SBAS Systems

Fundamentals
Title	SBAS Systems
Edited by	GMV
Level	Basic
Year of Publication	2011

SBAS systems are spreading out all over the world. More and more, it is believed that upon dual-frequency SBAS service provision, a seamless navigation will be possible from and to any two locations in the world.

SBAS in the World

SBAS Indicative Service Areas. Source: GSA User Technology Report 2018

From all the SBAS systems in the world, some of them are already operational (WAAS, MSAS/QZSS,GAGAN System, EGNOS), other are under implementation (SDCM, China’s Beidou SBAS BDSBAS, previously known as SNAS) while others are under feasibility studies, as is the case of SACCSA, ASECNA , KASS in South Korea planned for 2022 or SPAN (Southern Positioning Augmentation Network) in Australia and New Zealand.

According to the Interoperability Working Group (IWG) of SBAS System several evolutions are expected in the coming years:

• GNSS Dual Frequency Operations;
• GNSS Multiple-Constellation Operations (Galileo, BeiDou);
• EGNOS and MSAS reference network expansion;
• SDCM and other SBAS systems under development to .

When these evolutions are completed it is though that the global SBAS coverage will suffer an increase from the 7.54% at 99% (only WAAS, EGNOS and MSAS) to 92.65%, considering the use of multiple-constellation (GPS and Galileo).

Prediction of World Wide SBAS coverage

WAAS

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.

WAAS is foreseen to implement DFMC capabilities in the future.

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  WAAS overview

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  WAAS performances

MSAS/QZSS

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 augmenting GPS L1 signals.

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  MSAS architecture

QZSS (Quasi-Zenith Satellite System) I the Japanese satellite navigation program with a regional service coverage based on orbits for quasi-zenith satellites to broadcast radio signals from high elevation angle into urban canyons. MSAS evolutions will take advantage of the Japanese QZSS and to include DFMC capabilities in the future.

GAGAN

The GPS Aided Geo Augmented Navigation or GPS and Geo Augmented Navigation system (GAGAN) is the SBAS implementation by the Indian government. The Indian government states that it will use the experience of building the GAGAN system in the creation of an autonomous regional navigation system called the Indian Regional Navigational Satellite System (IRNSS).

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  GAGAN overview.

SDCM

The System for Differential Corrections and Monitoring (SDCM) is the SBAS currently being developed in the Russian Federation. SDCM is expected to be certified in the coming years, being this just the first step in the SDCM strategy which pursues also other broadcast means –potentially a polar MEO– with the aim of providing also a service to the North part of Russia.

The main differentiator of SDCM with respect to other SBAS systems is that it is conceived as an SBAS augmentation to GPS and GLONASS, whereas the rest of current SBAS initiatives provide corrections and integrity just to GPS satellites.

• Sdcm overview.png

  SDCM planned station network

SNAS/BDSBAS

The People's Republic of China is developing its own SBAS, called Satellite Navigation Augmentation System (SNAS). There is little public information available on this development.

Now, the Chinese SBAS initiatives refer to BeiDou Satellite-based Augmentation System (BDSBAS).

SACCSA

The SBAS initiative in South/Central America and the Caribbean is called SACCSA (Soluciόn de Aumentaciόn para Caribe, Centro y Sudamérica). SACCSA is an ICAO project founded by the Participants/Member States of the SACCSA Project: Argentina, Bolivia, Colombia, Costa Rica, Guatemala, Panama, Spain, Venezuela and COCESNA (Corporación Centroamerica de Servicios de Navegación Aérea). The objective is to study the improvement of the Air Navigation Environment in the Caribbean and South America (CAR/SAM) Regions with a SBAS solution. The program began in 2003 being at present in its Phase III which will determine the feasibility of the implementation of an own SBAS system in the CAR/SAM regions.