Extending 3DMA GNSS with Diffraction Features in Urban Areas: Feasibility Analysis and Preliminary Results

Accurate GNSS solutions are essential for location-based services, which is still challenging for urban areas. In recent years, the 3D mapping aided (3DMA) GNSS positioning algorithms are developed to sufficiently mitigate the non-line-of-sight (NLOS) receptions with significant pseudorange errors in urban areas. However, besides the NLOS reception, the diffraction effect frequently occurs on GNSS signal when its direct propagation path is close to the building edge. The diffracted signal will be misclassified into other propagation types, resulting in a faulty matching during the conventional 3DMA GNSS. On the other hand, the signal attenuation from diffraction depends on the propagation geometry related to the user position, which can be modelled via the uniform geometrical theory of diffraction. Thus, the diffraction effect is potential to be employed as a matching feature for positioning. In this study, three features are proposed to evaluate the matching between the simulated and real measurements, including instant C/N₀ difference, correlation of C/N₀ attenuation, and difference on C/N₀ attenuation gradient. The location dependencies of these features are investigated, which perform a good matching at the receiver true position and sufficiently low matching at the positions other than truth for position determination. Then, the feature of instant C/N₀ difference is applied with a standard 3DMA GNSS feature-matching-based positioning framework. By only using two satellites with diffraction from buildings, it achieves the positioning accuracy of 2.5 meters from real experimental data, which validates the feasibility of using the diffraction features to aid positioning in urban areas.