基于EM的低复杂度迭代载波同步算法

编码辅助载波同步算法充分利用译码软信息，可获得较理想的同步性能，但是目前 这类算法存在复杂度高、处理时间长的问题。首先在推导迭代载波同步中后验均值与译码软 信息关系的基础之上，通过选择性地进行译码判决反馈来减少不必要的计算点数，再根据前 两次的迭代结果自适应地减小频率搜索区间长度，从而大幅降低同步参数估计的运算量。仿 真结果表明，该算法能够有效工作在低信噪比环境下，可获得接近理想同步条件下的译码性 能。

An EM-based low complexity iterative carrier synchronization algorithm

The code-aided(CA) carrier synchronization algorithm exploits soft decoding information introduced by the decoder to gain the ideal synchronization perform ance. But the algorithm performs high complexity and long delay. In this paper, the relation between posterior average values and soft decoding info rmation in iterative carrier synchronization is derived and unnecessary calculat ing points are reduced by using selective soft decision feedback. Then the len gth of frequency search interval is decreased adaptively according to the previo us two iterat ive results. So the computational complexity of the estimation of synchronizatio n parameters is reduced greatly. The simulation results demonstrate that this al gorithm can work efficiently at low signal to noise ratio (SNR), and almost perf ect synchronization decoding performance is achieved.