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Old 11-10-2007, 03:46 AM   #17
TomW
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Joined: Jan 2006
Location: Ft. Payne, AL
Oddometer: 1,013
Quote:
Originally Posted by DRTBYK
...The Globalstar sat's are in geosynchronous orbits and if you look on their coverage map you will see that they certainly don't cover the globe. I believe I read somewhere that they are launching new sat's over the next two years that should help reliability and coverage. They are almost giving their phones and service plans away if you buy now with the expectation that it will work better three or four years from now....
No, their satellites are in low earth orbit (see below from the Globalstar website: http://www.globalstarusa.com/en/content.php?cid=601). They are launching new satellites -- four in May with another four scheduled 'later this year' -- which is a good thing, and their rates are very low at the moment ($50/mo for unlimited talk time in 2007, reduced to $20/mo in 2009). Pretty good deal although they indicate that service will be degraded until they get a new second generation 48-satellite system up beginning in 2009.

Although their coverage map looks like spotbeam coverage by a geosynchronous satellite, I think it their spotty coverage is dependent on the locations of their gateways (gound stations).

Here's the info from Globalstar (feel free not to read ):

"Our Technology
Here is a brief overview of some elements that contribute to the exceptional service and coverage of Globalstar:

Technology / LEO Satellites
A Low Earth Orbit (LEO) is any Earth orbit up to approximately 1,500 kilometers in altitude. Low-Earth-Orbit satellite systems offer significant advantages over Geosynchronous (GEO) systems for the delivery of mobile satellite services (MSSs). These advantages result from an orbit selection that enhances the quality of services to low-power mobile hand-held and vehicle-mounted user equipment. GEO satellite systems, located at an altitude of 35,800 kilometers above the Earth, are best suited for their missions of high-speed data, television transmission, and other wideband applications.

Mobile users, however, need systems that are specifically tailored to their needs. The true mobile user requires hand-held and vehicle-mounted telephone devices with omnidirectional antennas that are easily portable and can provide instant access to a global communication system. Furthermore, telephone users desire and require "telephone quality" transmissions. These users do not want long propagation delays inherent in GEO systems that produce the echo effect and also use bulky, expensive, directional antennas which must point or must be pointed at a satellite.

Also, technical limitations of current GEO satellite systems severely limit the capacity of such systems to service mobile users. The scarce spectrum available for MSSs communications requires deployment of systems that will provide services to the users in a manner that maximizes the use of spectrum while encouraging a multiplicity of systems to share the spectrum. GEO systems, as presently configured with frequency division multiple access-frequency modulation (FDMA-FM), require inefficient band segmentation to share the spectrum.

Compared with a Geostationary system, Globalstar will provide capacity even when a satellite fails. A GEO system, by contrast, would suffer an entire regional system outage if an operational satellite were to fail. Also, current and planned GEO systems cannot service the personal communications market due to the expense of supplying adequate satellite power and practical deployable antenna sizes...."
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TomW
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