Comparisons of Multipath Modeling Strategies for the Estimation of GPS Positioning Error

Inhalt:
For precise GPS positioning one major source of error is multipath. Therefore, it is important to get information about the possible multipath signals in a complex scenario such as urban or suburban man-made environments. We can distinguish three kinds of prediction models in the literature. Deterministic models, based on an electromagnetic description of multipath, require a precise description of the 3D receiver’s environment in order to predict channel parameters. Statistical models derive channel statistics by means of a statistical description of the environment based on extensive experimental data. Finally, hybrid deterministic-statistic models are based on both deterministic techniques to simulate the basic characteristics of the channel and statistical add-ons. The main interest of hybrid models is to achieve a realistic channel representation while maintaining an acceptable computation time in comparison to pure deterministic models. Here we focus on deterministic models. Most of them predict multipath by combining ray tracing techniques with geometrical optics (GO) or with the uniform theory of diffraction (UTD). Moreover, in these models the influence of small elements and material characteristics are generally not assessed in the simulation results. In this article, we aim at two main objectives. The first objective is to propose a model based on physical optics (PO) in which field propagation is not approximated by rays, and to compare its performance with GO and UTD. The second objective is to specify a suitable description of the 3D environment (level of details and material characteristics) for multipath simulations. In the next sections, we first introduce the GPS channel model, then we present GO, UTD and PO approaches. Finally simulations are performed to compare these approaches and to determine a suitable description of the environment.