2. Multiplexing
What is Multiplexing?
• Multiplexing is the process of combining multiple signals into
one signal, over a shared medium
• A multiplexer is combinational circuit that has 2n input lines and
single output line
• A multiplexer is an electronic switch that connects 1 out of ‘n’
inputs to an output
3. Multiplexing
1)we use select line to determine which input (I1,I2,I3,I4) is selected by an output.
2)so if we have 2^2(4) inputs then 4 sets and each set has 2pairs of binary 0,1.
here 0=S’ and 1=S,
4. Describe the Goals of Multiplexing
• Multiplexing is the set of techniques that allows the simultaneous transmission of
multiple signals across a single data link.
• Multiplexing is achieved by using a device called Multiplexer (MUX) that
combines n input lines to generate a single output line. Multiplexing follows many-
to-one, i.e., n input lines and one output line.
MUX=
• Demultiplexing is achieved by using a device called Demultiplexer (DEMUX)
available at the receiving end. DEMUX separates a signal into its component
signals (one input and n outputs). Therefore, we can say that demultiplexing
follows the one-to-many approach.
DEMUX=
7. 1. Frequency-Division Multiplexing
• Frequency-division multiplexing (FDM) is an analog technique that can be
applied when the bandwidth of a link (in hertz) is greater than the combined
bandwidths of the signals to be transmitted.
• Signal generated by each userare modulated into different carrier frequencies
& then combine into a single composite signal transported by link.
• In FDM, the total bandwidth is divided to a set of frequency bands that
do not overlap.
8. Frequency-Division Multiplexing
• Each of these bands is a carrier of a different signal that is
generated and modulated by one of the sending devices.
• The frequency bands are separated from one another by strips
of unused frequencies called the guard bands, to prevent
overlapping of signals.
• Used in broadcast radio & cable television.
9. Frequency-Division Multiplexing
• Above mentioned diagram we have three inputs analog frequencies and
these frequencies has individual carrier frequencies .
• Then these frequencies are modulated and create new frequencies shown
in (red color)
single composite
signal
10. Frequency-Division Multiplexing
• Then combined these modulated frequencies to form a single
composite signal
• This is done at multiplexing end means sender site.
• After all the DMUX is start its work.
11. Frequency-Division Multiplexing
• Then , at DMUX side the single composite signal is pass through the
filters.
• After passing through the filter the single composite signal is divided
into its previos three signals but filtered.
12. Frequency-Division Multiplexing
• Then these three signals are demodulate and find its carrier
frequency
• Then the original Analog signal is received at the demultiplexing site.
13. Advantages of FDM:
• FDM is simpler and easy demodulation
• Less expensive
• Using FDM system multimedia data can be transferred with very
high efficiency and low noise and distortion
• FDM system has high reliability
• It is used for analogue signals
• In this system due to slow narrowband fading, only one channel gets
affected
• A large number of the signal can be transmitted simultaneously
14. Disadvantages of FDM:
• It is suffering the problem of cross talk
• FDM is only used only when a few low-speed channels are desired
• The circuitry for FDM is complex than TDM
• FDM requires more hardware than TDM
• FDM system extremely expensive
• The full bandwidth of the channel cannot be used on the FDM
system
• The communication must have very large bandwidth
• A large number of modulator and filter required
• FDM system needs a carrier wave or carrier signal but TDM does not
need carrier signal
15. 2. Wavelength division multiplexing
• Wavelength division multiplexing, WDM, has long been the technology of
choice for transporting large amounts of data between sites.
• It increases bandwidth by allowing different data streams to be sent
simultaneously over a single optical fiber network.
• Wavelength-division multiplexing (WDM) is designed to use the high-data-rate
capability of fiber-optic cable.
• The optical fiber data rate is higher than the data rate of metallic transmission
cable
17. Wavelength division multiplexing
• One prism is multiplexer and the other is demultiplexr.
• WDM is conceptually the same as FDM, except that the multiplexing
and demultiplexing involve optical signals transmitted thoruh fiber
optic channel.
• The idea is the same: We are combining different signals of different
frequencies. The difference is that the frequencies are very high.
• Light Can be sent through different amount ,based on the angle of
incident and wavelength of light.
18. Advantages of WDM:
• Easier to reconfigure
• Full duplex transmission is possible
• It provides higher bandwidth
• Optical component are similar and more reliable
• High security
• This could be the best approach as it is simple to implement
19. Disadvantages of WDM:
• Signals cannot be very close
• Cost of the system increases with the addition of optical
components
• Difficulty in wavelength tuning
• Difficulty in a cascaded topology
20. Time Division Multiplexing
• TDM is a digital multiplexing technique for combining several low-rate
channels into one high-rate one.
•Time-division multiplexing (TDM) is a digital process that allows several
connections to share the high bandwidth of a line.
•Instead of sharing a portion of the bandwidth as in FDM, time is shared.
•Each connection occupies a portion of time in the link.
22. • Here data is must be sent in time frames(T1,T2,T3,T4)
• Link is divided in time slots.
Types of TDM
1. Synchronous TDM,
2. Statistical (or Asynchronous) Time Division Multiplexing
23. Synchronous TDM
• In synchronous TDM, the data flow of each input connection is divided into
units, where each input occupies one input time slot. A unit can be 1 bit,
one character, or one block of data.
• Each input unit becomes one output unit and occupies one output time
slot.
• However, the duration of an output time slot is n times shorter than the
duration of an input time slot.
• If an input time slot is T s, the output time slot is Tin s, where n is the
number of connections.
• In other words, a unit in the output connection has a shorter duration; it
travels faster.
25. Statistical (or Asynchronous) Time
Division Multiplexing
• As we saw in the previous section, in synchronous TOM,each
• Input has a reserved slot in the output frame.
• This can be inefficient if some input lines have no data to send.
• In statistical time-division multiplexing, slots are dynamically
allocated to improve bandwidth efficiency.
• In statistical TOM, a slot needs to carry data as well as the
address of the destination.
26. • It mean like in synchronios TDM if time slot is empty the it send it as it
is.
• But in statistical TDM stations send data along with its address of
destination that attach in header.
27.
28. Advantages:
• Time division multiplexing systems are more flexible than
frequency division multiplexing.
• Time division multiplexing circuitry is not complex.
• Problem of cross talk is not severe.
• Full available channel bandwidth can be utilized for each
channel.
• Disadvantage:
• In time-division multiplexing, synchronization is pretty much
essential
