Cellular telephony

Cellular telephony is the set of technology that makes possible the modern range of portable telephones. In the past, the most common assumption in mobile communications, such as two-radios, is that the transmitter had to have the range and power to reach the ultimate receiver.

Perhaps counterintuitively, cellular systems often reduce the range and power of the individual telephones, as there is no attempt to communicate with the distant destination. The only goal is communicating with the electronics in a local cell, which is a relatively small geographic area centered on an antenna tower, monitoring receivers that note when a given phone enters the cell (i.e., so it can be reached). Other receivers and transmitters have the same function as the end office in a conventional plain old telephone service (POTS) network: they are the first "on ramps" to the POTS accessible to the subscriber.

The more cells, the more capacity there is for calls to enter and leave the cells, which are the gateway between mobile phones and the pots. By lowering power and cell size, one can increase the capacity by avoiding call collisions.

While there are fixed cellular services in areas where it was uneconomic to cable copper or fiber to the individual customers, the more common case is that the cellular phone is moving. During that process, there must be handoffs from one cell to the next, without dropping the call. The call information, once a connection is made, is internal to the POTS networks; the cells have to know what phones are reachable through, which of those phones are making calls and how to connect to the ongoing call in the POTS network. There has to be an intelligent interaction among two cells and a telphone to manage a handoff.