Within its strategic research agenda, ACARE (Advisory Council for Aeronautical Research in Europe) indicates that powerful communication is a key enabling factor for future Air-Traffic Management (ATM) development in Europe, which is required to support the expected sustainable growth of European air transport.
However, there exist bottlenecks in Air Traffic Control (ATC) and ATM communication today. Moreover, the expected ATM paradigm shift towards more strategic and tactical planning requires additional communication capabilities which are not yet available in current ATC/ATM communication systems.
Currently there are several European research initiatives underway aimed at developing improved communication technologies for aeronautical communication. These initiatives comprise ground-based, satellite-based, aircraft-to-aircraft and airport communication for all different application classes, like ATC/ATM communication, airline operational and administrative communication, and aeronautical passenger communication. However, so far there has not been an initiative aimed at integrating existing and emerging communication technologies into a global approach. NEWSKY is designed to fill this gap.
The main goal of NEWSKY is to integrate all of the different communication technologies and different application classes into a global heterogeneous airborne network with appropriate priority properties.
NEWSKY aims to bring about improved communication capabilities and assists the expected ATM paradigm shift. Real air-ground integration has been achieved with NEWSKY and the information sharing concepts of collaborative decision-making (CDM) and System-Wide Information Management (SWIM) have been made available to the aircraft. As a consequence, the NEWSKY approach assists the realisation of the Single European Sky concept and helps to create a future European ATM system which is viable well beyond 2020.
NEWSKY will make possible, by 2020 and beyond, an innovative ATM network-enabled vision for which there already is an urgent need. Increases in current air-traffic movements and forecasts for the next 10 to 20 years reinforce the vital requirement for a fresh ATM perspective: an ATM transformation philosophy which includes new networking concepts, new ATM elements and new ATM operational concepts.
The 'networking the sky' concept of NEWSKY does not aim to develop new link technologies. Instead NEWSKY aims to develop an innovative networking concept to integrate different existing and emerging link technologies into a single, global ATM network for a secure, seamless and robustly redundant ATM system, which is also scalable to cope with future long-term increasing demands.
To achieve this objective, NEWSKY started by defining the requirements of this approach without restricting its view to current constraints. Secondly, an understanding of ATM particularities and constraints has been be developed, in order to define in a feasible way the network transformation required by NEWSKY, and how to implement it efficiently and on time.
Co-operation opportunities with related projects and initiatives have been identified and interactions have been defined to achieve synergy for future ATM research. Relevant initiatives and projects include SES initiative, SESAR, CASCADE, Nex-SAT, ATENAA, and B-VHF.
The NEWSKY objectives do not compete with other ATM initiatives; rather NEWSKY aims to mutually benefit from other related activities by efficiently disseminating and exchanging achievements from both sides.
Once the framework to enable ATM network transformation had been agreed on, the basic NEWSKY architecture was defined. Next, innovative networking concepts were developed, assessed, tested and validated by means of software simulations and limited laboratory trials.
The results of the simulations and the results of the test-bed trials have been analysed and recommendations have been derived. Furthermore, the NEWSKY system requirements were tracked and their fulfilment was verified, by design inspection and/or through the simulations and test-bed trials.
The assessment of the NEWSKY simulations results and tests showed that the NEWSKY system design does fulfil the identified requirements. No significant discrepancies have been identified.
The results of each simulation scenario have been analysed, addressing the topics of mobility, handover, link assignment, load balancing, traffic management, Quality of Service and transport layer adaptation. The major conclusions from the simulations are:
- Make-before-break handover:
The assessment of the simulation based evaluation of the NEWSKY system showed that IEEE 802.21 Media Independent Handover (MIH) functionality provides a significant improvement of the handover latency values, which additionally reduces the packet loss rate. In addition the periodic Router Advertisement (RA) message transmission interval can be decreased so that the RA transmission overhead in the wireless link becomes negligible. Further improvements towards true seamless handovers are expected by using multihoming protocols.
- Node based vs. network based mobility:
The benefits of the combination of PMIPv6 with MIPv6/NEMO over stand-alone MIPv6/NEMO are uncertain in the aeronautical domain. Stand-alone MIPv6/NEMO allows the use of multicast router advertisements (RA). Although assigning a common prefix to all mobiles is a non-standard deployment, this approach allows for a significant reduction of signalling traffic on the wireless link. PMIPv6 on the other side requires sending addressed RAs to each mobile router. This has the consequence that the load of the wireless link may be significantly increased in highly populated radio cells.
A benefit of PMIPv6 is that the MIPv6/NEMO tunnel is not required in the home domain. This result in small performance gains and a reduction of the wireless link load. However, this benefit is only given in the home domain and may be diminished by header compression.
- NEMO Route Optimization:
It has been shown that Global HAHA as Route Optimization approach can provide a significant reduction in end-to-end latency where inter-continental round-trip times are usually incurred. For intra-continental situations the advantages of Global HAHA i
The NEWSKY test-bed has demonstrated that the selected protocols (MIPv6 with NEMO extensions) are indeed capable of providing session continuity during handovers for ATS, AOC and APC applications:
- Session continuity for ATS and AOC FTP traffic (i.e. weather map download) has been demonstrated. The results of the test-bed trials indicate that most ATS and AOC applications (i.e. short COCR message exchanges) are not negatively affected by handovers.
- The TCP-based file transfer (e.g. weather map download) showed that the interruption of bulk TCP transfers by handovers may cause problems although session continuity is kept. The delay induced by the falsely triggered TCP congestion avoidance mechanisms is in the order of several seconds and the TCP connection may need a considerable amount of time (in the order of tens of seconds) to recover.
- Regarding the handover delay as seen by the IP layer without enhancement mechanisms such as IEEE 802.21 and/or multihoming, the test bed measurements indicate that 10s are to be the expected value when a handover between terrestrial link and satellite link takes place. This does not allow the use of time-critical ATS applications. However, for AOC and all other data applications the impact is acceptable.
- For UDP/VoIP the handover delay is lower (1.5s - 3.5s) and has to be compared to today’s situation when HF voice is being used. In this context this value seems to be acceptable. Of course, in addition, no manual operation is needed to perform the handover, which also reduces the risk of bad operations that would take time to detect and correct.
The NEWSKY results have been input to the following standardisation bodies:
- Strong involvement in ICAO ACP WG-I with 9 working paper contributions. WG-I has developed a technical manual and guidance material for the IPS (Internet Protocol Suite) based ATN, the main reference document being ICAO Doc 9896 ‘Manual for the ATN using IPS Standards and Protocols’;
- Involvement in AEEC NIS (Network Infrastructure and Security) with contributions to the MAGIC (Manager of Air-Ground Interface Communications) technical WG;
- Involvement in IETF MEXT WG (Mobility EXTensions for IPv6) with preparation of drafts and contributions to the mailing list.
The exploitable results of NEWSKY are the design, system architecture and initial validation through simulations and test-bed trials of an aeronautical telecommunication network based on IPv6 and integrating satellite and terrestrial data links.
The NEWSKY Consortium has contributed to the major standardisation activities. The project results will be used in follow-up activities pushing the technologies to higher technology readiness levels in SESAR JU and the FP7 project SANDRA.