Introduction to
Communication System
Definition of Communication
• Communication refers to sending, receiving and
processing of information by electronic means.
• The purpose of communication system is to
communicate information between two or more
locations called stations.
BLOCK DIAGRAM OF
COMMUNICATION SYSTEM
NOISE
SOURCE
INPUT
TRANSDUCER
TRANSMITTER
CHANNEL
RECEIVER
OUTPUT
TRANSDUCER
DESTINATION
Source : Originates a message signal such as audio,video
or data.
Input transducer : Converts non-electrical data or
message into electrical signal which is often referred as
baseband signal.
Transmitter :It modifies or strengthens the baseband
signal for efficient transmission.
Channel : Channel is a medium through which transmitter
output is sent. eg : wire , coaxial cable , optical fiber etc.
Noise : signal is contaminated by undesirable signal i.e
noise.
Receiver : The receiver reprocesses the signal received by
channel by undoing the signal modifications.
Output transducer : Receiver output is fed to output
transducer which converts electrical signal to original form.
Destination: It is the unit to which message or original
Signal is communicated.
Types of Electrical Signal
ANALOG SIGNAL:
 An analog signal can be any time-varying signal.
 Minimum and maximum values can be either
positive or negative.
 Video and Audio
DIGITAL SIGNAL:
 Digital signal are commonly referred to as square
waves or clock signals.
 Their minimum value must be 0 volts, and their
maximum value must be 5 volts.
Analog Signals
Digital Signals
 Continuous
 Discrete
 Infinite range of values
 More exact values, but
more difficult to work
with
 Finite range of values
 Not as exact as analog, but
easier to work with
Frequency Range & Bandwidth
 Audio frequency range : 20HZ to 20kHZ.
 Range of frequencies is called “Bandwidth”.
 Length of antenna = velocity of light/frequency of
signal.
 Suppose 20kHZ signal has to be transmitted, what
length antenna must be used?
Cont..
 For 20kHZ antenna of 15 km is required which is
impractical.
 Suppose if signal is made strong with carrier signal
say 1000 kHZ, then antenna of 300m is required
which is practical.
 This process is known as MODULATION.
Modulation
 Modulation is a process of mixing a baseband signal with
a High frequency signal to produce a new signal.
 A general function for a sinusoid: f(t)= Asin(wt +ф )
Where, A = amplitude
w = frequency
ф = phase angle
 The high frequency signal technically is known as carrier
signal
Cont..
 Demodulation : Reverse process of modulaion. i.e. it
converts modulated signal back to original information.
 The instrument used for modulation is known “modulator”
 The instrument used for demodulation is known
“demodulator”
Modulation techniques:
Continuous
Modulation
Pulse
Analog
Digital
Analog
Digital
Continuous:
Analog
Digital
• AM
• FM
• PM
• ASK
• FSK
• PSK
Pulse:
Analog
Digital
• PAM
• PWM
• PPM
• PCM
• DPCM
Need for Modulation
 Practicality of Antenna
 Operating range
 Multiplexing
 Improves quality of reception