FINAL REPORT - Stakeholders - Ofcom

longer term, there may be a requirement to provide air-ground applications so as to
provide enhanced accuracy position data.
The main opportunity is for ADS-B to support new air traffic control applications which
require air to air surveillance. Many new applications are being developed and validated
and there is operator pressure to introduce an initial batch known as “Package 1”. It is
expected that ADS-B in core European regions will initially be supported by 1090 ES
since the transponders will be in place because of the Mode S mandate (noting that
further adaptation of the transponders will be needed to support ADS-B applications).
Hence there is a marginal cost business case driving this choice but it will be important to
ensure that the required applications still operate under levels of increased interference.
However, from the spectrum utilisation point of view, neither UAT nor 1090 ES are good
choices:
• both systems are based on random transmissions and hence there is inefficient
use of the available spectrum;
• 1090ES operates in a crowded band and there is the expectation that medium
and long range air to air applications will not be capable of being supported.
The third candidate, VDL Mode 4, has the advantage of using an organised channel
access scheme and hence appears to be a much more efficient user of spectrum. For
example, a recent EUROCONTROL study showed that ADS-B requirements could be fully
met at short, medium and long range for representative traffic levels on four 25 kHz VHF
channels. This compares to rather limited performance for 1090ES operating within
1MHz of spectrum. The drawbacks of VDL Mode 4 include its need to operate in the
already congested VHF spectrum, the additional cost of fitting VDL Mode 4 transponders
and a general lack of industry consensus on the business case for VDL Mode 4.
3.3.9 Allocation Sharing Opportunities
There are not likely to be further technologies allocated to the 1030/1090MHz frequency
pair, due to the RF interference levels in-band, allied to the criticality of the applications
supported by the band.
However, the military are pressing for increased bandwidth allocation, in particular for
communications and identification systems such as JTIDS. DAP has granted the military
use of the 960-1215MHz on a secondary basis – although military needs must be taken
into account, the 1030MHz and 1090MHz frequencies should be protected from any
interference from these systems due to their relative criticality.
3.3.10 Possible Overall Spectrum Efficiency Improvements
The various technologies presented in this section are summarised in the following table:
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