Research On Anti-jamming Methods For GNSS Signal Acquisition Under Complex Interference Environment

The global navigation satellite system(GNSS)plays an increasingly important role in military and civil areas;however,the risk caused by the vulnerability of GNSS signals is getting more and more serious.Therefore,as an important method to effectively improve the anti-jamming ability of GNSS,array-antenna-based interferences mitigation techniques have been intensively studied and a series of research results have been achieved.However,with the increasingly crowded electromagnetic spectrum and new GNSS jamming technologies and strategies emerging in endlessly,there may be multiple types of interfering signals presenting simultaneously rather than only one or one type of interfering signals in the receiving environment.In addition,the performance of existing space-only or space-time interference supression methods will be decline when the number of wide-band interferences exceeds that of antenna elements.In this context,the thesis analyzes characteristics of different kinds of interfering signals and the space-time-frequency sparsity of compound interfering signals.On this basis,aiming at the problem that the lack of degree of freedom of space-based or space-time-based anti-jamming methods,this thesis digs out the sparse characteristics of interference signals in different dimensions,processes the received signals in different dimensions of information,detect and suppress interfering signals in different information dimensions.Then multi-dimensional joint interferences supression methods which are applicable to complex interfering environment are explored.The research achievements are as follows:1.Existing anti-interference methods are difficult to effectively detect and suppress the relatively weak interference signals when multiple types of interference signals are overlapped seriously in time-frequency domain.In view of this problem,an anti-interference method based on sparse decomposition of waveform information is proposed on the basis of analyzing the detectability of known waveform style interference signals in complex interference signals.First,the over complete dictionary of atoms is constructed based on prior information of interference signals.Then,in order to improve the timeliness of matching pursuit(MP)-based sparse decomposition,a HDCQGMP is introduced by combining an improved double chain quantum genetic algorithm(DCQGA)and the MP algorithm.This method can detect and suppress the known waveform style interference signals,and reduce the number of interferences in the subsequent interference suppression processing.2.The number of wide-band interfering signals which can be suppressed by an antenna array is limited to the number of antenna elements.To address this problem,a multiple interferences suppression method based on adaptive signal data regrouping for GNSS receivers is proposed on the basis of analyzing the generalized periodic and sparse property of the wide-band periodic frequency modulated(WBPFM)signals.An improved SVR-based period estimation method is introduced to estimate the minimum common period(MCP)of WBPFM interfering signals.Then regroup the signal data to construct space-time matrixes according to the estimated MCP.Then,an orthogonal minimum power distortionless response based space-time processor(OMPDR-STP)is adopted to nullify the interferences and protect GNSS signals.Simulation results show that the proposed method can suppress more wide-band interferences(WBI)without increasing the number of antenna elements.3.For interferences with sparsity in time-frequency domain,a space-time-frequency processing is proposed by combining time-frequency analysis with array signal processing theory.Firstly,construct space-time-frequency data matrixes by grouping the time frequency data whose interval is the integer multiple of the common period,then the underdetermined problem that the number of WBI is greater than the number of antenna elements can be converted into a non-underdetermined problem.Finally,a space-time-frequency minimum output power(STF-MOP)-based weight calculation method is introduced to suppress multiple interfering signals according to their sparse characteristics in TF and space domains.Simulation results show that the proposed methods can effectively improve the performance of GNSS reception against compound interferences by utilizing the time-frequency sparsity of the composite interfering signals.