Abstract: Based on the brief description of the non difference non combination theoretical model and parameter estimation, combined with IGS/MGEX precision orbit and precision clock difference products, this paper analyzes the performance of BDS/GPS/GLONASS system non difference non combination PPP in Yunnan, which is located at low latitude and high altitude. Through experimental research and analysis,it is concluded that the number of visual satellites in the single system positioning mode in this area is BDS>GPS>GLONASS. In the combined mode, the number of visual satellites of BDS system and other systems is basically greater than that of GPS and GLONASS system. The number of visible satellites is GRC>GC>RC>GR, and the PDOP value is GR>RC>GC>GRC. The number of visible satellites in the combined mode is basically 2~3 times that of the single system, indicating that the contribution of BDS system is greater than that of the other two systems in low latitude and high altitude areas. Multi system combination can obtain better satellite geometry, which has significant advantages over single system. In terms of positioning accuracy, the positioning accuracy can basically reach mm cm level under seven combined modes.

Key words: low latitude and high altitude, non difference non combination, PPP, positioning accuracy