Research On Spatial Anti-jamming Algorithms Of GNSS And FPGA Implementation

Global Navigation Satellite System(GNSS) is a kind of all-round, all-weather, continuous and real-time radio navigation and positioning system that provides highly accurate navigation, positioning and timing information. It has been applied in many fields of economic and social development, which has become one of the fastest developing information industries. However, due to the weakness of satellite signal reaching the ground, receivers are easily jammed by interferences. Hence the study on anti-jamming technology of GNSS is particularly important. These methods of traditional time domain filtering and frequency domain filtering can effectively suppress a small quantity of narrow-band interferences, but are not able to deal with broadband interferences and a great number of narrowband interferences. By weighting of each element of the array antennas beamforming technology makes main lobe of array pattern aligned with the desired signal, and nullings or side lobes in the direction of interferences, which can effectively inhibit broadband interferences and dozens of narrowband interferences. This paper focuses on research on spatial anti-jamming algorithms of GNSS and hardware Implementation, main contents is as follows:Firstly, the paper analyzes the reason why receives are susceptible to interferences, and introduces the basic theories of beamforming technology, including array signal model, optimal beamforming principles and adaptive beamforming algorithms. It focuses on analysis and comparison of common optimal beamforming principles and adaptive beamforming algorithms. And the relationship among steady-state error, step factor, and convergence speed of least mean square(LMS) algorithm is deeply studied.Secondly, variance distortionless response(MVDR) beamforming algorithm and power inversion(PI) algorithm are studied. Since MVDR algorithm must know the orientation of satellites and traditional power inversion algorithm has poor performance for the suppression of weak interferences, an improved power inversion algorithm is proposed. Simulation results show that the improved algorithm performs better than traditional power inversion algorithm in both anti-jamming and interference direction finding, but it is difficult to implement this algorithm on field-programmable gate array(FPGA) because of the high computational complexity of performing eigen-decomposition. Through simulation and analysis of traditional power inversion adaptive algorithms, finds that LMS algorithm can obtain the same anti-jamming effect as other adaptive algorithms, and has low computational complexity, which is easy to be implemented at low hardware cost. Therefore, chooses power inversion adaptive LMS algorithm for FPGA Implementation.Finally, for power inversion adaptive LMS algorithm, designs spatial anti-jamming system of GNSS. Implements important modules in the system such as digital automatic gain control(AGC) module,in-phase and quadrature(IQ) transform module, anti-jamming module and interference direction finding module,then simulates them by MATLAB and Modelsim. Analyzes resource usage of the whole system, and verifies the accuracy of anti-jamming function and interference direction finding function by hardware test, and the resource usage is conforming to requirements.