GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), is a standard set developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for second generation (2G) digital cellular networks used by mobile phones. It became the de facto global standard for mobile communications with over 80% market share.
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GSM introduction
1. By : Amit Kumar Sinha
Date:23-02-2010
8/5/2013 1
2. History……Yaaaaawn
When the acronym GSM was used for the first time in 1982,
it stood for Groupe Spéciale Mobile, a committee under the
umbrella of Conférence Européenne des Postes et
Télécommunications (CEPT), the European standardization
organization.
The task of GSM was to define a new standard for mobile
communications in the 900 MHz range. It was decided to
use digital technology. In the course of time, CEPT evolved
into a new organization, the European
Telecommunications Standard Institute (ETSI).
The first GSM network was launched in 1991 by Radiolinja
in Finlandwith joint technical infrastructure maintenance
from Ericsson.
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3. GSM Present……
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2,449,937309,907,068118,688,849
3,450,410,548
255,630,141133,286,097825,044 1,480,766 9,5930
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1,000,000,000
1,500,000,000
2,000,000,000
2,500,000,000
3,000,000,000
3,500,000,000
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5. GSM Air Interface
Bursts
Each carrier frequency used in GSM is divided into 8 independent
timeslots and into each of these timeslots a burst is placed. The
diagram shows the general format of a GSM burst. The receiver can
only receive the burst and decode it if it is received within the timeslot
designated for it. The timing, therefore, must be extremely accurate,
however, the structure does allow for a small margin of error by
incorporating a ‘guard period’ as shown in the diagram. To be precise,
the timeslot is 0.577ms long, whereas the burst is slightly shorter at
0.546ms. Eight bursts occupy one TDMA frame.
The ‘‘flag-bits” are set when the frame has been ‘stolen’ by FACCH (the
Fast Associated Control Channel).
The ‘‘training sequence” is used by the receiver’s equaliser as it
estimates the transfer characteristic of the physical path between the
base-station and the mobile.
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14. Erlang B
One Erlang is a measure of one traffic channel permanently
occupied at busy hour.
For example busy hour (if measured for hourly basis) in
Bangalore occurs twice in 24 hrs. Generally between 10 am
to 11 am and 8 pm to 9pm.
Then if I say 0.25 Erl corresponds to 1 resource occupied for
25 % of time(i.e. 15 minutes in our case)
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15. How is Erlang calculated???
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25 mE
10 mE
5 mE
16. TCH Calculation
8/5/2013 16
Max. traffic/subscriber at busy
hour = 25 mE
No. of subscriber = 1700
Then planned traffic in cell
including the 1700 subscriber=42.5
Erlang
No. of necessary resources with a
blocking rate of 2% obtained from
Erlang B table = 53 resources
TCH channels = 53 for 42.5
Erlang
17. SDCCH Calculation
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Now for SDCCH calculation,
If TCH = 42.5 Erlang then SDCCH = 28% of TCH
(i.e. 42.5)= 11.9 Erlang
So the no. of SDCCH resources at 0.1% blocking
rate = 24 (from table)
No. of SDCCH = 24/8 = 3 SDCCH TS
18. TRX Calculation
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No. of CCCH required = 1 per cell
Therefore we can conclude now
That , total no. of TS required = 53 + 3 + 1 = 57
Total of TRX= 57 / 8 = 8 (rounding to upper limit)
