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 2020

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) or SouthPAN (Southern Positioning Augmentation Network) in Australia and New Zealand, while others are under feasibility studies, as is the case of SACCSA, A-SBAS (ASECNA) or KASS in South Korea planned for 2022 .

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 become operational.

When these evolutions are completed it is thought 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.

The WAAS programme is continuously in evolution; three development phases have been already covered, and there are on-going plans to improve the capability of the system in parallel with the evolution of the SBAS standards towards a dual-frequency augmentation service.

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  WAAS overview

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  WAAS performances

EGNOS

EGNOS (European Geostationary Navigation Overlay Service) is the European SBAS system that complements the existing satellite navigation services provided by the US Global Positioning System (GPS). EGNOS constitutes together with Galileo the two major initiatives in Europe in terms of satellite navigation. Future evolutions such as EGNOS V3 are expected to augment both GPS and Galileo constellation data.

EGNOS currently supports the following services:

• The Open Service (OS), freely available to the public over Europe. This service was officially started on 1 October 2009.
• 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.
• The EGNOS Data Access System (EDAS) represents the provision of additional data for professional users not provided by the EGNOS signal broadcast by geostationary satellites but by other distribution channels.

MSAS/QZSS

The Multi-functional Satellite Augmentation System (MSAS) is the Japanese Satellite Based Augmentation System (SBAS) System: a GPS Augmentation system with the goal of improving its accuracy, integrity, and availability. First tests were accomplished successfully, and MSAS system for aviation use was declared operational in September 27, 2007, providing a service of horizontal guidance for En-route through Non-Precision Approach. The SBAS signal used to be transmitted from MTSAT (Multi-functional Transport Satellites) operated by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT). The SBAS signal that is made by MLIT is now transmitted from the QZS-3 GEO satellite using the QZSS SBAS transmission service since April 2020.

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  Actual MSAS V2 architecture

QZSS (Quasi-Zenith Satellite System) is 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. On 21 April 2015 it was certified for approach with vertical guidance (APV1) becoming the third SBAS in the world to achieve it and the first to do so operating in the equatorial region. It broadcasts SBAS navigation data using L1 signals and it is under development to also use the L5 signal for SBAS data broadcast.

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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 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).

BDSBAS Architecture. Source: Springer Open

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.

A-SBAS

A-SBAS (ASECNA) corresponds to the SBAS for Africa and Indian Ocean Development initiative. It is composed by international public organisations from 18 member states.

A-SBAS aims to provide early SBAS services from 2021/2022 for NPA, APV-1 and CAT-I operations. Full DFMC services are expected beyond 2028/2030 for CAT-I autoland operations and potentially further ones.

KASS

In October 2014, the Korea Aerospace Research Institute (KARI) was appointed as the leading research organization to develop and build Korea’s own Satellite Based Augmentation System (SBAS), known as KASS (Korea Augmentation Satellite System) in compliance with ICAO Annex 10.

It is expected to provide APV-1 safety-of-life service to airports located in South Korea in 2022.

SouthPAN

The Southern Positioning Augmentation System (SouthPAN) is the Australia and New Zealand’s operational SBAS and will be the first of its kind in the Southern Hemisphere when it reaches full operational capability in 2025. As of December 2020 the procurement phase is underway. Initial signals will be provided gradually and it is expected to broadcast a test transmission service similar to the test-bed of 2017 in 2022 at the latest. This test service will be developed until it becomes a fully operational and certified system .