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The global system for mobile communications (GSM), is
a world-wide standard for digital
wireless mobile phones. Developed in Europe as standard for the 2nd
Generation of mobile
phones, with the intention of creating a system that would be adopted
world-wide.
GSM has obtained wide support especially in Europe, where it is the major
mobile standard.
it is used throughout Asia and Australia, Japan and the USA originally
went their own way
using the D-AMPS and PCS system. recently GSM has made inroads in to the
American market.
GSM differs from its predecessors most significantly in that both
signalling and speech channels are digital. It has also been designed for
a moderate level of security. The commonality of the systems world wide
allow handsets from one county to be used in most places of the world this
makes production costs cheaper and allows international roaming
frequently enabled by "roaming agreements" between operators.
GSM exists in four main versions, based on the band used: GSM-900,
GSM-1800, GSM-850 and GSM-1900. GSM-900 (900 MHz) and GSM-1800 (1.8 GHz)
are used in most of the world, excluding the United States and Canada. The
United States and Canada use GSM-850 and GSM-1900 (1.9 GHz) instead, since
in the U.S. the 900 and 1800 bands were already allocated.
GSMs age as a system is starting to show, while its Data rate of 9600
bits/s is fine when in voice mode, it struggles in data mode as today's
user is expecting alot more from there phones. This is why GPRS was
developed which allows packet switched data transmission. GPRS has been
called 2.5G as it is viewed as a stepping stone toward pure 3G systems.
GPRS is backward compatible with GSM. This eases the migration path for a
GSM operator, who
can gradually upgrade the infrastructure to GPRS as the market expands.
Packet switched data under GPRS is achieved by allocating unused cell
bandwidth to transmit data. As dedicated voice (or data) channels are
setup by phones, the bandwidth available for packet switched data shrinks.
A consequence of this is that packet switched data has a poor
bitrate in busy cells. The theoretical limit for packet switched data is
approx. 170 kbit/s. A realistic bitrate is 30-70 kbit/s. A change to the
radio part of GPRS called EDGE will allow higher bit rates of between 20
and 200 kbit/s.
GSM cells have a range limit of around 30klm, which is fine in Europe
which has a high population density but in large countries like Australia,
dead spots are quite common between towns.
GSM introduced a few new features like SMS and WAP, SMS has become big
business it allows users to send and receive short text messages to family
and friends, While WAP is a system that allows internet web sites to be
displayed on GSM phones. Developed before GPRS, the idea was to get web sites
to make smaller WAP pages to speed up access on GSMs feeble 9600
bandwidth, it has had limited popularity.
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