ECE 401 Communication Systems - University of Dayton : Homepages

ECE 401 Communication
Dr. Russell Hardie
University of Dayton Department
of Electrical and Computer
Engineering
Systems

• Syllabus
• Historical perspective
• Anatomy of a communication system
• Analog vs. digital communications
• Types of channels
University of Dayton Department
of Electrical and Computer
Engineering
Outline

Focus on EM Signals
• Nearly all long distance modern communications
uses electro-magnetic (EM) signals
• EM signals may be in guided wireline channels
(twisted pair, coaxial, or optic fiber) or wireless
channels (free space)
• Relatively easy to generate, detect, manipulate,
amplifiy, etc.
• Travel at or near the speed of light
• Notable exception is underwater acoustic channels
University of Dayton Department
of Electrical and Computer
Engineering

1837
Samuel Morse
Electric Telegraph
Balt-Wash 1844
Historical Perspective
(EM Wireline Telecommunications)
1858 1876 1915 1953 1960
Trans-Atlantic
Telegraph
Alexander Bell
Telephone
Hundred Miles
Transcontinental
Telephone
Thanks to
Triode Amplifier
University of Dayton Department
of Electrical and Computer
Engineering
Trans-Atlantic
Telephone
First
Electronic
Switch
Thanks to
Transistor

More Recent Advances
(EM Wireline Telecommunications)
• Digital transmission of voice, video, and
data for more reliable communications
• Move to fiber optic cables yielding a
massive bandwidth increase
University of Dayton Department
of Electrical and Computer
Engineering

Here for more
1831
Michael Faraday
Current Produced
When Moving
A Magnet Near
Conductor*
1894
Oliver Lodge
Develops
Sensitive RF
Detector
150 yds
Historical Perspective
(EM Wireless Telecommunications)
1901
Marconi
Transmits
1700 Miles
University of Dayton Department
of Electrical and Computer
Engineering
1936 1965
1920 1933 1962
AM
Broadcasts
FM
Broadcasts
BBC Transmits
TV
* M. Guillen Five Equations That Changed the World, MJF Books, New York
Satellite
Relays TV
US-Europe
Commercial
Satellite
Comm.

1920 Spark Transmitter
University of Dayton Department
of Electrical and Computer
Engineering

More Recent Advances
(EM Wireless Telecommunications)
• Digital transmission of voice, video, and
data for more reliable communications
• Satellite communications
• Cell phones
• Wireless LAN
University of Dayton Department
of Electrical and Computer
Engineering

Information
Source
Received
Information
Anatomy of a Communication
Transmitter
Receiver
University of Dayton Department
of Electrical and Computer
Engineering
System
Transmission
Medium
(Channel)

Analog Communications
• Analog Signal: Continuous in time and value
• Analog communications: The channel carries
analog information
• Note DSP may be used in parts of the transmitter
and/or receiver, but the information content of the
signal passed through the channel is analog
University of Dayton Department
of Electrical and Computer
Engineering

Digital Communications
• Digital Signal: Discrete in time and value
• Digital Information: Sequence of symbols from a
finite set
• Digital communications: The channel carries digital
information
• Note that the waveforms transmitted through the
channel are analog, but the information content of
those waveforms is digital.
• Also note that some analog electronics may be
involved in the transmitter and receiver
University of Dayton Department
of Electrical and Computer
Engineering

Information
Source
Received
Information
Analog Communication System
Transducer
Transducer
Transmitter
Receiver
CW
Modulation*
CW
Demodulation*
University of Dayton Department
of Electrical and Computer
Engineering
Transmission
Medium
(Channel)
* Not Required for
Baseband Transmission.
CW = Continuous Wave

Analog Communications
• Transducer converts the energy from the
original information source into a suitable
electrical signal (e.g., microphone).
• Continuous wave (CW) modulation shifts
the frequency content of the signal into a
desired range for a given channel.
University of Dayton Department
of Electrical and Computer
Engineering

Acoustic Speech
Signal
Information
Source
Analog Comm. Sys. Example
Amplitude Modulation (AM)
v(t)
300
250
200
150
100
50
0
50 100 150 200 250
t
300 350 400 450 500
Transducer
University of Dayton Department
of Electrical and Computer
Engineering
v(t)
300
200
100
0
-100
-200
Transmitter
50 100 150 200 250
t
300 350 400 450 500
CW
Modulation
Antenna

¼-wavelength monopole
Virtual ¼-wavelength monopole
reflected through the ground plane
Antenna Example
(1/2 Wavelength Dipole)
λ /4
λ /4
University of Dayton Department
of Electrical and Computer
Engineering
λ =
Ground plane
c
f
Propagation velocity
Freq of time-variation

• Speech 300-3600 Hz
• CD Music 20-20 kHz
• Video 0-4 MHz
Baseband Signals
University of Dayton Department
of Electrical and Computer
Engineering
8
3× 10 m/s
λ = = 166,667 m/c
1800 Hz (c/s)
λ / 4 = 41,667 m/c
8
3× 10 m/s
λ = =
10,000 Hz (c/s)
λ / 4=7,500 m/c
8
3× 10 m/s
6
2× 10 Hz (c/s)
30,000 m/c
λ = = 150 m/c
λ / 4=37.5 m/c

Need for Radio Frequency (RF)
• To directly transmit most baseband signals, via
EM propagation, the antenna dimensions would be
wildly impractical!
• The modulator allows us to modify (modulate) an
RF signal in proportion to the message.
• The RF carrier is of high enough frequency to
allow for practical antenna dimensions for a given
application.
• The message signal can be recovered from the
modulated RF carrier at the receiver using
demodulation.
University of Dayton Department
of Electrical and Computer
Engineering

Commercial Broadcast FM
• 100 bands each 200 kHz wide centered at
88.1, 88.3, 88.5, … 107.9 MHz
8
3× 10 m/s
6
97.5× 10 Hz (c/s)
λ = =
λ / 4=0.77 m/c (30 in)
University of Dayton Department
of Electrical and Computer
Engineering
3.08 m/c

Commercial Broadcast TV &
• VHF:
– Channels 2-4: 54-72 MHz
– Channels 5-6: 76-88 MHz
– Channels 7-13: 174-216 MHz
• UHF:
– Channels 14-83: 470-890 MHz
– Channels 70-83 (806-890 MHz) is allocated for cell phones
• ¼-Wave Antenna Dimension Examples
– Channel 5 ¼-wave antenna = 38 in
– Channel 13 ¼-wave antenna = 14 in
– Channel 30 ¼-wave antenna = 5 in
– Mobile phone 859 MHz ¼-wave antenna = 3.4 in
University of Dayton Department
of Electrical and Computer
Engineering
Cell Phone

Continuous Wave Modulation
Amplitude
Modulation (AM)
mt ()
xt () = Amt () cos(2πf
t + θ )
mt ()
mt
()
Frequency
Modulation (FM)
Phase
Modulation (PM)
University of Dayton Department
of Electrical and Computer
Engineering
c c c
xt () = Acos( 2πf t+ 2 π f m(
τ ) dτ
+ θ )
c c d c
τ = 0
xt () = Acos(2 π ft+ k m()
t + θ )
c c p c
t
∫

CW Modulation
v(t)
Message @ baseband
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0 0.1 0.2 0.3 0.4 0.5
t
0.6 0.7 0.8 0.9 1
AM
FM
PM
University of Dayton Department
of Electrical and Computer
Engineering
v(t)
v(t)
v(t)
2
1.5
1
0.5
0
-0.5
-1
-1.5
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
Amplitude Modulation (AM)
0 0.1 0.2 0.3 0.4 0.5
t
0.6 0.7 0.8 0.9 1
Frequency Modulation (FM)
-1
0 0.1 0.2 0.3 0.4 0.5
t
0.6 0.7 0.8 0.9 1
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
Phase Modulation (PM)
-1
0 0.1 0.2 0.3 0.4 0.5
t
0.6 0.7 0.8 0.9 1

Information
Source
Received
Information
Digital Communication System
Source & Channel
Encoder
Transmitter
Digital
Modulation*
Codec Modem
Source & Channel
Decoder
Receiver
Digital
Demodulation*
University of Dayton Department
of Electrical and Computer
Engineering
Transmission
Medium
(Channel)
* May not be
required
for simple
baseband
transmission

Digital Communications
• Source coding involved coding the desired
information into a finite symbol set (preferably in
an efficient manner).
• Channel coding involves adding systematic
redundancy so that error in transmission can be
detected and corrected.
• Digital modulation generates a specific waveform
(suitable for the given channel) for each symbol to
be transmitted.
University of Dayton Department
of Electrical and Computer
Engineering

Acoustic
Speech
Signal
v(t)
300
250
200
150
100
50
0
Information
Source
Digital Comm. Sys. Example
50 100 150 200 250
t
300 350 400 450 500
Transmitter
Source & Channel
Encoder
v(t)
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
1
111 0 0 0 00
0
0 50 100 150
t
200 250 300
University of Dayton Department
of Electrical and Computer
Engineering
Frequency Shift Keying (FSK)
1
v(t)
0.8
0.6
0.4
0.2
-0.2
-0.4
-0.6
-0.8
Digital
Modulation
1
0
-1
0 50 100 150
t
200 250 300
Antenna

Digital Modulation
• One waveform is transmitted for each symbol
from a finite set.
• Lowpass channel signaling with baseband signals
– Pulse Modulation
– Custom Orthogonal Waveforms
• Bandpass channel signaling using carrier
modulation
– ASK, PSK, FSK
– QAM
– And many more…
University of Dayton Department
of Electrical and Computer
Engineering

EM Communication System
EM Communication Systems
Analog Comm Digital Comm
University of Dayton Department
of Electrical and Computer
Engineering
Categories
Wireless Wireline Wireless Wireline
Radio (AM, FM)
Broadcast TV (UHF, VHF)
Analog Cell Phones
Long Distance Phone (microwave)
Local Phone
Cable TV
Digital Cell Phones
Wireless LAN
Satellite Phone
Satellite TV
Long Distance Phone (microwave)
Phone/Cable Modem
Digital Cable TV
Fiber Optic
Ethernet
Long Distance Phone

• EM Wireline
– Wire
– Twisted pair
– Coaxial
– Fiber Optic
• EM Wireless
– Free space
Communications Channels
• Storage
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of Electrical and Computer
Engineering
– Optical (CD)
– Magnetic, etc.
• Acoustic
– Air (short range only)
– Water
• Seismic
– Earth

• Noise power
• Signal power
• Bandwidth
xt
()
LTI System
h(t)
University of Dayton Department
of Electrical and Computer
Engineering
Channel Issues
• Fidelity (analog)
• Data rate & probability
of error (digital)
∑
nt ()
y() t = x()* t h() t + n() t

• Hartley-Shannon Theorem
(band-limited channel with
additive white noise)
C = Blog (1 +
S/ N)
2
Channel Capacity
Capacity (bps)
7000
6000
5000
4000
3000
2000
1000
0
100
University of Dayton Department
of Electrical and Computer
Engineering
80
60
SNR
40
20
0
0
200
400
600
Bandwidth (Hz)
800
1000