Research On The Technologies Of High Degrees Of Freedom Interference Suppression For GNSS Receiver

Satellite navigation system has been widely applied in the national defense and the national economy. With the enhancement of civilian and military dependent on the satellite navigation, the competition in the field of satellite navigation will accelerate. Because GNSS is usually under unexpected interfer enviroment, GNSS interference mitigation becomes one of the most important research fields of military communication. All work of this thesis concentrates on the techniques of beam forming and compute burden reducing of GNSS anti-jamming adaptive process. Following issues are discussed.Based on the Givens rotation, Proposes a sliding window QR-RLS method,which is called SWGQR-RLS, and gives CORDIC realization ways. when the interference is pulse interference, the convergence performance of SWGQR-RLS better than conventional QR-RLS. Same as the QR-RLS method SWGQR-RLS method has modular structure and convenient for systolic array realization. This makes data throughput of the GNSS anti-interference system have been improved greatly, especially suitable for FPGA realization.In the condition of finity word length, the main error sources of the SWGQR-RLS method is analysed. Same as QR-RLS method, SWGQR-RLS method has modular structure, convenient for systolic array realization by using of CORDIC. CORDIC is one of the main error sources of the SWGQR-RLS method, error of CORDIC is analysed. The intermediate variables of the SWGQR-RLS method has been analysed and the stable conditon of SWGQR-RLS has been derived. simulation experiment result shows SWGQR-RLS has better numerical stability than orther adaptive algorithms, and has similar numerical stability as QR-RLS method.Using adaptive beamforming method can further improve the anti-interference ability of GNSS receiver. Based on the GSC structure, this thesis proposes an kind of multi-channal beamforming method, which is called per satellite constrained power minimization multi-channal filter groups beamforming method (PS-MDBF). Each of the filters sets main-lobe of array antennas aim at each expectation satellites. The adaptive part of this method realizes by SWGQR-RLS method, and reduced computation load of the"per satellite power minimization filter groups"based on the modular structures of SWGOR-RLS method. Compare with"joint satellite power minimizetion processor", SINR of this method is enhanced, and computation load of this method is inapparent enhanced. Simulation results reveal that this algorithm has better perfomance than joint satellite power minimization adaptive filter. In practical application, if the interference enter the main banch of the GSC, the anti-interference ability of the system will be serious affected. To solve this problem, the NPS-MDBP method is proposeed to remedying the PS-MDBP method.A simplified oblique projection method is proposed. It improves SINR of the GNSS anti-interference system observably. Projecting the receiving signal to the orthogonal subspace of the interference subspace can suppress the interference. Because of orthogonal projection algorithm does not use the DOA information of the GNSS signal, while the interference is suppressed, the useful signal also will be suppressed. Oblique projection algorithm overcomes this shortcoming of orthogonal projection. It can use the DOA information of the GNSS signal and can maximum retain useful signal. Simulation experiment results demonstrate this algorithm.According to the different characters of the GNSS signal, noise and interference, subspace separation algorithm can be used to suppress interference. The key problem of subspace separation algorithm is the subspace tracking.This thesis proposes a new subspace projection approach , which relaxes the requirement of the diagonal matrix in SVD to block lower triangular matrix and reduces the computation while the anti-jammer performance is not affected. The block lower triangular matrix can be computed by GIVENS rotation. GIVENS rotation has modular structures, is suitable for parallel computation.In GNSS anti-jamming system, a difficult problem in beamforming is traking the DOA of satellite signal. A new kind of low computational complexity subspace traking algorithm (Cyclic-FDPM ) based on cyclostationarity characteristic of GPS satellite C/A code signal is proposed. the cyclic-FDPM algorithm relizes DOA estimation on the GPS satellite signal. Beam forming with DOA vector can improve SINR. Under strong jamming scenario a cascaded space-time adaptive processing scheme was deviced with its first stage as ordinary space-time adaptive processing with certain constraint and the second stage as beam former aided with information extracted from cyclic-covariance matrix. In order to reduce the computational burden of space-time processing filter groups, a space-time processing filter groups designed method is proposed. This method can be easily implemented owing to low computational complexity and modular structures. Experiments showed that such a cascaded scheme could bring signal-to-noise-ratio improvement for the space-time processing.This thesis gives the FPGA hardware realization of the proposed algorithm, and experimental results are given. The experimental results show that SWGQR-RLS has better performance than QR-RLS method in the condition of pulse-modulated interfference and has similar performance as QR-RLS method in the condition of continuous interfference.