Robust High Precision Positioning For Combined BDS And GPS

There are growing demands for global navigation satellite system(GNSS)precise location services in crowded urban areas.Due to the high precision and instantaneity,real-time kinematics(RTK)positioning becomes the key technique for applications such as unmanned aerial vehicle,automatic drive,the internet of things,intelligent transportation system.Currently,RTK positioning for short to medium baseline will be widely adopted as the development of continuous operating reference stations in cities.However,satellite signal will be frequently blocked by dense buildings,and the continuity and availability of RTK positioning will be impacted seriously.To improve the robustness of RTK under such harsh environments,this paper makes some explorations from three aspects,namely introducing multiple system,modifying receiver algorithms and integrating external aiding information.The main innovative contributions are achieved as follows:(1)In order to improve the robustness of ambiguity resolution in harsh environments,a modified geometry-free/geometry-based three carrier ambiguity resolution(GF/GB-TCAR)algorithm is proposed for Bei Dou satellite navigation system(BDS),and a multiple frequency ambiguity resolution algorithm for BDS/GPS dual-system.Experimental results show that the proposed algorithms have high success rates under short to medium baseline,and could achieve high enough success rates in a single epoch.As a result,the robustness of the ambiguity resolution is enhanced.(2)In order to ensure the correctness of ambiguity solutions and RTK positioning results in harsh environments,a real-time ambiguity slips detection and repair algorithm for single and multiple constellation is proposed.Experimental results demonstrate that the proposed algorithm has a hight success rate for cycle slips detection and quantification,and could filter out the incorrectly fixed ambiguities to increase the fixing rate greatly under short to medium baseline.(3)In order to improve the reliability of tracking loops and the continuity of RTK positioning under signal blockage environment,a modified adaptive vector delay frequency lock loop(VDFLL)for BDS/GPS dual-system and two robust tracking algorithms based on the VDFLL are proposed.Experimental results show that the precision of position and velocity solution is improved with the modified VDFLL.Additionally,the proposed robust tracking algorithms could keep loops locked during signal blockage,and improve the RTK continuity.(4)In order to improve the base-band processing and positioning performance with the help of external aiding information,cooperative positioning algorithms based on receiver independent exchange format(RINEX)files and inter-user range measurements are proposed.Experimental results show that the GNSS-only cooperative positioning algorithm could decrease the time to first fix,and the hybrid cooperative positioning algorithm could help get correct position results even under deeply blocked environment.