Positioning and integrity monitoring using the new DFMC SBAS service in the road transport

Australia and New Zealand has initiated a two-year test-bed in 2017 for the new generation of Satellite-Based Augmentation System (SBAS). In addition to the legacy L1 service, the test-bed broadcasts SBAS messages through L5 to support the dual-frequency multi-constellation (DFMC) service for GPS and Galileo. Furthermore, PPP corrections were also sent via L1 and L5 to support the PPP service for dual-frequency GPS users and GPS/Galileo users, respectively.

The positioning and integrity monitoring process are currently defined for the aeronautical DFMC SBAS service in [1]. For land applications in road transport, users may encounter problems in complicated measurement environments like urban areas, e.g., more complicated multipath effects and frequent filter initializations of the carrier-smoothed code observations. In this study, a new weighting model related to the elevation angles, the signal-to-noise ratios (SNRs) and the filter smoothing time is developed. The weighting coefficients adjusting the impacts of these factors are studied for the open-sky, the suburban and the urban scenarios. Applying the corresponding weighting models, the overbounding cumulative distribution functions (CDFs) of the weighted noise/biases are searched and proposed for these scenarios.

Using real data collected under different measurement scenarios mentioned above, the DFMC SBAS positioning errors and protection levels are computed in the horizontal direction based on the proposed weighting models and the proposed overbounding CDFs. The results are compared with the case applying only the traditional elevation-dependent weighting model. While the positioning accuracy and protection levels did not change much for the open-sky scenario, the RMS of the positioning errors and the average protection levels are found to be reduced in both the suburban and urban scenarios. 

[1] EUROCAE (2019) Minimum operational performance standard for Galileo/global positioning system/satellite-based augmentation system airborne equipment. The European Organisation for civil aviation equipment, ED-259, February 2019