Communication is the process of establishing connection or link between two points for information exchange.
Communication is simply the basic process of exchanging information.
The electronics equipements which are used for communication purpose, are called communication equipments. Different communication equipments when assembled together form a communication system.
Typical example of communication system are line telephony and line telegraphy, radio telephony and radio telegraphy, radio broadcasting, point-to-point communication and mobile communication, computer communication, radar communication, television broadcasting, radio telemetry, radio aids to navigation, radio aids to aircraft landing etc.
The Communication Process
In the most fundamental sense, communication involves the transmission of information from one point to another through a succession of process as listed below :
- The generation of a thought pattern or image in the mind of an originator.
- The description of that image, with a certain measure of precision, by a set of oral visual symbols.
- The encoding of these symbols in a form that is suitable for transmission over a physical medium of interest.
- The transmission of the encoded symbols to the desired destination.
- The decoding and reproduction of the original symbols.
- The recreation of the original thought pattern or image, with a definable degradation in quality, in the mind of recipient.
Block Diagram of Communication System
Fig.1 shows the block diagram of a general communication system, in which the different functional elements are represented by blocks.
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The essential components of a communication system are information source, input transducer, transmitter, communication channel, receiver and destination.
Now, we shall discuss the functioning of these blocks.
(i) Information Source
As we know, a communication system serves to communicate a message or information. This 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 the desired message is selected and communicated.
Therefore, we can say that the function of information source is to produce required message which has to be transmitted.
(ii) Input Transducer
A transducer is a device which converts one form of energy into another form.
The message from the information source may or may not be electrical in nature. In a 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 massage which is in the form of sound waves into corresponding electrical signal.
The function of the transmitter is to process the electrical signal from different aspects.
For example in radio broadcasting the electrical signal obtained from sound signal, is processed to restrict its range of audio frequencies (upto 5 kHz in amplitude modulation radio broadcast ) and is often amplified.
In wire telephony, no real processing is needed. However, in long-distance radio communication, signal amplification is necessary before modulation.
Modulation is the main function of the transmitter. In modulation, the message signal is superimposed upon the high-frequency carrier signal.
In short, we can say that inside the transmitter, signal processings such as restriction of range of audio frequencies, amplification and modulation of signal are achieved.
All these processings of the message signal are done just to ease the transmission of the signal through the channel.
(iv) 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, namely point-to-point channels and broadcast channels.
Example of point-to-point channels are wire lines, microwave links and optical fibres. Wire-lines operate by guided electromagnetic waves and they are used for local telephone transmission.
In case of microwave links, the transmitted signal is radiated as an electromagnetic wave in free space. Microwave links are used in long distance telephone transmission.
An optical fibre is a low-loss, well-controlled, guided optical medium. Optical fibres are used in optical communications.
Although these three channels operate differently, they all provide a physical medium for the transmission of signals from one point to another point. Therefore, for these channels, the term point-to-point is used.
On the other hand, the broadcast channel provides a capability where several receiving stations can be reached simultaneously from a single transmitter.
An example of a broadcast channel is a satellite in geostationary orbit, which covers about one third of the earth’s surface.
During the process of transmission and reception the signal gets distorted due to noise introduced in the system.
Noise is an unwanted signal which tend to interfere with the required signal. Noise signal is always random in character. Noise may interfere with signal at any point in a communication system. However, the noise has its greatest effect on the signal in the channel.
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.
Destination is the final stage which is used to convert an electrical message signal into its original form.
For example in radio broadcasting, the destination is a loudspeaker which works as a transducer i.e. converts the electrical signal in the form of original sound signal.