GNSS-based High Accuracy Positioning for Railway Applications

The railway industry is facing a global increase in travel and freight demand, which requires extra capacity. Providing such capacity is limited by the current positioning systems used for railway traffic management. The past decade has seen a growing interest in GNSSbased positioning solutions for railway applications due to their global coverage, low cost and interoperability with existing systems. However, the railway operational environment presents a number of challenges to GNSS due to track side buildings, stations and tunnels which attenuate or block signals and generate multipath. This paper reviews the wide range of railway applications that can benefit from a GNSS-based enhanced positioning function, along with the existing requirements. It reviews the different positioning techniques that can be used and the different error sources the system has to deal with, including multipath. Finally it compares the effect of different multipath mitigation weighting techniques including elevation weighting, C/N0 weighting, residualbased weighting and multipath-based weighting. A novel adaptive weighting method based on the railway track geometry is introduced also and is compared to the current methods.