Research On GPS Navigation Nignal Quality Assessment

The quality of the GPS navigation signal is related to the performance of the navigation satellite system and the accuracy of its positioning.The integrity of the downlink signal is the foundation to guarantee the work of user terminals.In order to ensure that the GPS navigation system can provide users with high accuracy and continuity of position and time services,the quality of GPS navigation signals must be monitored and evaluated.The assessment of GPS navigation signal quality mainly includes frequency domain,time domain,and different channel conditions.The power spectrum,constellation diagram,eye diagram,chip zero-crossing distortion,S-curve,C/A code tracking error curve and BER performance of the GPS navigation signal are thoroughly studied.The main work of this thesis is as follows:1.An odd-numbered shift smoothing algorithm is proposed,where the power spetrum obtained by the Welch algorithm is smoothed.Then,the correlation coefficient between the power spectrum and the ideal power spectrum is calculated,and the parameters of the Welch algorithm and shift smoothing length is determined according to the magnitude of the correlation coefficient.This solve the difficult problem of parameter selection in the Welch algorithm.The power spectrum of navigation signals which are interfered by Gaussian white noise and multipath interference are evaluated by using the determined parameters2.The constellation of the navigation signal interfered by Gaussian white noise and multipath interference is modeled.According to the constellation model of the navigation signal,the quality of the navigation signal in the different SNR and multipath interference conditions is studied.The eye pattern of the satellite navigation signal interfered by Gaussian white noise is modeled,and the signal quality is evaluated based on the noise margin and distortion of the eye diagram.The linear interpolation method is used to analyze the zerocrossing distortion of the navigation signal affected by the filter and multipath interference.The measurement error caused by the filtering delay is 0.51 m,and the measurement error caused by the multipath interference is 5.53 m.The S-curve zero-crossing distortion and C/A code tracking error curve of the navigation signal interferd by multipath interference are analyzed and studied.According to the S-curve zero-crossing distortion and C/A code tracking error curve,the navigation signal quality is determined.3.Four kinds of channels: Gaussian channel,Rician channel,Rayleigh channel,and lognormal shadow fading are nodeled and simulated.The BER performance of five kinds of spread spectrum modulation signal BPSK-R(10),QPSK-R(10),BOC(10,5),BPSK-R(1)and BOC(1,1)in different signal channel environments are studied,and the quality of the five kinds of spread spectrum modulation signal is determined.