基于分段FFT的GPS L1/L2C信号快速捕获算法

Algorithm of GPS L1/L2C fast acquisition based on segmented FFT

软件接收机要实现对L1/L2C双频GPS信号的跟踪,必须捕获到L1信号中的C/A码和L2C信号中的CM或CL码。但由于L2C信号的长度较长,采用直接捕获的方法计算量大、占用存储空间大,无法在软件接收机上实现。针对以上问题,提出一种适合于软件接收机实现的基于分段FFT的GPS L1辅助L2C信号快速精确捕获算法。本算法通过捕获到的L1信号辅助L2C信号实现载波多普勒频移搜索,同时利用分段FFT技术进行L2C码相位并行搜索,最终对实现L2C信号的捕获。计算和仿真实验结果表明,该捕获算法的计算量减少了约200倍,并且大大节省了存储空间,实现了软件接收机中L1/L2C双频信号的快速精确捕获。

In tracking double-frequency L1/L2C GPS signal with software receiver, the C/A code of L1 signal and CM code or CL code of L2C signal must be acquired. However, L2C signal is so long that the direct acquisition algorithm needs large calculation and storage space, which can not be implemented on software receiver. Aiming at the above question, an L1-assisted L2C algorithm for fast acquisition based on segmented Fast Fourier Transform (FFT) is proposed which is suitable for implementation on software receiver. This algorithm searches carrier Doppler frequency shift through the L1-assisted L2C, and applies segmented FFT to search L2C code phase, finally L2C signal can be acquired. The results of calculation and simulation experiments show that the presented algorithm can reduce the calculating amount to about 1/200 and greatly save the storage space, which can achieve the acquisition of double-frequency L1/L2C signal by software receiver quickly and accurately.