Multipath modelisation of typical indoor environments optimisation of GNSS based indoor positioning

This paper describes a detailed numerical simulation study of indoor propagation carried out in order to evaluate multipath effects on the GNSS repeater based indoor positioning approach in various environments. Previous work [1] studied multipath effects in a very restricted area of about 50 square meters with metallic walls. The goal of the present paper is to provide the required complementary information to evaluate the multipath problem in typical indoor environments and to propose some directions of optimisation. The theory of the GNSS repeater based approach, together with experimental results validating its principle, was presented in previous paper [2]. The main idea of this method consists in using GNSS repeaters in a sequential mode in order to carry out measurements of code phase jumps at the instant of transition from one repeater to the next. Once obtained, three such jumps allow the indoor location calculation, through a classical GNSS computation. In order to carry out multipath evaluation, and optimisation, we use a deterministic propagation simulation software called Ergospace. Some extensions and customized features of the simulation package were developed to make the software more suitable for the GNSS repeater approach. The software takes into account all the elements concerning the satellites, the antennas and the environment, and can be used for both static and dynamic simulations. The considered environment is completely described using VRML (Virtual Reality Modelling Language). Each object encountered in the environment (wall, ceiling, floor or furniture) is characterized by its geometrical and electrical properties. The patterns of all considered antennas were measured in 3D in order to have a precise description of their performances. The propagation is determined using Ray Tracing algorithms. In order to consider multipath, the interactions (reflections, transmissions and diffractions) between rays and the considered environment are calculated until a maximum number is reached. Furthermore, the software is divided into two parts, the Outdoor Module and the Indoor Module. The main results given and discussed in the paper concern different aspects such as: • Various typical environments (exhibition halls, amphitheatres, office buildings, houses, laboratories, etc.) • Effect of limited displacements around a given location in order to evaluate the small scale variations of the multipath • Determination of criteria for an optimised deployment, depending on the environments, for both the repeater and the receiving antennas • Impact of different radiation patterns for the repeater antennas (standard GPS antenna, directional antenna, etc.) First simulations are also carried out in a specific configuration where the repeaters are located outside the building and are transmitting indoors. Such a deployment could be envisaged in a situation of emergency for fire brigade or police operations in a building where no on site repeaters are available.