低密度奇偶校验码的联合信源信道译码

Joint Source Channel Decoding for Low Density Parity Check Codes

为了进一步提高通信系统的可靠性,提出一种联合信源信道译码(JSCD)方案。该方案利用一个软输入软输出(SISO)译码器对可变长码(VLC)实施软译码。SISO-VLC译码器利用信源符号的先验信息,采用BCJR算法,得到压缩比特的后验概率。该方案将VLC与低密度奇偶校验(LDPC)码串行级联,在译码端SISO-VLC译码器将外信息传递给LDPC译码器,实现信源信道联合译码。在加性高斯白噪声环境下,对该方案的误码率和误符号率进行评估,并与分离信源信道译码(SSCD)比较。仿真结果表明,在一定复杂度的情况下,该方案在低信噪比下具有很高的可靠性;与SSCD相比,能获得0.2 d B的编码增益。

To further improve the reliability of communication system,an innovative joint source channel decoding(JSCD) scheme is proposed. The proposed approach enables soft decoding of variable length codes(VLCs) by means of a SISO decoder. The soft-in soft-out(SISO)-VLC decoder based on BCJR algorithm uses a priori knowledge of source symbols in order to obtain a posteriori probabilities of the compressed bits. The scheme concatenates a VLC with a low-density-parity-check(LDPC) code,and the SISO-VLC decoder delivers extrinsic information to the LDPC decoder. Its performance in the case of transmission over an additive white Gaussian noise channel is evaluated in terms of bit error rate and symbol error rate. Simulation results show that the JSCD scheme outperforms the separate source channel decoding(SSCD),and an additional coding gain of 0. 2 d B is achieved.