Research On Narrowband Interference Suppression Based On Volterra Filters In GPS Receiver

The GPS can provide accurate positioning and timing information that is useful in various applications. As GPS receiver is used widely both in the civil and military affairs, the interference problem is becoming visible in GPS. When GPS receiver can not work normally, it is necessary to use various narrowband interference (NBI) suppression measures, especially in strong jamming environment. The paper majors in interference suppression technologies of GPS. The NBI suppression techniques based on time-domain prediction has been widely researched. GPS satellites broadcast ranging codes and navigation data using the direct sequence spread spectrum technology, so the GPS signal is highly non-Gaussian. Optical predictors for predicting a narrowband interference at this condition are nonlinear but no longer linear. Therefore, the time-domain nonlinear NBI suppression techniques have become hot spot of research and will be one of the most important directions of research in future.This dissertation focuses on two aspects: the first is studying error whitening criterion (EWC) lms algorithm based on volterra filter (VF) and using this kind of algorithm suppress the NBI; the other is using the structure of lattice predictor based on adaptive volterra filter (LAVF) to suppress the NBI. The main efforts of research are as follows:1. The system model of GPS NBI suppression receiver based on volterra filter is built. The structures and the adaptive algorithms of volterra based on existing prediction filtering have been systematically studied and the inherent problems of those algorithms are analyzed. For many real-world applications, the noise free assumption is easily violated in nonlinear system and using LMS-based methods for parameter estimation will result in severe degradation in performance. So here we use EWC that presents a different approach to whiten the error sequence at the output of an adaptive nonlinear filter even in the presence of noisy inputs. This paper presents a novel stochastic gradient algorithm based on EWC to tackle the problem of VF estimation in the presence of additive white disturbances and NBI. The output SNR improvement performance and BER performance of GPS receivers with jamming signals (including AM-FM jamming and AR jamming) is analyzed. 2. In volterra adaptive filtering, the gradient descent adaptive filters exhibit eigenvalue disparity and slow convergence rate problem due to data correlation and nonlinear operation. In this paper, in order to improve the orthogonal process without any time delay, a lattice prediction error filter is employed for this purpose and using this filter suppress the NBI in GPS receiver.Computer simulation results are provided to illustrated that using the algorithm and filter structure of this paper can improve the output SNR and reduce the output BER of GPS receivers.