基于Turbo方法的乘积码脉冲位置迭代调制解调译码

Demodulation and Decoding of Product Coded Pulse Position Modulation Based on Turbo Method

脉冲位置调制（PPM）无线光通信系统易受到大气湍流影响，针对于此，将Turbo技术引入到PPM的解调和乘积码译码中。基于极大似然准则导出了PPM软检测解调方法，结合分组码的SISO译码，构建了检测解调和译码联合迭代的Turbo结构，推导了其迭代原理算法。仿真分析结果表明，误码性能可随迭代次数增加改善，其中，在大气闪烁指数0.1和误码率10-6条件下，迭代3~5次相比非迭代系统获得了0.8 dB以上的增益。

To reduce the influence of atmospheric turbulence, turbo technique was used in process of PPM demodulation and product code decoding. The soft detection demodulation method of PPM was deduced based on maximum likelihood rules, combined with SISO block decoding, the structure of Turbo demodulation and decoding was constituted, iterate algo-rithm was also given. Simulation results showed that, the performance could be improved with increasing of iterations, and under condition of 0.1 atmospheric index and BER 10-6 , with 3~5 iterations the iterate algorithm would provide more than 0.8 dB gain compared to no-iteration system.