Moving from one GPS signal to eight signals from four constellations

8 June 2018

The United States’ Global Positioning System (GPS) offers a single frequency service to many aviation systems and applications, including:

  • performance-based navigation (PBN);
  • automatic dependent surveillance-broadcast (ADS-B);
  • aircraft systems, such as terrain avoidance warning systems (TAWS).

In the future, Dual Frequency Multi Constellation services (DFMC) combining dual frequency signals from the United States’ GPS, the Russian Federation’s GLONASS, Europe’s Galileo and China’s BeiDou will help aviation both enhance its performance and benefit from additional robustness.  

The benefits

The term DFMC GNSS refers to the use of dual frequency signals from up to four GNSS constellations with the evolution of aircraft-based (ABAS),  satellite-based (SBAS) and ground-based (GBAS) augmentation systems.

Operational benefits will accrue progressively as aircraft become equipped with DFMC avionics and are able to use multiple GNSS elements on a global basis, in a way that is as transparent as possible to the crew and air traffic controllers.

The plan and the challenge

ICAO, RTCA and EUROCAE are already developing aviation standards. The operational introduction of DFMC GNSS could begin in the 2025-2028 timeframe.

Under EUROCONTROL’s leadership, ICAO’s Navigation Systems Panel has developed a concept of operations (CONOPS) for DFMC GNSS as a vehicle to promote consensus among stakeholders on how it will be used in aviation.

The aim is for DMFC to be introduced in the most cost-efficient way and to deliver operational benefits while overcoming technical, operational, political and institutional challenges.

The long-term goal is for all States to accept all GNSS elements that have been standardised by ICAO for lateral navigation.

The challenge facing ICAO, States and aviation stakeholders in the medium-term is to address individual States’ requirements for the use of specific GNSS elements, while simultaneously limiting the complexity of DFMC equipment and - most importantly for airspace users - ensuring backward compatibility for existing equipment.

We are working within ICAO because having an interoperable solution worldwide is a must. Today, GNSS is based on one constellation and one frequency: GPS L1. This is a very simple solution and it works. But if for some reason it fails or is not available, it could have a significant impact on capacity. We want to improve GNSS’s overall robustness and performance. We want to reduce risks and bring operational benefits to users, but without making GNSS too complex or too expensive,” points out Paco Salabert from the Navigation Unit at EUROCONTROL.

The big challenge has been to satisfy all stakeholders. We have been facilitating an agreement among different States’ interests, while respecting the interests of both airlines and industry,” explains Ken Ashton who has been working for EUROCONTROL on the CONOPS.

The next steps

ICAO will present a working paper at the 13th Air Navigation Conference (held from 9 to 19 October 2018). It will summarise the main outcomes of the DFMC CONOPS and make several recommendations on the way forward. 

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