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manner which allows correction, at the receiver, of crrors
incurred in Lhc transmission.
Gain-to-noise temperature ratio. The ratio, usually expressed
in dS/K, of the antenna gain to the noise at the receiver
output of the antenna subsystem. The noise is expressed as
the temperature that a 1 ohm resistor must be raised to
produce thc same noise power density.
Ground earth station {GES). An earth station in the fixed
satellite scrvice, or, in some cases, in the aeronautical
mobile-satellite service, located at a specified fixed point
on land to provide a fceder link for the aeronautical
mobile-satellite service.
Note.- This definition is used in the ITU's Radio Regulations
under the term "aeronautical earth station." The definition
herein as "GES" for use in the SARPs is to clearly
distinguish it from an uircruft earth station (AES), which is a
mobile station on an aircruft.
Mode S subnetwork. A means of pcrformjng an interchange
of digital data through the usc of secondary survsillance
radar (SSR) Mode S interrogators and transponde'rs in
accordance with defined protocols.
Packet. The basic unit of data transfer among communications
devices within the network laycr.
Puckst layer protocol (PLP). A protocol to establish and
maintain a connection between peer levcl entities at the
network layer, and to transfer data packets between them.
In the context of this standard, the term refers to the
protocol defined by the IS0 8208 standard usecl in this
document.
Point-lo-point. Pertaining or relating to the interconnection of
two devices, particularly end-uscr 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 ro
all uscrs, but there is no other co-ordination between the
users.
Switched virtual circuit (SVC). The primary circuit
management technique provided within the IS0 8208
protocol. The network resources arc dynamically allocated
when needed and rclcased when no longer required.
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 (TRMA). A channcl sharing
strategy in which packets of information from different
sources and with the same or different destinations arc
sequenced in time 011 thc same channel.
Transit delcry. In packet data systems, the elapsed time
between a request to transmit an.assembled data packer
and an indication at the receiving end that the corresponding
packet has been received and is ready ro be used
or forwarded.
7/11/Y 6
No. 71
CHAPTER 4. AERONAUTICAL
MOBILE-SATELLITE: SERVICE
4.1 DEFINITIONS AND DESCRIPTIONS
OF CHANNEL TYPES; GENERAL;
SYSTEM CAPABILITIES
4.1.1 Definitions and descriptions
of channel types
4.1.1.1 DEFINITIONS
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.
Aviation-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 kbitsls. A-BPSK is a modulation
technique which maps a "0" 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 Al-1 and A1-2 in Appendix 1 to Chapter 4.
Aviation-QPSK (A-QPSK). The particular fom of offset
quaternary phase shift keyed modulation which is used in
AMSS for channel rates greater than 2 400 bitsis. A-QPSK
is a modulation technique which maps a "0" into a 0
degrees and "1" into a 180 degrees, or "O"i11to 90 degrees
and "I" into 270 degrees. alternating between the two
options on successive bits. The encoded A-QPSK data
stream is then filtered such that the modulated spectrunl
meets the amplitude mask of Table AI-3 and the phase
mask defined in Table AI-2 in Appendix 1 to Chapter 4.
Rurst. A time-defined. contiguous set of one or more related
　
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