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loop compensation system) and the local oscillator of the AES.
Efforts are made to reduce the error caused by the first two as
described below. This Standard characterizes that portion of
the frequency error which is due to the AES and the aircraft
motion relative to the satellite. Consequently, the proper frame
of reference for measuring the transmit frequency is the satellite.
A practical test of this requirement would use the AES
frame of reference, and the corresponding value in the satellite
111 1/01
No. 76
Attachment A to Part I Annex 10 - Aeronautical Telecommunications
2.5.4.1 Intermodulation products (1M) that may be
emitted by a Level 4 AES in multicarrier operation arise both
from the high-power amplifier (HPA) and from other passivc
components that are subject to high AES RF power levels.
Passive components causing IM may include connectors,
particularly if they are subject to corrosion or looseness; and
the diodes used in phased-array antennas. Depending on the
choice of frequencies and levels in the GES, such IM can
appear at frequencies and levels in the AES receiver that will
degrade BER, disable reception, or affect reception of signals
by other aircraft equipment.
2.5.4.2 AES-transmitted IM can block GES receivers. The
HPA is a primary IM source because its linearity is limited by
technology and heat dissipation.
2.5.4.3 Intersystem effects may arise from Level 4 AESs
that may radiate IM. An AES operating with a global beam
satellite must transmit higher EIRP than an AES operating
with a more sensitive spot beam satellite. Therefore, this
higher level of IM would be more readily received by the spot
beam satellite for relay to its GES, where it could impair
reception of that channel. Even if the two satellites are using
separated portions of the frequency band and therefore cannot
reuse the same assigned channel frequencies, the global beam
AES transmitter's IM that is out of assigned channels could
fall into the spot beam satellite's band. All GES frequency and
EIRP level assignments should account for this possibility.
2.5.4.4 Frequency management techniques are used to
eliminate 3rd and 5th order products below 1 610 MHz as
described in 4.2.3.5.7. If GLONASS is to be installed on the
same aircraft as AMSS, it may be necessary to employ
frequency management techniques or other methods to ensure
that AMSS 7th and higher order intermodulation products will
not cause harmful interference to GLONASS operations.
2.5.5 Frequency management. Careful frequency
management is needed because:
a) AMSS includes safety services;
b) there is concern about the availability of adequate
AMSS spectrum, and adequate capacity for AMSS
safety services; and
c) the difficulty in co-ordinating mobile satellite networks
due to the poor discrimination characteristics of mobile
station antennas.
Guidelines that should be considered when co-ordinating
frequency plans to minimize intra and interservice interference
include:
a) compliance with the relevant ITU Radio Regulations;
b) each provider should provide monitoring facilities to
identify the actual usage of AMS(R)S and non-
AMS(R)S communications;
c) in those AMSS systems with global and spot beams.
operational measures to minimize the amount of global
bandwidth used and to maximize the use of spot beams;
d) using the ITU-R Recommendations M. 1089 and M. 1233
technical co-ordination method, wherever possible;
e) efficient spectrum use including the following:
1) using other system providers' satellite transponder
guard bands;
2) using frequency assignment by aircraft location;
3) taking advantage of improvements in aircraft earth
station antenna sidelobe discrimination;
4) using offset and interleaved carriers;
5) using satellite spotlshaped beams;
6) reducing spacecraft antenna sidelobe levels;
7) increasing the resistance of systems to interference;
8) using earth station power control;
9) using satellite transponder adjustable gain setting;
10) using knowledge of operational schedules to take
advantage of the difference in time zones;
1 1) appropriately grouping carriers;
12) repositioning satellites; and
13) taking advantage of high-gain AES antennas and the
resulting ability to use lower carrier powers.
2.5.6 Transmitted phase notre. The phase noise mask that
the AES transmitter must meet is illustrated in Figure A-2 of
this guidance material. The purpose of this mask is to
minimize the contribution of the AES transmitter phase noise
to the degradation of GES performance.
　
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