3D-mapping-aided GNSS exploiting Galileo for better accuracy in dense urban environments

Conventional single-epoch GNSS positioning in dense urban areas can exhibit errors of tens of meters due to blockage and reflection of signals by the surrounding buildings. Here, we present the first implementation of 3D-mapping-aided (3DMA) GNSS to use Galileo signals as well as GPS and GLONASS. Our intelligent urban positioning (IUP) concept combines conventional ranging-based GNSS positioning enhanced by 3D mapping with the GNSS shadow-matching technique. Shadow matching (SM) determines position by comparing the measured signal availability with that predicted over a grid of candidate positions using 3D mapping. Thus, IUP uses both pseudo-range and signal-to-noise measurements to determine position. All algorithms incorporate terrain-height aiding and use measurements from a single epoch in time. The 3DMA ranging algorithms presented in this work are based on computing the likelihoods of a grid of candidate position hypotheses. The likelihood-based ranging algorithm (LB-3DMA) uses the same candidate position hypotheses as shadow matching and makes different assumptions about which signals are direct line-of-sight (LOS) and non-line-of-sight (NLOS) at each candidate position. A strategy for integrating LB3DMA with shadow matching is presented. It uses a hypothesis-domain approach where candidate position scores from the LB-3DMA and shadow matching algorithms are combined prior to extracting a joint position solution. With the increase of the number of operational Galileo satellites in orbit, it becomes interesting to assess the performance of the proposed approach using Galileo signals. With more precise satellite clocks, faster satellite orbit determination and improved signal modulation and larger bandwidth, the Galileo system promises a better performance when it is fully operational, compared to existing fully operational GNSS (i.e., GPS and GLONASS), in particular in terms of the effect of multipath interference. GPS, GLONASS and Galileo test data were recorded using a u-blox EVK M8T consumer-grade GNSS receiver at 18 locations in the City of London area. The single-epoch RMS horizontal (i.e., 2D) error across all locations using all these constellations was 3.4 m using 3DMA GNSS, compared to 24.4 m for conventional positioning, a factor of 7.2 improvement. The corresponding accuracies using GPS and GLONASS only were 3.6m using 3DMA GNSS and 25.9m using conventional positioning.