Tutorial I : Basic Elements of Digital Communication System


Recently I started to revise the whole Communication Engineering. And here is the most dreamed of series, in fact I thought of this series when I dreamed of WirelessCafe, the so called “Tutorial Series”, by this series I aiming towards preparing for my PhD. This is the first post of the series ……….

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the whole digital communication system is divided as per the figure shown below. These are the basic elements of any digital communication system and It gives a basic understanding of communication systems. We will discuss these basic elements.

basic elements of digital communication system

basic elements of digital communication system

  1. Information Source and Input Transducer:

The source of information can be analog or digital, e.g. analog: aurdio or video signal, digital: like teletype signal. In digital communication the signal produced by this source is converted into digital signal consists of 1’s and 0’s. For this we need source encoder.


  1. Source Encoder

    In digital communication we convert the signal from source into digital signal as mentioned above. The point to remember is we should like to use as few binary digits as possible to represent the signal. In such a way this efficient representation of the source output results in little or no redundancy. This sequence of binary digits is called information sequence.

    Source Encoding or Data Compression: the process of efficiently converting the output of wither analog or digital source into a sequence of binary digits is known as source encoding.

  2. Channel Encoder:

    The information sequence is passed through the channel encoder. The purpose of the channel encoder is to introduced, in controlled manner, some redundancy in the binary information sequence that can be used at the receiver to overcome the effects of noise and interference encountered in the transmission on the signal through the channel.

    e.g. take k bits of the information sequence and map that k bits to unique n bit sequence called code word. The amount of redundancy introduced is measured by the ratio n/k and the reciprocal of this ratio (k/n) is known as rate of code or code rate.

  3. Digital Modulator:

    The binary sequence is passed to digital modulator which in turns convert the sequence into electric signals so that we can transmit them on channel (we will see channel later). The digital modulator maps the binary sequences into signal wave forms , for example if we represent 1 by sin x and 0 by cos x then we will transmit sin x for 1 and cos x for 0. ( a case similar to BPSK)

  4. Channel:

    The communication channel is the physical medium that is used for transmitting signals from transmitter to receiver. In wireless system, this channel consists of atmosphere , for traditional telephony, this channel is wired , there are optical channels, under water acoustic cahnenls etc.

    we further discriminate this channels on the basis of their property and characteristics, like AWGN channel etc.

  5. Digital Demodulator:

    The digital demodulator processes the channel corrupted transmitted waveform and reduces the waveform to the sequence of numbers that represents estimates of the transmitted data symbols.

  6. Channel Decoder:

    This sequence of numbers then passed through the channel decoder which attempts to reconstruct the original information sequence from the knowledge of the code used by the channel encoder and the redundancy contained in the received data

    The average probability of a bit error at the output of the decoder is a measure of the performance of the demodulator – decoder combination. THIS IS THE MOST IMPORTANT POINT, We will discuss a lot about this BER (Bit Error Rate) stuff in coming posts.

  7. Source Decoder

    At the end, if an analog signal is desired then source decoder tries to decode the sequence from the knowledge of the encoding algorithm. And which results in the approximate replica of the input at the transmitter end

  8. Output Transducer:

    Finally we get the desired signal in desired format analog or digital.

The point worth noting are :

  1. the source coding algorithm plays important role in higher code rate

  2. the channel encoder introduced redundancy in data

  3. the modulation scheme plays important role in deciding the data rate and immunity of signal towards the errors introduced by the channel

  4. channel introduced many types of errors like multi path, errors due to thermal noise etc.

  5. the demodulator and decoder should provide high BER.

In the coming articles of the series we will explore more the different elements along with their characteristics, types, and also analyze the results of simulations. The next post will be on communication channels and their characteristics and also their mathematical models.

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Author: Ashwini Patankar

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35 responses to “Tutorial I : Basic Elements of Digital Communication System

  1. Hey Guys,
    really a great place for revision. i’m also preparing for interviews so a short but effective revision is much needed.
    again thank you very much. keep post new tutorials.
    if any support is needed please tell.

  2. Dear Thangam,

    Thanks for the appreciation, We are just trying to do some thing useful for the beginners, If you too want to contribute then we will be pleased to have you in the WirelessCafe team.

    Thanks and Regards,
    Ashwini Patankar for WirelessCafe team !

  3. Pingback: 2010 in review « Wirelesscafe

  4. this is very nice …… but can some one give more examples of analog and digital signals……….

  5. @khusbhu

    speech,music are some of the signals which are analog in nature and in practical most of the signals are analog and for processing we are converting it into digital.

  6. infact am very delighted about the explanation. am planning to go for my masters in digital commmunication. thanks

  7. Do checkout this book on digital comms. It introduces technical concepts in the form of storytelling. Stories revolve around concepts, scientists and engineers who dared to think differently from the old analogue world.

    The Infinite Bit: An Inside Story of Digital Technology
    http://theinfinitebit.wordpress.com

  8. thank you Ashwini Bhaiya :) :) your experience helped me make my friends understand better in my seminar , i’m in 6th sem B.E and i must say this content is priceless :)

  9. Hi, My name is Lawrence, a student and quite new to IT. I have been struggling to workout the process of Digital Communication. Until I came across your website which explains digital communication in dept.
    Thank you.

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