FINAL REPORT - Stakeholders - Ofcom

efficient solution (this relates both to the data rate achievable in en-route and terminal
point to point scenarios and the need to use 25 kHz guard channels).
5.6.5 VHF voice: reducing long term spectrum requirements for voice
The introduction of 8.33 kHz channel spacing will alleviate current congestion. The
transfer of some voice services, such as ATIS, to data will also free up a small number of
voice channels. In the longer term, it can be expected that most other ATS
communication will be transferred to data. This development will lower the utilisation of
each voice channel such that the case for maintaining a single voice channel per sector
will become increasingly unattractive from the point of view of spectrum utilisation.
Furthermore, as the demand for data communication increases, voice spectrum will come
under increasing pressure for re-allocation to data services.
The study team is unaware of studies into the re-organisation of spectrum once there has
been significant movement to data services. However, it appears appropriate to
investigate now how such a re-organisation could take place.
A number of items for consideration are set out below.
5.6.5.1 Investigate long term channel utilisation
As described above, in current operations a very large cell size is required on account of
the need for party-line communication in large sectors. The utilisation of a single channel
reaches a typical maximum of 10-20% (meaning that the channel is being used for
communication 10-20% of the time and unused during the rest of the time) [ICAO Doc
9718]. However, although the channel is not particularly highly used, from the point of
view of the control process, communication is a regular event and essential to the control
process. Hence many channels are required to serve the large number of sectors in UK
airspace.
Contrast this with the operation of the emergency channel. Utilisation is very low,
presumably so low that the probability of two aircraft using it at the same time is very
small. In this case, a single frequency is used for the whole of the UK using offset carrier
techniques.
The transfer of ATS communication to data will result in a reducing channel utilisation
such that, at some point, it might become feasible to serve a number of sectors with the
same channel. The point at which such a development becomes acceptable to controllers
and the safety regulator requires further investigation. If it is possible to amalgamate
channels in this way, it becomes possible to derive a strategy for the introduction of data,
accompanied by an ongoing consolidation of voice allocations.
The study team is unaware of any studies of the utilisation of channels although it is
understood that CAA are about to carry out a study on utilisation in terms of how
effectively channels are planned against each other.
5.6.5.2 Investigate introduction of digital voice
An alternative strategy for voice in the longer term is to introduce digital voice. From the
point of view of efficient spectrum utilisation a system based on a commercial standard
which allows for trunking of voice calls seems the most attractive, since the provisioning
of channel allocation can simply be scaled according to need. In such a system, a
controller could maintain near immediate access to a particular aircraft. The need for
maintenance of a party line with a group of other aircraft could also be investigated.
The introduction of digital voice burdens operators with an additional system with which to
equip and hence such a solution is unlikely to be attractive in the short or medium term.
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