Research On Signal Synchronization And Interference Suppression Of GNSS Receiver Under New Signal System

The new generation of signal modulation-Binary Offset Carrier(BOC)and its derivation class modulation provide the possibility of frequency band sharing among different satellite navigation systems in different countries or organizations,and the ability of improving navigation,positioning accuracy of satellite navigation system and interference mitigation,which has important significance in promoting the wide application and rapid development of the new generation of satellite navigation system.However,when conventional GNSS receiver was directly used for the acquisition and tracking of BOC modulation signal,it may generate a synchronous ambiguity problem from several meters to tens of meters,on the other hand,multipath has a severe effect on receiver's positioning accuracy.Therefore,unambiguous synchronization and multipath mitigation method for BOC modulated signals should be studied.Meanwhile,due to the vulnerability of satellite signals,GNSS receiver is susceptible to all kinds of intentional or unintentional interference.Space-time adaptive interference suppression technology has attracted considerable attention due to its good anti-jamming performance of interference suppression in modern satellite signal,but its direct application will introduce additional positioning bias.So,on the issue of satellite signal anti-jamming,the research of unbiased space-time optimal filtering algorithm is a hot topic of current research.In addition,with the increasing threat of spoofing signal to GNSS receiver,effective detection and suppression technology for satellite signal spoofing is another hot topic in current stage.In this paper,the research of BOC modulation signal synchronization and interference suppression is carried out in view of the above problems.The main research work is as follows:To the ambiguity problem during the process of BOC signal acquisition,the thesis described the acquisition principle in traditional receiver first,and pointed out that multiple peak structure of BOC modulation signal's correlation function is the main reason introducing ambiguity problems during the process of BOC signal acquisition.The cross-correlation function between multilevel code chip waveform signal and BOC signal was derived,a general method of synthesis of correlation function with no side peak is provide through the analysis of correlation function properties.There appears a plurality of energy peaks when traditional detection statistics applied directly to the BOC modulation signals,a method of synthetic correlation function was proposed based on the basic principle that negative energy has no effect on energy detection criteria,and the waveform of locally generated modulation signal was derived.Since the proposed method needs two locally generated multilevel code signal and their corresponding multipliers and integrators,a fast realization structure,using gated integral calculator instead of the local spreading symbol modulator was designed to simplify the complexity of acquisition circuit..To solve the tracking ambiguity and multipath mitigation problems during the process of BOC signal tracking,through analyzing the discriminator curve of BOC modulation signal,the paper pointing that mitigating the side peaks of BOC signal's auto-correlation function or designing unambiguous discriminator curve is the potential solutions.In view of the shortcomings of traditional ambiguous mitigation techniques,the thesis proposed a multipath mitigation and ambiguity cancellation method through directly designing discriminator S-curve.Based on the mechanism of how multipath introducing phase errors at the output of discriminator,a multipath suppression and ambiguity mitigation discrimination curve is designed.Then,based on the designed target S curve,the weights of different sequences of multilevel chip waveforms are obtained by least square method.In order to eliminate the influence of carrier tracking error on phase discriminator,the target phase discrimination curve is designed as a product of two different shape curves,which promoting the robustness of the tracking loop.On the research of space-time adaptive interference mitigation method for BOC modulation signal,a wideband space-time adaptive interference suppression algorithm was proposed based on broadband space-time steering vector reconstruction to solve the problem of array output signal distortion and power reduction when traditional space-time adaptive interference suppression algorithm directly applied to wideband BOC modulation signal who has splitting spectrum characteristics.Because the wideband space-time adaptive filter has different filtering effects on the BOC modulated signals with different bandwidth and different modulation modes,the improved algorithm will focus on the main lobe frequency of the BOC modulated signal and further extend the effective processing bandwidth of the space-time filter.To the problem of GNSS positioning error caused by the space-time adaptive filter,a space-time adaptive interference suppression algorithm based on MVDR criteria was proposed through the selection of the specific structure of the reference space-time steering vector.The proposed algorithm makes the space-time equivalent optimal FIR filter conjugate symmetric on the center tap of equivalent FIR filter,which effectively avoided the positioning errors caused by system frequency response.The simulation results verify the effectiveness of the method in complex interference environment.On the research of spoofing detection and suppression,traditional spoofing detection method has the shortcomings of difficult to be realized,limited application issues,high cost and lack the ability for spoofing suppression.Therefore,beamspace DOA estimation and signal power estimation,cross-correlation peak monitoring and suppression method is put forward.The proposed method chose the desired space based on the actual scene and the application platform where the receiver located.Then undesired signals are effectively suppressed by using beamspace transformation.Beamspace DOA estimation is used to estimate directions of signals in the desired angle space,and SNR of these signals are calculated,spoofing signals can be effectively detected when combined with cross-correlation peak monitoring.Spoofing signals can be extracted by using oblique projection operation and then removed from the beamspace data.