SBAS Interoperability

EGNOS
Title	SBAS Interoperability
Author(s)	GMV
Level	Basic
Year of Publication	2011

In addition to EGNOS, there are other Satellite Based Augmentation Systems (SBAS) developed or under development, such as the Wide Area Augmentation System (WAAS) in USA, the multi-functional transport satellite (MTSAT) satellite-based augmentation system (MSAS), in Japan or the GAGAN system in India. Although all SBAS are currently defined as regional systems, it is commonly recognized the need to establish adequate co-operation/co-ordination among the different systems, so that their implementation becomes more effective and part of a seamless world-wide navigation system.

To guarantee seamless and worldwide system provision, it is essential that the existing systems do meet common standards and interoperability requirements. The service providers of the EGNOS, WAAS and MSAS systems are regularly meeting through the so called interoperability working group (IWG) to conclude on a the precise understanding of the term interoperability, and on the identification of the necessary interfaces among SBAS that each conceivable interoperability scenarios may imply.

The combination of SBAS Interoperability and SBAS expansion concepts should allow providing a true global world-wide navigation seamless service.

SBAS Systems

SBAS Interoperability

From all the SBAS systems in the world, three are already operational (WAAS, MSAS, EGNOS), two are under implementation (GAGAN, SDCM) while others are under feasibility studies, for instance SACCSA. As regards the operational SBAS:

• The Wide Area Augmentation System (WAAS) was jointly developed by the United States Department of Transportation (DOT) and the Federal Aviation Administration (FAA), beginning in 1994, to provide performance comparable to category I instrument landing system (ILS) for all aircraft possessing the appropriately certified equipment. On July 10, 2003, the WAAS signal was activated for safety-of-life aviation, covering 95% of the United States, and portions of Alaska. At present, WAAS supports en-route, terminal and approach operations down to a full LPV-200 (CAT-I like Approach Capability) for the CONUS, Mexico and Canada.
• The Multi-functional Satellite Augmentation System (MSAS) is the Japanese SBAS. NEC manufactured and delivered MSAS under contract with the Civil Aviation Bureau, Ministry of Land, Infrastructure, Transport and Tourism. MSAS is operational since 2007 supporting en-route, terminal and non-precision approach operations (RNP 0.1). Recently has completed successful LPV flight trials.
• EGNOS is the European satellite-based augmentation service (SBAS) that complements the existing satellite navigation services provided by the US Global Positioning System (GPS). EGNOS provides the first European GNSS services to users. The Safety of Life Service (SoL), that provides the most stringent level of signal-in-space performance to all communities of Safety of Life users over Europe. This service was officially started on 2 March 2011.

SBAS Standardisation

There are two sets of International Standards which SBAS’s shall be compliant in order to be used by Civil Aviation Authorities:

• The Standards and Recommended Practices (SARPS) Standard for SBAS systems established and controlled by the International Civil Aviation Organization (ICAO) and which provides Standards regarding the type and content of data which must be generated and transmitted by an SBAS system. In general, the SBAS provider shall broadcast a SBAS Signal in Space (SIS) compliant to this standard in terms of radio-frequency characteristics, and data content and format.
• The Minimum Operational Performance Standard (MOPS) DO229 established and controlled by the US Radio Technical Commission for Aeronautics (RTCA) and which provides standards for SBAS receiver equipment.

For more information, please refer to the article SBAS Standards.

SBAS System Cooperation

SBAS Interoperability refers to the ability of SBAS systems and the services they provide to be used together to provide better capabilities at the user level than those achieved by relying solely on one of the systems. The SBAS interoperability has always been a prerequisite for delivering a global seamless Safety-of-Life service.

Although all SBAS are regional systems, it is commonly recognised the need to establish adequate co-operation/coordination among SBAS providers so that their implementation becomes more effective and part of a seamless world-wide navigation system. SBAS co-operation is currently co-ordinated through the so-called Interoperability Working Groups (IWG). Although interoperability implies a large variety of complex issues (such as certification, standards, safety, operations,…), EGNOS, WAAS, CWAAS and MSAS SBAS providers have agreed on the following list of objectives concerning technical interoperability and co-operation among SBAS:

• Objective 1 – Validate SBAS Performance consistency and SARPs compliance.
• Objective 2 – Improve the service level available in the regions outside the nominal SBAS service volumes.
• Objective 3 – Improve individual system performance through SBAS data interchange.
• Objective 4 – Improve SBAS prediction capability through SBAS data interchange.
• Objective 5 – Identify possible future improvements.

SBAS interoperability studies and discussions are currently been focussed on two main set of topics:

• Interoperability issues concerning existing SBAS systems, in particular transition issues as observed by users crossing two SBAS service areas (GEO selection mechanism, activation of GEO ranging, etc).
• Interoperability issues for future SBAS evolutions:
  • Evolution of SBAS to become multi-constellation (e.g., GPS and GLONASS or GPS and Galileo).
  • Evolution of SBAS to become multi-frequency (L1, L5, L1/L5).
  • Potential evolution towards a combination of SBAS and RAIM techniques.