A design of base-station-aided LEO/GPS joint positioning framework

Aiming at the problem of insufficient available satellites for GPS-based positioning in challenging environments, we designed a joint positioning framework that uses low earth orbit (LEO) satellites broadcasting signals-of-opportunity (SOP) and a prior base-station with known positions to aid GPS. Since LEO satellites are designed for non-navigation purposes, their downlink signals do not contain fine-time information, making it difficult to determine the signal emission time and satellite states. Additionally, limited by system costs, LEO satellite onboard clocks face problems with inaccurate and asynchronous. To mitigate the impact of satellite clock errors, we employ Doppler as the typical measurement and introduce the coarse-time technique to propose a LEO satellite state determination and clock drift estimation method based on the prior base-station. For the unknown user, we first receive satellite clock correction information broadcast by the base-station. Next, we propose a stage-wise coarse-time positioning method based on Lagrangian interpolation to achieve real-time positioning. The field experiment uses ORBCOMM (ORB) satellites as SOP beacons. Only 1 ORB and 2 GPS are needed to solve the user position. Adding more ORB or GPS satellites improves the positioning accuracy from hundred or even kilometer meters to 29.4 m.