CNS (Communication, Navigation, Surveillance) Technology in SESAR

It could be easy for a casual observer to believe that the SESAR programme does not provide adequately for the development of CNS systems and technologies.

 

 

It is true that a fundamental principle in the SESAR approach is that all technology developments should deliver a capability which is directly derived from operational requirements and support the delivery of a performance benefit to the overall system.  In the past many people believe we have been guilty, in the CNS community, of developing technical systems first, and then wonder which problems they could solve.This does not however lead to the sidelining of CNS developments in SESAR, in fact the CNS infrastructure we are targeting will need to be more capable, and importantly, more flexible than ever to ensure that technical constraints do not limit the development of advanced procedures and applications. The activities in CNS constitute a significant level of investment within the SESAR programme.

It is important to recognise the iterative nature of this process, while technical constraints must of course set limits for some of the conceptual thinking, we must also allow the ‘did you know we could do this’ kind of feedback to those with the job of envisaging the future concept.Deploying new CNS technologies that reduce cost and provide the improved capabilities for new concepts is therefore at the very core of the SESAR programme. Equally important is to take into account legacy CNS systems as the approach evolves, while new developments are based on developments from other domains or contain COTS components, in order to move away from bespoke CNS solutions for ATM.

Communications

The future SESAR ATM concept demands datalink services supporting features such as 4D trajectory management, ASAS separation, automation, and SWIM. A reliable and efficient communication infrastructure will have to serve all airspace users in all types of airspace and phases of flight, providing the appropriate Quality of Service needed by the most demanding applications.  The mobile part of this infrastructure will be based on a multilink approach, composed of three different subnetworks:

  • A ground-based line of sight datalink as the main system in continental airspace and supporting Air/Ground services and possibly Air/Air services, offering a high Quality of Service which will be necessary in the high density areas; two systems are under consideration (LDACS 1and 2) with the objective to select one for implementation. Both operate in the L Band and are based on modern and efficient protocols;
  • A satellite based system providing the required capacity and Quality of Service to serve oceanic airspace whilst complementing ground-based continental datalink as a way of improving the total availability. The system is being defined in close cooperation with the European Space Agency. The type of satellite constellation to be used (dedicated or commercial) is still under consideration;
  • A system dedicated to airport operations, based on standards similar to WiFi, providing a broadband capacity to support the exchanges of a significant amount of information such as the uploading of databases or maps in the aircraft.

In addition, and to allow in the medium term interoperability with Military operations, a gateway is being defined to interconnect the ATM system and the military Link 16 system.

Navigation

Navigation system developments in SESAR are predominantly focussed on the evolution of GNSS-based navigation technologies which will be developed to fulfil navigation performance supporting RNP based operations as defined and validated in the operational projects of the programme.

The SESAR work programme integrates operational projects, which define new PBN procedures and concepts, with the technical projects, which develop the Navigation tools and systems according to the operational needs, which are validated by the operational projects.For the underlying navigation sensor and system developments SESAR projects aim to define the medium and long term GNSS baseline including the expected configuration of constellations, signals & augmentation systems (SBAS and ABAS) and complemented by classical navaids. This will drive the further developments within the programme covering EGNOS evolution from GPS L1 to multi constellation/Signals (GPSL1/L5 + Galileo E1/E5 over e.g. GEOs). Space-based components will also form part of the overall system providing this capability and the scope of the SESAR projects are aimed to complement the ESA European GNSS Evolution Program.

For approach operations, while ILS Cat II/III is expected to remain the main precision approach and landing system for major airports, in the medium term an increased use of GBAS to support precision approach operations is expected. Prototyping and validation of GBAS cat II/III will be progressed (based on GAST D and the GPS L1 SARPs) in a first step while GBAS ground-station supporting multi-frequencies will be defined and validated for meeting the Cat II/III requirements. The airborne architecture of the initial GBAS CAT II/IIII airborne system will also be defined.
The rationalisation of the ground Navaid infrastructure in support of the GNSS based systems must ensure we have a cost-effective, fit for purpose terrestrial back-up capability.

Surveillance

While the evolving role of the Surveillance capability is less obvious than the PBN ‘revolution’ in Navigation and the system wide connectivity driving Communication developments, Surveillance nevertheless continues to be an essential enabler to ATM modernisation.

Increasing traffic densities, pressures on the utilisation of RF spectrum, new modes of separation, including ASAS applications in the cockpit and improved safety nets are placing greater demands on surveillance systems.These needs stimulate the use of new surveillance techniques including ADS-B and Wide Area Multilateration which can deliver improved performance in terms of accuracy, update rate, coverage and are also potentially more efficient from an RF perspective than traditional SSR. Advanced multi-sensor surveillance data fusion can also maximise the use of common airborne components, depending on specific ground system requirements and the operational needs.

SESAR will develop an ADS-B ground-station to include the integration of WAM capability. On the airborne side the ability of 1090MHz ADS-B to continue to work in the ever more congested 1090MHz band is being investigated while the longer term view of a potential new ADS-B system is also planned. Other options in the future could include satellite based solutions and the evolution of the non-cooperative surveillance infrastructure.

The intelligent combination of these different surveillance techniques and the improved sharing of surveillance data will allow a rationalisation of the surveillance infrastructure (especially in terms of multiple overlapping SSR as we have today) which should lower costs and reduce the impact on the 1030/1090 spectrum extending its useful life as traffic increases.ACAS evolution will also take account of new separation modes and the coordination of airborne and ground-based safety nets also drives the development and validation of the ground system capability to receive ACAS alerts to be made available to the ground systems.

The ongoing development of Weather and wake vortex detection capabilities at aerodromes is another key thread within the SESAR surveillance projects to reduce the impact of adverse weather conditions on the ability of an airport to maintain capacity.

Conclusions

The added-value of SESAR, and its complexity, comes from interlinking operational and technical projects. Hence, our developments are no longer made in isolation; they are integrated in a consistent operational concept and architecture. The performance focus of SESAR is certainly the most important cultural change in ATM R&D. This, applied to CNS, will mean trade-offs between technical performance, real users’ requirements, and cost. We expect to move away from ATM specific solutions, in particular in Communications, in order to benefit from state of the art technologies.
CNS should become a much more integrated part of the overall European ATM system enabling performance based operations through the capabilities provided.

Underlying much of these evolutions will be a long term development of the future datalink technologies with a multilink approach to the mobile capability as well as a ground-ground communication infrastructure enabling SWIM between all stakeholders.

More use of Satellite-based Navigation capabilities leads to less reliance on ground infrastructure and therefore greater flexibility for airspace users and the definition of performance driven trajectory based operations delivering direct benefits to the user in terms of cost and environmental impact.
Ultimately the way we think about CNS will change, and the stand-alone nature of CNS that many of us have grown up with will evolve, but it is not that there is a reduced importance of these capabilities in the future system. All of the conceptual steps forward envisaged in the European ATM Masterplan ultimately rely on an ever more adept CNS capability made available to all the users whenever it is needed.

By David Bowen
As Head of ATM Systems, David Bowen provides guidance to the development of the architectural approach and the technical strategic direction of the SESAR programme. He is also responsible for the global coordination of technical issues and standardisation planning in the context of ICAO.