How Satellites Provide Cell Phone Coverage

Have you ever wondered just how cell phones work?  What are cells?  Is it satellites that make cell phones work?  If so, what makes cell phones different from satellite phones? 

Cell phones let you speak to people on other mobiles or on landlines by using small base stations that each cover a certain area, referred to as a cell.  Base stations are designed and placed to cover as much area as possible, so that you can move from one zone (cell) to the next and your call will simply be passed from one to the next. 

The ability to switch from one cell to the next during the same call is made possible by the capability for sending a special kind of signal back and forth from the cellular phone to the base stations taking care of the call.  The call is then connected with the Public Switched Telephone network (PSTN) by the Mobile Telephone Switching Office (MTSO).  MTSO is also responsible for controlling each of the cell zones.  Every cell phone in use is registered with the MTSO control channel so that the overall system is always able to locate the cell phone no matter what cell it's in.

Ideally, the entire world would be covered by cells, making its coverage look like a giant honeycomb.  Unfortunately, this kind of coverage is simply not possible.  It is in no way cost effective for cell service providers to erect cell coverage towers all over very rural or in many developing nations where the use of mobile devices would be extremely low.  This means that there are large parts of the United States and the rest of the world that don't have cells in which your phone will be able to make calls. 

Enter the satellite phone.  These don't require a cell or a cell tower in order to function.  They use signals to satellites in order to make a call.  Making a call from a satellite phone sends a signal to the nearest compatible satellite.  That signal is then sent back down to earth where it is received by either a gateway or a ground station and it is directed to the intended destination for the call.