FINAL REPORT - Stakeholders - Ofcom

Parameter Value Notes
Modulation scheme D8PSK D8PSK at 10.5 symbols/s
Bit rate 31.5 kbits per second
Channel access
method
Frequency availability
(allocation status)
p-persistence CSMA-CD Carrier Sense Multiple Access with Collision Detection
Currently only the CSC
(136.975 MHz) is
dedicated to VDL-2.
Expected that 4
frequencies will be
dedicated to VDL-2
(136.975, 136.925,
136.875, and 136.825).
Dependencies Airborne VDR supporting
VDL2 frame
transmission.
Ground VHF Data Radio
stations deployed by the
Air/ground
communication service
provider.
Table 5- 3 Characteristics of VDL Mode 2
This band is completely saturated in the western part of
Europe making the allocation of channels difficult in the
near future.
Some services used locally by some airports or ACCs
shall be moved from the 136.7MHz, 136.725 MHz and
136.750 MHz frequencies (in France, Germany,
Sweden, Italy).
SITA is granted licences for Amsterdam and CDG
airports on the CSC frequency.
Avionics implementation is specific: the physical and
MAC layer are implemented in the radio (VDR) while
the other layers (LME and above) are implemented in
the CMU/ATSU hosting all the communication stacks
(ATN router and application services).
5.6.4.1 Impact of VDL2 on spectrum efficiency
The replacement of ACARS by VDL Mode 2 is expected to provide a 10-fold increase in
spectrum utilisation from an ACARS baseline of typically 300bps. Simulations are ongoing
in EUROCONTROL to demonstrate the data capacity of a VDL Mode 2 channel.
There is also potential for the move of voice services to data, beginning with VDL2. The
obvious first choice of service is to move ATIS to digital since these are uplink broadcast
services which can make best use of the relatively high bit rate of VDL2 whilst having
lower vulnerability to message loss as a result of interfering transmissions from other
stations. Such a move would be spectrum efficient and could be accompanied by a
parallel decrease in the number of analogue voice channels allocated to ATIS.
A further stage of interest is the transfer of controller pilot dialogue as described above.
This is primarily of interest as a proving ground and is judged unlikely to offer a long term
solution. The reasons for this judgement include:
• VDL2 employs a random access mechanism with little protection against
overload and no priority mechanism;
• it is therefore unsuited to tactical controller/pilot dialogue and hence only a
fraction of controller/pilot dialogues could be transferred;
• hence there would be little or no impact on the requirements for voice channels
since a channel will still have to be reserved per sector.
Furthermore, issues relating to the data rate of VDL 2 for en-route and terminal area
airspace scenarios have been raised indicating that VDL2 may not be a particularly
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