what is digital communication , digital communication process : elements of a communication block diagram :-
Communication is the process of establishing connection or link between two points for information exchange.
Communication is simply the process of conveying message at a distance or communication is the basic process of exchanging information .
The electronic equipments which are used for communication purpose are called communication equipment.
Different communication equipments when assembled together from a communication system.
Typical examples of communication system are line telephony and line telegraphy , radio telephony and line 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 earliest communication system namely line-telegraphy originated in eighteen
Forties [1840s].In addition to this line telephony came a few decades later whereas radio-communication could become possible in the beginning of twentieth century on invention of triode valve. Radio commu-nicatio was further greatly improved during .World war 2.Itbecame more widely used through the invention of transistor , integrated circuits [ICs] and other semiconductor devices in the subsequent years Also in recent years ,communication has become more widespread with the use of satellites and fibre optics. Today there has been an increasing emphasis on the use of computers in communication.
1.2 THE COMMUNICATION PROCESS; ELEMENTS OF A COMMUNICATIONSYSTEM
In the most fundamental sense communication involves the transmission of information from one point to another through a succession of process as listed ahead;
- The generation of 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 aural or 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 a recipient.
Hence , as discussed above , the purpose of a communication system is to transmit an information bearing signal , from a source , located at one point , to a user or destination , located at another point some distance away. Given figure shows the block diagram of general communication system in which the different functional elements are represented by blocks . the essential components of a communication system are information source , input transducer , transmitter , communication channel , receiver and destination.
Block diagram of a communication system
- Information source : we know that 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 the desired message is selected and conveyed or communicated.
In short , we can say that the function of information source is to produce required message which has to be transmitted.
- 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 message which is in the form of sound waves into corresponding electrical signal.
- Transmitter : 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 or broadcast , signal amplification is necessary before modulation . modulation is the main function of the transmitter . In modulation , the message , the message signal is superimposed upon the high frequency carrier signal . In short , we can say that inside the transmitter , signal processing such as restriction of range of audio frequencies , amplification and modulation are achieved . all these processing of the message signal are done just to ease the transmission of the signal through the channel.
- The channel and the Noise : with reference to the block diagram of a communication system in figure. 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 Examples of point to point channels are wirelines , microwave links and optical fibres. Wirelines 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 fiber is a low loss well controlled , guided optical medium. Optical fibres are used in optical communication . Although these three channel 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 channels provide a capability where several receiving stations can be reached simultaneously from a signal 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.
- 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.
- Destination : 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. it converts the electrical signal in the form of original sound signal.