13-04-2012, 03:57 PM
CELLULAR MOBILE COMMUNICATIONS
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HISTORY & DEVELOPMENT
Cell phones have become the modern
fastest means of Communication on
move especially for the Business
Magnets & Professional job holders. The
roots of the cellular systems belong to
the years of 1940’s but the trial service
did not begin until 1970. Initially there
were only 2000 consumers could use
them, as there were only a few channels
& People who really needed Mobile
Communications capability installed
radio-telephones in their cars. In the
radio telephone system, there was one
central antenna tower per city, with
about 25 channels.
THE CELL & CLUSTER:
Cells are base stations (BS)
communicates with mobiles via a
channel & broadcast at very low power
levels (typically 200 mW to 1W). The
channel is made of two frequencies, one
for transmitting to the base station and
one to receive information from the base
station. Cell Size varies depending on
the landscape.
FUNCTIONAL DESCRIPTION:
All Cell phones have special codes.
These codes identify the phone, the
phone’s owner, & the service provider.
ROAMING
Roaming was the most challenging
issues the cell phone manufactures
faced. The goal was simple: the phone
could be used anywhere in the world
where compatible technology is used.
When the user turns his cell phone on in
a roaming area, the cell phone identifies
itself to the switch. The switch looks up
the information & discovers that the
phone is not a local phone.
Principles of GSM
Frequency Concepts -For Mobile
communication a Duplex Channel is
required which mean that two way both
at a time, it uses two frequencies: One to
the Mobile Station (MS) and one from
the Mobile Station. The direction from
the Mobile Station to the network is
referred to as uplink and the direction
from the network to the Mobile Station
is referred to as down link. Speech
coding-GSM is a digital system, so
speech that is inherently analog, has to
be digitized.
CODED DIVISION MULTIPLE ACCESS (CDMA):
CDMA is the most interesting & most
difficult to implement multiplexing
method, it have no channels. Instead
these encode each call as a coded
sequence across the entire frequency
spectrum. Each connversation is
modulated in the digital domain, with a
unique code that makes it
distinguishable from the other calls in
the frequency spectrum.
Advantages of CDMA:
The advantages of CDMA are: (1)
Increased cellular communications
security,(2) Simultaneous conversations,
(3) Increased efficiency, meaning that
the carrier can serve more subscribers,
(4) Smaller phones, (5) Low power
requirements and little cell-to-cell
coordination needed by operators, and
(6) Extended reach - beneficial to rural
users situated far from cells.
CONCLUSION
The battle between GSM and CDMA
technologies in India is hotting up!
While the initial tilt was towards the
GSM with players like Hutch, Spice,
BPL and BSNL preferring it, the TATA
and the Reliance have now entered the
market putting their bets on CDMA.