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Many people get the two confused on how the function and where they are able to function. Some believe or are told by their cellular phone provider that cellular phones do use satellites for their communication. When cellular phones use satellites it is in a very different way satellite phones use satellite communication. Many cellular providers tell their users, “yes your cellular phone uses satellites,” without even understanding how it works. Customers have been known to contact a satellite service provider asking for satellite service to be added to their cellular phone. That is about like asking for satellite service to be added to your refrigerator. It can’t be done! Cellular phones do not and cannot communicate directly to a satellite like a satellite phone must do.
Cellular phones work basically like this; cellular phones are basically fancy radios that use cellular towers. As you travel with your cell phone you enter cells, each cell is serviced by a cellular tower as you move outside a cell then the signal is transferred to the next cell you enter. This is all done without your knowledge as the cellular service hand-shakes to the next tower. From the cellular tower a call is switched to the public telephone system where it is sent to its call destination to another cellular network or to a landline. About the only time satellites are used is if the public telephone system finds it necessary to transfer the call to a satellite in a domestic or international long distance call. That is the only time a satellite would be used by a cellular phone.
Starting with the Globalstar phone, satellite phones work basically like this, calls from the Globalstar phone go up to one of its 28 relay satellites and then is sent back down to a Globalstar gateway where it is then switched to the public telephone network. The call is then connected to a cellular net work or landline if that is what you wanted to call. The same goes in reverse when someone is calling a Globalstar phone from a cellular phone or landline. Satellite calls are sent to one of the Globalstar gateways then that gateway sends the call up to a relay satellite then back down to the Globalstar satellite phone user. Globalstar calls this their “bent pipe technology.”
Calls from a Globalstar phone to a Globalstar phone within the same foot print of the servicing gateway goes up from the Globalstar phone to the satellite then down to the gateway where it is then sent back to a Globalstar satellite then relayed down to the receiving Globalstar phone. If you were in Florida using a Globalstar phone calling another Globalstar phone in Florida both phones would be connected to the Globalstar Gateway in Sebring, Florida. If you were in Texas both Globalstar phones would use the Globalstar Gateway in Texas. In this scenario the public telephone system is never utilized. If a call from a Globalstar phone goes to another Globalstar phone outside the foot print of the originating gateway it works this way. The call goes up to the satellite then down to the servicing gateway then is transferred by the public telephone system to the Globalstar gateway the other Globalstar satellite phone user is being service by. The call is then set up by that gateway to the satellite which sends the call back down to the second Globalstar user. If the public telephone system is disrupted to the gateway serviced by the receiving Globalstar phone the call will use a back-up T1 line Globalstar uses when a public telephone disruption occurs. This case even if the public telephone system is disrupted the Globalstar satellite service is still up and running.
The first generation Globalstar GSP-1600 satellite phone is the only satellite phone that has a cellular component. This phone basically has two pieces of hardware in one phone. The phone can be set up first for cellular service when in range then switched to satellite when outside of cellular range. Active calls currently with the Globalstar service cannot be switched from cellular to satellite or from satellite to cellular. Because the Globalstar GSP-1600 cellular component is not E911 compliant new cellular service cannot be activated on the Globalstar GSP-1600 phone.
Calls from an Iridium satellite phone work similar to a Globalstar phone but differently depending on how the call will need to be delivered. Calls from the Iridium phone goes up to one of Iridium’s 66 satellites then if the satellite is in range of an Iridium gateway it goes down to that gateway where the call is switched to the public telephone network and sent to its call destination by landline or cellular networks. This type of call delivery is very similar to the Globalstar service. If the Iridium satellite user is not in range of one of the gateways in the network the call is sent through the network of satellites in the constellation by interlinking till a gateway is found by another Iridium satellite. When a gateway is found then the call goes down to the gateway and is switch to the public telephone service. The same works in reverse when calling an Iridium phone.
Iridium phone to Iridium phone calls work differently than Globalstar. The call goes up from the Iridium satellite phone to one of the Iridium satellites then instead of going down to a gateway like Globalstar the call is sent back down from the satellite to the receiving Iridium phone. This type of call totally by passes the Iridium gateway. If the receiving Iridium phone is not in range of the call going to the first satellite then the call would be sent to other Iridium satellite(s) by the interlinking process till it comes to a satellite that is in range of the Iridium phone receiving the call. An example would be a call originating from the U.S. by an Iridium satellite phone user to a call destination to an Iridium satellite phone user in China the call would go from satellite to satellite by using their interlinking antennas till it reached the Iridium user in China. Iridium to Iridium calls do not use a gateway.
Calls from an IsatPhone phone to a IsatPhone phone within the same foot print of the servicing gateway goes up from the IsatPhone phone to the Inmarsat I-4 satellite then down to the gateway where it is then sent back to a Inmarsat I-4 satellite then relayed down to the receiving phone. If a call from an IsatPhone phone goes to another IsatPhone phone outside the foot print of the originating gateway it works this way. The call goes up to the satellite then down to the servicing gateway then is transferred by the public telephone system to the Inmarsat gateway the other IsatPhone satellite phone user is being service by. That call is then sent up by that gateway to the satellite which sends the call back down to the second IsatPhone user.
As you can see cellular and satellite phones work very differently. Cellular phones rely primarily on their cellular network and the public telephone system and only use satellites for long distance or International calling when necessary. If cellular or landline systems are disrupted by hurricanes, tornados or acts of terrorism your landline and cellular phone could fail to work. In the case of satellite phones that work independent of the public telephone system and cellular networks, satellite phones will provide service when the public telephone and cellular networks are disrupted. If the public telephone system is disrupted satellite phones would be able to call a landline or cellular phone because the link in communication between the different services has been disturbed.
Satellite phones are currently not for the everyday phone user. They are for communication outside of cellular and landline range and/or for emergency use when terrestrial phone networks are disrupted.