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for T channel capacity can be made over the R channel, or
over the T channel, if capacity has already been assigned. The
burst mode data channel characteristics for the T channel have
been specified in the SARPs, as has been the slot structure
used for its reservation TDMA protocol. The functional blocks
at the transmit (AES) end of each channel are as follows:
a) data scrambler;
4 3 R channel
b) FEC encoder;
4.3.1 General. All AESs will log on to AMSS using an
R channel that has been designated for that purpose in the
particular service area of the AES. For the duration of its
log-on period an AES will be assigned one or more R channels
(at the appropriate channel rates). Over these R channels,
the AES can mnsmit signalling, short data packets, and
requests for additional capacity on the T channel. The burst
mode data channel characteristics for the R channel have been
specified in the AMSS SARPs as has been the slot structure
used for its slotted-ALOHA random access protocol. The
functional blocks at the transmit (AES) end of each channel
are as follows:
a) data scrambler;
b) E C encoder;
c) interleaver;
d) preamble and unique word generator; and
e) modulator.
The functional blocks at the receive end of each R channel are
complementary to those at the transmit end. The cornplete
series of functional blocks form transmit end to receive end is
shown in Figure A-12 of this guidance material.
4.3.2 R c k l transmit riming. The R channel
transmits in slots derived from the P channel superframe. The
R channel slot length varies according to the channel bit rate.
The stan of any given R channel slot is referenced to the
leading edge of the first bit in the P channel f o m t identifier
field. An R channel burst may begin at an integer number of
slot durations after this time. For the R channel, the nominal
starting instant of the first bit of the preamble is the beginning
of the slot.
4.4 T channel
4.4.1 General. For the duration of its log-on period an
AES will be assigned one or more T channel frequencies (at
c) interleaver;
d) preamble and unique word generator; and
e) modulator.
The functional blocks at the receive end of each T channel are
complementary to those at the transmit end. The complete
series of functional blacks form transmit end to receive end is
shown in Figure A-12 of this guidance material.
4.4.2 T channel format. The T channel bust length can
vary from 2 to 31 signal units. The number of columns used
in the interleaver varies with the transmission bit rate and the
burst length according to the AMSS SARPs. Each burst
includes a special shoa signal unit, the burst identifier, which
ensures that the originating AES and destination GES are
always known. If a GES receives a burst in which the bunt
identifier is lost, absent or indicates a different GES, the GES
would discard the burst.
4.4.3 T charwnel transmit timing. The T channel is also
synchronized to the P channel superframe, but in his case the
supframe is subdivided into 1 024 slots of approximately 7.8
milliseconds. The shortest guard time between the burst of two
different AESs is under control of the receiving GES and is
set to approximately 39 milliseconds (5 slots).
4.5 C channel
4.5.1 Genernl. The C channel is a circuit-mode channel
used for digital voice or data communications. A C channel
can be requested by an AES over the R channel, and assigned
by the GES over the P channel. The functional blocks at the
transmit end of each C channel are as follows:
a) interfaces for primary (e.g. voice) and sub-band
channel;
b) primary channeusub-band channel data multiplexor;
Annex I0 - Aeronaulicai Teiecommunications Volume ZIZ
C) data scrambler;
d) FEC encoder (unless it is not used);
e) interleaver (unless FEC is not used):
f) preamble and unique word generator; and
g) modulator.
The functional blocks at the receive end of each C channel are
complementary to those at the transmit end. The complete
series of functional blocks from transmit end to receive end is
shown in Figure A-13 of this guidance material.
4.5.1.1 The C channel has been specified at a number of
different channel rates: 5.25, 6.0, 10.5 and 21.0 kbitsls. The
underlying motivation is to allow the evolution of the system
to lower channel rates as voice processing technology
improves. Two of these channel rates, 5.25 and 10.5 kbitsls,
do not include coding. Potential applications of these uncoded
channels include transmitting 4.8 and 9.6 kbits/s vocoded
speech in satellite systems that have limited spectrum but are
　
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