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achieve a gain-to-noise temperature ratio (GK) of not less
than -19 dB/K over not less than 85 per cent of the reference
coverage volume defined in 4.2.3.1.1. The only exception
to this is the region greater than 70 degrees in elevation
from the horizontal plane where the G/T shall be not less
than -2 1 dB/K.
4.2.3.6.2 Axial ratio. The axial ratio shall be less than
6 dB over 85 per cent of the reference coverage volume
referred to in 4.2.3.1.1 where the Gn must exceed -19 dB/K
or the AES antenna shall have sufficient gain to compensate
for the additional polarization loss in excess of that caused by
this axial ratio. The condition for including the compensation
shall assume the satellite axial ratio to be 2.5 dB, with the
major axes of the polarization ellipses orthogonal.
4.3.1.1 Modulation for channel rates 2.4 kbits/s and
below. For channel rates of 2.4, 1.2 and 0.6 kbitsls, the
modulation shall be aviation binary phase shift keying
(A-BPSK).
4.3.1.2 Modulation for channel rates above 2.4 kbitsh.
For channel rates above 2.4 kbitds the modulation shall be
aviation quadrature phase shift keying (A-QPSK).
4.3.2 Radiated power spectral density. The following
bounds on radiated power spectral density shall apply in any
direction normalized to the peak spectral density in that
direction. The bounds shall apply to a single carrier and shall
be centred at the carrier frequency. The lower bound shall not
apply when the AES is transmitting the unmodulated preamble
at the beginning of a burst.
4.3.2.1 Fmm-aircraft. The power spectrum radiated by the
AES shall fall within the mask defined by Table 4-5.
4.2.3.6.3 Recommendation.- The Gfl should be not 4.3.2.2 To-aircraft. The power spectrum received by the
Lss than -19 dB/K and the axial ratio should be less than AES shall be within the mask defined by Table 4-6 for
6 dB over 100 per cent of the reference coverage volume. A-BPSK and, Table 4-7 and Table 4-7A for A-QPSK.
211uoo
No. 75
4.3.3 Demodulator pe@~rrrzarzce Whcre the channel rates
are implemented as defined in 4.1, the bil error rate (BER)
perfomlance of the channel demodulators after dcscranlbling
shall be equal to or better than that shown in Table 4-8. This
performance shall be attained under the following conditions:
a) in the presence of two adjacent interfering carriers on
either side of the wanted carrier at a level of 5 dB higher
than the wanted carrier with a frequency uncertainty
from the nominal carrier spacing as specified and for the
AES demodulator, with the AES operating up to its
maxilnum allowable operating EIRP;
b) while receiving a signal transmitted with the maximum
phase noise characteristics described in 4.2.3.5.9;
c) during 12" RF phase discontinuities occurring at the rate
of one per second; and
d) under Rician channel condilions for fading bandwidths
of 20, 60 and 100 Hz with a carrier to mullipath ratio of
7 dB lor systems using a low gain antenna or low and
high gain antennas; or 10 dB for systems using only a
high gain antenna.
Note.- Bit er-ror performance ol?jec2ives .for AMS(R)S
radio link are corztuirzed in ITU-R Recommendntion M.1037.
4.3.4 Acquisition performance
4.3.4.1 Time to acquire supelframe synchron.ization. The
period from the command to the antenna to acquire the
satellite to superframe synchronization shall not exceed 16
seconds.
Note.- This assumes the AES is within the satellite service
area of that Y channel.
4.3.4.2 Recommendation.- The period ,from the
coininund to the antenn,a to acquire the satellite to superfrur~ze
synch~.on.izntions hould he UJ: small as possible.
4.3.4.3 C CHANNEL AES DEMODULATOR ACQUISITION
4.3.4.3.1.1 Frunze lock. The probability of failing to
achieve frame lock on the first unique word lollowing the burst
preamble shall be less than one in lo4 at an Es/No of 1.2 dB
in a Gaussian channel, including conditions of 4.3.3 a) and b),
and with a maximum bursl-to-burst frequency uncertainty of
a30 1-12 and maximum channel rate accuracy deviation
of 4.4.5. I .
4.3.4.3.1.2 False franze lock. The probability of false
frame lock shall be less than one in lo5 for an E$NO of 0 dB
in a Gaussian channel, including conclitions of 4.3.3 a) and b),
and with a' maxilnum burst-to-burst frequency uncertainty of
k30 Hz and maximum channel rate accuracy deviation
of 4.4.5.1.
4.3.4.3.1.3 Reacquisition of frume lock. Upon the loss of
frame lock, it shall be acquired within 3.0 seconds for 99 per
cent of the time, at an E,/NO of 0 dB in a Gaussian channel,
including conditions o14.3.3 a) and b), and with a maximum
　
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