FINAL REPORT - Stakeholders - Ofcom

Parameter Value Notes
Service topology Point-to-point This is a Mode S Specific Service.
Data collection is optimised thanks to an asynchronous
mechanism: on the air side, data extracted from the avionics
busses are periodically polled to refresh dedicated Mode S
transponder’s memory register. On the ground side, data
extraction through the Mode S link is initiated when required
according to ground users’ requests.
Aircraft data allocation to the transponder’s memory is predetermined/standardised
by ICAO doc 9688.
The retained parameters for initial implementation of Mode S
enhanced surveillance in Europe are the following:
1) For CAP D/L service: Magnetic Heading, IAS/Mach nr
2) For CAP & SAP: Selected Altitude
3) For SAP: Vertical Rate, Track Angle Rate, Roll Angle,
Ground Speed, True Track Angle
These data fit into 2 Mode S GICB registers (BDS 50/60).
Wind vector, as required by ODIAC/CAP, would require a
third register to be extracted (BDS 44)
For Mode S Specific Protocol (MSP):
Limited addressing at the application level with 63 channels
available. Non-connected mode, no flow-control mechanism.
ATN compliance No
Frequency band 1030, 1090
MHz
RF Channels Two distinct
channel
Modulation
scheme
DPSK and
PPM
Bit rate Uplink: 4 Mb/s
Downlink: 1
Mb/s
Channel access
method
Frequency
availability
(allocation
status)
Managed via
Mode S
interrogation
scheduling
Frequencies
available.
1030 MHz for uplink transponder interrogations
1090 MHz for downlink replies
Uplink: Differential Phase Shift Keying (DPSK)
Downlink: Pulse Position Modulation (PPM)
Note: Data transfer is only available during the beam dwell;
hence effective data rate for a 6 second rotation is
approximately 600 bps.
Access is managed according to air situation (in order to
reduce interference/FRUIT) and user demand for GICB
transactions.
Global allocation of 1090/1030 MHz to SSR and Mode S
systems
1030/1090 RF channels are also used by: classical SSR
Surveillance, Mode S elementary surveillance, Mode S
squitter & ACAS, Mode S extended squitter, and other Mode
S data services described above. Mode S elementary
surveillance is a pre-requisite for Mode S datalink; It can be
anticipated that the available bandwidth in the antenna’s
beam for a given aircraft will be shared between Mode S
Enhanced Surveillance and SVC/MSP. However, the impact
of the deployment of Mode S Enhanced surveillance on
critical systems/services like Mode S elementary
surveillance, ACAS II and 1090ES/ADS-B/TIS-B/ASAS are to
be assessed. Also used by military IFF system.
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