2. INTRODUCTION
• Multiplexing is the set of techniques that allows the
simultaneous transmission of multiple signals across a
single data link.
• If the bandwidth of a link is greater than the bandwidth
needs of the devices connected to it, the bandwidth is
wasted. An efficient system maximizes the utilization of
all resources; bandwidth is one of the most precious
resources we have in data communications.
• In a multiplexed system, n lines share the bandwidth of
one link.
FIG 1: MULTIPLEXING
3. • MULTIPLEXER (MUX): It combines n input lines to
generate a single output line.
• DEMULTIPLEXER (DEMUX): It separates a signal
into its component signals at the receiving end.
NEED of MULTIPLEXING:
• To share a single medium by multiple of signals
• Medium must be divided such that each signal is given
some portion of bandwidth.
• To avoid the possibility of signal collision.
• Several telephone calls are carried through a single wire.
• ADVANTAGES OF MULTIPLEXING:
i. Many signals can be sent over one single medium.
ii. Bandwidth of a medium can be utilised effectively.
4. MULTIPLEXING TECHNIQUES:
a)Frequency Division Multiplexing (FDM)
• FDM is an analog multiplexing technique that
combines analog signals.
• FDM is a technique used in telecommunications
and broadcasting to transmit multiple signals
simultaneously over a shared medium by
dividing the available frequency spectrum.
5. • FDM involves dividing the total bandwidth of the
transmission medium into multiple non-
overlapping frequency bands
• Each signal to be transmitted is allocated a unique
frequency band within the spectrum.
• Signals are modulated onto carrier waves of
different frequencies before being combined for
transmission
FIG 2: FREQUENCY-DIVISION MULTIPLEXING
6. How FDM Works?
• Input signals are modulated onto carrier waves of
different frequencies using modulation techniques such
as amplitude modulation (AM) or frequency
modulation (FM).
• The modulated signals are combined into a composite
signal using a multiplexer.
FIG 3: FDM PROCESS
7. • At the receiving end, the composite signal is
passed through a demultiplexer, which separates
the individual signals based on their assigned
frequency bands.
• Each demultiplexed signal is then demodulated
to recover the original data.
FIG 4: FDM DEMULTIPLEXING
8. Advantages of FDM
• Efficient Use of Bandwidth: Allows multiple signals
to share the same transmission medium without
interference.
• Simplicity: Relatively straightforward implementation
compared to other multiplexing techniques.
• It is used for analog signals.
• Scalability: Can accommodate a varying number of
channels by adjusting frequency allocations.
• It does not need any synchronisation between sender
and receiver.
9. Disadvantages of FDM
• It is used only when low speed channels are required.
• Crosstalk: Interference between adjacent frequency
bands can degrade signal quality, requiring careful
frequency planning and filtering.
• Bandwidth Allocation: Efficient allocation of frequency
bands is crucial to avoid underutilization or
overcrowding.
• Signal Interference: External factors such as
electromagnetic interference (EMI) or noise can disrupt
FDM systems, necessitating proper shielding and signal
processing techniques.
• A large number of modulators are required.
10. Applications of FDM
• Telecommunications: Used in long-distance
communication systems such as telephone networks to
transmit multiple voice or data channels over a single
cable.
• Broadcasting: Enables the simultaneous transmission of
multiple TV or radio channels over the airwaves.
• Cable Television (CATV): Distributes multiple
television channels over cable networks to subscribers'
homes.
• Satellite Communication: Utilizes FDM to maximize
the use of satellite bandwidth for various
communication services.
