Marc Heddebaut

Land mobile GNSS availability and multipath evaluation tool

Applications of global navigation satellite system (GNSS) 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 that 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 reflected ray 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.

Leaky Waveguide for Train-to-Wayside Communication-Based Train Control

In guided urban automated transportation systems, the maintenance of a high-quality broadband train-to-wayside communication at all locations along the track poses a major problem. Several techniques are currently used. However, to achieve sufficient rates, a communication frequency range of 2-6 GHz is widely in use. At these frequencies, the natural propagation in tunnels usually works efficiently, but the communication through a leaky waveguide that is continuously laid along the track has several advantages. Over the required communication ranges of several hundred meters, between stations, such waveguides provide low longitudinal attenuation and remain of reasonable size. They also provide predictable communication ranges that could offer significant advantages over the natural propagation approach. This paper will theoretically and experimentally describe such a technical solution. Using ray-optical modeling of the radio propagation in a railway-type tunnel, the radiation characteristics of such a system will be evaluated. At the same operating frequencies, it will be compared with a conventional base solution using antennas separated a few hundred meters apart. An example of a recently operational implemented system will be presented.