基于FFT的二维并行长码捕获算法

Two-dimensional parallel long code acquisition algorithm based on FFT

导航伪随机长码周期一般为7天,在时间不确定度为±1 s,码速率为10.23 MHz的情况下,需要搜索码片数最多达20 460 000个,普通方法难以实现短时间内捕获。通过增加硬件资源消耗及减少相干积分时间能加快捕获速度,但由于硬件资源有限,而减少相干积分时间会导致捕获灵敏度降低。为了在有限的硬件资源下,不影响捕获灵敏度而又能快速实现捕获,研究了一种基于快速傅里叶变换(FFT)的二维并行搜索算法。通过与传统基于FFT的码相位并行多普勒串行搜索及匹配滤波+FFT方法在捕获时间、灵敏度及硬件资源3方面对比,验证了基于FFT的二维并行捕获方法在长码捕获中具有捕获速度快、捕获灵敏度较高、硬件资源的利用更加合理等优势。

The navigation pseudo random long code period is 7 days generally. When the time uncertainty is ±1 s and the code rate is 10.23 MHz, the chips needed to search are up to 20 460 000. So it is difficult to realize acquisition in short time with common methods. By increasing the consumption of hardware resource and reducing the coherent integration time, the acquisition speed will be increased. Nevertheless this will lead to the decrease of the acquisition sensitivity due to the limited hardware resources. In order to realize the acquisition quickly without affecting the acquisition sensitivity with the limited hardware resources, the two-dimensional parallel search method based on Fast Fourier Transform(FFT) is presented. By comparing with the methods of code phase parallel searching based on FFT and matched filtering +FFT in three aspects: acquisiton time, sensitivity, and hardware resources, the proposed algorithm is demonstrated to have advantages of fast acquisition speed, high sensitivity, and rational use of the hardware resources in the long code acquisition.