一种改进的基于FFT的GPS弱信号捕获算法

An Improved Weak GPS Signal Acquisition Algorithm Based on FFT

传统的GPS弱信号捕获通过延长相干积分时间来提高信噪比,但受到导航电文比特位翻转的影响,相干积分时间一般不超过20ms,且存在捕获算法运行效率不高等问题。针对在弱信号环境下有效克服比特位翻转并增加运算效率的问题,给出了两种翻转位预测算法。基于预测结果本文提出了一种改进的捕获方案,即舍弃存在位翻转的5ms数据从而消除其影响,并对其余数据进行15ms的"先累加后相关"分块相干积分。最后,利用Matlab仿真的信号对改进捕获算法进行验证并与传统捕获算法进行对比。结果表明,改进的捕获算法能有效地捕获到信噪比低至-40dB的微弱信号,将相干积分时间延长至15ms,相较于传统捕获算法捕获灵敏度更高,执行时间更短。

Traditional acquisition algorithm of Global Positioning System weak signal used to improve the SNR gain by extending the coherent integration.But it is limited in the navigation data bit flipping.Coherent integration time is generally not more than 20 ms and the operation efficiency is not high.Two improved prediction algorithms are proposed to solve the problem of overcoming the navigation data bit flipping and increasing the computational efficiency in the weak signal environment.Based on the prediction results,an improved capture scheme is proposed in this paper.Firstly,the 5ms signal with possible involve bit-flipping was canceled to eliminate its influence,then coherent integration was applied to its sub-block signal in the remaining 15 ms,which the summation operation was done ahead of coherent integration.Finally,by verifying and comparing with the traditional acquisition algorithm on the Matlab platform,the simulation show that the improved acquisition algorithm even can capture weak signals with Signal-to-Noise-Ratio（SNR）as low as-40 dB.The coherent integration time have been increased to 15 ms by predicting the navigation data bit flipping.Compared with the traditional capture algorithm,the acquisition sensitivity and the execution time have been improved.