The document discusses digital communication and is presented by Dr. Varun Kumar. It begins with an introduction to communication and the communication process. It then discusses different types of signals that can be communicated, including text, audio, images, and video. The document outlines various classifications of signals and why digital communication provides advantages over analog communication, such as less physical space requirements, noise immunity, storage capabilities, and encryption. It presents a block diagram of a basic communication system and explains how digital signals fit within this system.

1. Need of Digital Communication
Dr. Varun Kumar
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2. Outlines
1 Introduction to Communication
2 Types of Communication
3 Merit and Scope of Digital Communication
4 References
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3. Introduction to Communication
⇒ Communication is a process for sending information/signal/data from
source to sink.
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4. Source of information
Source of information
Text
⇒ SMS
⇒ E-mail, etc
Audio
⇒ Listening a music or telephonic conversation
⇒ Bronchial sound measured by stethoscope, etc
Image
⇒ Pi-chart
⇒ Graph
⇒ Simulation plot
⇒ Remote sensing image, etc
Video
⇒ Watching a movie
⇒ Tele heart surgery, etc
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5. Signal and their classification
Signal and their classification
Signal: It is a fundamental quantity that carry the information in terms of
electrical waves.
⇒ For understanding the information and communication technology
(ICT), we should be familiar with electrical signal and their types.
Classification :
1. Continuous time vs discrete time signals
A signal that is specify for every value of time t is a continuous time
signal, and a signal is specified only at discrete points of t = nT is discrete
time signal.
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6. Continued–
2. Periodic and aperiodic signals
A signal g(t) is said to be periodic if there exists a positive constant
T0 such that
g(t) = g(t + T0) ∀ t
The smallest value of T0 is called as fundamental period.
3. Energy and power signals
A signal with finite energy is an energy signal, and a signal with
finite power is a power signal. Mathematically, energy and power
signals are
E =
∞
−∞
|g(t)|2
dt < ∞ and P = lim
T→∞
1
T
T/2
−T/2
|g(t)|2
dt < ∞
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7. Continued–
4 Deterministic vs random signals.
(a) A signal whose physical description is known completely, either in a
mathematical or a graphical form is a deterministic signal.
(b) A signal that is known only in terms of probabilistic description, such
as mean value, variance, and distributions rather then its full
mathematical or graphical description is a random signal.
5 Analog vs digital signal
(a) A signal whose amplitude can take on any value in a continuous range
is an analog signal.
(b) A signal whose amplitude can take on finite number of values is a
digital signal.
Note :
1 Analog signal may be continuous as well as discrete.
2 Digital signal may be continuous as well as discrete.
3 Analog is not the synonyms of continuous time signal.
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8. Continued–
Analog vs digital
⇒ Figure (a) is analog and continuous time signal.
⇒ Figure (b) is digital and continuous time signal.
⇒ Figure (c) is analog and discrete time signal
⇒ Figure (d) is digital and discrete time signal.
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9. Need of digital
Communication perspective:
⇒ As per the nature of signal (analog and digital), it is categorized into
two parts.
Analog communication ⇒ When analog signal is transmitted from
source to sink.
Digital communication ⇒ When digital signal is transmitted from
source to sink.
⇒ By default all physical signals are analog in nature.
Merit of digital communication or technology
⇒ Digital signal is a man-made signal.
⇒ Advantage, like
Less requirement of physical space
Noise immunity
Storage
Encryption
Economical and many more
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10. Block diagram of communication system
⇒ In modern wired (landlines phones) and wireless (mobile phone,
walkie talkie, etc) communication; digital signal is the raw ingredient
for effective communication.
Block diagram of communication system
Note:
⇒ Input message/information is a physical world signal. Ex- Pressure,
temperature, flow of fluid, etc
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11. Continued–
⇒ Input transducer is device that convert physical world signal into
electrical signal.
⇒ Input signal is a electrical signal which is analog by nature. If it is
processed (passing through analog to digital converter ADC) then the
resultant signal becomes digital.
⇒ Transmitter is electromagnetic transducer or device that assists for
transmitting the signal.
⇒ Channel provides a media for transmitting the signal.
o Wired channel
o Wireless channel
⇒ Distortion and noise: It produces the detrimental effect that corrupt
the quality of signal.
⇒ Receiver is a device that receives the transmitted signal.
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12. Continued–
⇒ Output transducer : It is a device that converts the electrical signal
into understandable message.
Understanding of above diagram as per communication
perspective
♦ In above diagram, if input signal is a analog then the whole
communication set-up address the analog communication.
♦ In above diagram, if input signal is a digital then the whole
communication set-up address the digital communication.
♦ In above diagram, if transmitter and receiver are connected via wired
medium then the whole communication set-up address the wired or
wire-line communication.
♦ In above diagram, if transmitter and receiver are connected via
wireless or air media then the whole communication set-up address
the wireless communication.
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13. References
B. P. Lathi, Z. Ding et al., “Modern Digital and Analog Communication Systems /
BP Lathi, Zhi Ding.” 2010.
A. Goldsmith, Wireless communications. Cambridge university press, 2005.
D. Tse and P. Viswanath, Fundamentals of wireless communication. Cambridge
university press, 2005.
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