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mobile-sa~ellite service, located at a specified fixed point
on land to provide a feeder link for the aeronautical
mobile-satellite service.
Note.- This definition is used in the ITU's Radio Regularions
under the tenn "aeronautical earth station." The de$-
nition herein as "GES" for use in the SARPs is to clearly
disringuish it from an aircrafr earzh station (AES), which is a
mobile statiorz on an aircraft
Point-to-poinl. Pertaining or relating to the interconnection of
two devices, particularly end-user instruments. A communication
path of service intended to connecl two
discrete end-users; as distinguished from broadcast or
multipoint service.
Slotted aloha. A random access strategy whereby multiple
users access the same communications channel independently,
but each communication must be confined to a
fixed time slot. The same timing slot structure is known to
all users, but there is no other co-ordination between the
users.
Time division multiplex (TDM). A channel sharing strategy in
which packets of information from the same source but
with different destinations are sequenced in time on the
same channel.
Time division multiple access (TDMA). A channel sharing
strategy in which packets of information from different
sources and with the same or different destinations are
sequenced in time on the same channel.
Transit delay. In packet data systems, the elapsed time
between a request to transmit an assembled data packet
and an indication at the receiving end that the corresponding
packet has been received and is ready to be used
or forwarded.
CHAPTER 2. GENERAL
[to be developed]
ANNEX 10 - VOLUME 111
CHAPTER 3. AERONAUTICAL
TELECOMMUNICATIONS NETWORK
[to be developed]
CHAPTER 4. AERONAUTICAL
MOBILE-SATELLITE SERVICE
4.1 DEFINITIONS AND DESCNPTIONS
OF CHANNEL TYPES; GENERAL;
SYSTEM CAPABILITXIES
4.1.1 Dehitions and descriptions
of channel types
Adjacent beams. Beams which have the minimum spatial
separation in a given direction and whose corresponding
phase shifter states differ for at least one element.
Application. The ultimate use of an information system. as
distinguished from the system itself.
Avktion-BPSK (A-BPSK). The particular form of binary phase
shift keyed modulation which is used in AMSS for channel
rates of 2.4, 1.2 and 0.6 kbitsts. A-BPSK is a modulation
technique which maps a "O" to a phase shift of -90" and "1"
to a phase shift of +90°. The phase-encoded A-BPSK data
stream is then filtered with a filter which satisfies the
amplitude and phase versus frequency limits defined by
Tables A 1 - 1 and A 1-2 in Appendix 1 to Chapter 4.
+
Aviation-QPSK (A-QPSK). The particular form of offset
quaternary phase shift keyed modulation which is used in
AMSS for channel rates greater than 2 400 bitsls. A-QPSK
is a modulation technique which maps a " 0 into a 0
degrees and "1" into a 180 degrees, or "0" into 90 degrees
and "1" into 270 degrees, alternating between the two
options on successive bits. The encoded A-QPSK data
stream is then filtered such that the modulated spectrum
meets the amplitude mask of Table A1-3 and the phase
mask defined in Table Al-2 in Appendix 1 to Chapter 4.
Burst. A time-defined, contiguous set of one or more related
signal units which may convey user information and
protocols, signalling, and any necessary preamble.
Cyclic redundancy check. The last two bytes of each signal
unit form a cyclic redundancy check of the whole signal
unit as follows. The check bits for error detection are
calculated from the first 10 octets of a standard length
signal unit, or from the first 17 octets of an extended
length signal unit or from the first 4 octets of the burst
identifier, using the following generator polynomial:
Note.- See CCITT (Red Book) Recommendatiort X.25,
Section 2.2.7 for the method qf calculation arul tile bit order.
Direct link service (DLS). A data communications service
which makes no attempt to automatically correct errors,
detected or undetected, at the link layer of the satellite
communications path. (Error control may be effected by
end-user systems.)
Epoch. A span of time related to the beginning and end, or
lifetime, of an event or a sequence of associated events.
Frame. A structured, repeating time-segment of a communication
link architecture that provides for time-predictable
communication activities between its beginning and end.
Global beam. Satellite antenna directivity whose main lobe
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