Communication Systems



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Introduction to basics of communication

Communication is the process of sending, receiving, and processing of information from one point to another point through a communication channel by electronic means or electronic signals. It requires a source of information, a mode of encode the information so that it can be transmitted, a means of transmitting and receiving the information, and a means of decoding it.

During communication between any two people each person is a source of information, encoding it in the form of words and gestures and transmits it. Now, as a receiver of information the person has to decode the word, gestures and assign meaning to it.

  • Block diagram of communication system


Communication system has following basic components:

  1. Information source and input transducer
  2. Transmitter
  3. Channel
  4. Receiver and
  5. Output transducer

Information source: any communication system used to communicate a message or information, which originates in the information source. It can be an audio, an image, a text or data.

Input transducer: the message produced by information source is converted by a transducer into electric signal.

Transmitter: its function is to process the electrical signal to produce a signal suits to the characteristics of the transmission channel. For example in radio broadcasting the electrical

signal obtained from sound signal is processed to restrict its range of audio frequencies (20 Hz – 20 kHz).

Transmitter perform functions like:

  • Modulation
  • Amplification
  • Restriction of range of video frequencies
  • Restriction of range of audio frequencies

Channel: it means the medium through which the information or message travels from transmitter to receiver. Channel can have different forms like:- wire lines, fibre optic cable , atmosphere, coaxial cable. Most channels often adds noise or weaken and distort signal.

Communication channels are divided in to two categories:

  1. Wireline communication
  2. Wireless or radio communication

Wireline or line communication uses a pair of conductors called transmission line. Each transmission line can normally convey one message at a time.

  1. Twisted pair
  2. Cable
  3. Waveguide
  4. Fibre optics

they all come under wireline communication media.

Wireless or radio communication: message is transmitted through open space by electromagnetic waves also called as radio waves.

  1. Ground wave
  2. Sky wave
  3. Line of sight
  4. Acoustic channels

they are the various radio channels which are used in transmission.

Receiver : extracts the desired signal from the received signal at the channel output and to convert it to a form suitable for the output transducer. It also performs amplification, demodulation and filtering.

Output transducer: converts electric signal into usable form. Example: speaker, monitor, tape recorders.

There are two primary communication resources:

  1. Transmitted power: it is the average power of the transmitted signal.
  2. Channel bandwidth: it is defined as the band of frequencies allocated for the transmission of the message signal.

In most communication channels one resource may be considered more important than other. Because of this, we may classify communication channels as power limited or band limited.

During the process of transmission and reception, the signal get distorted due to:

(i) Insufficient channel bandwidth,

(ii) Random variations in the channel characteristics,

(ii) External interference, and

(iv) Noise.

 

The noise refers to an unwanted wave or energy usually of random character that tend to disturb the transmission and processing of message signals in a communication system. The source of noise may be internal or external to the system.

The effect of noise can be measured using signal-to-noise ratio (SNR. It is a measure of the sensitivity performance of receiver. It is defined as the ratio of average signal power to the average noise power.

 

Hence, SNR= S/N. In dB, SNR= 10 log10

Where, S = signal power, N = noise power.

  • Table given below shows frequency ranges of various spectrum:

 

 

  • Table given below shows some most widely used spectrum with their frequency range:

 

 

Author : Arusha Ahmed


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