Abstract
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.
Highlights
The Global Satellite Navigation System (GNSS) plays a leading role in outdoor positioning and is the basis of location services for public users with low-cost receivers
GNSS cannot provide a continuous, high-precision location service in constrained environments like urban canyons, because: GNSS satellites, which are obstructed by high-density and tall buildings, result in poor positioning performance or even positioning failure [1,2], serious electromagnetic interference, dramatically degraded signal power, and severe multi-path error caused by reflation as a result of mirror building or minor structures, leading to low-quality observation data, especially for low-cost receivers [1,3]
In order to evaluate the performance of the Precise Point Positioning algorithm for a pseudolite combined with GNSS in a constrained observation environment, a GNSS/pseudolite Precision Point Positioning (PPP) testbed was built in an urban canyon, as shown in Figures 1 and 2
Summary
The Global Satellite Navigation System (GNSS) plays a leading role in outdoor positioning and is the basis of location services for public users with low-cost receivers. For complex urban canyon environments, the addition of a pseudolite can significantly improve the availability of GNSS-like satellites and enhance the spatial geometry of GNSS [3], which is a foundation of high-precision GNSS positioning [7,8,9,10]; the use of a pseudolite with good spatial distribution provides an important technique for high-precise positioning in a constrained environment This distributed pseudolite heavily relies on highly precise time synchronization for every pseudolite [11], which requires the support of a complex time-synchronization device with dedicated manipulation; the larger multi-path error of the pseudorange and the ambiguity initiation require known coordinates with high precision, problems which urgently need to be solved [12,13]. High-precision positioning of distributed pseudolite combined with GNSS in an urban canyon was conducted with a low-cost receiver
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