基于模糊函数频率轴投影的CDMA信号时/频差估计

Estimation of CDMA Signal Time / frequency Differences Based on Projection of Ambiguity Function on Frequency Axis

对地面辐射源的定位可以通过估计两颗卫星接收信号的时差和频差来实现。CDMA信号具有带宽大、数据长的特点,传统的时差和频差估计方法运算量大,难以实时处理。利用CDMA信号模糊函数具有图钉型的特点,对两路CDMA信号的模糊函数在频率轴上进行投影,根据投影峰值位置估计两路CDMA信号中各用户的频差,再对信号补偿频率后通过一次相关估计各用户的时差。由于模糊函数在频率轴上投影的计算可以通过若干次FFT快速实现,因此本文提出的算法相对传统的二维搜索模糊函数峰值的算法运算量显著降低。仿真结果表明,该方法能够快速精确地估计出CDMA信号中各用户的时/频差。

The location of radiation source on the earth can be implemented by estimating time/ frequency differ-ences between the signals received by two satellites. CDMA signals are featured with broad bandwidth and long data, using traditional method of estimating time/frequency differences is difficult to realize real-time processing since its bulk operand. According to the fact that the ambiguity function of CDMA signals look like a thumbtack, frequency difference of each user between two CDMA signals can be estimated by peak position of ambiguity function projection on frequency axis, then the time difference of each user can be estimated by a correlating after the frequency of signal is compensated. Since computing of the ambiguity function projection on frequency axis can be implemented quickly by some FFT processing, using the proposed algorithm can reduce the operand obviously comparing with the algorithm of using traditional 2-dimensional search ambiguity function peak. The simulated results indicate that using this algo-rithm can estimate time/frequency differences of each user among CDMA signals fast and accurately.