Research On Mitigation Of GNSS Tone Interference Based On Adaptive Notch Filter

Global Navigation Satellite System(GNSS)is easily affected by different electromagnetic interference with different properties due to its low signal power.The usability,reliability and continuity of GNSS are greatly challenged.Therefore,it is imperative to improve the robustness of GNSS.In this paper,the Global Positioning System(GPS)is taken as an example.The research is based on the processing flow of navigation receiver,aiming at tone interference,which is one of the typical electromagnetic interference.The research work includes jamming influence analysis,jamming detection and identification methods,as well as comprehensive jamming suppression scheme.In this paper,three kinds of typical tone interference,namely continuous wave interference,sweep wave interference and pulse interference,are studied.According to the essence of tone interference,the parameter characteristics and mechanism of tone interference are studied.The research results show that different tone interferences are all continuous wave signals at a certain frequency point as well as a certain time,thus the same interference detection and identification technology can be adopted at the front end stage.However,different interferences have different unique characteristics in time domain and frequency domain.After a series of data processing flows,they have different effects on different stages of the receiver.When interference power reaches-70 d Bm or above,the receiver will be threatened.A single anti-interference algorithm can not achieve a comprehensive suppression effect under all types of interferences,so it is necessary to study targeted interference suppression algorithms in different stages of the receiver.The first step to improve the anti-jamming capability of receiver is interference detection,interference type identification and interference parameter estimation.In frequency domain,timefrequency domain and time-domain,the parameter estimation methods of tone interferences are studied.In frequency domain,according to the signal spectrum distortion caused by interference,abnormal spectrum noise is used to detect interferences.In time-frequency domain,according to the obvious timefrequency characteristics of interference,time-frequency analysis is used to estimate the parameters of interference,including frequency,period,duty cycle,and bandwidth.However,the frequency-domain method needs Fourier transform and is limited by Heisenberg principle.The time-domain interference detection and identification method,which is based on phase-amplitude locked loop,does not need Fourier transform,and the estimation accuracy of the time-domain interference detection and identification method is irrelevant with Heisenberg principle.Therefore,the time-domain method is used to detect and identify the interferences.The experimental results show that the time-domain interference detection and identification probability for tone interference whose power is above-70 d Bm are higher than 99%.The time-domain interference detection and identification method can provide precise realtime interference frequency and amplitude estimation,and provide an important basis for adaptive interference suppression algorithm.To suppress the influence of interference on the receiver means to improve the robustness of the tracking loop of the receiver under interference and to improve the accuracy of the positioning algorithm under interference.Therefore,based on the interference detection and identification results,this paper proposes a three-stage anti-interference algorithm.In the first stage,the adaptive notch filter with variable notch frequency and trap depth adjusting to the interference instantanues frequency and amplitude is designed to remove the interference.The adaptive notch filter is able to effectively filter out tone interferences whose power is above-100 d Bm.In the baseband processing stage,for the discontinuous characteristics of pulse interference in time domain,the closed/open switched tracking loop is designed.The loop jitter caused by the pulse signal is eliminated by the switched tracking loop.The two stages can reduce the Doppler error within 2Hz under pulsed interference.Finally,in the receiver positioning stage,the positioning algorithm based on adaptive Kalman filter is used to replace the traditional least square positioning algorithm,which can smooth the positioning error caused by interference.The positioning algorithm reduces the three-dimensional positioning error to 3m under the continuous wave and sweep wave interferences.Finally,under the blind signal environment,in which there exist unknown interferences,an integrated anti-jamming method,including interference detection,identification and suppression,based on front end stage,baseband processing stage and positioning stage,is designed.The simulation platform to test the method performance is realized.The experimental results show that the integrated antijamming method can effectively detect a variety of tone interferences that have severe effects on the receiver,and can accurately estimate the interference parameters,such as frequency,duty cycle,period,bandwidth and amplitude.The robustness of the anti-jamming method protected receiver is 20 d B higher than that of the unprotected receiver,and the positioning and velocity accuracy of the anti-jamming method protected receiver are both increased by above 30% compared with the unprotected receiver.