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Migration strategy to a future VHF communications system


Several reports have been issued in the frame of this study covering the following aspects:
- An overview of the current VHF band usage: the analysis of the effect of the various type of communication services on the spectrum congestion showing that the upper airspace ATC control sector services contribute the most to the spectrum congestion.
- A review of the work undertaken at the international level (ICAO or other standardisation bodies) concerning the evolution of the VHF band.
- The study of possible scenarios of transition from 25 kHz channel spacing to 8.33 kHz channel spacing leading to the following conclusions:

- the use of a dedicated sub-band to introduce the 8.33 kHz channel spacing is the best scenario
- the transition plan could only be established in close consultation with all the partners (service provider/State, aircraft operators)
OM - the introduction of 8.33 kHz channel spacing must be limited to the congested areas (upper airspace of the core area of Europe)
- the introduction of 8.33 kHz channel spacing will be done on an exclusive basis, that is to say that only aircraft equipped could operate in the 8.33 kHz airspace
- the various constraints must be carefully handled (technical constraints, operational constraints, economic constraints and time-scale constraints).

- The analysis of the effect of the introduction of 8.33 kHz channel spacing on the future spectrum needs to satisfy voice and data communication demands. This results in the identification of three sub-bands to cover:

- the need to support voice communication using 25 kHz channels
- the need to support voice communication using 8.33 kHz channels
- the need to support data communication using 25 kHz channels
- the need to ensure sufficient spare capacity for possible introduction of a future VHF digital system by 2008/2010.

- The wide-spread use of VHF datalink (VDL) to provide ATS communications will make it imperative to move to a system which makes efficient use of channels assigned to it while also providing a realistic transition path. The transition to VDL from ACARS VHF will provide more efficient use of each VHF channel and hence reduce the number of frequency channels and ground stations required to transport the same overall load of user data. The implementation of VDL cannot take place in isolation since it will be necessary to develop ATN processing in the avionics and a Datalink Service Processor (DSP) at each side of the VDL system. The transition from ACARS VHF to VDL is essential to justify the implementation of the ATN internetwork protocol. - The use of VHF datalink for Controller Pilot Datalink Communications will
require the development of computer systems to process the messages. This separation should allow the ATC process to move to using more strategic approach than a tactical approach requiring immediate action. The use of datalink will reduce pilot workload and provide a more accurate presentation of the information in the cockpit, in particular when providing Flight Information Services or ATIS. The first ATN/VDL ground stations are currently being deployed and the first ATN/VDL avionics are planned to be installed on board an air transport by the end of 1995. It is impossible to predict how soon such avionics will be installed systematically on newly delivered aircraft but this should hopefully be the case by 2000. The extent to which VHF datalink could be used for Automatic Dependent Surveillance (ADS) is difficult to judge since ADS has not yet been introduced in areas where VHF datalink coverage is available. There is no overall set of ATS requirements that a VHF datalink system must meet. There are many ATS services and a specific set of requirements will need to be identified for each new service to be provided using VHF datalink and the capacity of the VHF datalink system may need to be increased to meet them. Up to 2005, the VHF datalink will be the only candidate datalink for the support of many ATS services in continental areas. In that timeframe the decision on whether to provide an ATS service using VHF datalink will, in fact, be a decision on whether to provide that ATS service using any datalink.
- In the future CNS/ATM system, VHF low-speed datalink and a number of voice communications will be replaced by VHF high-speed datalinks handling all routine aeronautical communications among aircraft and providers of air traffic services. Various datalinks are being developed, and it is acknowledged that none can meet on its own the CNS/ATM requirements, and that these different types of datalinks will have to be implemented and operated simultaneously. Besides surveillance function, Mode S technology can be used to convey messages at a low cost when no real-time requirement is asked. VDL must be used for urgent operational data exchanges. Because of the high cost of its hardware satellite equipment, the AMSS sub-network shall be bounded to areas where ground facilities line of sight cannot be possible such as oceanic regions. A low-cost alternative to AMSS could be the HF technology. The overall economic gain expected from the CNS/ATM system is to enable efficient, safe and cost-effective interoperability between the various air-ground and ground-ground datalinks that will be used for ATC. A back up voice capability will be retained for non-routine (e.g. tactical controller instructions) or emergency situations. This voice capability should be segregated from the VHF datalink system rather than integrated with it in order to achieve the required availability and safety. Regardless of the technical aspects, datalink will change existing procedures both for controllers and pilots and will lead them to perform their duties differently from today. The specification and development of any new VHF data communications system must take into account evolution of the operational procedures to ensure a safe and efficient transition.
VHF voice communication is the safety-critical medium supporting all operational ATC dialogues between controllers and pilots, for both commercial airliners and general aviation. Current pilot/controller communications in the VHF frequency band (118-137 MHz) use radios providing analogue modulation of voice on a set of 25 kHz spaced VHF channels. The need to provide the appropriate number of channels to support pilot/controller communication demand leads to the introduction of a new channel spacing at 8.33 kHz. This system is essentially keeping the basic functionality of the current 25 kHz system. The only data communication system currently available in the VHF band uses the Aircraft Communication Addressing and Reporting System (ACARS) protocol which was originally developed for airlines, and relies on the same analogue radios as for 25 kHz voice.

From this starting point, the three global objectives addressed by the NEWCOM study were:
- provision of a transition scenario for voice communication, from the current 25 kHz to the new 8.33 kHz channel spacing, to alleviate the VHF congestion constraint
- provision of the introduction scenario for VHF data communication based upon the ICAO system definition in the context of the Aeronautical Telecommunications Network (ATN)
- definition of the European strategy for using the VHF band from 1995 to 2010 and development of a R&D programme to support its implementation.

Exploitation potential

The results of this study provide:
- a contribution to the ICAO European region concerning the scenario for the introduction of the new 8.33 kHz channel spacing to alleviate VHF congestion in the short term, without sacrificing more ambitious longer term objectives
- a contribution to the ICAO Aeronautical Mobile Communication Panel (AMCP) concerning the introduction of data communication in Europe and concerning the future system objectives and requirements associated with the European region
- a contribution to Eurocontrol activities within the EATCHIP framework to identify a European-wide outline implementation plan for the first steps of the migration to the new system.


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Carrefour de Weiden 3
92441 Issy-les-Moulineaux

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