Research On Interference Suppression Of GPS Receiver

The navigation system is used in a variety of battlefield weapon platforms and aircrafts, but it is susceptible to interference. Therefore, interference suppression for navigation signal is serious concerned, which deserves thorough research in terms of theory, implementation, and technology. The research is major originated from two research projects: 1. a project commissioned by an institute of the Department of Aerospace ‘Three Models(GPS/GLONASS/Beidou I) Anti-jam System in Middle Frequency’; 2. a project supported by National Key Laboratory Fund ‘Multi-dimensional space-time-frequency DOA estimation and direction constraint used as anti-jam filter techniques’. These two projects are closely related to GPS anti-jam technology.The joint space-time processing is good at its relative high degree of freedom, it is an effective solution in interfering scenario. Generally, to avoid singular value decomposition, the orthogonal projection method can be adopted in STAP. There is a problem exists in orthogonal projection, which is: there exist an optimal projection times, when it is exceeded, the output SINR will drop, which is more prominent in implementation of the algorithm. To solve this problem, two solutions are proposed. 1. Introduce diagonal loading into a typical orthogonal projection algorithm Multi-stage Weiner Filter(MWF) algorithm, which promote the robustness of algorithm, thus make it stable in interference suppression in real environment. 2. Use MWF to analyze the observed data vector, by which estimates the optimal projection times, thus the best interference suppression effect is obtained.To make the navigation platform work stable in the environment of multiple interferences, it is necessary to maximize the performance of the array with limited array elements. Cascaded way is introduced to achieve this aim, in which the narrow band interferences are detected and mitigated among all other interferences, after that, the reserved interferences are suppressed through the processing of adaptive array. As there are multiple kinds of interferences exist in the received signal, the spectrum is complex, so it is hard to detect narrow band interferences using the general method. To solve this problem, a spectrum processing method using the sliding window is proposed in the paper, which can detect the single tone and narrow band interferences in the complex spectrum. In the succeeded spatial processing, a parallel rotation Jacobi algorithm is proposed, which can reduce the computation in Eigen decomposition of the covariance matrix.In battle environment, the non stationary interferences and the high speed movement of aircraft may have serious influences on anti-jam processing, so it is necessary to find effective solutions. Linear Frequency Modulation(LFM) is a kind of typical non stationary interference, which can be processed as follow: firstly extract the parameters of LFM interferences through time-frequency analysis, then construct the interference subspace using the parameters, finally mitigated the interferences through subspace projection. In this paper, a method is proposed to estimate the parameter of LFM interferences, compared to the traditional processing way Wigner Hough transformation, the computation is reduced of a considerable degree. In this paper, the influence of parameter estimation error on subspace projection is analyzed, and the corresponding solution is proposed. The general type of non stationary interference can be cancelled by adaptive array, the DOA(Direction Of Arrival) estimation of this type of interference is researched in section 4.2 of this paper, but the cancellation of this type of interference is left to section 4.3 to be discussed together with the stationary interferences. That is because the non stationary and stationary interferences can be processed in the same way when using adaptive array. So it is unnecessary to discuss non stationary cancellation in section 4.2 desperately. In the optimization processing of Time-Frequency Distribution, the trace expressions of STFD matrix corresponding to ‘auto term point’ and ‘cross term point’ are deduced, which can be used to select the ‘auto term point’. Because of the high speed movement and high frequency vibration of the aircraft, there may be some variation of the incident angle of interference, which may bring out substantial decline of SINR, so it is necessary to find some solutions. It can be discussed in two situations. When the directions of interferences are given, the traditional solution can be used to solve the problem mentioned above. For the situation that the directions of interferences are unknown, a method is proposed in the paper, which use the constraint suit to real situation in optimization expression, and deduce the null broadening adaptive weight based on it, which can solve the problem of the variation of interference direction effectively.There is a prominent problem exists in current GPS anti-jam research and system design: the simulation environment is set arbitrarily, which doesn’t reflect the real receiving environment. To solve this problem, the received GPS signal of adaptive array is modeled, both in simulation and design environment, thus the corresponding simulation and testing platform are generated, which can create the environment approximate the real one. The design of the anti-jam system is described in the same chapter, which can be used to suppress interferences in three navigation system. The system is tested by the aid of the simulated signal, which makes it more convenient to improve the design. After that, the design is tested in real environment after implementation, and is verified by the intermediate results and final positioning results.