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6.8.9 Possible Overall Spectrum Efficiency Improvements
The introduction of 12.5 kHz channel spacing would considerably increase spectrum
efficiency. It will of course not double frequency use, because it is on the one hand
unrealistic to believe that the entire maritime VHF spectrum will be used on a 12.5 kHz
basis and because on the other hand the reduction in the channel width with the ensuing
reduction in frequency deviation will result in a degradation of the overall system
performance. However, there will be a satisfactory net result in frequency efficiency. For
additional information concerning a move from 25 kHz to 12.5 kHz channel spacing see
section 6.12.7.
The implementation of digital technology will result in a much better frequency efficiency,
which cannot, however, be quantified at this point in time because the system
characteristics are not yet known.
6.8.10 Re-arranging the Frequency Spectrum of Appendix 18 to the Radio
Regulations and Releasing Part of it for Other Applications
The following concept for re-arranging the use of the Appendix 18 channels and using the
remainder together with part of the frequencies available for VHF private maritime
communications was considered by the Consultant based on the following assumptions:
a) There is no need to maintain maritime VHF public correspondence channels
due to the non-availability of commercial services and the availability in
many coastal areas of alternative communication means (e.g. GSM).
b) For a similar reason mirroring the situation with UK PBR licences, the need
for private maritime VHF communications would decrease over time
resulting in a reduced need to continue to provide as many frequencies as
are now available for this purpose.
c) There is increasing simplex and decreasing duplex use.
d) The channel spacing is 12.5 kHz, thus doubling the number of available
channels, with technical parameters as specified in Recommendation ITU-R
M. 1084.
e) The service requirements, except for public correspondence, of the current
Appendix 18 are met.
f) The re-arrangement does not prejudice a later transition to digital
technology.
g) Any implementation of the concept would require coordination with
neighbouring countries.
h) The use of split channels could be considered in accordance with ITU WRC-
2000 revisions to Appendix 18.
It may therefore have been feasible as an interim step prior to an all digital solution to
take account of the demise of public correspondence and relocate users from the lower
part of the international band to the upper part and at the same time implement 12.5 kHz
spacing, initially in a block of channels between 156.075 and 156.275 MHz. The following
bands would then have remained available for international maritime use as contained in
Appendix 18 of the Radio Regulations, but without public correspondence:
• Circa 156-156.9 MHz for DSC for distress, safety and calling, for inter-ship, for
single- and two-frequency port operations and ship movement;
• Circa 160.6-160.975 MHz inter-ship, single- and two-frequency port operations
and ship movement paired with the band 156-156.9 MHz, as applicable, with a
duplex spacing of 4.6 MHz;
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