1
Analog Communications
Amplitude Modulation (AM)
Frequency Modulation (FM)
Lecture 3
Principles of Communications
2
Radio broadcasting
30-300M Hz
SOURCE
Source
Transmitter
Analog baseband signal
Lecture 3
Transmitted
signal
Channel
Received
signal
Rec
Todays Lecture
Review of signals and spectral analysis
Signal representation
Introduction of linear time-invariant (LTI)
system
Fourier series and Fourier transform
ENGG2310A Principle of Commun. Systems
1
Introduction
Information: Voice, data, image, vid
1
Lecture 8. Digital Communications
Part III. Digital Demodulation
Binary Detection
M-ary Detection
Lecture 8
Principles of Communications
2
Digital Communications
Analog Signal
Bit sequence
0001101110
t
Source
SOURCE
A-D
Conversion
Digital
Baseband
Mod
2.C. Fourier Transform
1
Formal Definition of Spectrum
Given a time-domain signal s(t), its Fourier transform is defined as follows.
S( f )
Fourier transform:
s t e j 2 ft dt
S(f) is referred to as the Fourier spectrum (or simply spectrum) of s(t).
Somet
Chapter 2
Frequency Domain Analysis
1
2.A. Basic Concepts
2
Frequency Domain Analysis
Frequency domain analysis can also be called spectrum analysis. It is a
basic tool for engineering. However, it is not a subject of this course. Rather,
you will learn t
Chapter 4
Receiver Design
1
Overview
So far we have considered the frequency domain properties of digital systems.
In this chapter we consider transmitting such signals through a noisy channel.
We first focus on the baseband, which refers to the transmiss
2.B. Fourier Series
1
Fourier Series
We start our discussion with Fourier series analysis. Please review your notes on
this topic. (I presume that you have learned it before.) The different between a
Fourier series and a Fourier transform is as follows:
Chapter 3
Digital Baseband Modulation Techniques
1
Outline
In a modern communication system, the basic unit of information is bit.
Mathematically, a bit represents either 0 or 1. The goal of a communication
system is to tell the receiver which one, i.e.,
Communication Systems
Chapter 1
Introduction
1
Contacts and Notes
Professor Ping Li
Telephone: 3442 9574
Office: G6417
Email: eeliping@cityu.edu.hk
EE3008 has co-requisites:
EE3210 Signals & Systems or
EE3118 Linear Systems and Signal Analysis
Linear syst
Chapter 5
Digital Bandpass Modulation and
Demodulation Techniques
1
Motivations and Goals
In a radio system, the signals are often modulated to radio frequency (typically
at very high frequency range). For this reason, we will study the modulation
and dem
Chapter 8
Analog-to-Digital and Digital-to-Analog
Conversion
1
8.A Overview
2
Introduction
Most digital systems, such as phones and TV, are actually used to deliver
analogue signals. (After all, we are human beings and we can only see and
listen to analog
EE3008 Test 1 Answers
Q1) Based on the time scaling property, the Fourier transform of x(t)=s(2t) is
Xf
1 f
S .
2 2
t
Based on the time shift property, the Fourier transform of s '(t ) x t 0 is
2
t0
2
1 f j ft0
S e
.
2 2
Q2) We can rewrite s(t) as s t
Chapter 6
Analog Modulation and Demodulation
(Part 1. Amplitude Modulation)
1
Analog Transmission
We can obtain analog signals using various electronic devices. For example, we
can use a microphone to transform sound to electronic form.
Our next question
Chapter 6
Analog Modulation and Demodulation
(Part 2. Frequency Modulation)
1
6.A Basic Principles
2
Frequency Modulation
We have seen that information can be
transmitted by varying the amplitude of the
carrier signal in AM. Next we will see that
informat
EE 3008: Principles of Communications Test 1:
Name_ ID_
Q1) Let S(f) be the Fourier transform of s(t).
(a) Write down the expression of the Fourier transform of s1(t)= s(0.5t-t0) in terms of S(f).
(5 marks)
(b) Write down the expression of the Fourier tra
EE3008 Test 1 Answers
Q1) Based on the time scaling property, the Fourier transform of g1(t)=s(0.5t) is
G1 f 2S 2 f .
Based on the time shift property, the Fourier transform of g 2 (t ) g1 t 2t0 s 0.5t t0 is
G2 f G1 f e j 2 f 2t0 2 S 2 f e j 4 ft0 .
Based
Examination Solution Manual
Section 1
Q1) (a) Since cfw_ x(t) = X(f), we have
cfw_x(t t0 ) X ( f )e j 2 ft0 .
(b) The Fourier transform of sin(2f0t) is
1 j 2 ft0
j
cfw_e
e j 2 ft0 cfw_e j 2 ft0 e j 2 ft0
2j
2
j
cfw_sin(2 f 0t ) cfw_ ( f f 0 ) ( f f 0 )
CITY UNIVERSITY OF HONG KONG
-Module code & title :
EE3008 Principles of Communications
Session
:
Semester A 2009/2010
Time Allowed
:
Two hours
-This paper has FIVE pages (including this cover page).
-1.
This paper consists of FOUR sections.
2.
Attempt al
Systems and Channels
1
Communication System
Noise
SOURCE
Source
Info.
Received
Received
Transmitted
info.
signal
signal
Receiver
Transmitter
User
Channel
So far, our discussions on communication systems have been based on very
abstract models, such as the
QUIZ FOR MULTI-LEVEL MODULATION
Note: The following questions will not be selected for mini test during tutorial sessions. They
are nevertheless provided below to broaden your view.
Problem: Consider a communication system, modeled as y = xC + n, where y
Extra reading in AM modulator
AM is quite simple in theory. It can be represented as s(t)cos(2fct). However, in practice, it is actually
not easy to implement a multiplier involved. The questions below are about implementing an AM
modulation. You can see
Extra tutorial on matched filter receiver:
The following questions are related to a matched filter receiver that is an alternative to a correlation
receiver. The matched filter receiver is widely used in practice. Consider a bipolar scheme. The
transmitte
CHAPTER 8
1. In PCM, the quantization noise depends on
(a) sampling rate
(b)
(c) signal power
(d)
number of quantization levels
none of the above
2. Which of the following modulations is digital in nature?
(a) FM
(b) AM
(c) DM
(d)
none of the above
(d)
no
EE3008: QUIZ QUESTIONS FOR CHAPTER 6 PART 2
1. The AM-DSB-C rise to a maximum value of 12V and drop to a minimum value of 4V. The
modulation index assuming single tone modulation is
(a)
3
(b)
1/3
(c)
1/4
(d)
1/2
2. The most suitable method for detecting a
EE3008: QUIZ QUESTIONS FOR CHAPTER 6 PART 3
1. The frequency doubler in an Armstrong FM transmitter is
(a) to increase the overall S/N ratio
(b) to reduce bandwidth
(c) to convert the signal to the desired carrier frequency as well as frequency deviation
EE 3008. Receiver Design Tutorial Questions
Q1) Suppose we are transmitting a variable v, which can be either 1 or 0. Suppose during the
transmission v is distorted by a Gaussian random variable n with zero mean and variance 2,
so the receiver actually re
EE 3008 Chapter 5 Tutorial Questions
Q1) Consider data rate 10 kbps and carrier frequency 1MHz. Roughly sketch the amplitude
spectrum for (a) BPSK modulation; and (b) On-off ASK modulation.
Q2)
A BPSK has carrier signal Abcos(2109t)V where b=+1 and -1. Le
EE 3008. Fourier Transform Tutorial Solutions
Q1) This is already given in the notes. We repeat the result below.
G( f )
g (t )e
j 2 ft
T /2
dt
Ae j 2 ft dt
T / 2
e j 2 ft
A
j 2 f
t T / 2
t T / 2
e j fT e j fT
A
j 2 f
e j fT e j fT 1
A
j2
f
A sin(
Q1)
EE 3008. Random Process Tutorial Questions
A coin is tossed three times. What is the probability of two heads and one tail?
Q2)
Given that the random variable X has density function
0 < x <1
2x
f ( x)
otherwise
0
Find Pr(0.5<x<3/4) and Pr(-0.5<x<0.5)
CITY UNIVERSITY OF HONG KONG
Course code & title : EE3 008 Principles of Communications
Session : Semester A 2009/20010
Time Allowed : Two hours
1. This paper consists of FOUR sections.
2. Attempt all the questions in these FOUR sections.
. 3. Start a new
CITY UNIVERSITY OF HONG KONG
_
Course code & title : EE3008 Principles of Communications
Session : Semester A 2008/09
Time allowed : Two hours
1. This paper consists of FOUR questions.
2. Attempt all the FOUR questions.
3. Start a new page in the answerin
Test 2 Solutions
Q1) (a) Average power for each symbol =
1
2
2
(Ab) cos (2f0t )dt
0.5(Ab )2
0
(1 cos(2 2f t )dt
0
0.5A 2b 2 .
0
For A = 0.1 and b= -7, -5, 3, 1, 1, 3, 5, and 7, the average transmission power is
Ps = 0.5 0.12 (-7)2+(-5)2+(-3)2+(-1)2+12
EE 3008: Principles of Communications Test 1:
Name_ ID_
Q1) Find the mathematical expression of the Fourier transform of x(t) below. (Note: No need to
draw the spectrum.)
(10 marks)
x(t)
2
1
t
1
0
2
3
4
5
6
Fig. 1
(Hint: Consider the Fourier transform pai
EE 3008: Principles of Communications Test 2:
Name_ ID_
Q1) An 8-ary ASK signal is expressed as Abcos(2f0t) V, with A=0.1 and b= -7, -5, 3, 1, 1, 3, 5, 7
with equal probability. The duration of each symbol is =10-3sec. Let the loading resistance be 1.
(a)