Iridium Network Data Capabilities - Iridium NAL SHOUT ns User Manual

SHOUT ns/nsx User Guide Version D
beams are shut down. The satellite footprint is approximately 4,700 km in diameter. Under
each footprint, a satellite is power-limited to approximately 1,100 simultaneous circuits.
The Iridium network uses a time division duplex (TDD) method and transmits and receives in an
allotted time window within the frame structure. Since the system is TDD, the ISU transmit and
receive in the same frequency band. The access technology is a frequency division multiple
access/time division multiple access (FDMA/TDMA) method whereby an ISU is assigned a
channel composed of a frequency and time slot in any particular beam. Channel assignments
may be changed across cell/beam boundaries and are controlled by the satellite. The system
provides an average link margin of 13.1 dB.
Although there are multiple gateways, a user is registered to a single gateway. The gateways
perform call connection setup and administrative duties such as billing and resource
management. The satellite constellation provides connectivity between users, from a user to
the Iridium system gateway, and between gateways. Within the Iridium network architecture,
the satellites are cross-linked, which allows ISU-to-ISU communication independent of gateway
intervention once the call connection is established.
There are currently two commercial Iridium gateways located in Arizona, United States; and
Fucino, Italy. The U.S. government owns and operates an Iridium gateway located in Hawaii,
United States. Each gateway generates and controls all user information pertaining to its
registered users, such as user identity, geolocation, and billing items. The gateway also provides
connectivity from the Iridium system to the terrestrial-based networks such as the public
switched telephone network (PSTN) or the internet.
I N D C
RIDIUM ETWORK ATA APABILITIES
For data communications, the Iridium network supports five different modes of operation as
shown in Figure 34: dial-up data service, direct internet connection, SBD, short-messaging
service (SMS), and router-based unrestricted digital internetworking connectivity solution
(RUDICS).
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