Specifications

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Cell structures
Base stations are positioned to give maximal coverage. The area covered by a
base station is called a cell.
The entire GSM network is organised with cells of varying sizes. A cell
can cover areas with a radius of 200 metre (656 ft) up to areas with a
radius of ~30 km (18.64 mi). This depends on where the base station is
located and the surrounding environment.
Other factors that affect the installation are, among others, the output
power and whether the base station is located in an environment that
is problematic for radio trafc. The cell structure results in the reuse of
frequencies in the base stations. In the gure on the left shows that the
frequency A1 can be reused in the third ring without the risk of crosstalk
between cells with the same frequency.
If you travel through an area it is necessary to switch between the cells through
which you pass. This is known as handover.
Radio transmissions between MS and BSS
In the eighties when the GSM specication was drawn up, the ITU (International
Telecommunication Union) reserved two frequency bands of 25 MHz for GSM
radio transmissions:
… 880–915 MHz “uplink” transfers from MS to BSS.
… 925–960 MHz “downlink” transfers from BSS to MS.
The development within mobile communication has resulted in the need to use
multiple frequencies to satisfy demand. Today there are ve standardised
frequencies 400, 850, 900, 1800 as well as 1900 MHz. The latter frequency is
generally used in the USA and in some parts of Asia, while 900 and 1800 are
more globally used.
Services on the GSM network
There are a number of services available via GSM such as:
… Telephony.
… CSD (
Circuit Switched Data, data transfer).
… SMS (
Short Message Service).
… MMS (
Multimedia Message Service).
… FAX.
… GPRS (
General Packet Radio Service).
E21
E21
E21
E21
E21
D2
A1
A1
A1
A1
A1
A1
C8
B2
B5
B6
B7
B4
B3
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
D2
D2 D2
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