ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﻴﻢ
University of Khartoum
B.Sc. of Communication Engineering
4th Year Electrical Engineering
Communications Systems I
EEE 41201
LECTURE 1
INTRODUCTION
Moutaman Mirghani
sites.google.com/site/moutamanpage
Overview
Communications between persons, as well as
the communication between machines (M2M),
are essential in order to convey information.
The information conveyed can be speech, text,
images, video stream or other sorts of data.
Communication media can be the ground, sea,
air, space, wire or fiber optics cable.
Information is carried through signals, which
are in form of sound waves, electric currents
or electromagnetic waves, including light.
Communication systems link information from
the information source to the destination.
A typical communication system is composed
of a transmitter, channel and a receiver.
Transmitter Channel Receiver
Information Information
Source Destination
Interference
and Noise
During transmission of information signals via
the channel, they are affected by noise and
interfering signals from other sources.
Speech Signals in Edison Telephone
Signals and Systems
A signal is a varying quantity that is a
function
What isofa signal
an independent
? variable, such
as the time or the space.
A system is a module (or a box) that
receives
What issignals at its
a system ? inputs and produces a
signal at its output.
Processing of signals is achieved with the
aidWhy
of systems, either to
we use systems ? modify signals or
to extract useful information contained in
those signals. 3:57 AM
A signal can be a voltage signal, current,
acoustic or microwave, light, temperature,
pressure, vibration, etc.
Electrical signals may possibly be audio,
video, control, telemetry or radio signals.
Speech signals are audio signals.
Sensors are transducers that receive and
convert non-electrical signals into analogue
voltage or current signals, like a photo cell,
microphone, seismic sensor or a thermostat.
Actuators are transducers convert electrical
signals into non-electrical signals, such as
headphones, antenna or piezoelectric cell.
A signal is either continuous, i.e., defined for
all intervals of time or space, or discrete
which is defined only for specific intervals of
time or space.
A deterministic signal that has a predictable
waveform and its instantaneous value can be
expressed mathematically.
Random signal instantaneous value can’t be
explicitly expressed mathematically. Yet, it
can be expressed statistically.
In general, information signals and noise are
random, thus they are not easily predicted.
Examples of Signals
Sinusoidal Signals
Digital Signal
Telegram Signal Noise Signal
A 0 ≤ t ≤τ αt 0≤t ≤T /2
p(t ) = v (t ) =
0 elsewhere α (T − t ) T /2≤t ≤T
Rectangular Signal Triangular Signal
0
u (t ) =
t<0 v(t) = Σ δ(t - kT)
1 t≥0 δ(t - kT) = 0 t ≠ kT
Step Signal Impulse Signals
Impulse and Delta Function
An impulse is a rectangular pulse of zero width
and a unity area. Though it does not exist, it is
so useful in signal and systems analysis.
Delta function is used to represent impulses in
time domain and sinusoids in frequency domain.
Analog and Digital Signals
Analogue signals are normally continuous,
i.e. defined for all values of time or space.
Digital signals are discrete, i.e. they are
defined at specific intervals of time or space.
In order to process, transmit or store analog
signals with the aid of digital devices, they
need be converted into digital.
They are sampled to become discrete, and
Howencoded
then do we convert analog signal
into numbers to digital?
or codes.
3:57 AM
Analog and Discrete Systems
Systems carry operations on signals, such as
amplification, attenuation, filtering, correlation,
modulation, demodulation, prediction, etc.
Analog or digital signal processor is designed to
realize some algorithm or mathematical model.
Course Description
Review
• Signal and systems analysis. Introduction to
communication systems including effects of
noise. Principles of modulation, amplitude,
frequency, and pulse modulation. Comparison
of analog and digital transmission. Time and
frequency division multiplexing. Pulse and
Digital communications.
Pre-Requisite Courses
• Signals and Systems (EEE32203)
Computer Usage
• Matlab 3:57 AM
References
1. Haykin & Moher, Introduction to Analog and Digital
Communications, 2nd Ed., Wiley (major reference).
2. Communication System Engineering, Proakis and Salehi, Prentice-
Hall, 1994.
3. Contemporary Communication Systems Using Matlab, Proakis and
Salehi, PWS Publishing, 1998.
4. Modern Digital and Analog Communication Systems, B.P. Lathi,
Oxford Press, 1989.
5. Principles of Digital and Analog Communications, Jerry Gibson,
Macmillan, 1989.
6. Communications Systems, S. Haykin, Wiley, 1994.
7. M. Mirghani, Signal Analysis and Processing, Arabic Text Book,
CNRC, Karary University, 2012.
Course Website
sites.google.com/site/moutamanpage/current-courses/CommSys1.pptx
End of Lecture 1
