Gnss Performance Enhancement in Urban Environment Based on Pseudo-range Error Model

Today, GNSS (Global Navigation Satellite System) systems made their entrance in the transport field through applications such as monitoring of containers or fleet management. These applications do not necessarily request a high availability, integrity and accuracy of the positioning system. For safety applications (for instance management of level crossing), the performances require to be more stringent. Moreover all these transport applications are used in dense urban or sub-urban areas, resulting in signal propagation variations. This increases difficulty of getting the best reception conditions for each available satellite signal. The consequences of environmental obstructions are unavailability of the service and multipath reception that degrades in particular the accuracy of the positioning. Our works consist in two main tasks. The first one concerns the pseudo-range error model. Indeed, the model differs in relation of the satellite state of reception. When the state of reception is direct, as described in literature, the associated pseudo-range error model is a Gaussian distribution. However, when the state of reception is NLOS (Non Line Of Sight), this assumption is no more valid. We have shown that the associated model can be approximated by a Gaussian mixture. The Second contribution concerns the reception state evolution. We have modeled the propagation channel with a Markov chain. From the state of reception of each satellite, we deduce the appropriated error model. This model is then used in a filtering process to estimate the position. The approach is based on filtering methodology and on the application of a Jump Markov System algorithm.