A new tool for simulation of geospecific multipath and obscuration of GPS/GNSS signals with relation to realistic 3-D city models

摘要

Positioning and navigation with GPS and other Global Navigation Satellite Systems (GNSS) usually work well in open sky conditions like in the air and in flat landscapes. However, reception problems have been observed in mountainous and urban areas, where high structures obscure some or many Line of Sight Signals (LOS) of satellites and where the signal interacts with the local environment and multipath (MP) such as reflections, diffractions and transmissions can reach the receiver. These echoes can lead to a lack of signals and to erroneous input to the receiver front end resulting in less accurate and imprecise position fixes and sometimes to a position blackout. For many years, GNSS hardware simulators, have been used to emulate realistic GPS, Galileo, Beidou and GLONASS signal environments and to reproduce multiple atmospheric, environmental, vehicular, antenna and satellite error effects in a controlled and repeatable way. Obscuration and multipath have been represented by different models, usually in a mathematical, stochastic, geotypical way, representing a certain type of environment but not a specific location, city map, 3D building structure or mountain profile. One of the main obstacles was the huge wealth of data needed to define the shapes and surfaces of the structures and the physical properties of the surfaces. Another main obstacle was the processing power needed to handle both the 3D map data, the vehicle motion and the behaviour of RF signals interacting with these surfaces. In last few years, these problems have been solved by Oktal Synthetic Environment (Oktal-SE), who have programmed a deterministic software simulation tool capable of handling the massive amount of mapping and of calculating signal multipath and obscuration in real-time. This tool uses a GPU-oriented raytracing algorithm to compute, in record times, the masks generated by the environment as well as the impact of the multipath on the performance of the system. For some types of GNSS receiver testing, it is useful to be able to test multipath and obscuration for specific locations and not just in a general way. Thus a new tool has been created which combines GNSS software simulation and hardware simulation by remote control, in order to enable the simulation of more realistic, geospecific obscuration and multipaths effects of GNSS signals as seen by the antenna of a moving vehicle in real-time.