GPS软件接收机中的一种实用高灵敏度快速捕获算法

A High Sensitive Fast Acquisition Algorithm Suitable to Implement in Software GPS Receiver

C/A码的捕获,在软件GPS接收机中的地位举足轻重.通常软件GPS接收机中没有专门用于相关运算的硬件部件,提高软件GPS接收机的捕获灵敏度的同时降低捕获的运算量,是软件接收机实用化的关键.利用先叠加再相关的方法,可以减少相关运算的次数,但必须考虑载波误差对相关函数峰值的影响.在此基础上,研究了数据预处理中,线性插值的参数选择问题,最后,提出了最佳路径算法,进行进一步的相关累积,在延长相干累积时间长度的同时,避免导航数据跳变对累积的影响,提高捕获的灵敏度.仿真结果表明,在信噪比SNR=-37dB的情况下,算法仍能捕获到所有卫星信号.实际接收的数据也表明,算法能明显增加捕获到的卫星数量.由于算法采用了多种措施来降低运算量,因此算法的运算量适中,非常适合在软件接收机中采用.

Acquisition of C/A code is most important for software GPS receiver in weak signal environment.Traditionally there is no special hardware dedicate to perform correlation in software receiver,it is a key issue to promote the acquisition sensitivity with less computation burden in software GPS receiver.In this paper,the algorithm of cumulating first then correlating is employed to reduce computation burden efficiently,at the same time the error of carrier frequency has to be taken into consideration which has negative effect on the peak value of coherent correlation function.Furthermore,the selection of linear interpolation parameters in data pretreatment has been discussed.Finally,optimum path algorithm is proposed to process coherently with long integration time which reduces the impact of navigation data bits transition on correlation integration and improves the sensitivity of software GPS receiver.Simulations show that the new algorithm can still acquire all the satellite signals when SNR equals -37dB.Field test data also show that the new algorithm can remarkably improve the ability to acquire more satellite signals.Moreover,because the new algorithm has made use of many measures to reduce the computation burden such as algorithm of cumulating first then correlating and optimum path algorithm,it is most suitable to implement in software GPS receiver.