An approach to improve the GPS positioning performance under urban environment conditions

Satellite deficiency degrades the performance of GPS single point positioning (SPP) in city urban areas. If the number of observed satellites is smaller than that of the unknown independent parameters in the data processing, extended Kalman filter (EKF) methods will usually be employed to transit the variable values epoch by epoch. In this case, the prediction model in EKF is very important for the positioning results. This paper focuses on the receiver clock offset models in the prediction equation. The investigation shows that, the clock offset model with clock shift is able to improve the accuracy of the clock offset prediction for internal crystal clocks within a short time span, compared with the clock offset model without clock shift. Besides, in order to further improve the performance of positioning in the case of satellite deficiency, an adaptive EKF is developed to enhance the clock prediction. The experiments show that this approach can improve the positioning accuracy in the scenarios that only fewer satellites are available.