极低信噪比环境下的P码二维直接捕获改进算法

An Improved Algorithm for P-Code Two Dimension Direct Capture in Extra-low SNR Condition

针对极低信噪比环境下GPS系统中超长精密测距码(P码)直接捕获的问题,传统的滑动相关法已无法满足P码直接快速捕获的要求,分析了现有常用FFT校频快速捕获技术性能以及FFT运算长度与信号输入信噪比的关系,指出了现有算法的不足,在此基础上提出一种在极低信噪比环境下的码捕获新方法———利用非对称FFT计算和视频积累相结合的P码直接捕获改进算法,仿真结果表明,即使在-35 dB的极低信噪比情况下,算法也可快速实现P码的直接捕获,最后给出算法的FPGA实测结果,进一步验证了算法的可实现性及有效性。

This paper investigates the synchronization of digitalized DSSS receiver in high - dynamic and Extra - low SNR environment, presents and realizes the methods of direct P - code acquisition in GPS. This paper introduces several conventional code acquisition methods and the reason why they are not fit for direct P - code acquisition. In the precondition of good cross correlation and partial autocorrelation of P - code, a direct P - code acquisition scheme based on Unsymmetrical FFT is proposed and realized in FPGA. Compared with the conventional slipping con＇elation method, the time of direct P - code acquisition scheme based on Unsymmetrical FFT is reduced by more than ten times and the calculation is reduced rapidly. It＇s useful for other direct long PRN codes acquisition.