基于数字匹配滤波器与多径合并的CDMA码跟踪环

CDMA Code Tracking Loop Based on Digital Matched Filter And Multipath Timing Error Combing

PN码跟踪环是DS-CDMA蜂窝移动通信系统的关键技术。本文针对第三代(3G)移动通信系统,着眼于对下行公共导频信道的充分利用,提出了一种基于数字匹配滤波器(DMF)和多径误差合并的全数字式码跟踪环。导频信道的DMF输出,一方面可用于信道估计与多径搜索,另一方面用于提取码定时误差,二者结合可以进行码定时误差的多径RAKE合并。理论推导与仿真结果表明,该跟踪环性能良好,具有较高的实用价值。

PN code tracking is investigated for direct-sequence code division multiple access (DS-CDMA) cellular mobile radio such as WCDMA. Two chip clocks with half-chip phase offset are used to sample the received signals, which are de-spreaded by two digital matched filters (DMF) respectively. Pilot correlation outputs at integer sampling instants are used for channel estimation and multi-path search, and those outputs at half-integer sampling instants for timing error extraction. Taking advantage of the inherent diversity with maximal ratio combing (MRC) based on selected multi-path components, the code tracking loop performance is improved with reduced hardware complexity.