The Design Of GNSS Software Receiver Based On FPGA/DSP Architecture

Researches on GNSS receivers are gaining momentum with the advance of GPS and BDS technologies.The GNSS software receiver,running on an open and flexible platform,greatly facilitates the researches on baseband signal processing algorithms which aim to enhance the longterm stability of the receiver in harsh environments.The algorithms in this paper are designed based on the analysis of the baseband signal processing,namely,signal acquisition,tracking,and multipath signal processing.In signal acquisition,the paper mainly introduces three acquisition algorithms:linear search,parallel frequency search,and parallel code phase search.Applicable to different kinds of receivers,the acquisition algorithms introduced have their own advantages and disadvantages.In FPGA,signal acquiring channel shares the correlator with the signal tracking channel.To improve the linear search performance,the six-road correlator was used.Considering hardware implementation,pseudo-random code was generated by phase querying,and carrier signal by table look-up.Regarding the tracking loop,basic technical principles for signal tracking are presented,followed by more details about the carrier tracking loop and PRN code tracking loop.Multiple code loop phase detectors are analyzed,compared,and simulated,based on which a GNSS tracking loop software correlator and intelligent adaptive tracking method are proposed.The method overcomes the limitations settled by contradictory elements(SNR,computing complexity,and tracking accuracy),better balances computing amount and signal quality,and locates targets more precisely no matter it is in a normal environment,high dynamic environment,or weak-signal environment.In terms of multipath signal processing,causes of multipath effects and common suppression methods are firstly introduced.Narrow correlation and Strobe correlator methods are used to estimate and eliminate multipath signals during signal processing and simulated on the MATLAB platform.For noise and dimension reduce purposes,the principle component analysis method is used:Main signal components are extracted and applied in the analysis model,while minor components are not.After that,signal feature extraction and scene recognition experiments are conducted several times for the wireless channel models under different circumstances.The results prove the performance of the proposed algorithm,providing references for the application of GNSS receiver in complex multipath environments.This paper proposes a MATLAB-based GPS L1/L2 receiver and a BDS B1 receiver and verifies their correctness by a comparison with commercial receivers.Besides,the FPGA/DSP-based architecture design for the baseband signal processing module and its upper computer monitoring software is also provided,which enables IF signal sampling,satellite signal acquisition and tracking,PVT calculation,and operating control data setting.The output includes the UTC/Beijing time,positioning results,speed,clock error,smooth pseudo distance between satellite carrier phases,Doppler frequency,satellite elevation angle,azimuth angle,SNR,and ephemeris information.The positioning accuracy is within the range of about 3m.