Transcript
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4.3 MultiplexingOutlines
FDM
TDM
WDM
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Introduction
Definition
1. The transmission of information from one ormore source to one or more destination over
the same medium.
2. The process which two or more signals
are combined for transmission over a single
communications path.
3. A process where multiple analog message
signals or digital data streams are combined into
one signal with the aim is to share an
expensive resource.
http://en.wikipedia.org/wiki/Multiplexing
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Make the communications ver economical
b transmitting thousands of independentsignals over a single transmission line.
Three predominant was to multiplex
1. !re"uenc Division Multiplexing #!DM$
2. Time Division Multiplexing #TDM$
3. %avelength Division Multiplexing #%DM$
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Multiplexing allows several analog signals to
be processed b one analog&to&digitalconverter #AD'$ ( ).g. *everal phone calls ma be transferred using
one wire.
The multiplexed signal is transmitted over acommunication channel which ma be a
phsical transmission medium.
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The multiplexing divides the capacit of the
low&level communication channel into severalhigher&level logical channels+ one for each
message signal or data stream to be
transferred.
A reverse process+ known as demultiplexing+can extract the original channels on the
receiver side.
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A multiplexing techni"ue ma be further extendedinto a multiple access method or channel access
method. ( ).g. Time Division Multiple Access #TDMA$
Multiple access method makes it possible forseveral transmitters connected to the same
phsical medium to share its capacit.
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'oncept of multiplexing
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Frequency Division Multiplexing (FDM)
,redominantl used in analog
communications.%idel used in !M stereo broadcast.
'ompatibilit with mono&receivers.
-e"uires onl a slight increase in %.
/reat advantage in increasing sstem
capacit.
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Transmitting end of an !DM *stem
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,rocess ( )ach signal assigned s different carrier
fre"uenc.
( Modulated carrier fre"uencies are combined fortransmission over a single line b M0.
( At -x+ a D)M0 separates channels b their
fre"uencies routes them to the proper endusers.
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ime-Division Multiplexing
This technique combines time-domainsamples from different message signals
(sampled at the same rate) and transmitsthem together across the same channel.
Performed using a commutator (switch).
t the receiver a decommutator (switch)is used in s!nchronism with thecommutator to demultiplex the data.
ver! sensitive to s!mbol dispersion" thatis" to variation of amplitude withfrequenc! or lac# of proportionalit! ofphase with frequenc!. This problem ma!be solved through equali$ation of both
magnitude and phase.
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Time Division Multiplexing (TDM)4ffers greater sstem improvement.
'apable of combining various protocols different
tpes of signals onto a single high speed
transmission link. ( ).g. voice and data
More efficient than !DM
% Methods used to s!nchroni$e the operations ofmultiplexing and demultiplexing & organi$e the
multiplexed stream of data as frames with a
special pattern. The pattern is #nown to the
receiver and can be detected ver! easil!.
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,rocess (
The transmission must be digital in nature. ( To transmit telephone conversations #voice is
analog signal$ Analog signal is converted to digital and transmitted
-econverted into analog at the -x telephone.
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'loc# diagram of DM-P(M
communication s!stem
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Drawbacks ( /reater complexit.
( /reater transmission % re"uired.
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Wvelengt! Division Multiplexing
(WDM)
'ost effective wa to increase the capacit of
fiber optic communications.Make use of the optical fiber5s available %
b multiplexing man wavelengths along a
single mode optical fiber channel.
)ach wavelength of light can transmitencoded information at the optimum data
rate.
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