多径衰落信道下的正交频分复用符号同步算法

OFDM Symbol Synchronization Algorithm in Multi-Path Fading Channel

传统的基于循环前缀的正交频分复用同步最大似然算法,在多径衰落信道下,由于多径时延和多普勒频移的缘故,部分循环前缀受到码间干扰,相关运算的峰值不明显,而且具有峰值平顶效应,在不加优化的条件下,几乎不可以使用.现提出了一套改进方案,根据信噪比的高低和多径时延的大小,动态调整参与相关运算的循环前缀长度,并采用多点相关求均值的方法.仿真结果表明,该方案在信噪比低的高斯白噪声信道和多径衰落信道下,均可以得到尖锐的相关峰值,显著减少多径衰落信道下的峰值平顶效应,并且提高符号同步精度.

Conventional maximum likelihood algorithm based on cyclic prefix has plateau effect and has no obvious peak correlation value in multi-path channels, because some of the cyclic prefixes have been polluted by Inter-Symbol Interference（ISI） due to the multi-path delays and Doppler effects. The algorithm can not be used in multi-path channels without optimization. An optimized method based on the cyclic prefixes is proposed in this paper, which reduces the number of cyclic prefixes in correlation calculation according to the signal-noise ratio and multi-path delays and uses average correlation values in multi sampling points. The proposed method proves to be able to get sharp peak values and improve the symbol precision compared with the existing methods both in Additive white Gaussian noise （AWGN） channels and in multi-path channels. In multi-path channel, plateau effect decreases significantly.