Compass receiver positioning algorithm under bad conditions based on unequal interval clock prediction

In the typical urban environment where the satellite visibility is limited or the satellite signal is weak due to the blockage or signal jamming, the availability of the navigation satellite system would be degraded, resulting in conventional four-satellite positioning method is very hard to satisfy the requirement of continuous positioning. To solve this problem, a combined prediction model based on the improved polynomial model and the improved grey model is proposed, which adopts a time interval coefficient and a dynamic weighting factor to predict the receiver clock bias (RCB), and then a predicted clock value from the proposed model is introduced to aid positioning. The experimental results based on BeiDou Navigation Satellite System (COMPASS/BDS) observation data demonstrate that the model is more suitable for predicting RCB both under unequal and equal conditions. Moreover, for 50 s RCB predictions duration of the short satellite signal shading outages, the three-dimensional (3-D) position error using the clock-aided position algorithm is slightly larger than about 2.76% than four-satellite 3-D position error, and thus, the availability of positions can be improved efficiently.