Q. Explain Cellular Telephone Systems?

Today radio-based systems make it possible for mobile people to communicate via cellular telephone systems while traveling on airplanes and motor vehicles. For radio telephone service, the FCC in the United States has assigned parts of the UHF band in the range of 806-890 MHz. For efficient use of the available frequency spectrum, especially in highly populated metropolitan areas with the greatest demand for mobile telephone services, the cellular radio concept has been adopted, inwhich a geographic area is subdivided into cells, each ofwhich contains a base station, as shown in Figure. Each base station is connected by telephone lines to amobile telephone switching office (MTSO),which in turn is connected through telephone lines to a telephone central office of the terrestrial telephone network.

When amobile user (identified by the telephone number and telephone serial number assigned by themanufacturer) communicates via radio with the base station within the cell, the base station routes the call through the MTSO to another base station if the called party is located in another cell, or to the central office if the called party is not mobile. Once the desired telephone number is keyed and the "send" button is pressed, theMTSOchecks the authentication of themobile user and assigns (via a supervisory control channel) an available frequency channel for radio transmission of the voice signal from the mobile telephone to the base station. A second frequency is assigned for radio transmission fromthe base station to themobile user. Simultaneous transmission between two parties is known as full-duplex operation. In order to complete the connection to the called party, the MTSO interfaces with the central office of the telephone network by means of wide-band trunk lines, which carry speech signals from many users. When the two parties hang up upon completion of the telephone call, the radio channel then becomes available for another user.