Precise Point Positioning Algorithm for Pseudolite Combined with GNSS in a Constrained Observation Environment

• Published in: Sensors (Basel, Switzerland) Vol. 20; no. 4; p. 1120
• Main Authors: Sheng, Chuanzhen, Gan, Xingli, Yu, Baoguo, Zhang, Jingkui
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI 18.02.2020; MDPI AG
• Subjects: ambiguity resolution and validation; distributed pseudolite; gnss/pseudolite precise point positioning; high-precision time synchronization; low-cost receiver; urban canyon; urban canyon; distributed pseudolite; low-cost receiver; ambiguity resolution and validation; GNSS/pseudolite precise point positioning; high-precision time synchronization
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s20041120

In urban canyon environments, Global Navigation Satellite System (GNSS) satellites are heavily obstructed with frequent rise and fall and severe multi-path errors induced by signal reflection, making it difficult to acquire precise, continuous, and reliable positioning information. To meet imperative demands for high-precision positioning of public users in complex environments, like urban canyons, and to solve the problems for GNSS/pseudolite positioning under these circumstances, the Global Navigation Satellite System (GNSS) Precision Point Positioning (PPP) algorithm combined with a pseudolite (PLS) was introduced. The former problems with the pseudolite PPP technique with distributed pseudo-satellites, which relies heavily on known points for initiation and prerequisite for previous high-precision time synchronization, were solved by means of a real-time equivalent clock error estimation algorithm, ambiguity fixing, and validation method. Experiments based on a low-cost receiver were performed, and the results show that in a weak obstructed environment with low-density building where the number of GNSS satellites was greater than seven, the accuracy of pseudolite/GNSS PPP with fixed ambiguity was better than 0.15 m; when there were less than four GNSS satellites in severely obstructed circumstances, it was impossible to obtain position by GNSS alone, but with the support of a pseudolite, the accuracy of PPP was able to be better than 0.3 m. Even without GNSS, the accuracy of PPP could be better than 0.5 m with only four pseudolites. The pseudolite/GNSS PPP algorithm presented in this paper can effectively improve availability with less GNSS or even without GNSS in constrained environments, like urban canyons in cities.