双多进制正交扩频系统的比特软值输出算法

Bit Soft-Output Algorithm for Dual N-ary Orthogonal Spread Spectrum System

该文针对双多进制正交扩频与Turbo码的联合系统,基于最大后验概率(MAP)准则,提出了双多进制正交扩频输出比特软值的MAP算法,并给出了简化MAP算法:同时,对算法的定点和浮点性能进行了仿真,且与现有的软值算法进行了比较。结果表明,MAP算法能使整个系统获得相当的增益,L=3的简化MAP算法在基本不增加复杂度情况下好于现有的双最大值算法约0．4dB。

Focusing on Turbo-coded dual N-ary orthogonal spread spectrum system, this paper proposes an algorithm for computing bit soft metric based on Maximum a Posteriori Probability （MAP） criterion, and then presents a simplified MAP algorithm. Meanwhile, the fixed-point and float-point performances are simulated and compared with several existing algorithms. It is shown that MAP algorithm greatly improves the whole system performance; the simplified MAP algorithm with L=3 outperforms the dual-maxima algorithms 0.4dB without extra cost in complexity..