一种LDPC系统中的似然值计算方法

摘要

The adoption of LDPC (Low Density Parity Check) code and scrambler in a communication system could make the information randomized and acquire fairly high coding gain. The scrambling may be done before or after the LDPC coding. For scrambling LDPC-coded communication system, the LLR computing method necessary for LDPC decoding through soft demodulating and descrambling is proposed. First, the result of this cascade system is described, then the calculation of LLR is theorectically derived, and finally the simulation system combined with LDPC and scramble module is established, thus to verify the LLR computing method.%在通信系统中采用低密度奇偶校验码（LDPC）与扰码，一方面能够使得信息随机化，同时也能得到较高的编码增益，加扰可以在 LDPC 编码前进行，也可以在编码后进行。针对 LDPC 编码后进行加扰的通信系统，提出了一种通过软解调与软解扰进行LDPC译码所需的似然值的计算方法。首先对这种级联系统的结果进行描述，其次对似然值的计算进行了理论推导，最后构建仿真系统，与 LDPC 结合进行仿真验证。