BDS/GPS/LEO triple-frequency uncombined precise point positioning and its performance in harsh environments

Precise point positioning (PPP) usually takes a few tens of minutes to achieve centimeter-level positioning accuracy, and reliable ambiguity resolution also requires a relatively long observation time. In addition, the time required will be longer in harsh environments such as urban and canyons. These problems limit the application of PPP. Currently, low earth orbit (LEO) enhanced Global Navigation Satellite System (GNSS) can increase the number of visible satellites and optimize observation structure, which is expected to improve the positioning performance of GNSS-only PPP under complex conditions. In this paper, the performance of LEO/GNSS combined PPP in harsh environments is evaluated initially. First, triple-frequency uncombined PPP model is developed. Then, a LEO constellation consisting of 180 polar-orbiting satellites is designed, and BDS-3 and current GPS constellation are also simulated for subsequent analysis. Besides, the corresponding observation simulation is also carried out. In order to better analyze the performance of LEO enhanced GNSS PPP in harsh environments, six sets of contrast experiments are designed. Both PPP float solution and fixed solution are processed. In term of float solution, it usually takes about 30 min for BDS-only to converge into 5 cm, while the BDS/LEO combination only takes about 10 min in extremely harsh environments. Compared with BDS-only, the accuracy of float solution of BDS/GPS, BDS/LEO, BDS/GPS/LEO combined PPP is improved by 42.44%, 73.77%, and 77.43%, respectively. In term of fixed solution, compared BDS-only, the average time to first fix (TTFF) of BDS/ GPS, BDS/LEO, BDS/GPS/LEO combination can be shortened from 20.0 min to 10.3 min, 4.8 min and 4.0 min respectively. The fix rate of epochs increases from 83.8% to 91.6%. 96.1% and 96.7% in harsh environments, respectively. Compared with the float solution, the positioning accuracy of fixed solution in N, E, and U directions increases by 3.6%, 4.6%, and 3.2%, respectively. (C) 2019 Published by Elsevier Ltd.