BASIC CONCEPTS OF CELLULAR RADIO
the other user may be another mobile terminal. Most of the connectivity is extending "plain
old telephone service" (POTS) to mobile users. Data and facsimile services are in various
stages of implementation. Some of the terms used in this section have a strictly North
Figure 18.1 illustrates a conceptual layout of a cellular radio system. The heart of
the system for a specific serving area is the MTSO (mobile telephone switching office).
The MTSO is connected by a trunk group to a nearby telephone exchange providing an
interface to and connectivity with the PSTN.
The area to be served by a cellular geographic serving area (CGSA) is divided into
small geographic cells, which ideally are hexagonal.
Cells are initially laid out with
centers spaced about 48 m (6.412.8 km) apart. The basic system components are the
cell sites, the MTSO, and mobile units. These mobile units may be hand-held or vehicle-
Each cell has a radio facility housed in a building or shelter. The facility's radio equip-
ment can connect and control any mobile unit within the cell's responsible geographic
area. Radio transmitters located at the cell site have a maximum effective radiated power
(ERP) of 100 W.
Combiners are used to connect multiple transmitters to a common
antenna on a radio tower, usually between 50 ft and 300 ft (15 m and 92 m) high. Com-
panion receivers use a separate antenna system mounted on the same tower. The receive
antennas are often arranged in a space diversity configuration.
Conceptual layout of a cellular radio system.
CGSA is a term coined by the U.S. FCC. We do not believe it is used in other countries.
Care must be taken with terminology. In this instance, ERP and EIRP are not the same. The reference antenna
in this case is the dipole, which has a 2.15-dBi gain.