一种改进的数字GPS接收机基带环路设计

A Modified Base Band Loop Design for Digital GPS Receiver

针对GPS接收机设计中,接收机信号跟踪精度同信号处理的实时性不能兼顾的特点,设计了一种基于DSP+FPGA的数字GPS接收机实时高精度基带环路。阐述了基带信号处理原理及原有方法的不足,提出了一种改进的GPS信号快速、高精度捕获、跟踪方法。利用信号粗捕后先进行精捕,在提高了信号的捕获精度后再结合二阶锁频环路辅助,最终利用三阶载波科斯塔斯锁相环完成GPS载波信号的高精度稳定闭环跟踪,同时使用载波来实时的辅助码环跟踪,从而完成整个GPS信号的实时高精度跟踪。实验结果表明该基带环路能够实现对GPS信号的快速捕获、实时稳定的高精度跟踪,并具有良好的动态性能。

The design of baseband signal processing is the key for GPS receiver.In order to assure the precise and real-time performance of GPS receiver,a baseband loop is designed based on DSP＋FPGA in this paper after introducing the principle and method used before,then a modified fast acquisition and tracking method is introduced.After coarse code and frequency acquisition,a second precise signal detection is used for accurate carrier frequency,and the 2nd-FLL is designed for aiding carrier frequency＇ s 3nd-costas-PLL at the start of tracking.After steadily tracking,there will be 3nd-costas-PLL working solely for higher precise frequency.At the same time the carrier doppler frequency is used to help code phase lock loop for getting more precise phase.Finally this method can get more precise signal steadily. Examination proves the method can get good output in signal＇s real-time,fast acquisition and precision tracking.