Research And Implementation Of Key Technologies In Anti-Jamming GPS Receiver

The performance of satellite navigation system under Radio Frequency Interference (RFI) is more and more noteworthy since it is widely used in the military and civil area. This dissertation is devoted to dealing with problems in RFI suppression, which mainly including space time adaptive processing (STAP) and space frequency adaptive processing (SFAP). The main content and contribution are as follows:After introducing principles of GPS, influence of interferences and suppression technologies, this dissertation laid special stress on discussing various constraint conditions of the linearly constrained minimum variance (LCMV) criteria. STAP has an effect on satellite signals while suppress the interference. The effect of code phase and carrier to noise ratio by STAP is analized, and then STAP influence scopes are simulated, which could provide a reference for satellite choice.A new cascaded algorithm is proposed to improve the performace of STAP, and could suppress suppress narrow band interferences (NBI) from the satellite direction. The NBI is suppressed firstly using a nonlinear Kalman-type adaptive filter named augment state approximate condition mean (ASACM) filter, subsequently, results of preprocessors are transmitted to STAP to suppress wideband interferences. Different from block operation in FFT, ASACM is formulated using a three-coefficient finite impulse response (FIR) model, could improve real-time performance of the system.The effective STAP model of sub-band adaptive array processing is established and a new algorithm is proposed based on wavelet packet transform. Stable weights of effective STAP are affected by not only samples but also the transform basis. The implementation structure of the sub-band filter banks is discussed. Based on output signal interference Noise Ratio (SINR), the sub-band adaptive array processing using wavelet packet transform (WPT) is compared with SFAP adding types of windows. Results show that the sub-band adaptive array processing outperforms SFAP at the ends of the snap samples, and need fewer samples for overlap processing.A new SFAP algorithm is proposed in this dissertation, in which the received signal is firstly preprocessed with adaptive filtering in the frequency domain, and then transmitted to the further SFAP to suppressing wideband interferences. The new algorithm could reduce the loss of expected satellite signals and the error of the constrained steer vector. Simulation results show that the new algorithm outperforms the ordinary SFAP, especially when NBI illuminating from the direction of the satellite signal. At last, an anti-jamming GPS system is implemented and tested. The system includes a four channel radio frequency front end and a base-band signal processing board. The multi-channel RF front end is designed based on GP2015chip produced by Zarlink Corporation. The base-band functions are all implemented in a FPGA chip, which mainly include interference suppressing and GPS inception. The interference suppressing processor realizes space only processing and space time adaptive processing using classical LMS algorithm and Power Inversion criteria. Test results show that compared to single antenna GPS system, the anti-jamming system could improve about30dB for suppressing the interference.