Communication System

The word communication means the transfer of information from one place to another place either one way or two ways, where as systems are the components or sub-system that act together to accomplish information transfer or exchange. So communication system is defined as “The exchange of information between one place to another place or between global, either one way or two ways via some transmission medium and system”. The main purpose of a communication system is to transmit an information bearing signal from a source located at a point to a user or destination located at another point some distant away.

Communication should be done

1. ·         As efficiently as possible
2. ·         With as much fidelity / reliability as possible
3. ·         As securely as possible

The basic block diagram of communication system is shown in fig below:

Fig: Block Diagram of Communication System

The building blocks or the important terms we face in the communication system are as:

1.      Information Source

2.      Input Transducer

3.      Transmitter

4.      Channel

5.      Receiver

6.      Output Transducer

7.      Noise

v  Information Source: Source of data or information that is to be transmitted (words, symbols, codes, etc). There can be various messages in the form of words, groups, groups of words, codes, symbols, etc that has to be transmitted. Out of these messages, only the desired message is selected and conveyed or communicated.

v  Input Transducer: The message produced by a source must be converted by a transducer to a form suitable for the particular type of communication system i.e. input transducer is a device that converts the non-electrical signal to electrical signal.

Example:  In electrical communications, speech waves are converted by a microphone to

voltage variation.

v  Transmitter: The transmitter processes the input signal to produce a signal suits to the characteristics of the transmission channel i.e. transmitter changes the information signal into transmittable or transferable signal by a method known as modulation.

Signal processing for transmission almost always involves modulation and may also include coding. In addition to modulation, other functions performed by the transmitter are amplification, filtering and coupling the modulated signal to the channel.

v  Channel: The channel is a physical or non physical medium through which the message travels from transmitter to the receiver. The medium of transmission of modulated signal from transmitter can have different forms like the atmosphere (or free space), coaxial cable, fiber optic, waveguide, etc. the function of channel is to provide a physical connection between transmitter and the receiver. The term channel is often used to refer to the frequency range allocated to a particular service or transmission such as a television channel, radio channel, etc.

The signal undergoes some amount of degradation from noise, interference and distortion.

v  Receiver: The receiver’s function is to extract and reproduce the desired signal from the received signal in electrical form at the channel output and to convert it to a form suitable for the output transducer. This means the receivers receives the information through channel and demodulate it to get the desired information or the transmitted signal. The reproduction of the original signal is accomplished by a process known as demodulation or detection. Demodulation is the reverse process of modulation carried out in transmitter.

Other functions performed by the receiver: amplification (the received signal may be extremely weak), demodulation and filtering.

v  Output Transducer: The signal produced by receiver must be converted to a form suitable for the user i.e. it is a device that converts the electric signal at its input into the form desired by the system user. So output transducer converts an electrical signal to a non-electrical signal.

Example: Loudspeaker, personal computer (PC), tape recorders.

v  Noise: The signal will deteriorate during the process of transmission and reception as a result of some distortion in the system or because of introduction of noise. The noise is the unwanted signals or energy that is random in natures which deteriorates the information signal and are present in the transmission system. Noise may interfere with signal at any point in a communication system and it will have its greatest effect when the signal is weakest.