Home' RTCA Documents for Review : DO-343B Contents Appendix C
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APPENDIX C: INTERFERENCE ANALYSIS FOR INTERACTION BETWEEN INMARSAT
EQUIPPED AND IRIDIUM EQUIPPED AIRCRAFT OPERATING IN THE SAME AIRSPACE
Inmarsat and Iridium satellite communication systems are both approved for FANS1/A
operations in oceanic airspace. A 2008 analysis  presented to ICAO Aeronautical
Communication Panel (ACP) Working Group M indicated that the probability of Inmarsat
transmissions causing harmful interference to Iridium-equipped aircraft in the relatively
congested North Atlantic Track was negligibly small.
In the main body of this document, the use of satellite communications is being
extended into enroute airspace. Initially DO-343A will include Inmarsat Swift
Broadband (SBB) equipment-specific requirements, with the expectation that Iridium
Block 1 and/or Iridium Certus equipment will be added at the appropriate time.
The purpose of this Appendix is to provide an interference analysis to estimate the
probability of interference between Inmarsat SwiftBroadband transmitters and Iridium
receivers operating in the same continental airspace. At the time of the first publication
of this material, no details were available regarding Iridium Certus for aviation, therefore
this appendix is based solely on the description of Iridium Block 1 equipment contained
in DO-262B, Change 1 . The focus of this Appendix is on interference to aircraft
operating above the final approach, landing, taxi, takeoff, and gate phases of flight. The
process developed here is completely applicable to those phases, once a need for such
analysis has been determined.
This Appendix provides a series of approximations that provide an upper bound
prediction on the probability that a single Inmarsat SBB transmitter causes interference
to a single Iridium receiver, that the ensemble of SBB transmitters that are
simultaneously transmitting in a given SBB spot beam cause interference to any Iridium
receivers that are attempting to receive a satellite-to-aircraft downlink at the same time
as the Inmarsat transmitters are active, and some estimates of the probability that
Iridium receivers are affected in each case. The effect of the interference, should it
occur, is near certain loss of an individual transmission burst, but not necessarily loss
of a particular Iridium message. Readers should also note that Iridium uplink (aircraft-
to-space) transmissions are not affected.
This Appendix is based on an analysis of a Core Europe 2035 traffic scenario
extrapolated from 2013 data and a 2001 Eurocontrol TLAT traffic scenario .
The Iridium performance used in this analysis is the performance of Iridium Block 1,
equipment as specified in RTCA Document DO-262B, Change 1. At the time of
publication of this appendix, there is no corresponding Minimum Aviation Performance
Standard (MASPS) for provision of safety communications services in enroute
continental airspace for either Iridium Block 1 or the planned Iridium Certus services.
Despite the fact that this appendix is based on Block 1, it is not certain that Block 1
equipment will be used for safety services continental airspace. Nevertheless, the
methodology developed in this appendix will be applicable to Iridium Certus when and
if a MASPS update to include Iridium Certus is created. The actual arithmetic results,
that is, the specific computations of numerical values for various probabilities will, of
course, change depending on the performance and requirements of Iridium Certus.
C.1.1 Summary of Conclusions
The analysis outlined here, reaches four conclusions. All of these conclusions apply to
TMA airspace above the approach and landing, takeoff, taxi, and gate segments of
1. The probability of undesired signal out of band and spurious emissions from a
single Inmarsat SBB transmitter causing interference to a message arriving at
a single Iridium Block 1 receiver operating in the same Core Europe Airspace
is small, on the order of
, depending on the specific terminal type
and emissions type. See section C.3.3 , below
2. Despite recent changes to the receiver susceptibility specification for Iridium
Block 1 receivers contained in DO-262B, Change 1, the probability of desired
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