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Multiplexing
Groupmembers
* Harpreetkaur
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What is Multiplexing
It is the process of sending signalsfrom two or more different sourcessimultaneously over a singlecommunication channel.
Multiplexing is done by using adevice called multiplexer(MUX) thatcombines n input lines to gernate oneoutput line i.e (many to one).Thereforemultiplexer (MUX) has serval inputs oneoutput.
At the receiving end , a device
demultiplexer (DEMUX) is used that
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Types of Multiplexing
Frequency Division Multiplexing (FDM) Wave Division Multiplexing (WDM) Time Division Multiplexing (TDM)
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Frequency Division Multiplexing
It is analog technique. In FDM, signals of different frequencies arecombined into a single composite signal and
is transmitted on single link.
FDM requires that the bandwidth of a linkshould be greater than the combinedbandwidths of various signals to betransmitted. Thus each signal having different frequency
from a particular logical channel on the linkand follow this channel only. These channels are then separeted by thestrips of unused bandwidth called gurad
band.These gurad bands band prevent the
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Frequency Division Multiplexing
In FDM signals to be transmitted must beanalog signals. Thus digital signals need to beconverted to analog form, if they are to useFDM.
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Applications of FDM
FDM is used for FM & AM radio broadcasting.Each AM & FM radio stations uses a differentcarries frequency . FDM is used in television broadcasting.
First generation cellular telephone also usesFDM.
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Wave Division Multiplexing
WDM is the analog multiplexingtechnique.WDM is conceptually similar to FDM,in sense that it combines different signals ofdifferent signals of different frequencies into
single composite signal and transmit it on asingle link. In WDM the different signals are optical orlight signals that are transmitted throughoptical fiber.Wavelength goes up down and
vice-verse. In WDM various waves from different sourcesare combined to form composite light signalthat is transmitted across the channels to the
different receiver.
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Wave Division Multiplexing
At the receiver side, this composite lightsignal is broken into different light waves bydemultiplexer. This combines and splitting of light waves is
not by using a prism. One prism is used at the sender side toperform multiplexing and another prism is usedat receiver side that perform demultiplexing. The basic principal behind the usage of prism
is that,the prism bends a beam of light basedon the angle of incidence and the frequency oflight wave.
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Applications of WDM
WDM is used in SONET(Synchronous OpticalNetwork).It makes use of multiple optical fiberlines which are multiplexed & demultiplexed.
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Time Division Multiplexing
TDM is a digital multiplexing technique. In TDM, the channels is not divided on thebasis of frequency but on the basic of time. Total time available in the channel is divided
between serveral users. Each time is allotted a particular a timeinterval called time slot during which the datais transmitted by that user. Each sending device takes control of entire
bandwidth .
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Time Division Multiplexing
There are two types of TDM* Synchronous TDM* Asynchronous TDM
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Synchronous TDM
Multiplexer allots the same time slot to eachdevice at all time either device having data ornot. If there are n input lines then there are n
slots in one frame. Number of slots = No ofinput lines. Synchronous TDM does not give guaranteethat full capacity of link is used . The no of time slot in a frame is always based
on no of input devices . The time slots are fixed and predefined.
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Asynchronous TDM
It is also known as STATISTICAL TDM.Multiplexer does not allots same time slot toeach device at all time . Time slots are flexibleand not fixed.
If there are n input lines then there are mslots perform. m is less than n. Asynchronous TDM give guarantee that fullcapacity of link is used . The no of time slot in a frame is always based
on statistical analysis of no of input devices. The time slots are not fixed and predefined.
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Reference: Charanjeet singh(kalyani Publisher)