Seven-array Navigation Adaptive Anti-jamming Algorithm And Its FPGA Implementation

Satellite navigation has been widely used in various fields of the country since its birth.However,due to the characteristics of satellite signal power,it is often unable to locate accurately due to electromagnetic interference.Therefore,in order to ensure the accuracy of navigation,it is necessary to study various anti-interference measures to eliminate the interference signal from the effective navigation signal.Through the improved space-time two-dimensional anti-interference,the GPS receiver studied in this paper can suppress different interferences such as broadband and narrowband,greatly improve the degree of freedom without additional array elements,and can distinguish signals with different frequencies in the same direction,integrating the advantages of time domain,frequency domain and space domain.This paper focuses on the space-time two-dimensional anti-jamming theory of GPS receiver,and realizes the space-time two-dimensional anti-jamming system on FPGA.Firstly,this paper discusses the GPS anti-jamming receiver based on the narrow-band signal.Two anti-interference technologies for narrowband interference are introduced: time-domain anti-interference and frequency-domain anti-interference.For the time-domain adaptive anti-jamming,the corresponding adaptive optimal criterion and corresponding adaptive algorithm are given.Through the case of input narrowband interference,the conclusion that the time-domain adaptive anti-jamming system can suppress narrowband interference is verified.For frequency domain adaptive anti-jamming,the principle of anti-jamming is given,which is to distinguish the spectrum of narrow-band signal and filter it through Fourier transform.Secondly,frequency domain adaptation is mainly reflected in the adaptation of threshold.Therefore,this paper deduces the adaptive threshold method and compares it with the first-order moment threshold method.Through simulation analysis,it is concluded that the adaptive threshold method can change with the size of narrowband power.The anti-jamming system in time domain and frequency domain can only resist narrowband,but the usual interference signal is wideband signal.Therefore,solving wideband interference has become the main content of GPS receiver research.In this paper,the spatial adaptive filtering system is adopted.Taking advantage of the fact that the power of GPS signal is lower than that of thermal noise,a power inversion(PI)algorithm suitable for GPS anti-interference is proposed,which is put on the structure of spatial filtering system.The effectiveness of power inversion algorithm is verified by inputting broadband interference signal.Because of the restriction of the number of antennas,the spatial adaptive filtering system can not filter the interference signals with more than degrees of freedom.Therefore,while increasing the number of anti-interference without increasing the number of antennas,this study introduces a space-time two-dimensional filtering structure.By building a power inversion algorithm on this structure,a good simulation effect is achieved.It can not only increase the degree of freedom,but also distinguish the signals of different frequencies in the same direction,which can not be achieved by spatial filtering.Space-time two-dimensional adaptive anti-jamming system has many advantages in,but the amount of calculation is too large and matrix inversion is required,which is not suitable for hardware implementation.In order to find the optimal solution of the inverse matrix,the iterative LMS algorithm is used to solve the problem.But at the same time,according to the calculation,the demand of LMS algorithm for multiplier is too high,and the hardware is not easy to meet so many multiplier requirements.Therefore,an improved sign LMS algorithm is derived.The multiplier requirement of this algorithm is only half of that of LMS algorithm.Through simulation,the sign LMS algorithm can also achieve good results.Finally,based on the theoretical simulation,whole space-time two-dimensional anti-jamming system is built on FPGA.The function of orthogonal down conversion of input signal completed by using Verilog HDL language,including NCO numerical control oscillator module,FIR low-pass filter module and multi rate extraction module.After completing the signal preprocessing,the space-time conversion module is designed for multi-channel data,so as to complete the transformation from multi-channel signal to space-time signal.Finally,the hardware module based on LMS algorithm is designed by hardware description language,and the feasibility of the system is proved by test.At the end of the paper,the problems solved in this paper are summarized,and the direction of improvement for this system in the future is also pointed out.