Tracking Technologies Of Navigation Signal Based On DS/FH Modulation

The traditional GNSS signal adopts a kind of direct sequence spread spectrum technology to improve the signal concealment,but its near-far effect is obvious and the resistance to narrowband interference is weak.Facing the increasingly complex electromagnetic environment and growing demands of user privacy,a single spread spectrum is unable to meet the current anti-jamming requirements.It is of great significance to apply the hybrid spread spectrum with lower interception rate to the tracking technology of navigation signal.Based on the characteristics of the traditional GNSS signal and the advantages of DS/FH hybrid spread spectrum technology,this paper analyzes some new problems brought by the introduction of the hybrid method to the navigation signal: caused by the frequency-hopping carrier,the hopping Doppler shift and ionospheric delay can make the accuracy of the tracking loop reduced or even lost.In order to solve this problem,a carrier tracking loop based on frequency hopping pattern is adopted,and the Doppler jump deviation is compensated by using the agile factor to modulate the output frequency of the carrier NCO,making the loop return to normal.The frequency hopping aid eliminates the hopping Doppler shift,but it can't avoid deviation of the carrier phase and the pseudo-code caused by the ionospheric delay.Considering the multi-frequency carrier delay of the ionospheric dispersion effect,an improved ionospheric compensation method is proposed based on the effect of frequency hopping aid.The changed loop in that method can obtain the assistance information of the ionospheric delay from the frequency hopping generator,and it compensates the advance phase value for the carrier NCO and the delayed pseudo-code for the pseudo-code NCO,thus correct the the frequency or phase deviation and improve the tracking accuracy.Through the Matlab comparison simulation experiment,the ionospheric delay deviation is verified exist.Addition to that,the improved ionospheric compensation method can effectively improve the performance of the tracking loop.