Khulna University
of Engineering & Technology
Lecture 1: Introduction
• Instructor Prof. Dr. Md. Faruque Hossain
ECE, KUET
Phone: 01714087376
Email: fhossain@ece.kuet.ac.bd
Course Information
EEE 3231: Networks and Communication Systems Cr. Hrs. 3.00
• Syllabus Overview of communication systems: Digital communication; Topologies;
Protocols and standards; Protocol hierarchies; OSI model; Data link control;
HDLC; LAN protocols; Standards IEEE 802, Switches and hubs, Bridges, FDDI,
Fast Ethernet; Routing algorithm; Congestion control; Internetworking
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About the Classes
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References
1. Data and Computer Communication
- William Stallings
2. Data Communications and Networking
- Behrouz A. Forouzan
3. Computer Networks - A Systems Approach
- Larry L. Peterson and Bruce S. Davie
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References
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Significance of Human
Communication
• Communication is the process of exchanging information.
• Main barriers are language and distance.
• Methods of communication:
1. Face to face
2. Signals
3. Written word (letters)
4. Electrical innovations:
•Telegraph
•Telephone
•Radio
•Television
•Internet (computer)
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Milestones in Communication
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Milestones (2)
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Communication Systems
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Communication Systems
Input Transducer: The source originates a message, which could be
a human voice, a television picture or data. The source is converted by
an input transducer into an electrical waveform referred to as the
baseband signal or message signal.
Example: In electrical communications, speech waves are converted by a
microphone to voltage variation.
Transmitter: The transmitter processes the input baseband signal to produce a
signal suits to the characteristics of the transmission channel for efficient
transmission.
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, pre-emphasizer and coupling the
modulated signal to the channel.
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Why Modulation?
Modulation …
- Continuous carrier wave modulation
- Pulse modulation
Modulation is used in communication system for-
Matching signal characteristics to channel characteristics.
Reducing noise and interference.
Simultaneously transmitting several signals over a single channel.
Overcoming some equipment limitations.
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Communication Systems
Channel: The channel is a medium through which the transmitter output
is sent, which could be a wire, a coaxial cable, an optical fiber, or a radio
link, etc.
The signal undergoes some amount of degradation from noise, interference and
distortion
Receiver: The task of the receiver is to extract the desired signal from the
distorted and noisy received signal at the channel output and to convert it to a
form suitable for the output transducer.
The receiver may consist of a demodulator, a decoder, a filter, and a de-
emphasizer.
Output Transducer: The receiver output is fed to the output transducer, which
converts the electrical signal to its original form desired by system user.
Example: Loudspeaker, personal computer (PC), tape recorders.
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Noise, Interference and Distortion
• Noise
unwanted signals that coincide with the desired
signals.
Two types of noises: internal and external noise.
- Internal noise
Caused by internal devices/components in the circuits
–thermal noise, random emission in electronic circuits.
- External noise
noise that is generated outside the circuit.
E.g. atmospheric noise, solar noise, cosmic noise, man
made noise.
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Noise, Interference and Distortion
• Interference
Contamination by extraneous signals from human
sources.
e.g. from other transmitters, power lines and
machineries.
Occurs most often in radio systems whose receiving
antennas usually intercept several signals at the same
time
One type of noise.
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Noise, Interference and Distortion
• Distortion
Signals or waves perturbation caused by imperfect
response of the system to the desired signal itself.
May be corrected or reduced with the help of
equalizers.
Transmitters and receivers are carefully designed to
overcome the distortion and noise. The Goal of Physical
layer Communication System is to transmit information
accurately and efficiently (power and spectrum).
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Limitations in Communication System
• Technological problems
Includes equipment availability, economic factors, federal
regulations and interaction with existing systems.
Problem solved in theory but perfect solutions may not be
practical.
• Physical limitations
Bandwidth limitation
Measure of speed
The system ability to follow signal variations depends on the
transmission bandwidth.
Available bandwidth determines the maximum signal speed.
Noise limitation
Unavoidable.
Noise relative to an information signal is measured in
terms of signal to noise ratio (SNR). 16
Communication System Design
• Compromise within:
Transmission time and power
SNR performance
Cost of equipments
Channel capacity
Bandwidth
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Objectives of System Design
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