Classification of Communication

Classification of communication

(i)                Line Communication

(ii)             Wire or Radio Communication

Line communication

In line communication the medium of transmission is a pair of conductor called transmission line. This is also called as line channel. This means that in the communication, the transmitter and the receiver are connected through a wire or line.the installation and maintenance of a transmission line is not only costly and complex but also over crowds the open source. Apart from this its message transmission capability is also limited.

Wire or Radio Communication

In Wireless or radio communication, a message is transmitted through open space by electromagnetic  waves called a radio waves. Radio Waves are radiated from the transmitter in open space through a device called antenna. A receiving antenna intercepta the radio waves at the receiver. All the radio, TV and satellite broadcasting are wireless or radio communication. The advantage of wireless communication are cost effectiveness, possible long distance communication and simplicity.

Communication Process

The Communication Process

1.      Information Process

 We know that a communication system serves to communication 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 the desired message is selected and conveyed or communicated.

2.      Input Transducer

A transducer is a device which converts one form of energy into another form. The messages from the information source may not be electrical in nature. In a case when the message produced by the information source is not the 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 messages which is in the form of sound waves into corresponding electrical signal.

3.      Transmitter

The function of the transmitter is to process the electrical signal from different aspects. For example in radio broadcasting signal obtained from signal, is processed to restrict its range of audio frequencies and is often amplified. In wire telephony no real processing is needed, however in long distance radio main function of the transmitter, in modulation the message signal processing such as restriction of range of audio frequency, amplified,  and modulation are achieved. All these processings of the message signal are done just to case the transmission of the signal through the channel.

4.      The channel and the Noise

With reference to the block diagram of a communication system the term channel means the medium through which the message travels fom 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. Examples of point to point channels are wirelines, microwaves link and optical fibres . Wirelines operated by guided electromagnetic waves and they are used for local telephonic transmission. In case of microwaves links are used in long distance telephone transmission. an optical fibre is a low loss, well controlled, guided optical differently, they all provides a physical medium for the transmission of signals from one point to another point. For these channels the term point to point is used.

Source of information

Source of information.

As a matter of fact, The telecommunication environment is dominated by the following four important sources of information.

(i)                 Speech

(ii)               Television

(iii)             Facsimile and

(iv)              Personal computer

A source of nformation may be characterized in term of signal which carrier the information. Further, a signal is defined as a signal valued function of the time that play the role of the depedent variable. At every instant of time, the function has a unique value.

Speech

(a)   Production: an intended message in the speaker mind is represented by the speech signal that consist of sounds generated inside the speaker mouth and whose arrangement is governed by the rule of language.

(b)   Propagation: The siund waves propagates through the air, reaching the listener’s ears.

(c)     Perception: The incoming sounds are deciphered by the listener into a received message, and thus completing the chain of events that results in the transfer of information from the speaker to the listener.

Television

The second source of information, television refers to the transmission of picture in motion by means of electrical signal. To accomplished this transmission, each complete picture has to be sequentially scanned. The scanning process is carried out in a TV camera. In a black and white TV, the camera contains optics designed to focus an image on a photocathode consisting of a large number of photosensitive elements.

The charge pattern so generated on the photosensitive surface is scanned by an electron beam, and thus producing an output current which vaies temporally in accordance with the way in which the brightness of the original picture varies spatially form one point to another. This resulting output current is called a video signal.

The type of scanning used in television is a form spatial sampling called raster scanning. The purpose of raster scanning is basically to convert a two dimensional image intensity into a one dimension waveform.

Facsimile

The purpose of the third source of information, facsimile machine, is to transmit still picture over a communication channel a telephone. Such a machine provide a highly popular facility for the transmission of hand written or printed text from one point to another. Further, transmitting text by facsimile is treated simply like transmitted a picture.

The basic principal employed fo signal generation in a facsimile machine is to scan an original document and use an image sensor to convert the light to an electrical signal.

Personal Computer

As a matter of fact, personal computer are becoming increasingly an important part of our daily lives. We use them for electronic mail, exchange of software, and sharing of resource. It is estimated that over 30 percent of the personal computer in use today are already networked and the number is increasing rapidely. The text transmitted by a PC is usually encoded using the American standard code for information interchange, ASCII which is the first code developed specifically for computer communication.

Each character in ASCII is represented by seven data bits constituting a unique binary pattern made up of 0s and 1s. hence a total of seven power of two = 128 different characters can be represented in ASCII. The character symbols are various lowercase and uppercase letters, numbers, special control symbols, and punctuation symbols commonly used such as @,$ and %. Some of the special “control” symbols such as BS ( back space ) and CR (carriage return), are used to control the printing of characters on a page Other symbols, such as ENQ (enquiry) and ETB (end of transmission block), are used for communication purpose.

The even data bits are ordered starting with the most significant bit b7 down to the least significant bit b1.

At the end of the data bits, an extra bit b8 is appended for the purpose of error detection. This error detected bit is called a parity bit.

Communication System

Communication System

Information Source : Comminication system serve to communication a message or information. This message or information originates in the information source. In general, there can be various message in the form of words, group of words, code, symbols, sound signal etc. however out of these message, only the desired message is selected and conveyed or communicted.

Input Transducer : A Transducer is a device which converts one from of energy into another form. The message from the information source may or may not be electrical in nature. Transuder converts non electrical signal into electrical signals. for examples, a microphone converts sound signal as sound waves into is electrical signal.

Transmitter : The function of the transmitter is to process the electrical signal from different aspects. for examples, in redio broadcasting the electrical signal obtained from sound signal is processed to restrict its range of audio frequencies and amplified.

The Channel and the Noise : The channel means the medium through which the message travels from the transmitter to the receiver. The function of the channel is to provide a signal connnection between the transmitter and the receiver. Microwave link are used in long distance telephone transmisssion
Noise is an unwanted signl which tend to interfere with the required signal. noise signal is always random in character. Noise is an unwanted signal which tend to interfere with the required signal. Noise signal at any point in a communication system.

Receiver : The main function of the receiver is to receiver is to reproduce the message signal in electrical form from the dstrorted received signal. This reprodulation of the original signal is accomplished by a process known as demodulation or detected. Demodulation is the reverse process of modulation carried out in transmitter.

Destinaton : It is the final stage which is used to convert an electrical message signal into its original form. For examples, in radio broadcasting the destination is a loudspeaker which works as a transducer i.e it converts electrical signal into sound signal