A simulation system for GNSS multipath mitigation using spatial statistical methods

Multipath is one of the main causes of degraded position accuracy in the Global Navigation Satellite System (GNSS) because portions of the signals can be reflected by high buildings in dense urban areas. Multipath mitigation techniques based on hardware enhancement or signal processing help to improve GNSS accuracy for high-precision surveying. A Geographic Information System (GIS) is also used in the signal propagation model to predict multipath effects. In addition to these existing approaches, we found that spatial statistical methods are useful in multipath mitigation because the multipath produces a unique spatial distribution of user positions. In this paper, we present a spatial statistics-based simulation system for mitigating multipath and improving the accuracy in GNSS positioning. Multipath tends to be associated with spatial outliers in simulated user positions (SUPs) and contributes little to the spatial clustering of SUPs. Using these spatial characteristics, we developed a method called the “satellite participation ratio in outliers versus cluster” (SPROC) to identify multipath satellites. Once the identified multipath satellites are excluded, a user position is determined using a mean spatial center of the SUPs from the remaining satellites. The effects of such multipath mitigation were validated by examining whether the SPROC method correctly identified multipath satellites and by comparing the position errors with and without SPROC. We demonstrated the applicability of our system with a simulation experiment using a precise ephemeris for the Global Positioning System (GPS) and the orbital parameters for the proposed constellations of the GALILEO and the Quasi-Zenith Satellite System (QZSS). In our simulation of Shinjuku ward in Tokyo, the user-equivalent range error (UERE) other than multipath was virtually generated and added to the multipath delay. The pattern of position errors with and without SPROC showed that the improvements in accuracy were considerable at locations close to buildings.