A3LA-R-MIL-MOD User Guide Version B
Document Number: 451-93156-001A
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SMSC. Unlike standard GSM, the Iridium SMS can only acknowledge that the message was
delivered to the SMSC and not the end destination.
SMS messages can be sent and received simultaneously while a voice call is in progress. This is
possible because SMS messages travel over and above the radio channel using the signaling
path, whereas the voice call uses a dedicated “traffic” radio channel for the duration of the call.
G.6 RUDICS
RUDICS is an enhanced gateway termination and origination capability for circuit-switched data
calls across the Iridium satellite network. When an Iridium modem places a call to the RUDICS
Server located at the Iridium gateway, the RUDICS server connects the call to a predefined IP
address, allowing an end-to-end IP connection between the host application and the Iridium
modem. There are three key benefits of using RUDICS over the conventional PSTN circuit-
switched data connectivity or mobile-to-mobile data solutions: (1) elimination of analog
modem training time, (2) increased call connection quality, reliability, and maximized
throughput, and (3) protocol independence.
G.7 I
RIDIUM
G
EOLOCATION
The Iridium network makes calculations of the geographical location (geolocation) of an ISU
each time a call is placed. The technique employed to determine the geolocation of an ISU is
based on measurements of the ISU and satellite propagation delay and Doppler frequency shift.
These measurements are used to estimate cosines of spherical angles that identify the ISU’s
location relative to the satellite by the gateway.
The Iridium network can locate an ISU to within 10 km only about 78% of the time. The so-
called error ellipse can have a large eccentricity with the major axis oriented in the azimuth
dimension and the minor axis oriented in the radial dimension. The position of the ISU in the
radial dimension relative to the satellite can almost always be determined to within 10 km with
just one measurement. Errors in the azimuth dimension relative to the satellite are largest
along the satellite’s ground path and tend to increase with distance from the satellite.
Geolocation errors in the east-west dimension, therefore, are sometimes more than 100 times
greater than in the north-south dimension.