GSM

Throughout Europe, a new part of the spectrum in the area around 900 MHz has been made
available for 2G systems. This allocation was followed later by allocation of frequencies at
the 1800 MHz band. 2G activities in Europe were initiated in 1982 with the formation of a
study group that aimed to specify a common pan-European standard. Its name was ‘Groupe
Speciale Mobile’ (later renamed Global System for Mobile Communications). GSM [3],
which comes from the initials of the group’s name, was the resulting standard. Nowadays,
it is the most popular 2G technology; by 1999 it had 1 million new subscribers every week.
This popularity is not only due to its performance, but also due to the fact that it is the only 2G
standard in Europe. This can be thought of as an advantage, since it simplifies roaming of
subscribers between different operators and countries.
The first commercial deployment of GSM was made in 1992 and used the 900 MHz band.
The system that uses the 1800 MHz band is known as DCS 1800 but it is essentially GSM.
GSM can also operate in the 1900 MHz band used in America for several digital networks and
in the 450 MHz band in order to provide a migration path from the 1G NMT standard that
uses this band to 2G systems.
As far as operation is concerned, GSM defines a number of frequency channels, which are
organized into frames and are in turn divided into time slots. The exact structure of GSM
channels is described later in the book; here we just mention that slots are used to construct
both channels for user traffic and control operations, such as handover control, registration,
call setup, etc. User traffic can be either voice or low rate data, around 14.4 kbps.