Technical Provisions for Mode S Services and Extended Squitter

Appendix CD CD-31
CD.4 IMPLEMENTATION GUIDELINES FOR EXTENDED SQUITTER GROUND SYSTEMS
CD.4.1 INTRODUCTION
The provisions presented within the following subsections are focused on requirements applicable to specific classes of
airborne and ground transmitting systems that support the applications of ADS-B, TIS-B and ADS-R. Airborne systems
transmit ADS-B messages. Ground stations may transmit extended squitter messages containing TIS-B and/or the
rebroadcast of ADS-B information (referred to as ADS-Rebroadcast or ADS-R). TIS-B uses surveillance data received
by a non-ADS-B source (e.g. SSR). ADS-R uses ADS-B information received via other than an extended squitter ADS-B
link, to generate and transmit messages, via the extended squitter link, that convey essentially the same information as
included in ADS-B messages.
C4D.4.2 SIGNAL-IN-SPACE CHARACTERISTICS
Ground stations supporting TIS-B and/or ADS-R transmit on 1 090 MHz with the same signal-in-space characteristics as
defined in Annex 10, Volume IV, Chapter 3 for replies from Mode S transponders, with the exception that only the long
format containing 112 information bits are used.
CD.4.3 DATA STRUCTURES
Ground stations supporting TIS-B and/or ADS-R transmit using the same data structure as defined in Annex 10,
Volume IV, Chapter 3 for Mode S replies containing 112 information bits transmitted by Mode S transponders. This
includes the requirements defined under 3.1.2.3.1 for data encoding, under 3.1.2.3.2 and 3.1.2.8.7 for the format of
Mode S replies with DF=18, and the requirements defined under 3.1.2.3.3 for error protection of Mode S replies.
CD.4.4 GROUND STATION TRANSMISSION CHARACTERISTICS
Ground stations supporting TIS-B and/or ADS-R use an extended squitter transmission capability. The characteristics of
such ground stations, in terms of transmitter power, antenna gain, transmission rates, etc., are tailored to provide the
required performance of the service over the desired TIS-B/ADS-R service volume of the specific ground station,
assuming that airborne users are equipped with (at least) Class A1 receiving systems as defined in Annex 10, Volume
IV, Chapter 5.
Specifically:
DRAFT - Working Paper ASP TSGWP11-01 for review by the TSG during the meeting in June 2011 in Paris
Draft
a. The minimum trigger threshold level (MTL) of a class A1 airborne receiver is specified as –79 dBm (as listed in
Annex 10, Volume IV, Chapter 5). When moderate to high levels of interference are expected to exist within the
defined TIS-B/ADS-R service volume, increased ground station Effective Isotropic Radiated Power (EIRP) levels
and/or increased transmission rates may be necessary to overcome the degraded reception performance (i.e. by
the airborne receiver) caused by the interfering signals. The following example shows the maximum ground-to-air
line-of-sight range that can reliably be supported versus the ground station’s EIRP for the case of a class A1
equipped airborne receiver operating in an environment with a very low level of interference on the 1 090 MHz
channel. This represents the minimum EIRP that should be considered and provision of a higher EIRP may be
necessary in order to provide RF link margin to accommodate less than ideal performance from the airborne or
ground installation. The combination of the ground station’s transmitter power, cable losses and antenna
gain/pattern are selected such that the EIRP from the ground station is sufficient to ensure that when a class A1
equipped aircraft is located at the extreme edge of the TIS-B/ADS-R service volume (e.g. at the maximum range
from the ground station), the received signal strength will be at –79 dBm or greater.
DRAFT - Working Paper ASP TSGWP11-01 for review by the TSG during the meeting in June 2011 in Paris