1
Wireless Transmission Systems
2
Telecommunication Engineering Technology, Texas A&M University Wireless Transmission Systems Lecture Notes - Copyright Jeff M. McDougall 2001
Instructor
Mr. Jeff McDougall
Education:
BS - EE Texas A&M University 93-97
MS - EE Johns Hopkins University 97-99
PhD - EE Texas A&M University 99- ??
Applicable Experience:
•
APL (DoD contractor), RF systems engineer for prototype Navy and DoT
initiatives including VHF marine links, ISM DSRC links, Doppler radar,
unique transmission systems, UAV communication links, and project
management
•
SwRI (DoD, CIA and “other” contractor), Unique ‘over the horizon’
communication link analysis and waveform study.
•
Invisix (Mobile Carrier Systems Integrator), Design, implementation and
documentation of a Wireless Internet Service Provider network
3
Course Placement within TET Program
Intro to
Telecom
215
Data
Comm
435
Telecom
Services
325
Telecom
Testing
345
LAN/
WAN
425
Transmission
& Switching
415
Private
Networks
465
Wireless Trans
Systems
455
Senior
Project
420
Telecommunication Engineering Technology, Texas A&M University Wireless Transmission Systems Lecture Notes - Copyright Jeff M. McDougall 2001
Course Overview
Wireless Trans
Systems
455
The Wireless Radio
-Analog Modulation (wk 1-2)
Digital Modulation (wk 3-5)
Propagation and Link Design
-Antennas (wk 6)
Propagation and Microwave Links (wk 7)
Mobile Fading (wk 8)
Atmospheric Effects (wk 9)
Wireless Communication Systems
5
Ground Rules
• NO CHEATING
• Treat this class as your job
– 4 hr credit = 12 hours of work each WEEK
– Prepare for class (read notes and book)
– Turn in assignments on time
– Attend lecture and lab (without attendance, your test grades will
suffer! Not all notes are contained on the slides, new material will
be presented in class)
• Be respectful of your classmates and your instructor
– There are no stupid questions
– Come to class ON TIME, and AWAKE
• Approach this class with the right attitude, don’t take it to
graduate, take it to learn about Wireless communications!
6
Telecommunication Engineering Technology, Texas A&M University Wireless Transmission Systems Lecture Notes - Copyright Jeff M. McDougall 2001
Syllabus Overview
•
TEXT - Buy it!
•
Prerequisite - ENTC 415
•
No Late assignments will be accepted w/o TAMU excuse
•
No Make-up tests
•
Term paper
•
Random Quizzes to test class preparation
•
Homework, this is a problem solving course unlike 415! Homework
will count for an entire test grade.
•
Passing lab grade is mandatory
7
Introduction to Wireless Communications
• What is meant by wireless?
– The physical phenomena known as radio waves were first known
as ‘Hertzian Waves’. Hertz showed that the electro-magnetic
phenomena (under study by Tesla) could be used to transfer energy
between locations without a physical connection.
– Guglielmo Marconi began work in 1894 to reproduce the Hertz
laboratory experiment over greater distances. His study and efforts
brought about the first radio link in the form of wireless telegraph.
His efforts gave him the title: “Father of Radio”
– The combined works of Tesla, Hertz, and Marconi proved that
electro-magnetic phenomena (such as a large spark) generated at
one location could be detected at another location without a direct
physical connection between locations. Thus, the ability to
communicate without wires i.e. ‘Wireless’.
Telecommunication Engineering Technology, Texas A&M University Wireless Transmission Systems Lecture Notes - Copyright Jeff M. McDougall 2001
Introduction to Wireless Communications
• Why not employ only wireless communications?
– Wireless links inherently are more complex than wireline links
– Wireless links suffer from unfavorable channel characteristics
– There is a very limited spectrum for wireless communication
– Wireless communication is susceptible to intercept
• Why employ any wireless communications?
– Mobility (generally a luxury item)
– Minimize required infrastructure (countries with little to no wired
infrastructure)
9
Introduction to Wireless Communications
• Challenges of Wireless Communications:
– VERY limited resources
– Unstable channel characteristics
– Multi-user Interference
– Line of Sight (LOS) for frequencies ~>100MHz
– Mobility Issues
• Battery power
• Low antenna apertures
• RF radiation levels
– Antenna Size
– Extremely low receive power levels
10
Telecommunication Engineering Technology, Texas A&M University Wireless Transmission Systems Lecture Notes - Copyright Jeff M. McDougall 2001
Introduction to Wireless Communications
Types of Wireless
Communications
– Microwave Link
– Satellite Link
– Mobile Cellular
– Infrared Links
– ISM applications
• Cordless phones
• Wireless LANs
– Military
– Marine
– Scientific
Insert picture from pg
17 of comm Sys
Engineering
11
The ‘digital’ communication model
Introduction to Wireless Communications
Information
Source and
input transducer
Source
Encoder
Channel
Encoder
Modulation
Channel
Output
Transducer
Source
Decoder
Channel
Decoder
Demodulator
Sound
waves
‘k’ Digital
Bits
‘n<k’
Digital
Bits
‘d>n’ Digital
Bits
‘N’ Digital
Symbols
‘N’ Digital
Symbols
Telecommunication Engineering Technology, Texas A&M University Wireless Transmission Systems Lecture Notes - Copyright Jeff M. McDougall 2001
Modulation Overview
Modulation
is a process that causes a shift in the range of
frequencies in a signal. Modulation takes a message signal
at
baseband
and shifts the range of frequencies to achieve
carrier communication
.
The term baseband is used to designate the band of
frequencies of the signal delivered by the source or the
input transducer.
The term carrier communication describes the use of a carrier
to shift the frequency range and encode the basband signal
13
A message signal ‘m(t)’ is transmitted through a
communication channel by impressing it upon a carrier
signal of the form:
Where
A
c
is the amplitude,
f
c
is the carrier frequency, and
c
is the carrier phase. The message signal
m(t)
modulate the
carrier signal c(t) in either amplitude, frequency, or phase.
In effect, modulation translates the message signal to a
higher frequency.
Signal Representation
( )
t
A
c
(
f
c
t
c
)
c
=
cos
2
π
+
φ
14
Telecommunication Engineering Technology, Texas A&M University Wireless Transmission Systems Lecture Notes - Copyright Jeff M. McDougall 2001
Signal Representation
The most basic form of Amplitude modulation (DSB-SC) is
obtained by multiplying the message signal
m(t)
with the
carrier signal c(t).
( )
t
A
c
m
( ) (
t
f
c
t
c
)
u
=
cos
2
π
+
φ
0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 -1 - 0 . 8 - 0 . 6 - 0 . 4 - 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1 C a r r i e r f r e q u e n c y 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 - 1 . 5 -1 - 0 . 5 0 0 . 5 1 1 . 5 m ( t ) a t 2 0 d B S N R 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 - 1 . 5 -1 - 0 . 5 0 0 . 5 1 1 . 5 s i g n a l u ( t )*
=
15
Signal Representation
The most basic representation of frequency modulation is
accomplished by altering the instantaneous frequency of
the carrier by a message signal.
( )
t
A
c
(
(
f
c
f
m
( )
t
)
t
c
)
u
=
cos
2
π
+
+
φ
( )
t
k
m
( )
t
f
m
=
f
0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 -1 - 0 . 8 - 0 . 6 - 0 . 4 - 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 -6 -4 -2 0 2 4 6 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 -1 - 0 . 8 - 0 . 6 - 0 . 4 - 0 . 2 0 0 . 2 0 . 4 0 . 6 0 . 8 1=
Modulated
by
Telecommunication Engineering Technology, Texas A&M University Wireless Transmission Systems Lecture Notes - Copyright Jeff M. McDougall 2001
