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Operational Use
Although many large aircraft are equipped with a minimum Mode S capability, this does
not include the Extended Squitter function. A very small number of commercial aircraft
have already been upgraded to transmit extended squitter. British Airways have six such
aircraft.
Parameter Value Notes
Service topology Air-ground
datalink, Air-air
broadcast,
Uplink
broadcast,
Downlink
broadcast
ATN compliance No
1090 MHz Extended Squitter includes a ‘crosslink’ for ACAS, which
is a simple data link
Frequency band 1090 MHz Complementary uplink broadcast service could be provided at 1030
MHz.
RF Channels Single. One channel at 1090 MHz provides air-air, air-ground and groundair
broadcast services.
Modulation
scheme
PPM Pulse Position Modulation
Bit rate 1 Megabit/sec
Channel access
method
Frequency
availability
(allocation status)
Random
Frequencies
already
allocated and
available.
Mode S operates on 1030 MHz and 1090 MHz. International
spectrum allocation of the required 3 MHz channel exists. No further
actions are required to secure suitable frequencies.
Dependencies No Not dependent upon the deployment of other technologies.
May impact on other systems operating at the same frequency –
ACAS and SSR (Mode A/C and Mode S)
Other issues Security issues and potential vulnerabilities still to be assessed by
the aeronautical community.
Table 3-9: 1090ES summary
3.3.8 Replacement Technologies (radio, other or none)
3.3.8.1 Introduction
The possible introduction of competing ADS-B datalinks on other bands (e.g. VDL Mode 4
in the VHF band; UAT probably at 978MHz) may reduce the reliance on 1090MHz
Extended Squitter datalink, thus freeing up some of the channel. This introduction will
depend on the uptake of ADS-B in Europe, in particular the airlines’ view of the benefits
accrued.
The uptake of ADS-B also depends on airline and ANSP economics. Economies of scale
have meant that 1090ES is the preferred solution for the short-medium term (with aircraft
already mandated to equip with Mode S transponders). VDL Mode 4 is a viable
alternative, but requires a separate on-board transponder.
VDL Mode 4 also provides a point to point communication service – details are given in
section 4. Details on UAT are given below.
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