Three systems covered briefly here (satellite element only, not
cellular) are:
Iridium
The first global system to become operational but which subsequently
ceased service for business (financial) reasons. At the time of writing
the Iridium system has just come back into commercial service.
Globalstar
The second global system to come on-line but with limited coverage
at sea (see figure 8.11).
Thuraya
A regional system promising coverage in Europe, north and central
Africa, central Asia, the Middle East and the Indian subcontinent by
mid-2001.Iridium
Using polar orbiting satellites (i.e. the satellites orbit in a North-
South path over the polar regions), the Iridium satellites were designed
to connect calls from remote regions (e.g. the southern ocean) using
satellite-to-satellite links until the call could be connected to a land station
- from where it could be routed to the destination number. The satellite-
to-satellite link would allow global coverage even when there were only
a few land stations operational.
Globalstar
The Globalstar system uses simple 'bent pipe' communications
through the satellite system. This means that you can only make a
(satellite) call when you can see a satellite that is also in Sight of a land
station. At the time of writing, the current and planned service coverage
from the Globalstar system was as depicted in figure 8.11.
In countries with, or adjacent to, a gateway (a land station), good
coastal coverage is expected (especially in areas like NW Europe and
much of the Mediterranean Sea and around the coasts of Australia and
the Americas).
Coverage in ocean areas is described as 'Extended Gateway
Coverage', which is not guaranteed, neither for quality nor duration (i.e.
call quality may not match that in coastal waters, and calls may be cut
off without warning). If you are moving away from your home gateway,
you need to check that your service provider has activated roaming
arrangements with any other gateway that you may want to communicate
through. You will also have to put your telephone into search mode
MARINE COMMUNICATIONS 177