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MAYURBHANJ SCHOOL OF ENGINEERING � LAXMIPOSI ,BARIPADA,757107

  • DEPARTMENT- E&TC ENGG.
  • SEMISTAR- 5TH
  • SUBJECT-A & D Communication
  • TOPIC – Element Of Communication System
  • NAME OF TOPIC –Element of Communication System and Modulation
  • PREPARED BY - U S Panda (Sr. Lect. E & TC Engineering)
  • AY – 2021-2022, WINTER-2021

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Chapter 1: Communication System

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An Introduction

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Communications

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  • Communications

Transfer of information from one place to another. Should be efficient, reliable and secured.

“A communication system is a process of conveying information from a source to a destination”

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  • Communication system Components/subsystems act together to accomplish information transfer/exchange

“An electronic communication system is transferring information using an electrical field as a mean of signal”

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Requirements

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  • Rate of information transfer
    • The rate of information transfer is defined as the amount of information that must be communicated from source to destination.
    • It will determined the physical form and technique used to transmit and receive information and therefore determines the way system is designed and constructed

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  • Purity of signal received
    • The received signal must be the same as the transmitted signal

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Requirements

  • Simplicity of the system
    • Any communication system must be convenient in order to be effective and efficient and easy to use

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  • Reliability
    • Users must be able to depend on a communication system. It must work when needed and transmit and receive information without errors or with an acceptable error.

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Elements of Communication system

Input Transducer

Transmitter

Channel

Receiver

Output Transducer

Input Message

Output Message

Transmission

medium

noise

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Elements of Communication system

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Input Transducer

To convert the message to a form suitable for the particular type of communication system.

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Eg: Speech waves are converted to voltage variation by a microphone.

Transmitter

Processes the input signal  to produce a transmitted signal that suited the characteristic of transmission channel.

eg: modulation, coding

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Other functions performed: Amplification, filtering

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Elements of Communication system

Channel (Transmission medium)

A medium that bridges the distance from source to destination.

eg: Atmosphere (free space), coaxial cable, fiber optic, waveguide

Signal undergoes degradation from noise, interference and distortion.

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Transmission systems can be evaluated according to five (5) main criteria:

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 Capacity  Performance

 Distance  Security

 Cost which include installation, operation and maintenance

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Elements of Communication system

The two main categories of channel commonly used are:

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  • Line (conducted media)
    • The channel is made up metallic cable (such as coaxial cable, twisted pair, parallel wires, and others) or fibre optic cable.

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  • Free space or radiated media
    • This is the medium where the transmission of signal is carried out by the propagation of electromagnet wave.
    • The main applications are in radio broadcasting, microwaves and satellites transmission systems.

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Elements of Communication system

  • Loses in medium of transmission

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    • However, each medium introduces losses termed as attenuation, distortion and adds noise to some degree to the transmitted signal. The amount of attenuation, distortion and noise depends on the type of transmission medium used.

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    • There is normally no signal processing in the transmission medium, it is just the medium where the transmitter is connected to the receiver.

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Elements of Communication system

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Receiver

To extract the desired signal from the output channel and to convert it to a form suitable for the output transducer.

eg: Demodulation, decoding

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Other functions performed:

Amplification, filtering.

Output Transducer

Converts the electrical signal at its input into a form desired by the system used.

Eg: Loudspeaker, PC and tape-recorders.

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Losses in Communication System

Various unwanted undesirable effect crop up in transmissions

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  • Attenuation
    • Reduces signal strength at the receiver

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  • Distortion
    • Waveform perturbation caused by imperfect response of the system to the desired signal itself
    • Equalizer can be used to reduced the effect

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  • Interference
    • Contamination by extraneous signals from human sources

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Losses in Communication System

  • Noise
    • Random and unpredictable electrical signals from internal or external to the system
    • The term SNR (signal to noise ratio) is used to measure performance (noise) relative to an information analog signal
    • The term BER (Bit Error Rate) is used in digital system to measure the deterioration of the signal

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Analog vs. Digital

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The signal can be analog or digital message:

  • Analog
    • Continuous Variation
      • Assumes the total range of frequencies/time
    • All information is transmitted.

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  • Digital
    • Takes samples
      • non-continuous stream of on/off pulses
    • Translates to 1s and 0s

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Analog Vs Digital (Advantages and Disadvantages)

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Digital CS Analog CS

Advantages:

  • Inexpensive
  • Privacy preserved (Data encrypt.)
  • Can merge different data
  • Error correction

Disadvantages:

  • Expensive
  • No privacy preserved
  • Cannot merge different data
  • No error correction capability

Disadvantages:

  • Larger bandwidth
  • Synchronization problem is relatively difficult.

Advantages:

  • Smaller bandwidth
  • Synchronization problem is relatively easier.

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