A cellular mobile network (CMN) provides communication services for mobile stations that are operating in its service area. A service area typically covers a metropolis and its surrounding suburbs, or a number of medium-sized cities. The size of a service area is typically in the range of 100-4000 square miles.

The CMN service area is divided into a number of MSC areas, each of which contains an exchange known as a mobile switching center (MSC)—see Fig. 12.1-1. A MSC provides service to all MSs in its area. Some rural CMNs consist of just one MSC area. A MSC area is divided into a number of location areas, and each of these areas is divided into a number of cells. The cells are approximately circular, with radii that range from about 2 to 15 miles. Each cell has a base station (BS)—also known as land station and cell site—which houses radio-frequency (RF) transmitters and receivers.

A MSC has trunk groups (TG) to nearby exchanges in the public switched telecommunication network (PSTN) (also known as the "fixed" or "wire-line" network), and a base station trunk group (BSTG) to each base station—Fig. 12.1-2(a). When a CMN has several MSCs, there are also trunk groups (MSCTG) between these MSCs—Fig. 12.1-2(b).

A MS operating in a cell communicates on a RF channel with the BS of the cell. There are two channel types: voice channels and control channels.

Voice Channels. In a base station, each BS trunk is permanently wired to the transmitter and receiver of a RF voice channel. The combination of a BS trunk and its associated voice channel is the functional counterpart of a trunk in PSTN. A BS trunk and voice channel is assigned to a mobile at the start of a call, and released when the call ends. Figure 12.1-3 shows the connection for a call

Cellular Network

Tandem Exchange

Local Exchange

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