Page 10 - Mobile Computing

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Cellular Telephony

Cellular telephony is designed to provide communications between two moving
unites, called mobile stations (MSs), or between one Mobile unit and one
stationary unit, often called a land unit. A service provides must be able to locate
and track a caller, assign a channel to the call, and transfer the channel the base
station to base station as the caller moves out of range.
To make this tracking possible, each cellular service area is divided into
small regions called cells. Each cell contains an antenna and controlled by a solar
or AC powered network station, called the basic station (BS). Each base station,
in tum, is controlled by a switching office, called a mobile switching centre
(MSC). Coordinates communications between all the base station and the
telephone central office, It is a computerized centre that is responsible for
connecting cells, recoding call information, and billing.
Cell size is not fixed and can be increased or depending on the population
of the area. The typical radius of cell a 1 to 12 mi. High-density areas require
more, geographically smaller cells to meet traffic demands than do low-density
areas. Once determined, cell size is optimized to prevent the interference of
adjacent cell signals. The transmission power of each cell is kept low to prevent
its signal from interfering with those of other cells.

Cellular Telephone System

Cellular system comprises the following basic components:

 Mobile Stations (MS): Mobile handsets, which is used by an user to
communicate with another user

 Cell: Each cellular service area is divided into small regions called cell (5
to 20 Km)

 Base Stations (BS): Each cell contains an antenna, which is controlled by
a small office.
 Mobile Switching Centre (MSC): Each base station is controlled by a

switching office, called mobile switching centre.

Frequency Reuse Principle

Cellular telephone systems rely on an intelligent allocation and reuse of channels.
Each base station is given a group of radio channels to be used within a cell. Base
stations in neighbouring cells are assigned completely different set of channel
frequencies. By limiting the coverage areas, called footprints, within cell
boundaries, the same set of channels may be used to cover different cells