Study On Key Techniques Of The Satellite Navigation Signals Carrier Tracking In The Presence Of Ionospheric Scintillation

Ionospheric scintillation is the diffraction and scattering of Global Navigation Satellite System(GNSS)signals caused by the small-scale plasma density irregularities of ionosphere,resulting in random and rapid fluctuation on the amplitude and phase of GNSS signals.In the worst case,loss of lock on enough satellites could result in losing positioning service,which would significantly affect the continuity and stability of the system monitoring equipment.Therefore,it is becoming increasingly urgent to evaluate the impacts of ionospheric scintillation on the GNSS and to study the signal reception under ionospheric scintillation conditions.Based on the demands of China?s self-determinational GNSS,this dissertation focuses on the following four topics within the ionospheric scintillation scope.(1)Taking the measurements(I and Q intergrations)of carrier tracking as a breakthrough point,this work models the impact of ionospheric scintillation on carrier tracking from system perspective,and demonstrates that the carrier phase estimation in presence of ionospheric scintillation is a non-stationary,non-Gaussian and strong-nonlinear parameter estimation problem.Then based on the simulation of ionospheric scintillation,this paper evaluates the impact of ionospheric scintillation on carrier tracking by theoretical analysis and simulation validation,and proposed a comprehensive evaluation method for analyzing the impacts of ionospheric scintillation on carrier tracking.(2)Ionospheric scintillation would incur in an additive non-Gaussian noise superimposed on I and Q corrector outputs,which will degrade the tracking performance of CPLL remarkably.This paper proposed the non-Gaussian noise denoising algorithm based on the adaptive wavelet denoising(WD),which reduced the non-Gaussian superimposed on the integrations of I and Q channels directly.Moreover,this work optimizes the key parameters: denoising threshold and width of sliding window according to different scintillation scenarios adaptively.Simulation results show that,the proposed algorithm outperforms the CPLL under ionospheric scintillation conditions.In particular,the frequency and phase error of WD-PLL decrease 0.7Hz(29%)and 2.3°(16%)respectively in the moderare sicintillation,while the cycle slip of WD-PLL decrease 55% in the severe scintillation.(3)Ionospheric scintillation can cause random and rapid fluctuations on the amplitude and phase of the integrations of I and Q channels,which will dramatically degrade the accuracy and robustness of linear approximation-based carrier tacking algorithms,e.g.CPLL and EKF-PLL.Moreover,the application of UKF in carrier tracking is limited by the non-Gaussian noise caused by ionospheric scintillation.To overcome this problem,this work employs the phase lock indicator(PLI)to estimate the covariance of the measurement noise adaptively according to different scintillation scenarios.Moreover,the joint adaptive wavelet de-noising unscented Kalman filter(WDUKF)-based carrier tracking algorithm is proposed to mitigate the adverse impacts of ionospheric scintillation.Numerical results show that the proposed algorithm can improve the accuracy and robustness significantly,especially in severe scintillation.Compared with EKF-PLL,the frequency error and cycle slips of WDUKF-PLL decrease about 1.1Hz(47.8%)and 75% respectively,while the decrease is 2.5Hz(68.1%)and 84% compared with CPLL.(4)In the presense of ionospheric scintillation,the carrier state transition between different periods is difficult to be modeled accurately because of the random and rapid fluctuations of carrier phase.Therefore,the stationary state model will incur in the intractable model error for closed-loop.This work proposes the open-loop carrier tracking scheme based on the joint frequency estimation and phase correction to avoid the model error between carrier state transitions under ionospheric scintillation conditions.The open-loop architecture carrier tracking is more flexible,and could overcome the limitations of closed-loop,e.g.the contradiction between bandwithd and denoising performance.Furthermore,compared with the WDUKF-PLL,the proposed open-loop carrier tracking algorithm is easily applied to engineeting,and its and robustness of carrier tracking is improved.In severe scintillation,the cycle slip of open loop is decrease from 4 times to 3 times(25%).Moreover,the real data results indicate that the cycle slip of open loop is also decreased about 28%.At last,the work of this thesis was summarized,and some prospects for further research were proposed.The research results have been already applied to multi-system navigation signal simulator and the multi-GNSS receiver.