GNSS-based Cooperative Positioning: Approaches and Demonstration

Ciro Gioia and Daniele Borio

Peer Reviewed

Abstract:	The development of techniques and algorithms for merging measurements from different collaborative GNSS devices is an open challenge. The typical user of smart-phone moves around the city, in this scenario GNSS signals can be blocked or affected by multipath. In these circumstances, the navigation solution may experience severe degradation. If a measurement is affected by a gross error, it can be identified and excluded. In urban navigation, the presence of multiple outliers is common and the exclusion of several measurements affected by errors can cause a significant reduction of the satellite geometry. A possible solution is the identification of the blunders and the replacement of such measurements with observables provided by a nearby device. This replacement can compensate for the geometry degradation due to the rejection of multiple satellite signals. In this paper, three methods to merge measurements obtained from two nearby smart-phones are presented. The proposed methods allow the joint use of measurements collected by mobile devices operating in an independent mode and thus not connected to the same external clock. In order to jointly use measurements from different devices, the differences between the clocks of the devices have to be taken into account. Hence, their parameters need to be included in the estimation process. The three approaches proposed are: Direct Measurement Sharing (DMS), Augmented Measurement Sharing (AMS) and Correct Measurement Sharing (CMS). In the first one, cooperating devices share raw pseudorange and Doppler shift measurements; in this case, measurements from one satellite are scarified to estimate the additional unknowns related to the parameter of the clock of the aiding device. In the AMS, the cooperating devices share the measurements as well as the estimates of the clock parameters and their accuracy. In this case, the parameters of the clock of the aiding device can be directly observed introducing additional equations (containing the shared clock bias and drift) into the measurement model. In the CMS case, the cooperating devices share pseudoranges and Doppler shifts corrected for the clock bias and clock drift, respectively. With this approach, the clock parameters of the aiding device do not need to be estimated. The methods have been validated using static and kinematic real data: tests were performed using devices from three manufacturers with different versions of operating system. From the tests, the effectiveness of the proposed methods was demonstrated and the benefits of the combined solutions with respect to the single device solutions were shown.
Published in:	Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019) September 16 - 20, 2019 Hyatt Regency Miami Miami, Florida
Pages:	3832 - 3846
Cite this article:	Gioia, Ciro, Borio, Daniele, "GNSS-based Cooperative Positioning: Approaches and Demonstration," Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019), Miami, Florida, September 2019, pp. 3832-3846. https://doi.org/10.33012/2019.17071
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