A coarse-time positioning method for improved availability

Coarse-time positioning (CTP) is a rough positioning method using digitized samples from Global Navigation Satellite System (GNSS) receiver correlators. Since it does not require signal tracking, it can reduce power consumption dramatically. To improve the positioning availability of CTP, we propose a new method that is applicable even with four visible satellites as compared with the conventional methods requiring at least five visible satellites. The proposed method sequentially estimates the coarse-time error (CTE) at first and estimates the user position and clock bias next. For the CTE estimation, the reconstructed range rate and the estimated range rate are compared at a set of test time instants (TTIs). By finding the TTI corresponding to the smallest magnitude of the difference between the reconstructed and estimated range rates, the CTE can be estimated. After the CTE has been estimated, the user position and clock bias can be estimated even with four visible satellites. To compare the proposed method and the conventional CTP method, we performed an experiment with field-collected measurements. At the sampling rate of 20 mega samples per second, the position accuracy was about 10 m in the open area and about 20 m in the urban area.