A Study Of Differential GPS Signal Demodulation And Decoding Technology

Nowadays,differential GPS technology has been widely utilized.To better study differential GPS which can obtain real-time and high-precision signals,we have done much research into demodulation algorithm and the decoding algorithm about differential GPS.Firstly,this thesis has introduced the related technologies of differential GPS system,including the composition of GPS system,the source of GPS positioning error,and the principle of differential GPS positioning.Then,the different versions of the differential GPS data transmission protocol are compared in detail,and the similarities and differences between different versions of the protocol are obtained by comparision.Secondly,the demodulation algorithms of differential GPS signal are studied.Modulation mode of differential GPS signal employs the minimun frequency shift keying.Firstly,in this paper,the modulation and demodulation principle of MSK signal,symbol synchronization algorithm and carrier synchronization algorithm are studied.Moreover,several demodulation algorithms of MSK signal are simultated and compared.Then,an algorithm to optimize DFT demodulation is proposed,the results has shown that the performance of optimized demodulation algorithm has the advantages of small computation amount,insensitive to carrier frequency offset and bit offset.Finally,the optimized demodulation algorithm which was proposed based on DFT has demodulated the differential GPS signal correctly.Finally,we have studied the decoding algorithms of differential GPS signal.In this paper,the decoding algorithms for RTCM SC-104 protocol are designed by studying the coding principle of the protocol,the parity check algorithm and the CRC check algorithm.Furthermore,the C programs are written to realize the complete decoding process of all the current messages,and the validity and correctness of the algorithms and programs are verified by the actual data test.