rules based on convolution codes couldn't completely fit for LDPC-BICM and LDPC-BICM-ID. The performance of BICM-ID based on convolution codes improved dramatically by comparing to BICM with the same constituent code. However, it increases inconspicuously by comparing to LDPC-BICM with the same constituent code. The reason of this phenomenon is analyzed and an improved joint demodulate decoding method is proposed by combining the characteristics of LDPC and BICM-ID. Simulation results show that not only the performance of this enhanced LDPC-BICM-ID is improved, but also the mean iterative times of LDPC decoding decreased compared to the former methods. So this method has preferable application value. At last, it is proved that the bit log-likelihood ratio probability density function has symmetry properties with 8-PSK modulation Gray mapping. Therefore, the density evolvement (DE) algorithm can be used to analyze the performance of LDPC. Several SNR threshold values of a series of LDPC are researched under the condition of this modulation mapping. The simulation result is very close to the threshold value of DE algorithm. It's obvious that the DE algorithm fits for the analyzing of performance when using 8-PSK modulation Gray mapping, this conclusion can provide some reference for optimizing design of the LDPC code in LDPC-BICM.