National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Spectral Characteristics of AngleModulated
Signals
Due to the inherent nonlinearity of anglemodulation
systems, the precise characterization of their spectral
properties, even for simple message signals, is
mathematically difficult.
The derivation of
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Signal Multiplexing
If two or more message signals are transmitted simultaneously
over the communications channel
Various message signals occupy separate frequency bands of the
channel and do not interfere with one another in transmission over the
chann
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Super heterodyne receiver
What is the intermediate frequency fif?
It is fixed frequency located at 455 kHz
The IF filter is bandpass with center frequency of 455 kHz
and bandwidth equal to the bandwidth of one AM channel
approximately =10 kHz.
Fc
Fif
F
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Multiple Random Processes
Multiple random processes arise when dealing with
two or more random processes.
For example, we pass a random process X(t) through a
linear timeinvariant (LTI) system.
For each sample function input x(t; i), we have a sample
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Angle Modulators
Angle modulators are generally timevarying
and nonlinear systems.
Methods for generating an FM signal
Direct generation using a Voltagecontrolled
oscillator (VCO)
Varactor diode based oscillator
Reactancetube based oscillator
Ind
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Implementation of Amplitude Modulators and
Demodulators
There are several different methods for
generating AMmodulated signals
The process of modulation involves the
generation of new frequency components
Modulators are generally characterized as
nonl
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
19Oct16
EFFECT OF NOISE ON AMPLITUDE MODULATION
SYSTEMS
Effect of Noise on Analog
Communication Systems
Effect of Noise on a Baseband System
In this case, there is no carrier demodulation to be
performed.
The receiver consists only of an ideal lowpas
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Random Processes
Random Processes: Basic Concept
A random process is the natural extension of random variables when
dealing with signals.
In analyzing communication systems, sometimes, it is more
appropriate to model signals as random rather than determ
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Angle Demodulators
FM demodulation Phase Locked Loop (PLL)
Block diagram of
a PLLFM demodulator.
Linearized PLL
Angle Demodulators
FM Demodulation PLL Advantages
The output of the loop filter with the frequency
response G(f) is the desired message s
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
The demodulation of an FM signal involves
finding the instantaneous frequency of the
modulated signal and then subtracting the carrier
frequency from it.
The demodulation of PM is done by finding the
phase of the signal and then recovering m(t).
The maxi
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Mathematical Models for Communication Channels
We construct mathematical models that
reflect the most important characteristics of
the transmission medium.
The mathematical model for the channel is
used in the design of the channel encoder and
modulator
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
02Sep16
Conventional Amplitude Modulation
A conventional AM signal consists of a large carrier
component, in addition to the DSB AMmodulated signal.
The transmitted signal is expressed mathematically as
u(t) = Ac[l + m(t)]cos(2 fc t),
where the messa
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
17Aug16
Digital and Analog Sources
A digital information source produces a finite set
of possible messages.
A telephone touchtone pad is a good example of a
digital source.
There is a finite number of characters (messages) that
can be emitted by this
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
31Aug16
Demodulation of DSBSC AM Signals
Suppose that the DSBSC AM signal u(t) is
transmitted through an ideal channel (with no
channel distortion and no noise).
The received signal is equal to the modulated
signal, i.e.,
r(t) = u(t)
= Acm(t) cos(2f
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
30Aug16
Introduction
Amplitude Modulation
A large number of information sources produce analog
signals.
Analog signals can be modulated and transmitted
directly, or they can be converted into digital data and
transmitted using digitalmodulation techn
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
24Aug16
Power & Energy
Power & Energy
The energy and power of a signal represent the energy or
power delivered by the signal when it is interpreted as a
voltage or current source feeding a 1 resistor.
The energy content of a (generally complexvalued
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
16Aug16
Course Objectives
The main objective of this course is to introduce
fundamentals of both analog and digital
communication systems.
The concepts will be mainly building on the
knowledge gained during courses such as Signals
& Systems, and Proba
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
26Aug16
Hilbert Transform and its Properties
The Hilbert transform is unlike many other transforms
because it does not involve a change of domain
The Hilbert transform of a signal x(t) is a signal x (t )
whose frequency components lag the frequency
co
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
Digital Communication Systems
Digital Communication Systems  Elements
Source Encoding
The process of efficiently converting the output of either an
analog or a digital source into a sequence of binary digits is
called source encoding or data compressio
National University of Computer and Emerging Sciences, Islamabad
ADC
TELECOM 1144

Fall 2016
20Sep16
Angle Modulation
Introduction
Amplitudemodulation methods are also called linearmodulation methods, although conventional AM is not
linear in the strict sense.
On the other hand, nonlinear modulation techniques
include
Frequency Modulation (