OFDM码元定时和频率偏差估计中的最佳相关长度分析

Optimal correlation length of symbol timing and frequency offset estimation in OFDM systems

码元定时和频率偏差估计是OFDM系统的关键技术之一.以相关运算为核心的最大似然算法(ML)在OFDM码元定时和频率偏差估计中得到广泛的应用.如何确定多径传播环境中接收机最佳相关长度是影响ML算法实际应用的关键.通过分析得出:减小ML中相关窗长度可以有效地抑制多径传播的影响;其最佳相关长度等于循环前缀与最大多径时延之差.部分相关ML算法首先利用子空间分解技术动态跟踪多径信道变化,再实时计算出最佳相关长度用于码元定时和频率偏差估计.仿真结果证明新算法可以有效地抑制多径传播对同步估计性能的影响.

Symbol timing and frequency offset estimation are key techniques in OFDM systems. Maximum likelihood algorithms based on correlation operation are widely used. Optimal correlation length plays an important role in correlation operation. This paper proves that the performance of maximum likelihood estimation method based on cyclic prefix can be improved by decreasing correlation length. The optimal correlation length under multipath propagation environment equals the length of cyclic prefix minus the maxiumum multipath length. The partial correlation algorithm tracks maximum multipath length by subspace decomposition and calculates optimal correlation length subsequently for symbol timing and frquency offset estimation. Simulation results show that the algorithm can efficiently suppress the effect of multipath on synchronization estimation.