GSM

Global System for Mobile Communications (GSM) is the European standard
for digital cellular systems operating in the 900-MHz band. This technology
was developed out of the need for increased service capacity due to the analog
systems’ limited growth. This technology offers international roaming,
high-speech quality, increased security, and the capability to develop
advanced systems features. The development of this technology was completed
by a consortium of pan-European countries working together to provide
integrated cellular systems across different borders and cultures.
GSM is a European standard that has achieved worldwide success.GSM
has many unique features and attributes that make it an excellent digital
radio standard to utilize. GSM has the unique advantage of being the most
widely accepted radio communication standard at this time. GSM was
developed as a communication standard that would be utilized throughout
all of Europe in response to the problem of multiple and incompatible standards
that still exist there today.

GSM consists of the following major building blocks: the Switching System
(SS), the Base Station System (BSS), and the Operations and Support
System(OSS). The BSS is comprised of both the Base Station Controller
(BSC) and the Base Transceiver Stations (BTS). In an ordinary configuration,
several BTSs are connected to a BSC and then several BSCs are connected
to the Mobile Switching Center (MSC).
The GSM radio channel is 200 kHz wide. GSM has been deployed in several
frequency bands, namely the 900-, 1800-, and 1900-MHz bands. Both
the 1800- and 1900-MHz bands required some level of spectrum clearing
before the GSM channel could be utilized. However, the 900-MHz spectrum
was used by an analog system Enhanced Total Access Communiction
System (ETACS), which occupied 25-kHz channels. The introduction of GSM into this band required the reallocation of traffic or rather channels to
accommodate GSM.