Research On Key Technologies Of GNSS Interference Suppression In Direct Data Domain

Global Navigation Satellite Systems (GNSS) have the abilities of providing highprecision positioning, speed and timing service in wide range and all weather. Theyhave been widely applied in the national defense and the national economy. Meanwhile,the weak anti-interference ability is one of the serious restriction factors of GNSSapplying in the complex battlefield environment; and improving the anti-jammingability of GNSS is the important guarantee to win the future navigation warfare. As aresult, to study and realize the technologies of ensuring the reliability for GNSSreceivers in the complex electromagnetic circumstances is of great importance inmilitary field.The classical statistical anti-jamming methods are based on the covariance matrixof array receiving data. To get the estimate of covariance matrix, a series of snapshotdata are required. And the big amount of calculation brings the difficulties inengineering realizing. Statistical methods assume that the environment is stable, so it isapplied only in the steady environment. But in the actual environment especially in thecomplex electromagnetic environment, the signal is usually unsteady and time-varying,which would lead to the performance degradation with the statistical method. In order tobe better adapted in the non-stationary environment, the algorithms in direct datadomain (DDD) should be proposed and applied. The DDD algorithm is a signalsnapshot processing method, which avoids the statistical operation, such as the samplecovariance matrix estimates. In this thesis, the key and theoretical problems, whichrelate to GNSS array error correction, interference suppression, subspace tracking,estimation of direction of arrival (DOA), as well as beam forming, are systematicallystudied in the direct data domain; The corresponding algorithm validation andimplementation in engineering practice are also investigated.The GNSS adaptive algorithms belonging to the direct data domain is studied. Theimprovement is emphasis on the stability of the least mean square (LMS) algorithm andits convergence speed. A kind of calibration technique to GNSS array error is proposedin this thesis and the influence of GNSS anti-jamming performance is also analyzed. Asimulation analysis of GNSS space-time processing based on the improved LMSalgorithm is accomplished. All the processing is carried out in direct data domain, whichis convenient in time-varying environmental engineering application.The subspace tracking algorithms belonging to the direct data domain is studied.Through in-depth study on the physical meaning of data projection method (DPM) andOJA algorithms, the subspace tracking based on subspace distance (STSD) is proposed,which is based on the minimum space distance criterion. The STSD algorithm has thelowest computational complexity of3NL+O(N) in the congener algorithms. The numerical stability theory proof and simulation verification is also carried out for theproposed algorithm in the signal subspace and noise subspace tracking. In finiteprecision conditions, this algorithm is not sensitive to rounding error accumulation, andcan guarantee orthogonal convergence to the subspace base. A simulation analysis ofGNSS space-time processing based on the proposed STSD algorithm is alsoaccomplished. The STSD algorithm exploits a novel view to the development ofsubspace tracking algorithms, and simulation results reveal that it has good performancein GNSS anti-jamming application.The DOA estimation of coherent signals in direct data domain is studied. First ofall, this thesis proposes two DOA estimation methods. One of the novel approachsconstructs the spatial spectrum by utilizing the steady-state weights from the improvedLMS algorithm; the other constructs the spatial spectrum by utilizing the estimation ofnoise subspace base. Then the DOA estimation of interference signal could be obtainedfrom searching spectral peak. Furthermore, in order to deal with coherent interferencesignals, the symmetric conjugate vector method and the virtual space smooth algorithmin direct data domain are proposed, respectively. The proposed approaches do not needto estimate the source number or the covariance matrix. Also, they do not need theeigendecomposition, meanwhile the computational complexity is greatly reduced, andthe proposed approaches can be applied to complex time-varying environment.The GNSS robust beamforming method in direct data domain is studied. Amulti-beamforming method, which form beam to each satellite, is proposed. The stronginterference suppression is finished through the noise subspace projection. Then, thedespread processing which uses the designated satellite pseudorandom noise (PRN)code is carried out to outstanding the satellite signal. The blind beamforming methodcombines with the one-order constant modulus (CM) algorithm. The proposed methodis a blind adaptive beamforming algorithm which does not require the information aboutnavigation symbols or satellite orientations. It also adopts the low complexity algorithmin direct data domain, which mitigates the computational consumption of the receiverand guarantees the real time implementation.A cascaded structure and module design for GNSS anti-jamming are studied andtwo GNSS anti-jamming systems have been implemented. Based on the improved LMSalgorithm, the GNSS space-time adaptive processor is designed and implemented. Amulti-beam GNSS anti-jamming system is also be proposed, which combines thesubspace tracking algorithm, the CM algorithm and the DOA estimation method indirect data domain. Experimental results show that such a cascaded scheme could bringsignal-to-noise-ratio improvement for the space-time processing. The system design,algorithm validation and functional testing are completed, and relevant research resultsare significant in both theory and engineering application.Partial correlation results of this thesis have been used to a certain type of carrier receiver transformation, aviation bomb finalize the design, a new type of high speedmissile design. In addition, as important anti-jamming measures, they have been used indemonstration and realization of the second generation “beidou” anti-jamming receiversystem.