Research On Adaptive GNSS Carrier Tracking Using Multiple Loops

Satellite navigation receivers have been widely used in many fields with the rapid development of global navigation satellite system(GNSS),and the application environment is also increasingly complicated.In aerospace and aerospace applications,most aircrafts are in high dynamic environments,there is a drastic relative movement between the receiver and the navigation satellite.Because of the relative movement,each satellite signal received by the receiver contains a large Doppler frequency shift and Doppler frequency shift rate.If the estimation of Doppler frequency shift is inaccurate in the process of tracking,the satellite carrier signal cannot be stripped out clearly,causing the receiver lose lock of satellite signals.In addition,in the applications of geodesy surveying and pedestrian navigation,the power of satellite signal is seriously weakened in the environment such as forests,valleys and urban areas,easily making the receiver lose lock of tracking.Therefore,faced with different applications requirements,it is of great value in engineering applications to develop a type of receiver which is able to keep signal tracking adaptively in both high dynamic environment and weak signal environment.Firstly,the paper analyzes the dynamic stress error and thermal noise error of carrier tracking,based on the research of carrier tracking principle.To improve the dynamic adaptability of tracking and the ability of noise suppression,the paper analyzes the tracking performance from structures,parameters and coherent integration times of carrier tracking loops,providing a theoretical basis for the research of carrier tracking algorithms in high dynamic environment and weak signal environment.Subsequently,a scheme of multi-loop parallel fusion is proposed to solve the problem of the loss of lock in weak signal environment.The scheme considers advantages and disadvantages of phase lock loop(PLL),frequency lock loop(FLL)and the coherent integration times.The impact of noise for the estimation of Doppler shift is reduced by fusing the loops with different structures and coherent integration times to avoid the loss of lock due to the wrong Doppler shift from each single loop.Simultaneously,an adaptive bandwidth tracking algorithm is proposed to solve the problem of the loss of lock in high dynamic environment.Based on fuzzy logic theory,this algorithm adaptively adjusts the bandwidth by sensing the change of dynamic environment,improving the dynamic performance and tracking accuracy.Finally,adaptive carrier tracking algorithm with multiple loops is proposed to solve the problem of the loss of lock in high dynamic environment and weak signal environment.Considering both multi-loop fusion algorithm in weak signal environment and the advantages of fuzzy adaptive variable bandwidth algorithm in high dynamic environment,this algorithm improves the dynamic performance and tracking accuracy,and is verified by establishing a simulation platform.This paper offers a good reference scheme for the research of universal receivers which meet the requirements of tracking high dynamic and weak signal,and is of good engineering application value.