How Wireless Mobile Phones Work

Millions of people own cell phones, alphanumeric pagers, and other wireless devices, but few people have even the slightest clue how they actually work. While cell phones may mimic normal telephones in appearance and basic function, they aren't telephones at all,they are two-way radios. Every cell phone is a low-power, high-frequency transceiver (transmitter-receiver). When you use your handset, it is transmitting over the public radio spectrum in all directions. Because they look like telephones, we expect the same privacy and quality of service that we get from the plain-old-telephone-service (POTS). Before we investigate how cell phone networks operate, it's best to have an understanding of how POTS networks work.

When you place a call on a POTS phone, the phone converts your voice to an electrical signal and transmits it over wires to your local telephone exchange. The exchange routes the call to its final destination over the phone company's network. For the most part, the call never leaves the network, except perhaps in cases where you call a cell phone from a landline, or when your phone company routes a long distance call through a satellite.

Mobile phones are commonly called eel/ phones because of the basic design of the network that they operate within. In a mobile network, a number of transceiver sites are arranged so that their signals or coverage areas overlap. A cell is the name given to the coverage area of a particular transceiver site, or cell tower .
The cell towers in a particular area link together through a central mobile telephone switching office (MTSO). Each MTSO authenticates and routes calls between transceivers in its service area, and handles billing. The software that handles calls at an MTSO is incredibly sophisticated. The MTSO also connects to the conventional telephone network and routes calls between cell phones and POTS phones

While the technology differs from carrier to carrier, the same general thing happens when you place a call with your mobile phone. When you turn your phone on, it notifies the network and authenticates itself. Authentication usually consists of the phone transmitting several pieces of information to identify itself and your account. One of these pieces of information is the electronic serial number (ESN).

Manufacturers encode the ESN on a chip within the phone. The other piece of information is the mobile identification number (MIN). The MIN is your cell phone's area code and phone number. Depending on the carrier and the underlying network, there may be more codes used to authenticate your phone or establish calls.

When your phone transmits this data, the closest cell tower receives it and routes it to the MTSO. Once the MTSO verifies your phone, it then accepts calls and routes them accordingly. If you have called a POTS number, your MTSO routes that call to the conventional phone network and routes the return voice signal back to your cell phone through the tower handling your call, where it is sent to you as a radio signal. If you have called another mobile phone, then the MTSO routes the call to the transceiver handling that phone, and then back to you.

While you are connected to the mobile network, the MTSO tracks your signal strength. The MTSO assigns your phone to whichever transceiver receives the strongest signal from your handset. As you move away from one transceiver your signal grows weaker, while at the same time, as you get closer to a new transceiver it receives a stronger signal from you. The MTSO then assigns the next transceiver to handle your call, where you must authenticate again, and switch to the new transceiver's frequency. This hand-off between cells occurs without you even noticing it and with no interruption in your call.