基于分裂基FFT的L1辅助L2C双频GPS信号快速捕获

室外无人搬运车(automatic guided vehicle, AGV)运输和未来的无人驾驶智能汽车等对全球定位系统(global positioning system, GPS)高精度定位精度要求较高,GPS L1/L2C双频信号可以校正电离层误差从而提高GPS单机的定位精度。但L2C 民用中码/民用长码(civil moderate/civil long code, CM/CL)的长度远大于L1 粗捕获码(coarse/acquisition code, C/A),传统的捕获算法直接用于L2C信号会使捕获时间延长甚至导致捕获失效。对此,提出了利用捕获到的L1信号的多普勒频移和C/A码相位对L2 CM码进行辅助捕获,然后利用CM码码相位对CL码进行辅助捕获的方法,减小了L2C信号捕获的二维搜索范围;同时在相关运算中利用分裂基快速傅里叶变换(split radix fast Fourier transform, SFFT)代替传统的基2 FFT进一步降低了计算量。仿真结果表明，所提算法在运算量明显降低的情况下可以实现对L1/L2C双频信号的精确捕获。

Fast acquisition of L1 aiding L2C dual-frequency GPS signal based on SFFT

Outdoor automatic guided vehicle (AGV) transportation and future intelligent unmanned vehicles require positioning accuracy high for the global positioning system (GPS), GPS L1/L2C dual-frequency signals can improve the location accuracy by correcting ionospheric delay.However, L2 civil moderate/civil long (CM/CL) codes are both much longer than L1 coarse/acquisition(C/A) codes. If the traditional acquisition algorithm is applied to L2C acquisition directly, it will lead to much longer acquisition time and even failed acquisition. Therefore, an algorithm is proposed, which accomplishes CM acquisition by using the acquired Doppler shift and C/A code phase of L1 signals, then similarly finishes CL acquisition by the CM aided code phase, which makes the two dimension searching process for L2C acquisition narrow down to searching one dimension code phase with fewer discrete points. Meanwhile, the split-radix fast Fourier transform (SFFT) instead of traditional radix 2 FFT is introduced into correlation operation, which can reduce the calculated quantity further. Simulation results show that the suggested algorithm can achieve accurate acquisition of dual-frequency signals with much lower calculated amount.