Type Approval of SBAS Enabled Maritime Navigation Receivers

Abstract

Space Based Augmentation System (SBAS), initially built to provide navigation services for aviation and SBAS, is increasingly being taken into use in the maritime domain. However, whereas RTCA DO229 provides performance standards for use of SBAS in aviation, there does not yet exist such standards for type approval of equipment with SBAS in maritime navigation. Work is therefore ongoing to develop performance standards for the maritime domain. IMO Res. MSC.401 (95) on Performance Standards for Multi-System Shipborne Radionavigation Receivers was adopted in 2015 including SBAS as an augmentation system for maritime. IEC TC 80 is expected to prepare test specifications for the type approval of multisystem shipborne radionavigation receivers. To support this work, a set of Guidelines for implementation of SBAS in shipborne receivers has been proposed, and the Guidelines have been presented and discussed at IALA and RTCM. To further support this process, GSA established the MAREC project in order to make early implementation of shipborne SBAS receivers following the Guidelines, including testing according to the proposed test standard. This paper will present the results of the MAREC project. The objectives of the MAREC project were to: - Secure the availability of commercial products from European manufacturers of SBAS-enabled Shipborne Receivers. - Develop and test SBAS-enabled Shipborne Receivers according to the Guidelines. - Support the finalisation of the Guidelines based on the results of the implementation and the results of the tests. - Support the SBAS standardisation process at RTCM and IEC including the definition of test specifications for the type approval. The work in MAREC consisted in implementing SBAS processing in existing SOLAS and non-SOLAS navigation equipment and performing testing in accordance with the Guidelines. Further, to study the approval process for SOLAS equipment according to EU Marine Equipment Directive (MED). Part of the work was also to assess impacts on using SBAS in equipment for Automatic Identification System (AIS). The implementation of SBAS functionality was done in KONGSBERG maritime navigation equipment previously type approved for GPS and DGPS. Based on the experience from the implementation and test and looking at how type approval was done for equipment under IEC test standards for GPS and DGPS, there was a feedback loop to the Guidelines, leading to further updates. The equipment testing was first done with simulator, and then with real GPS + EGNOS signals, both static and dynamic on a vessel. The simulator testing allowed introducing error conditions in SBAS messages to check that the receiver reacted correctly. This included setting alarm conditions, for example don’t use for a set of satellites and observing that the corresponding pseudo ranges were rejected from processing. It was checked that the equipment correctly flagged integrity status as SAFE, CAUTION and UNSAFE depending upon the state of the SBAS message. Setting up error conditions in SBAS on the simulator was relatively complex, but once done this can be reused in follow on test campaigns and could also be included as a test signal in the test standard. Testing with live signals over 24 hours characterized the accuracy of the position measurements when using GPS+EGNOS, which was then compared to IEC test requirements for GPS and DGPS equipment, 100 m and 10 m respectively. Other equipment features checked was the estimation of accuracy, in the form of Estimated Position Error (EPE 95%), RMS error and error ellipses. The equipment was set up to provide data output on NMEA format. Part of the analysis was to investigate how use of SBAS shall be reflected in NMEA sentences. Basically, use of SBAS was shown as a differential position, hence similar to DGPS. Check of NMEA output was then included in the equipment testing. This lead to a recommendation for how the NMEA standard shall be interpreted when it comes to reporting position information derived from SBAS. The MAREC project has contributed to the development and quality check of the Guidelines, paving the way for taking the Guidelines as basis for development of equipment standard at IEC level. Testing has shown that implementation and type approval test of SBAS is feasible, and that using SBAS will at least meet the performance standards for DGPS.