FINAL REPORT - Stakeholders - Ofcom

6.8.5 Possible Improvements to Existing Technology
In recent years the Appendix 18 channels have been severely congested in some regions
of the world. The concept of alleviating the situation through the introduction of innovative
technology has been postulated, with some advocating a reduction in channel spacing to
12.5 kHz whilst others including the United Kingdom suggesting a move to narrow-band
spectrally efficient digital technologies. The ensuing debate was reminiscent of
discussions in the aeronautical sector concerning the move to 8.33 kHz channelling and
whether or not to digitise. In the absence of an international agreement it has been left
that administrations having an urgent need to reduce local congestion may apply 12.5
kHz channel interleaving on a non-interference basis to 25 kHz channels under certain
conditions. The situation is similar to that which prevailed when the channel spacing was
reduced from 50 to 25 kHz some thirty years ago. However with the reduction in public
correspondence traffic and the use of GSM in coastal areas, congestion may now have
reduced to an acceptable level and other factors may now require consideration. It should
be borne in mind in this connection that the United Kingdom no longer operates VHF
coast stations open for public correspondence.
Recommendation ITU-R M.1084 provides interim solutions for improved efficiency in the
use of the band 156-174 MHz by stations in the maritime mobile service. It offers a
number of alternative solutions to go from the present 25 kHz channel spacing to 12.5,
6.25 and 5 kHz channels. In view of the fact that more modern systems are being studied
in ITU-R with preliminary results already available, it is suggested that the interim method
chosen, if required for reasons of congestion, should in no way prejudice the
implementation of the longer term solution resulting from the on-going studies which may
result in the use of advanced technologies and channel spacing other than 12.5 kHz. In
summary, if required, an interim system with interleaved narrow-band channels at 12.5
kHz offset spacing using conventional FM technology with characteristics as specified in
Annex 3 of Recommendation ITU-R M.1084 may be implemented.
However, it would be preferential to wait for a more advanced digital system as outlined in
Section 6.8.6.
6.8.6 Possible New Technologies (in-band)
The long-term requirement within the international community is for an advanced
spectrally efficient digital system to provide improved efficiency in the use of the band
156-174 MHz. Digital technologies offer a variety of advantages in terms of frequency
efficiency, quality of service and equipment costs. The great success of GSM would have
never been possible in an analogue environment. The dramatic decrease of equipment
price has only been possible with digital technologies. It is therefore obvious that the
maritime service should also benefit from this technological development.
The transition to digital technologies must be implemented in such a way that distress and
safety communications in the maritime VHF band are not disrupted and that the new
system is able to co-exist with existing equipment. Transition from the present FM system
to a fully digital system will pose serious problems in maintaining the required grade of
service because the systems are completely incompatible with each other as opposed to
a transition within an FM system with a reduction of channel spacing. In particular, the
availability of all functions of the GMDSS must be guaranteed without any disruption. The
transition will therefore only be a gradual one with long periods of operational overlap.
Studies on digital maritime VHF systems are underway in ITU-R; partial answers can be
found in Recommendation ITU-R M.1312. They are not yet that advanced that any
recommendation in the context of this study can be given on possible system
characteristics. In particular, further study is required into the question of whether the
future digital system should be a narrow-band system with e.g. 8.33 kHz channel spacing
or a TDMA system with a given number of traffic channels per RF carrier similar to GSM
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