BASIC CONCEPTS ON MULTIPLEXING IN COMMUNICATION


Introduction :

To combine multiple signals ( analog or digital) for transmission over a single line or media.

A common type of multiplexing combines several low-speed signals for transmission over a single high-speed connection.

The technique of transmitting multiple signals over a single medium is defined asMultiplexing.

It is a technique showed at physical layer of OSI model.

The different types of multiplexing technologies are as below:

§  Wavelength Division Multiplexing

§  Frequency Division Multiplexing

§  Dense Wavelength Division Multiplexing

§  Conventional Wavelength Division Multiplexing

§  Reconfigurable Optical Add-Drop Multiplexer

§  Orthogonal Frequency Division Multiplexing

§  Add/Drop Multiplexing

§  Inverse Multiplexing

Multiplexing is done by using a device called multiplexer (MUX).

It combines n input lines to generate one output line i.e. (many to one).

Therefore multiplexer (MUX) has several inputs and one output.

At the receiving end, a device called demultiplexer (DEMUX) is used that separates signal into its component signals.

So DEMUX has one input and several outputs.

Concept of Multiplexer:

§  The Multiplexer acts as a multiple-input and single-output switch.

§  Multiple signals share one device or transmission conductor such as a copper wire or fibber optic cable.

§  In telecommunications, the analog or digital signals transmitted on several communication channels by a multiplex method.

§  These signals are single-output higher-speed signals.

§  A 4-to-1 multiplexer contains four input signals and 2-to-1 multiplexer has two input signals and one output signal.

Types of Multiplexer:

  • Analog

 

  • Digital

 

Analog Multiplexer

Analoge is divided into further parts. These are:

  • Frequency Division Multiplexing

 

  • Wavelength Division Multiplexing

Frequency Division Multiplexing:

§  Frequency Division Multiplexing is a technique which uses various frequencies to combine many streams of data for sending signals over a medium for communication purpose.

§  It carries frequency to each data stream and later combines various modulated frequencies to transmission.

§  Television Transmitters are the best example for FDM, which uses FDM to broad cast many channels at a time.

Wavelength Division Multiplexing:

§  WDM is analog multiplexing technique and it modulates many data streams on light spectrum.

§  This multiplexing is used in optical fibber.

§  Various signals in WDM are optical signal that will be light and were transmitted through optical fibber.

§  WDM similar to FDM as it mixes many signals of different frequencies into single signal and transfer on one link.

§  The main principle in using prisms is that they bend a light beam depending on angle of incidence and frequency of light wave or ray.

§  At receiver end the light signal is split into different light waves by demux.

§  Single prism is used at the end of sender for multiplexing and other prism is used at receiver end for demultiplexing as shown in fig.

Digital Multiplexer

Digital is divided into further parts. These are:

  • Time Division Multiplexing

 

Time Division Multiplexing:

§  Time division multiplexing (TDM) is a communications process that transmits two or more streaming digital signals over a common channel.

§  In TDM, incoming signals are divided into equal fixed-length time slots.

§  After multiplexing, these signals are transmitted over a shared medium and reassembled into their original format after de-multiplexing.

§  Time slot selection is directly proportional to overall system efficiency.

§  Time division multiplexing (TDM) is also known as a digital circuit switched.

Advantages of Multiplexer:

§  If no multiplexing is used between the users at two different sites that are distance apart, then separate communication lines would be required as shown in fig.

§  This is not only costly but also become difficult to manage. If multiplexing is used then, only one line is required.

§  It reduces number of wires.

§  It reduces circuit complexity and cost.

§  It simplifies logic design.

§  We can implement many combinational circuits using MUX.


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