Multiplexing Definition
Multiplexing is a technique which combines multiple signals into one
signal, suitable for transmission over a communication channel such as coaxial
cable or optical fiber.
The multiplexing
technique divides the communication channel into several logical sub-channels.
Each logical sub-channel is dedicated to an individual signal.
Multiplexing is
done by using a device called Multiplexer or MUX. The multiplexer combines n
input lines to generate one output line.
Types of Multiplexing
Multiplexing
is mainly classified into two types:
o Analog multiplexing
o Digital multiplexing
1.Analog multiplexing is again
classified into two types:
1.
Frequency
Division Multiplexing
2.
Wavelength
Division Multiplexing
2.The time division multiplexing(Digital multiplexing) is again classified into two types:
i.
Synchronous TDM
ii.
Asynchronous TDM
Analog Multiplexing
The process of combining multiple analog signals into one signal
is called analog multiplexing. It multiplexes the analog signals according to
their frequency or wavelength. This can be achieved by separating the signal in frequency.
There are two types of analog multiplexing:
i.
Frequency
division multiplexing
ii.
Wavelength
division multiplexing
Frequency
Division Multiplexing
Frequency division multiplexing is an analog technique. This
technique combines multiple signals into one signal and transmitted over the
communication channel. Frequency division multiplexing is also known as FDM.
In this technique, the bandwidth of the communication channel
should be greater than the combined bandwidth of individual signals.
The frequency division multiplexing divides the bandwidth of a
channel into several logical sub-channels. Each logical sub-channel is
allotted for a different signal frequency.
In this technique, each logical sub-channel is allotted to each
user. Each logical sub-channel is separated by an unused bandwidth called Guard
Band to prevent overlapping of signals. A guard band is a narrow frequency
range that separates two signal frequencies.
Advantages
of Frequency Division Multiplexing (FDM)
1. It transmits multiple signals simultaneously.
2. In frequency division multiplexing, the demodulation process is
easy.
3. It does not need Synchronization between transmitter and
receiver.
Disadvantages of Frequency Division Multiplexing (FDM)
It needs a large bandwidth communication channel.
Applications of Frequency Division Multiplexing (FDM)
1. Frequency division multiplexing is used for FM and AM radio
broadcasting.
2. It is used in first generation cellular telephone.
3. It is used in television broadcasting.
Wavelength
Division Multiplexing
Wavelength division multiplexing is an analog technique. It is the
most important and most popular method to increase the capacity of an optical
fiber.
We know that wavelength and frequency are inversely proportional
to each. Therefore, the working principle of wavelength division multiplexing
is similar to frequency division multiplexing.
Wavelength division multiplexing is a technology in which multiple
optical signals of different wavelengths or colors are combined into one signal
and is transmitted over the communication channel. Thus multiple signals are
transmitted simultaneously over a single communication channel.
Or
Wavelength division multiplexing is a technology that increases
the bandwidth of a communication channel by simultaneously allowing multiple
optical signals through it.
Wavelength division multiplexing is also known as WDM. A
demultiplexer at the receiver end separates the optical signal wavelengths or
colors.
In this technique, the bandwidth of the communication channel
should be greater than the combined bandwidth of individual signals.
The main advantage of WDM system is that you only need to upgrade
the multiplexer and demultiplexer at each end, you no need to buy more fibers
which are more expensive.
Wavelength division multiplexing enables bi-directional
communication and multiplication of optical signal capacity.
Types of
Wavelength Division Multiplexing
WDM techniques are of two types:
i.
Dense Wavelength Division
Multiplexing
ii.
Coarse Wavelength Division
Multiplexing
Dense
Wavelength Division Multiplexing
Dense Wavelength Division Multiplexing is also known as DWDM.
It is a technology in which a large number of optical signals of
different wavelengths or colors are combined into one signal and is transmitted
over the communication channel to a long distance.
The DWDM technology is mainly useful for long distance
communication (>100 km).
Coarse
Wavelength Division Multiplexing
Coarse wavelength division multiplexing is a technology in which
multiple optical signals of different wavelengths or colors are combined into
one signal and is transmitted over the communication channel for a short
distance.
Coarse wavelength division multiplexing is also known as CWDM
Coarse
Wavelength Division Multiplexing has the ability to transport up to 18 optical
signals per optical fiber. It is designed for short distance.
Advantages
of Wavelength Division Multiplexing (WDM)
1. WDM allows transmission of data in two directions
simultaneously
2. Low cost
3. Greater transmission capacity
4. High security
5. Long distance communication with low signal loss
Digital
Multiplexing (Time
Division Multiplexing)
The process of combining multiple digital signals into one signal
is called digital multiplexing.
Time Division Multiplexing is a technique in which multiple
signals are combined and transmitted one after another on the same
communication channel.
Time Division Multiplexing is also known as TDM. It is the digital
multiplexing technique.
The time division multiplexing technique is used to multiplex
analog signals or digital signals. However, the time division multiplexing is
more suitable for digital signal multiplexing.
In time division multiplexing, the bandwidth capacity of the
communication channel should be greater than the multiple input signals.
Types of TDM
(Time Division Multiplexing) : -
Time Division Multiplexing is
mainly classified into two types:
i.
Synchronous TDM (Time Division
Multiplexing)
ii.
Asynchronous TDM (Time Division
Multiplexing)
Synchronous
TDM (Time Division Multiplexing) : -
In synchronous time division multiplexing, each device
(transmitter) is allotted with a fixed time slot, regardless of the fact that
the device (transmitter) has any data to transmit or not.
The device has to transmit data within this time slot. If the
device (transmitter) does not have any data to send then its time slot remains
empty.
The main drawback of synchronous time division multiplexing
is that the channel capacity is not fully utilized. Hence, the bandwidth goes
wasted.
Asynchronous
TDM (Time Division Multiplexing)
In Asynchronous time division multiplexing, the time slots are not
fixed. The asynchronous TDM is also known as statistical time division multiplexing.
In Asynchronous TDM, the number of time slots is not equal to the
number of devices. The time slots in asynchronous TDM are always less than the
number of devices.
Advantages
of Time Division Multiplexing (TDM)
1. Full bandwidth is utilized by a user at a particular time.
2. The time division multiplexing technique is more flexible than
frequency division multiplexing.
3. In time division multiplexing, the problem of crosstalk is very
less.
Disadvantages of Time
Division Multiplexing (TDM)
In time division multiplexing, synchronization is required.
Advantages
of multiplexing
1. Multiple signals can be sent simultaneously over a single
communication channel.
2. Effective use of channel bandwidth
3. Multiplexing reduces cost
4. Multiplexing reduces circuit complexity
Applications
of Multiplexing :
-
1. Communication system
2. Computer memory
3. Telephone systems
4. TV broadcasting
5. Telemetry
6. Satellites