Design Of Tracking Loop And Research On Algorithm For Vector-based GPS Receiver

With the constant development of society, the demand for positioning accuracy and stability of Global Positioning System(GPS) receivers in the city is becoming more and more.The traditional GPS scalar receiver tracks each satellite signal in one channel separately, so it cannot make full use of the information of each channel. This can lead to poor solution precision in harsh scenarios. GPS vector receiver based on vector tracking loop can transmit the measurements of each channel to the navigation filter. Then through the navigation filter,the local signal generator of each channel is forming a closed loop. However,the Extended Kalman Filter (EKF) doesn't meet the requirement of the positioning accuracy and stability of the complex scenes,when it's used in weak signal,high dynamic environments and some other complex scenes. This paper presents a new tracking loop structure and a new navigation filtering algorithm to solve the problem of low positioning precision and poor stability in the harsh environment.Firstly, this paper analyzes the GPS navigation system, including the principle of GPS navigation system and the system error source. Then it establishes the mathematical model including the position equation and the pseudorange equation. Secondly, this paper analyzes the structure of vector tracking method, including the structure of the centralized vector tracking and the structure of the federal vector tracking. Thirdly, the vector tracking algorithm based on the position equation and the centralized vector tracking structure is compared with the scalar tracking algorithm through using weighted least square method. It's proved that the vector tracking algorithm can utilize more than four satellites to carry out the positioning solution.In this paper, a vector tracking loop called Vector/Delay Frequency Look Loop (VDFLL)is proposed. A simulation is presented to compare the performances of vector tracking loop and scalar tracking loop which is based on Delay Lock Loop (DLL) and Phase Lock Loop(PLL). The simulation results show that new method can make full use of the information of each channel. It's proved that the vector tracking algorithm has a good performance to solve the issue of precision and stability problem of algorithm, especially when there are more than four satellites.Finally, to the problem of low accuracy and divergence in strong nonlinearity and some other harsh environments, this paper proposes an improved EKF method that the covariance matrix of process noise of the online adaptive adjustment system is achieved by using the particle swarm optimization(PSO) algorithm. Performance comparison between the PSO-EKF and the conventional EKF is provided. It's proved that the vector tracking method based on PSO-EKF is more sensitive to the speed variation and it can get better solution precision.