FINAL REPORT - Stakeholders - Ofcom

Parameter Value Notes
Dependencies UTC
synchronisatio
n is required in
ground
stations to
enable time
stamping of
collected
aircraft data
Data in the Mode S transponder’s registers does not include
timestamps
Table 3-8: Mode S summary
3.3.7 Possible New Technologies (in-band)
3.3.7.1 Introduction
New technologies operating on the same frequency include new uses of the same data,
and developments of existing concepts. Multilateration and 1090 Extended Squitter are
two systems likely to be introduced in the next few years.
3.3.7.2 Multilateration
Multilateration is a triangulation technique whereby SSR signals sent from an aircraft are
received at several ground sensors in the vicinity (normally, airport surface). A
measurement is made of the difference of the ‘time-of-arrival’ (TOA) of each signal at
each sensor by a central computer. The time difference of arrival can then be used to
accurately determine the location of the origin of the signal (i.e. aircraft). Three ground
sensors enable a 2-D position to be determined; four or more sensors enable a 3-D
position measurement, as well as greater accuracy in the 2-D position measurement.
3.3.7.3 1090MHz Extended Squitter
The 1090 MHz Extended Squitter (1090 ES) is an extension of Mode S technology. A
number of extended squitters are transmitted at a high rate (five times a second). Each
message consists of 112 bits, 24 bits of which are used for parity. The data rate used is
one megabit per second, within a message. Access to the 1090 MHz channel is
randomised, and the channel is shared with Secondary Surveillance Radar (Mode A/C
and Mode S) and the Airborne Collision Avoidance System (ACAS).
1090 ES provides air-air, air-ground and ground-air broadcast services (i.e. ADS-B –
Automatic Dependent Surveillance- Broadcast and TIS-B - Traffic Information Services -
Broadcast). A complementary uplink broadcast service could be provided at 1030 MHz
i.e. the SSR interrogation frequency.
Numerous simulations have been conducted by the FAA and UK Civil Aviation Authority
to ensure that 1090 ES does not have an adverse effect on the ACAS and SSR. These
simulations show that 1090 ES can operate along side these other systems.
1090 ES enjoys support from the FAA and some European ANSPs. Support in Europe is
considered ‘medium’.
The risk in developing 1090 ES into an operational system is considered low. Certifiable
equipment already exists which is very close to the anticipated final requirements for 1090
ES.
For air-air surveillance 1090 ES could be used in all airspace types. For air-ground
surveillance, 1090 ES requires a relatively high density of ground stations and is therefore
not suitable for oceanic and remote areas.
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