This document provides an outline for a course on communication systems. It covers several key topics: 1) The different types of modulation techniques used in analog and digital communication systems including amplitude, frequency, phase, and pulse modulation. 2) The basic components and functioning of a communication system including information sources, encoding, transmission over a channel, reception and decoding. 3) Characteristics of communication channels such as bandwidth, transmitted power, and how these resources are used efficiently. 4) Differences between analog and digital communication systems and some advantages of digital systems.

1. DIT
Dar es Salaam institute of Technology (DIT)
ETU 07123
Introduction to Communication Systems
Ally, J
jumannea@gmail.com

2. Course Outline
 Principles of Communication Systems
 Analogue Modulation
 Angle Modulation
 Pulse Modulation
 Digital Modulation
Reference:
Introduction to Analogue and Digital
Communication, by Simon Haykin
DIT

3. DIT
Principle of Communication System

4. DIT
Information Representation
 Communication systems convert information into a format
appropriate for the transmission medium.
 Channels convey electromagnetic waves (signals).
 Analog communication systems convert (modulate) analog
signals into modulated (analog) signals
 Digital communication systems convert information in the form of
bits into binary/digital signals
 Types of Information:
 Analog Signals: Voice, Music, Temperature readings
 Analog signals or bits: Video, Images
 Bits: Text, Computer Data
 Analog signals can be converted into bits by quantizing/digitizing

5. DIT
Basic Mode of Communication
There are two basic modes of communication:
 Broadcasting: which involves the use of a single powerful
transmitter and numerous receivers that are relatively inexpensive
to build. Here information-bearing signals flow only in one
direction.
 Point-to-point communication: in which the communication
process takes place over a link between a single transmitter and a
receiver. In this case, there is usually a bidirectional flow of
information-bearing signals, which requires the use of a transmitter
and receiver at each end of the link.

6. DIT
Primary Communication Resources
In a communication system, two primary resources are employed:
Transmitted Power and Channel Bandwidth.
 The Transmitted Power: is the average power of the transmitted signal
 The channel bandwidth is defined as the band of frequencies allocated for
the transmission of the message signal
NB:
 A general system design objective is to use these two resources as
efficiently as possible.
 In most communication channels, one resource may be considered
more important than the other.
 Therefore we may classify communication channels as Power limited or
Band-limited.
 Example, the telephone circuit is a typical Band-limited channel, whereas
a space communication link or satellite channel is typically Power limited.

7. DIT
Source of Information
The telecommunications environment is dominated by four important
sources of information: speech, music, pictures, and computer data
 Speech is the primary method of human communication
 Music is the one originates from instruments such as the piano,
violin, and flute
 Pictures is the one relies on the human visual system for its
perception. The picture can be dynamic, as in television, or static,
as in fascimile (fax) machine
 Computer data is the information transmitted or exchanged through
computer or other electronic devices

8. DIT
Communication System Block Diagram
 Source encoder converts message into message signal or bits.
 Transmitter converts message signal or bits into format appropriate for
channel transmission (analog/digital signal).
 Channel introduces distortion, noise, and interference.
 Receiver decodes received signal back to message signal.
 Source decoder decodes message signal back into original message.
NB: The good communication system is to produce at the destination
(receiver) an acceptable replica of the source message.

9. DIT
Modulation and Demodulation
 Modulation
 Is the process of changing ore or more properties such
as amplitude, frequency, and phase of the analog carrier
in proportion with the information signal
 Performed in a transmitter by a circuit called a modulator
 Demodulation
 Is the reverse process of modulation and converts the
modulated carrier back to the original information
 Performed in a receiver by a circuit called a demodulator

10. DIT
Electromagnetic Frequency Spectrum
 The purpose of an electronic communications system
is to communicate information between two or more
locations commonly called stations.
 Accomplished by converting the original information
into electromagnetic energy and then transmitting it
to one or more receive stations where it converted
back to its original form.
 Electromagnetic energy can propagate as a voltage
or current along a metallic wire, as emitted radio
waves through free space, or as a light waves down
an optical fiber.
 Electromagnetic energy is distributed throughout an
almost infinite range of frequencies.

11. DIT
The electromagnetic Spectrum

12. DIT
Bandwidth
 Bandwidth of an information of signal: is the difference
between the highest and lowest frequencies contained in
the information.
 Bandwidth of a communication channel: is the difference
between the highest and lowest frequencies that the
channel will allow to pass through it.
 The bandwidth of the communications channel must be
equal to or greater than the bandwidth of the information.
 For example, voice frequencies contain signals between
300 Hz and 3000 Hz. Therefore, a voice frequency
channel must have a bandwidth equal to or greater than
2700 Hz (300 Hz-3000 Hz).
 If a cable television transmission system has a passband
from 500kHz to 5000kHz, it has a bandwidth of 4500 kHz.

13. DIT
Information Capacity
 Information theory: is a theoretical study of the efficient
use of bandwidth to propagate information through
electronic communications systems.
 Information theory can be used to determine the
information capacity of a data communications system.
 Information capacity: represents the number of
independent symbols that can be carried through a system
in a given unit of time.
 The most basic digital symbol used to represent
information is the binary digit or bit.
 It is convenient to express the information capacity of a
system as a bit rate.
 Bit rate: is the number of bits transmitted during one
second and is expressed in bits per second (bps).

14. DIT
Information Capacity (2)
 In 1928, R. Hartley (Bell Telephone Laboratories)
developed a useful relationship among bandwidth
(B), transmission time (t), and information capacity
(I). Simply stated, Hartley’s law is
I α B x t
 In 1948, mathematician Claude E. shannon (Bell
Telephone Laboratories) published a paper relating
the information capacity of a communication
channel to bandwidth and signal-to-noise power
ratio (S/N).
 Mathematically stated, the shannon limit for
information capacity is






+=
N
S
BI 1log2 





+=
N
S
BI 1log32.3 10

15. DIT
Two Basic of Electronic Communication
System
 An analog communication system
 Is a system in which energy is transmitted and received in analog
form (a continuously varying signal such as sine wave)
 Both the information and the carriers are analog signal
 The digital communication system
Covers a broad range of communication techniques, including
digital transmission and digital radio

16. DIT
Two Basic of Electronic Communication System(2)
 Digital transmission
- Is a true digital system where digital pulses are transferred between
two or more point a communication system
- There is no analog carrier, and the original source may be in digital or
analog form
- Require physical transmission medium such as metallic cable or optical
fiber
 Digital Radio
- Is the transmitted of digitally modulated carrier between two or
more points in a communication system
- The modulating signal and the demodulated signal are digital
pulses
- Digital pulse modulate an analog carrier
- Transmission medium may be a physical facility or free space
(i.e. The Earth’s atmosphere)

17. DIT
Advantage of using Digital transmission compared
to Analog transmission
 Increased immunity to channel noise and external
interference
 Flexible operation of the system
 A common format for the transmission of different kinds
of message signals (e.g. voice signals, video signals,
computer data)
 Improved security of communication through the use of
encryption

18. DIT
Summary of various modulation technique
 Analog Modulation Types
 Amplitude Modulation (AM): is the one if the information signal is analog and the
amplitude (V) of the carrier is varied proportional to the information signal
 Frequency Modulation (FM): is the one if the frequency (f) of the carrier is varied
proportional to the information signal
 Phase modulation (PM): is the one if the phase (θ) of the carrier is varied proportional
to the information signal
 Digital Modulation Types
 Amplitude Shift Keying (ASK): is the one if the information signal is digital and the
amplitude (V) of the carrier is varied proportional to the information signal
 Frequency Shift Keying (FSK): is the one if the frequency (f) of the carrier is varied
proportional to the information signal
 Phase Shift Keying (PSK): is the one if the phase (θ) of the carrier is varied
proportional to the information signal
 Quadrature Amplitude Modulation (QAM): is the one if both the amplitude (V) and the
phase (θ) of the carrier are varied proportional to the information signal

19. DIT
Why Modulation is necessary
 It is extremely difficult to radiate low frequency
signals from an antenna in the form of
electromagnetic energy
 It is possible to combine a number of baseband
(information) signal and send them through the
medium, provided different carrier frequencies
are used for different baseband signals
 Transmitting signals over large distance,
because low frequency signals have poor
radiation characteristics

20. DIT
Analog vs. Digital Systems
 Analog signals
 The amplitude changes continuously
with respect to time with no discontinuities
 Digital signals
 The one which are discrete and their
amplitudes maintains a constant level
for prescribed period of time and then it
changes to another level
 Binary signals
 Has at most 2 values
 Used to represent bit values
 Bit time T needed to send 1 bit
 Data rate R=1/T bits per second
t
x(t)
t
x(t)
t
x(t) 1
0 0 0
1 1
0T
Digital systems more robust

21. DIT
Fourier Transforms
 Let the frequency spacing approach zero, and the index n approach
infinity such that the product approaches a continuous frequency variable f. Then
 The bracketed term is the Fourier transform of v(t) symbolized by or
and defined as:
The time function v(t) is recovered from V(f) by the inverse Fourier transform

22. DIT
Frequency Translation and Modulation
 Besides generating new transform pairs, duality can be used to generate
transform theorems. In particular, a dual of the time-delay theorem is
 Since is not a real time function and cannot occur as a
communication signal. However, signals of the form are
common-in fact, they are the basis of carrier modulation-and by direct
extension of the equation above we have the following modulation theorem:
 The theorem is easily proved with the aid of Euler’s theorem

23. DIT
Special Functions
 Dirac delta function
 Exponentials
 Sinusoids
 Delta Function Train
δ(t)
0
fc
Αδ(f-fc)
Aej2πfct
⇔
Acos(2πfct) ⇔
fc
.5Αδ(f-fc)
-fc
.5Αδ(f+fc)
Ts∑nδ(t-nTs)
0
∑nδ(t-n/Ts)
0 Ts 2Ts 3Ts
-Ts-2Ts-3Ts 1/Ts-1/Ts

24. DIT