ION GNSS 2012
Session C3: GNSS Space Based Augmentation Systems (SBAS)

Title: On the Performance of Dual-frequency Multi-constellation SBAS: Real Data Results with Operational State-of-the-art SBAS Prototype
Author(s): J. Simon, J. Ostolaza, J. Moran, J. Caro, A. Madrazo, GMV, Spain
Date/Time: Thursday, September 20, 2012, 8:57 a.m.
Room: 205 (NCC)

The analysis of the current trends observed in the navigation community suggests that, for the coming years, the GNSS integrity solutions may rely on Satellite Based Augmentation Systems (SBAS), Ground Based Augmentation Systems (GBAS), Receiver Autonomous Integrity Monitoring (RAIM) or new techniques including integration with other sensors. In the aviation community, SBAS already enjoyed recognition at regulatory level and is considered as a reference navigation aid. Recently, ICAO has developed the Performance Based Navigation concept - PBN - and established an international schedule for APV at all instrument runway ends either as the primary approach or as a back-up for precision approaches. Most countries are producing their PBN implementation plans to meet ICAO recommendation and the use of the SBAS technology seems to be the most adequate solution for many countries.
Development and deployment of a SBAS system in any region of the world is a serious technological challenge. Besides, each region may have different characteristics and requirements. The ionosphere behaviour is, for instance, a key issue for implementation of SBAS in some regions. At the current moment, WAAS and EGNOS systems have been declared operational and available for civil aviation. At the same time that both SBAS systems have reached their full operational capability the development of GNSS constellations, like GLONASS, Galileo and COMPASS continues. And so it also continues the studies for the definition of new generation SBAS systems. The current discussions on SBAS evolution rely on enhancements towards multi-constellation and dual-frequency capabilities.

As a consequence of the technological challenge, it is usual that SBAS development plans envisage the deployment of SBAS testbeds (e.g.; WAAS NSTB, EGNOS ESTB) and pre-operational, non-certified, services in parallel to the operational system development. Testbeds offer numerous advantages, in particular provide the system developers with powerful platforms to validate architecture, design and performance assumptions, thus mitigating design risks and helping to optimize the design to satisfy the requirements of the region.

magicSBAS is a state-of-the-art operational SBAS testbed developed by GMV to offer non-safety critical SBAS augmentation to any interested region. The algorithms implemented in magicSBAS have been fully developed by GMV and are the result of more than 15 years of experience in the development of EGNOS and other SBAS programmes. The magicSBAS algorithms have been optimized to provide the best performance in the most demanding conditions and have been tested in many regions of the world.

Recently, magicSBAS has been upgraded with new capabilities, being major ones the generation of SBAS message MT28, the multi-constellation capability and the provision of service to dual-frequency users. The paper shows first that magicSBAS is representative of EGNOS performances. This is achieved by comparing EGNOS and magicSBAS performances maps (availability, accuracy, integrity and continuity) for the same period of time. Once the representativeness is proven, different analyses are run to show SBAS service improvements using the new magicSBAS capabilities:

1. Generation of SBAS message MT28 vs. the provision of service using MT27 message. 2. Incorporation of the GLONASS constellation for the computation of the ionosphere monitoring, which is one of the drivers for SBAS performances. 3. Provision of service to dual-frequency users. Dual-frequency users are capable of getting rid of the ionosphere delay and consequently they do not need from ionosphere corrections and integrity parameters (GIVD and GIVE). Although a standard for these users is not yet available, the paper will detail the assumptions made for simulating these service to users. 4. Service availability using a second augmented constellation at user level (GPS+GLONASS). 5. Introduction of new ground stations. It is depicted how some SBAS improvements, like the multi-constellation capability, reduce the need of new ground stations for SBAS service area extensions.

One of the key advantages of magicSBAS is the capability to process raw data in standard formats like NTRIP, RINEX, EDAS, SPEED or EGNOS formats. There are currently hundreds of Continuous Operating Reference Stations (CORS) worldwide providing data in these formats that can be used together with magicSBAS to quickly evaluate the SBAS performances. This capability has been used during the study to show EGNOS service improvements in areas like Africa and Eastern Europe thanks to the new magicSBAS capabilities, or even the performance of a SBAS system in countries like Australia and New Zealand. The study shows service availability for service levels like APV-I or LPV-200. It is important to remark that all performances shown in this study have been obtained using real data.

Thanks to all these analyses, the study provides a clear picture of the performances that will be reached by future SBAS systems, once the multi-constellation and multi-frequency capabilities are developed. Because of the extensive use of real data, and because of having based the algorithms proposed on EGNOS, the authors are confident that the results shown in this paper are representative of the ones expected in the future operational SBAS evolutions.

Previous Abstract Return to Session C3 Next Abstract