Theory Of Operation; Gsm System Overview; General Cellular Concept; Gsm Description - Motorola 880 Service Manual

Cellular Subscriber Sector

Theory of Operation

GSM System Overview

NOTE
The following description is intended only
as a preliminary general introduction to
the Global System for Mobile communi-
cations (GSM) cellular network. This
description is greatly simplified and does
not illustrate the full operating capabili-
ties, techniques, or technology incorpo-
rated in the system.

General Cellular Concept

The cellular systems are used to provide
radiotelephone service in the frequency
range 890-960 MHz for GSM and 1710-1880
MHz for DCS. A cellular system provides
higher call handling capacity and system
availability than would be possible with
conventional radiotelephone systems (those
which require total system area coverage on
every operating channel) by dividing the
system coverage area into several adjoining
sub-areas or cells.
Each cell contains a base station (cell site)
which provides transmitting and receiving
facilities, for an allocated set of duplex
frequency pairs (channels). Since each cell is
a relatively small area, both the cell site and
the radiotelephone that it supports can
operate at lower power levels than would be
used in conventional systems.
© 1997 Motorola, Inc.
THEORY OF OPERATION
Dual Band 880/890 (DCS/GSM)
Using this technique, radiation on a given
channel is virtually contained in the cell
operating on that channel and, to some
extent, those cells directly adjacent to that
cell.
Since the coverage area of a cell on a given
channel is limited to a small area (relative to
the total system coverage area), a channel
may be reused in another cell outside the
coverage area of the first. By this means,
several subscribers may operate within the
same geographic area, without interference
with each other, on a single channel.

GSM Description

Unlike previous cellular systems, GSM uses
digital radio techniques. The GSM system
has the following advantages over previous
analogue systems:-
• International
international
standardization, it will be possible to make
and receive calls in any country which
supports a GSM system.
• Digital Air Interface - The GSM phone
will provide an entirely digital link
between the telephone and the base
station, which is, in turn, digitally linked
into the switching subsystems and on into
the PSTN.
• ISDN Compatibility - ISDN is a digital
communications standard that many
countries are committed to implementing.
68P09403A50
Roaming - Due
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