Enhancing the Quality of Kinematic PPP in Partially and Heavily Obscured-Sky Using Stand-Alone Double Differencing Carrier Phase Relative Positioning

Kinematic Precise Point Positioning (PPP) provides high-accuracy absolute positioning but suffers from performance degradation and solution outages in partially and heavily obscured GNSS environments due to satellite blockage, cycle slips, and ambiguity reconvergence. This study proposes a loosely coupled integration of Stand-Alone Double-Differenced Carrier Phase (SADDCP) relative positioning with raw kinematic PPP using forward and reverse Kalman filtering to enhance solution continuity and reliability. In the proposed scheme, precise 3D relative positioning from SADDCP, when at least three healthy satellites are available, is used to bridge PPP solution gaps caused by fewer than five satellites or during ambiguity reconvergence. When only two satellites are available, a planar (2D) solution is maintained until full PPP restoration. Experimental validation was conducted along a pre-surveyed trajectory spanning open-sky, partially obscured, and heavily obstructed urban environments. In open-sky conditions, raw PPP achieved 3–5 cm accuracy in all components with 100% 3D continuity, while the integrated solution showed comparable performance with slight improvement, particularly in height. In partially obscured environments, integration improved PPP accuracy by approximately 0.7 m, 0.9 m, and 1.15 m in the E, N, and H components, respectively, while maintaining 100% continuity. In heavily obscured areas, raw PPP covered only 21% of the trajectory with accuracy of 2.64, 3.26, 5.37 m in E, N & H components, respectively, whereas the integrated solution achieved 65% (2D) and 89% (3D) continuity with accuracies of about 1.3 m in plan and 1.7 m in height. The results demonstrate that SADDCP/PPP integration significantly enhances positioning continuity and accuracy in challenging GNSS environments. Future work will investigate further integration with MEMS-based INS to mitigate solution outages and cumulative drift in severely obstructed conditions.