Analog Communication Multiplexing - Analog Communication

What is Multiplexing? How many types of Multiplexers are there?

Multiplexing is the process of combination of multiple signals that send through one signal, over a shared medium. Analog multiplexing is the process of multiplexing analog signals where as the digital multiplexing is the process of multiplexing digital signals.

Multiplexing was first developed in telephony. A number of signals were formed together to send through a single cable. In the process of multiplexing communication channels are divided into several number of logical channels. Each logical channel is allotted to different message signal or a data stream that is to be transferred. The device that does multiplexing can be called as Multiplexer or MUX.
The reverse process, i.e., extracting the number of channels from one, which is performed at the receiver is called as de-multiplexing. The device that does de-multiplexing can be called as de-multiplexer or DEMUX.
The following figures illustrates the concept of MUX and DEMUX. Their primary use is in the field of communications.
multiplexing demultiplex

Types of Multiplexers

Multiplexes are classified into two types, namely analog and digital. They are again divided into Frequency Division Multiplexing (FDM), Wavelength Division Multiplexing (WDM), and Time Division Multiplexing (TDM). The following figure gives a detailed idea about this classification.
types of multiplexs
There are many types of multiplexing techniques. Out of which, we have the main types with general classification, mentioned in the above figure. Let us have a look at them individually.

Analog Multiplexing

The signals used in analog multiplexing techniques are analog in nature. The analog signals are multiplexed based on their frequency (FDM) or wavelength (WDM).

Frequency Division Multiplexing

In analog multiplexing, the most popular technique used is Frequency Division Multiplexing (FDM). This technique uses various frequencies in order to combine streams of data, and sends them on a communication medium, as a single signal.
Example − A traditional television transmitter, where a number of channels are sent through a single cable uses FDM.

Wavelength Division Multiplexing

Wavelength Division multiplexing (WDM) is a type of analog technique, in which modulating many data streams of different wavelengths in the light spectrum. If the wavelength increases, the frequency of the signal decreases. A prism, where refraction takes place which can turn different wavelengths into a single line, can be used at the output of MUX and input of DEMUX.
Example − Optical fiber communications use WDM technique, where different wavelengths cane be merged into a single light for communication.

Digital Multiplexing

The term digital itself represents the information in the form of discrete bits. Hence, the available data will be in the form of frames or packets, which are discrete. in other words the this multiplexer divides the communication channel into many logical channels thereby providing each channel to each message signal.

Time Division Multiplexing

In Time Division Multiplexing (TDM), the time frame is divided into slots. In this technique each message is allotted one slot and is used to transmit a signal over a single communication channel.
Time Division Multiplexing (TDM) is divided into Synchronous TDM and Asynchronous TDM.

Synchronous TDM

In Synchronous TDM, the input is connected to a frame. If the frame consists of ‘n’ number of connections, then the frame is divided into ‘n’ time slots. One slot is allocated for each input line. it is useless if each device have nothing to transmitt in allocated time. it is of no use when allocated time slots are being used properly.
In this technique, for all the signals the sampling rate is same and hence the same clock input is required. The same slot is allocated to each device by MUX at all times.

Asynchronous TDM

In Asynchronous TDM, the rate of sampling is different for each of the signals and a same clock is not required. If the allocated device for a time slot does not transmit anything and sits idle, then that slot can be allotted to another device, unlike synchronous
This type of TDM is used in Asynchronous transfer mode networks.

De-Multiplexer

De-multiplexers are quiet reverse of multiplexing. This is used to connect a single input line to multiple destinations (i.e more than one output). As mentioned previously, it is used mostly at the receivers. De multiplexer reverses what multiplexer does. DEMUX has many applications. It is used in receivers in the communication systems. It is used in arithmetic and logical unit in computers in order to supply power and to pass on communication, etc.
De-multiplexers are used as serial to parallel converters. The serial data is given as input to DEMUX at regular intervals and a counter is attached to it to control the output of the de-multiplexer.
On a whole both the multiplexers and de-multiplexers play an important role in communication systems, both at the transmitter section and the receiver section.

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