A cell phone is nothing but a radio, but very high-tech. It is basically like a CB radio or walkie-talkie. But CB radio or walkie-talkie is a simplex system, where at a time a person can talk or listen. But a cell phone is a duplex device, where a person can listen and talk at the same time. One frequency is used for talking and another for listening. In CB radio 40 channels are used. But in cell phone you can communicate on 1664 channels.
Lets clarify why this phone is called cell phone or cellular phone. The whole network area of the provider is divided into small cells or areas. Each area or cell contains an antenna. When a person moves within the network area carrying a cell phone, the cell phone keeps contact with the local antenna. That's why it is called a cell phone.
From the service provider each cell phone gets a unique code. This code is used to identify the phone and distinguish from the other. When someone tries to make a call from the cell phone and you turn on the phone a series of events takes place.
When you turn on the phone it seeks a system identification code to identify the provider on the control channel. The control channel is a special frequency, which is used for talking. If the phone can't find any frequency it declares "No Service" message.
When the phone gets the frequency it matches it with the system identification code programmed in the phone. Then the mobile telephone switching office (MTSO) tracks your phone and locates the area your phone is located. After getting a call MTSO looks into the database to locate your phone and identifies the cell you are using. It picks a frequency pair of that cell in which your phone would communicate. MTSO communicates with the phone through control channel and directs which frequency to use. As soon as the phone and tower tracks the frequency, your phone is connected.
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