Introduction and elements of digital communication system.

Introduction:-
Communications is the process of establishing connections or link between two points for information exchange.
OR
Communication is simply the basic process of exchanging information.
The electronic equipments which are used for communication purpose, are called communication equipments. Different communication equipments when assembled together form a communication system.

Typical examples of communication system are:-

 Line telephony and telegraphy
 Radio telephony and radio telegraphy
 Radio broadcasting
 Point- to- point communication and mobile communication
 Computer communication
 Radar communications
 Television broadcasting
 Radio telemetry
 Radio aids navigation
 Radio aids to aircraft landing etc.

Elements of communication system:-
1).Information source
2)Input transducer
3)Transmitter
4)Chanel
5)Receiver
6)Output transducer
7)Information in the original form
8)Noice

1) Information source:-
A communication system serves to communicate a message or information.
This message or information originates in the information source.In general, there can be various messages in the form of words, group of words,code,symbols,sound signal etc. However , out of these messages, only desired message is selected and conveyed or communicated.

2)Input transducer:-
 A Transducer is a device which converts one form to energy into another form.The message from the information source may or may not be electrical in nature.In case When the message produced by the information source is not electrical in nature ,an input transducer is used to convert it into a time - varying electrical signal.

For example , in case of radio - broadcasting , a microphone converts the information or message which is in the form of sound waves into corresponding electrical signal.

3)Transmitter:-
The funcation of the transmitter is to process the electrical signal from different aspects.

For examples , in radio broadcasting the electrical signal obtained from sound signals , is processed to restrict its range of audio frequencies (upto 5khz in amplitude modulation radio broadcast) and is often amplified.

4)The Channel and the Noise:-The term channel means the medium through which the message travels from the transmitter to the receiver. In other words, we can say that the function of the channel is to provide a physical connection between  the transmitter and the receiver.

There are two types of channels:-
1.Point - to - point channels
2.Broadcast channels

Examples of point to point communication channels , wire lines ,microwave links and optical fibers.
Optical fiber are used in optical communications.Although these three channels operate differently, they all provied a physical medium for the transmission of the signals from one point to another point.There fore , for these channels , the term point to point is used.
On the other hand,the broadcast channels provide a capability where several receiving stations can be reached simultaneously from a single transmitter.

Example of the broadcast channel is a satellite in geostationary orbit, which covers about one third og the earth 's surface.During the process of transmission and reception the signal gets distorted due to noise introduced in the system.Noise is always random in character.

5)Receiver:-
 The main function of the receiver is to reproduce the message signal in electrical form from the distorted received signal.This reproduction of the original signal is accomplished by a process known as the demodulation or detection. Demodulation is the reverse process of modulation carried out in transmitter.

6)Distination:-
Destination is the final stage which is used to convert an electrical message signal into its original forms.
For example in radio broadcasting, the destination is a loudespeaker which works as a transducer i.e. it converts the electrical signal in the form of original sound signal.