Paul D. Groves, Qiming Zhong, University College London, United Kingdom; Ramsey Faragher, Paulo Esteves, Focal Point Positioning, United Kingdom

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Abstract:

Conventional GNSS positioning in dense urban areas exhibits errors of tens of meters due to non-line-of-sight (NLOS) reception and multipath interference. Inertially-aided extended coherent integration within the GNSS receiver, as in the case of supercorrelation or S-GPS/GNSS, mitigates these effects by making the receiver more sensitive to directly received signals than reflected signals whenever the receiver is moving. This reduces multipath interference and makes NLOS signals easier to detect using signal-to-noise measurements. 3D-mapping-aided (3DMA) GNSS uses predictions of which signals are NLOS to enhance the positioning algorithms. 3DMA GNSS ranging algorithms can be combined with shadow matching, which uses the signal-tonoise measurements. Both supercorrelation and 3DMA GNSS can improve positioning accuracy in dense urban areas by more than a factor of two. As supercorrelation takes place at the receiver signal processing stage while 3DMA GNSS operates at the positioning algorithm stage, the two techniques are potentially complementary. This paper therefore investigates the benefits of combining them. GNSS signals were recorded using a Racelogic Labsat 3 GNSS front end on a trials van in the Canary Wharf area of London and subsequently processed to generate conventional and supercorrelated ranging and signal-to-noise measurements from the GPS and Galileo satellites. These are then input to several different positioning algorithms, including conventional positioning, shadow matching and likelihood-based 3DMA ranging and a combination of shadow matching and likelihood-based 3DMA ranging. Single-epoch positioning results using code-only pseudo-ranges clearly demonstrate the benefit of supercorrelation with position errors using S-GNSS measurements 40% smaller than those using conventional least-squares positioning techniques. 3DMA GNSS improves the position accuracy by about 25% in the denser environments, but does not bring any benefits in the more open areas. When supercorrelation is combined with filtered carrier-smoothed pseudo-ranges using outlier detection to reject code components that inconsistent with the carrier-based component, the least-squares position errors are reduced by a factor of 5.7 in the densest of environments and a factor of 3.5 elsewhere. With these filtered measurements, 3DMA GNSS techniques have little impact on the positioning accuracy. Thus, 3DMA GNSS techniques are likely to be more useful for snapshot positioning techniques and potentially for the initialization of filtered solutions than for continuous positioning.