EE 433
Wireless and Cellular Communications
Course Introduction
Fall 2015
Dr. C. R. Anderson
1
Homework/Absence Policies
Assignments approximately weekly, as posted on the EE433 website.
We have 5-6 “Labs” scheduled throughout the semester. Labs will be
graded using a new “Interview Grading” technique pioneered at CU
Boulder.
Homework is due in class. Late homework will only be accepted for a
valid excuse. If you know ahead of time that you are going to be out for
an excused absence, you must coordinate with me prior to the missed
class.
Homework Grading: Organized, legible, self contained, and in the
prescribed format. Solutions will be graded in class and collected by
the instructor.
Travel: Travel is an extremely vital and important component of Dr.
Anderson’s research program, and this semester is no exception.
Currently, plans are on the books to remote-teach EE433 from Sept.
21-30; other instructors may fill in other travel dates as necessary.
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1
Notes on My Teaching Style
I intentionally present the material in a slightly different
manner than the textbook. The reason is that if I teach
exactly like the book, you gain nothing from reading the
book.
I believe in emphasizing the fundamentals and
understanding the material over simply memorizing
equations. As a result, you may find a quiz or two with
(gasp!) no numbers or (double gasp!) an essay question.
Test and quiz grading: I’m fairly lenient if you can
demonstrate that you understand the underlying concept.
I’m also a stickler for things like significant figures, units,
etc. because accuracy and precision are primary aspects of
all forms of engineering.
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Sampling Theorem
Sampling Theorem
If a signal is bandlimited such that S ( f ) = 0 for f ≥ B then
s ( t ) is completely determined by its samples s ( nT0 ) ,
provided that the sampling frequency f s ≥ 2 B.
A/D Conversion Process
1. Bandlimit the signal to a maximum bandwidth of interest.
2. Sample the signal with f s ≥ 2 B (Discrete Time, Continuous Amplitude)
3. Quantize the signal into one of 2
N
amplitudes.
4. Represent (code) the amplitudes as an N-bit binary word.
4
2
Complex Representation of Signals
Communication signals can be represented in a couple
of different ways:
1. Quadrature Notation
s( t ) = x ( t ) cos(2 πf c t ) − y ( t ) sin(2 πf c t )
where x(t) and y(t) are real-valued baseband signals called
the in-phase and quadrature components of s(t)
2. Magnitude and Phase
s( t ) = a ( t ) cos( 2πf c t + θ( t ))
where
and
a (t ) =
x 2 (t ) + y 2 (t )
 y (t ) 
θ( t ) = tan −1 
 x (t ) 
is the magnitude of s(t),
is the phase of s(t).
5
Basics of Modulation
A sinusoidal signal can be modulated in three different ways…
A cos(2π fc t + φ )
Amplitude
Frequency
Phase
Angle Modulation
6
3
Amplitude modulation (AM)
Amplitude modulated signal sAM
Information signal m(t)
×
sam = Ac 1 + m ( t )  cos ( 2π f c t )
Carrier signal vc
(carrier frequency fc = 5-kHz)
The AM signal (sAM) is the product of the
carrier and the information signal
7
Frequency Modulation
(
sFM ( t ) = Ac cos 2π ( f c + k f m(t ) ) t
)
input signal (±1-V, 1-kHz square wave)
Voltage (V)
1
0.5
0
-0.5
-1
0
0.5
1
1.5
2
T ime (msec)
2.5
3
3.5
4
-3
x 10
FM signal (fc = 10-kHz, fd = 4-kHz)
Voltage (V)
1
0.5
0
-0.5
-1
0
0.5
f = 10-kHz
1
1.5
2
T ime (msec)
2.5
3
3.5
4
-3
x 10
f = 6-kHz
f = 6-kHz
f = 14-kHz
f = 14-kHz
f = 14-kHz
8
4
Frequency Shift Keying
(
sFSK ( t ) = Ac cos 2π ( f c + m f sm (t ) ) t
)
Or another way of thinking of it:
sFSK ( t ) = Ac cos ( 2π fi t )
01
11
00
11
01
00
11
Example of 4-FSK waveform in time domain
9
Spectrum and Performance of FSK
2-FSK Coherent Demod:
 Eb 
Pe = Q 
 N 
0 

Eb
2-FSK Incoherent Demod:
M-FSK Coherent Demod:
1 −
Pe = e 2 N 0
2
 ES 
Pe = M ⋅ Q 

 N0 
ES
M-FSK Incoherent Demod:
Pe ≈
M − 1 − 2 N0
e
2
Spectrum of 4-FSK Signal
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5
Performance of FSK
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Phase Shift Keying
sPSK ( t ) = Ac cos ( 2π f ct + θi )
0
1
1
0
1
0
1
Example of 2-PSK waveform in the time domain
12
6
Spectrum and Performance of PSK
Bandwidth:
BW =
2Rb
N
Prob. Error BPSK:
Prob. Error MPSK:
 2 Eb
Pe = Q 
 N0



 2 NEb
 π 
Pe ≈ 2Q 
sin   
N
 M 
0

2 Rb
N
Spectrum of PSK Signal
13
Performance of PSK
14
7
Superheterodyne Receiver
RF Section
IF Section
Baseband
Definition:
Heterodyning is the process of translating a signal from a highfrequency carrier to a lower intermediate frequency.
RF – Radio Frequency
IF – Intermediate Frequency
Baseband – Original Message
15
Image Frequency Problem
Low
Side
Injection
High
Side
Injection
In both cases we have TWO frequencies that are downconverted to
the EXACT SAME IF frequency.
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