Accuracy Trend Analysis of Low-cost GNSS Chips: The Case of Multi-constellation GNSS PPP

The recent market release of a new generation of state-of-the-art, low-cost receivers capable of tracking multifrequency, multi-GNSS signals offers a glimpse into the level of improvement in augmented GNSS user solution accuracy. Using PPP to assess point positioning accuracy, this paper investigates various low-cost, multi-GNSS receiver chipsets, including the Piksi Multi Module, Unicorecomm Nebulas II and U-blox F9 sensors. The testing and analysis can be grouped into 3 main categories: measurement quality analysis, uncombined float PPP solution processing, and residual analysis. Static and kinematic scenarios were considered in all of tests performed on the chipset sensors. Reference solutions were obtained from a collocated geodetic receiver. To appreciate the quality of the observations obtained from the sensors, pseudorange multipath observables were formed to generate a full multipath profile. The results indicated that the quality of the solutions is equivalent to the geodetic receiver in terms of availability and positioning, especially in the static case. Significant customization was made to our York-PPP processing engine, especially in the quality control and residual analysis functions, in order to successfully process these datasets. Results from the relatively low-cost receivers indicated on average a decimetre-level of accuracy with geodetic grade antennas. However, centimetre- to millimetre-level of differences were observed among the sensors when a signal splitter was used to connect them to one antenna. While the positioning performance is typically limited to the decimetre-level, this performance is orders of magnitude better than metre-level point positioning. Future work would involve the resolution of float ambiguities for all available constellations.