Land Mobile GNSS Availability and Multipath Evaluation Tool

Abstract

-Applications of GNSS (Global Navigation Satellite System) in land transportation systems are already extensively deployed and will certainly continue to grow especially in the framework of Intelligent Transport Systems. However, one of the best-known drawbacks of such a system is the lack of satellite visibility in dense urban areas as well as in some specific embedded railway environments. This restricts considerably GNSS use for extended safety related applications. In this paper, a new tool is proposed to predict the availability of a satellite constellation from the point of view of the land transportation user. Knowing the trajectory of a land vehicle, the tool predicts the number of satellites which will be received and produces a safety criterion able to qualify the GNSS localization result. A first version of the tool, already in operation, merges an image processing approach providing the knowledge of the land environment, and the output of a satellite tracking program predicting satellite positions in the sky. This allows us to determine, using a simple optical approach, the number of satellites received in line-of-sight or blocked, with regard to the nearby environment of the receiving antenna. Results obtained in railway as well as in road environments show that satellite signals received by multipath are often used by GNSS receivers in the localization process. Thus, propagation characteristics of the satellite signals in an urban canyon configuration were characterized to determine when a signal received by multipath is used by the receiver or not. A criterion related to the satellite elevation is defined to improve the overall performance of the predictive tool. Comparisons with real measurements are commented on. Both simulations and measurements are very similar.

Toward accurate localization in guided transport: Combining GNSS data and imaging information

“…This structure can be obtained by images provided by several cameras installed on the roof of the vehicle. The approach has already been validated with the PREDISSAT tool (Marais 2005). PREDISSAT is, however, not a real time process and can largely benefit from new image processing improvements.…”

Investigation on the influence of diffraction by wedges in satellite navigation systems

“…Furthermore, the derived geometric formulation was only valid for the scenario under investigation. A GNSS prediction tool was presented in [6], which was able to predict power contributions from different propagation effects. Even when diffraction in urban canyons was reported, the diffraction model was not explained and the introduced biases were not studied.…”

High-accuracy GPS and GLONASS positioning by multipath mitigation using omnidirectional infrared camera

“…Mobile mapping systems [4], for example, require continuous, accurate self-positioning even near high-rise buildings, which are particularly responsible for generating multipath error. It is therefore essential to establish a positioning technique that will sort out the available satellites and use only those with the least multipath errors [6]- [13].…”

“…A multipath simulation method that uses 3D geographic information systems (GIS) [12], which simulate multipath by pre-measuring building height information, has been proposed. An evaluation tool to predict the availability of a satellite's constellation service along a given terrestrial trajectory by means of a visible light fish-eye optic system [13] has also been proposed.…”