Satellite Phone Networks
Geosynchronous Satellite Networks
There are two basic types of satellite networks. You have the geosynchronous networks or GEO and you have the low earth orbiting or LEO systems. Both have their advantages and disadvantages when providing service.
The Geosynchronous satellite networks can maintain high quality global coverage with only three or four satellites unlike the 50 to 60 satellites needed with LEO satellite systems. The Geosynchronous satellites are stationary providing service like a large flashlight beaming down to earth. They do not orbit the earth like LEO satellite systems. The Geosynchronous satellites are very heavy and expensive to build and launch. The geosynchronous satellites are at a higher altitude than the LEO satellites at about 22,000 miles. This distance can cause phone and internet connections to have a noticeable delay because of the great distance the signal must travel. One great advantage of geosynchronous satellite networks is they can provide substantially higher band width than that of the LEO systems.
A disadvantage of the geosynchronous satellite networks is in areas of limited view of the sky you may not be able to obtain “line of site” to the satellite from your satellite phone terminal. Tall buildings, trees and other tall structures can block the “line of site” to the one satellite you need to obtain a signal. You may need to move to higher ground or you can in most cases get a signal through a window that is facing the geosynchronous satellite. This is not the case with Low Earth Orbiting satellite networks because LEO satellites are constantly moving and there are numerous satellites in orbit. You can usually wait till a satellite moves in view and receive a signal. It is recommended you have 80% view of the sky to receive good service using LEO satellite networks.
Inmarsat is the oldest satellite phone provider that uses geosynchronous satellite networks. Inmarsat was founded in 1979 originally providing large fixed satellite installations used on ships. Inmarsat has recently entered the handheld satellite phone market in a partnership with ACeS. The new phone is called the IsatPhone. It will be in the price range of $500 and is currently being tested in Europe. Inmarsat operates eleven satellites with a twelfth satellite planned for launch in 2008. Inmarsat provides satellite voice and internet service worldwide excluding only the poles.
Thuraya is a system based in the UAE providing satellite service to Eurasia, Africa, and Australia with two geosynchronous satellites, some overlapping coverage.
MSAT/Mobile Satellite Ventures is bases in the U.S. which uses satellite phones similar to Inmarsat equipment. It plans to provide handheld satellite service similar to Thuraya in the Americas using geosynchronous satellites.
ACeS is a same regional satellite provider using one satellite providing service in East Asia.
Low Earth Orbit Satellite Networks
LEO satellite phone networks utilize Low Earth Orbit satellite technology. LEO satellite phone service provides worldwide coverage with no gaps in service as long as all satellites are fully functional in the LEO constellation. LEO satellites orbit at high speed with an orbital time of 70 to 90 minutes, with an altitude of 400 to 700 miles. LEO satellites are not geosynchronous; they are always on the move and must fly complete orbits. The Iridium satellite constellation provides complete coverage from at least one satellite at all times.
Two LEO systems based in the U.S. started up in the 1990s, but went bankrupt after they failed to sign up enough customers to fund the enormous cost of satellite phone networks. They were both bought out of bankruptcy by new owners who bought them at pennies on the dollar. They both plan to launch replacement constellations that will provide higher quality voice and larger bandwidth satellite service. Current data speeds for the Iridium satellites are 2400 baud while the Globalstar is faster at 9600 baud. There are compression services that will speed this slow rate up somewhat.
Globalstar coverage includes 32 countries using 44 satellites. The reason Globalstar cannot provide complete worldwide coverage is that their satellites must be in range of a Globalstar ground station. Unlike Iridium the Globalstar system uses bent pipe technology where the signal goes up from a Globalstar phone to a satellite then straight down to a ground station. There are a limited number of ground stations, so because of the curvature of the earth blocking line of site to all the ground stations Globalstar cannot provide worldwide coverage. The Globalstar satellite network has in an inclined orbit of 52 degrees so Polar Regions are not covered.
Iridium coverage is worldwide using its network of 66 satellites that follow a polar orbit. Unlike Globalstar’s bent pipe technology, Iridium uses a radio cross link technology between the satellites, passing the satellite signal from satellite to satellite then down to the nearest ground station. This insures the customer of worldwide coverage.