一种基于EM算法的码辅助载波同步算法

Code-Assisted Carrier Synchronization Algorithm Based on EM Algorithm

对于采用LDPC编码的通信体制,当接收信号存在残留频偏或相偏时,LDPC译码器的性能会急剧恶化。针对以上问题,提出了一种LDPC码辅助的载波同步算法。提出的载波同步算法包括基于代价函数的载波粗估计算法与基于EM算法的载波细估计算法。针对基于代价函数的载波粗估计算法,提出了一种只与残留频偏有关,与残留相偏无关的代价函数,将遍历搜索范围由二维降低到了一维,解决了预补偿遍历消耗资源较多的问题。针对载波细估计算法,基于EM算法提出了一种使用LDPC译码器输出后验概率信量的迭代载波细估计算法,并推导出了该算法的解析解,仿真结果表明,采用解析解与采用遍历算法求解的结果基本一致。根据理论推导与仿真结果,提出的算法有较大的频偏相偏估计范围,在较低的信噪比下仍可实现有效的载波同步与LDPC译码,相较于传统算法复杂度较低,是一种较为理想的载波估计算法。

The performance of the LDPC decoder will deteriorate sharply when receiving signals with residual carrier bias.To solve this problem,a carrier synchronization algorithm assisted by LDPC code is proposed.The carrier synchronization algorithms proposed in this paper include rough carrier estimation and carrier fine estimation based on the EM algorithm.A cost function that is only related to residual frequency bias is proposed to solve the problem of high resource consumption in pre-compensated traversal by reducing the traversal search range from two dimensions to one dimension.An iterative carrier fine estimation algorithm using posterior probability outputted by the LDPC decoder is proposed based on the EM algorithm,and the analytic solution of the algorithm is derived in this article.According to the theoretical derivation and simulation results,the proposed algorithm has a large estimation range,and can still realize effective carrier synchronization and LDPC decoding at a low signal-to-noise ratio.