Lecture 1:
Communications systems
History
Aliazam Abbasfar
Outline
 Course Information and policies
 Course Syllabus
 Communication Systems
 Design Challenges
Course Information
 Instructor : Aliazam Abbasfar


abbasfar@ece.ut.ac.ir
Office Hours : ?
 Classes: Su-Tu 11am-12:30pm
 Email list ?, webpage ?
 Grading: HWs 20%, Midterm 50%, Final
30%
 Prerequisites:
 ECE2092 Probability
 ECE2144 signals and systems
Class policies
 Exam dates are fixed (No make-up
exams)
 Midterm: TBD
 Final: 88/11/7
 Academic honesty
 HW should be your own work
 Turn off your cell phones during lectures
Course Syllabus
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Communication systems overview
(1)
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Fourier Review
Energy/Power Spectral Density
Random Processes and Signals
Transmission Media
(1)
(2)
(3)
(2)
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Amplitude Modulation
Frequency Modulation
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Comparison of different modulations
(6)
(4)
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Analog to digital conversion
Digital Modulation
Course Summary and Hot Topics
(3)
(6)
(1)
(1)
References
 A.B. Carlson, P.B. Crilly and J.C. Rutlege, Communication
Systems, 4th ed.; McGraw-Hill, 2002
 S. Haykin, Communication systems, 3rd ed., John Wiley,
1994
 J.G. Proakis and M. Salehi, Communication Systems
Engineering, 2nd ed., Prentice Hall, 2002
 L.W. Couch, II, "Digital and Analog Communication
Systems," Sixth Edition, Prentice-Hall, New York, 2001
 B.P. Lathi, "Modern Digital and Analog Communications
Systems," 3rd edition, Oxford University Press, 1998

F.G. Stremler, "Introduction to Communication Systems," 3rd ed., Addison-Wesley
Publishing Co., 1990

Simon Haykin, Michael Moher, "An Introduction to Analog and Digital Communications,"
2nd Edition
Communication Systems
 Reliable (electronic) exchange of information
 Voice, data, video, music, email, web pages, etc
 Modern era started by telegraph (S. Morse 1837)
 First telegraph line linked Washington with Baltimore
in 1844
 Binary digital communications system
 Transatlantic cable (US-Europe) in 1858
 Telephone was the next breakthrough (A.G. Bell
1876)
 driven so many great inventions
 Wireless communication (G. Marconi 1890)
 Communication Networks (Bell Labs 70’s)
Communication System
Block Diagram
 Source encoder converts message into message signal or bits
 Transmitter converts message signal or bits into format
appropriate for channel transmission (analog/digital signal)
 Channel introduces distortion, noise, and interference
 Receiver decodes received signal back to message signal
 Source decoder decodes message signal back into original
message
Communication medias
 Wireline (wired)
 Telephony (voice, fax, modem, DSL)
 Ethernet/LAN
 Cable TV
 Backplane copper links
 Wireless (Electromagnetic)
 Over the air communication
 Radio and TV broadcast
 WLAN
 Cellular
 Radar
 Fiber optics
 High speed long haul data communication
 High traffic data transfer
Over the air communication
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Frequency allocation needed in shared environment
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Band allocation to applications
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To avoid interference
Spectrum is a very valuable resource
Government regulations and policies
ITU coordinates between nations
Freq band:
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3-30KHz Very low freq. (VLF)
30-300KHz Low freq. (LF)
300K-3MHz Medium freq. (MF)
3-30MHz High freq (HF)
30-300MHz Very high freq (VHF)
300M-3G Ultra high freq (UHF)
3-3GHz Super high freq. (SHF)
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L : 1-2G
S : 2-4G
C : 4-8G
X : 8-12G
Ku: 12-18G
...
Electromagnetic waves propagations
 Ground waves travels along
the surface of the earth
 ( freq < 2 MHz)
 Sky waves reflected by
ionosphere
 Very variable – seasonal
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Angle and loss of reflection
Freq < 30 MHz
 Line of sight (LOS)
 No reflection or refraction
 Non Line of sight
 Local reflections/refractions
Communication systems today
 Public Switched Telephone Network
(voice, fax, modem, DSL)
 Radio and TV broadcasting
 Satellite systems (TV broadcast,
voice/data , pagers)
 Computer networks (LANs, WANs, and the
Internet)
 Cellular Phones
 Bluetooth/wireless devices
 Sensor networks
Public Switched Telephone Network
 Circuit switched network designed for voice
 Local exchange handles local calls and routes long
distance calls over high-speed lines
 Fax, modem, DSL use advanced modulation to send
data over voice channel
 Fiber optics are rapidly replacing copper
Radio and TV broadcasting
 AM radio broadcast started in 1920
 E. Armstrong invented super heterodyne AM
receiver
 FM was invented in 1933
 TV broadcast
 Commercial TV began in London (BBC 1936)
 FCC authorized 1941
 Satellite broadcast services
 Rapid migration to digital broadcast
Satellite systems
 Satellite types:
 Geosynchronous (GEO)
 Medium-earth orbit (MEO)
 Low-earth orbit (LEO)
40,000Km
9000 Km
2000 Km
 GEOs first suggested in a sci-fi book (A.C. Clark 1945)
 First deployed satellites
 No Geo
 Soviet Union’s Sputnik in 1957
 NASA/Bell Laboratories’ Echo-1 in 1960
 Telestar I was launched in 1962

Relay TV signals between US and Europe
 First commercial Sat (Early Bird – 1965)
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 GEOs
 Wide coverage
 Good for downlink broadcast
 no good in uplink (high power)
 large delay (bad for voice service)
Satellite systems
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LEOs
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Lower power
Smaller delay
Need many satellites
Shift towards LEOs in 1990
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Global domination
Compete with cellular systems
Failed miserably (Iridium )
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Big, power hungry mobile terminals
 Global Positioning System (GPS)
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Satellite signals used to pinpoint location
Popular in cars, cell phones, and navigation devices
Natural area for satellite systems is broadcasting
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Now operate in 12GHz band
100s of TV and radio channels
All over the world
Communication networks
 LAN/Ethernet technology in 1970
 wireline was popular again
 10 Mbps data rate far exceeded anything available
using radio
 Wireless LAN was enabled by ISM band (FCC 85)
 No license – free band
 But, must have low power profile
 resulted in high costs ($1400 vs $200 Ethernet)
 Wired Ethernets today offer data rates over 1 Gbps
 Performance gap between wired and wireless LANs is
likely to increase over time
 Additional spectrum allocation might help
 WLANs are preferred due to their convenience
 freedom from wires
Wireless LAN overview
 Provides high-speed data within a small region
 1G : 26 MHz spectrum - 900 MHz ISM band
 Data rate : 1-2 Mbps
 No standard
 Not very successful
 2G : 80 MHz spectrum - 2.4 GHz ISM band
 Data rate : 1.6 Mbps (raw data rates of 11 Mbps)
 IEEE 802.11b standard
 Direct sequence spread spectrum
 range : 150m
 IEEE 802.11a wireless LAN standard operates with 300 MHz of
spectrum in the 5 GHz U-NII band.
 Data rate : 20-70 Mbps
 multicarrier modulation
 European counterpart : HIPERLAN
 Type 1, is similar to the IEEE 802.11a wireless LAN standard
Latest standards
 802.11n is the latest WLAN standard
 Close to finalization
 Operates in 2.4 and 5.0 GHz ISM bands
 Adaptive OFDM technology
 MIMO technology (2-4 antenna)
 Data rates up to 600 Mbps
 Range 60 m
 Wimax (802.16) : Wide area wireless network standard
 System architecture similar to cellular
 Hopes to compete with cellular
 OFDM/MIMO is core link technology
 Operates in 2.5 and 3.5 GHz bands
 Bandwidth is 3.5-10 MHz
 Fixed (802.16d) : 75 Mbps max, up to 50 mile cell radius
 Mobile (802.16e) : 15 Mbps max, up to 1-2 mile cell radius
Network Protocols and OSI Model
Cellular systems
 The most successful application of wireless networking
 It began in 1915, wireless voice transmission between New
York and San Francisco
 1946 public mobile telephone service in 25 cities across US
 Initial systems used a central transmitter to cover an
entire metropolitan area
 limited capacity

the maximum # of users was only 534 (30 years after first link)
 Solution came in 50's and 60's (Bell Labs)
 Cellular concept
 Frequency reuse
 First cellular system deployed in Chicago in 1983
 Analog system
 Very popular - already saturated by 1984
Cellular systems
 2nd Generation (2G)
 Digital communications
 Higher capacity
 More services (voice, data, paging)
 So many competitors
 Only 3 standards in US!
 GSM is most popular
 Multi-mode devices
 3G
 CDMA technology
 4G ?
Other wireless systems
 Bluetooth and wireless devices
 Sensor networks
 Automated highways, UAVs
 In-body networks
Summary
 Communication systems send information
electronically over communication channels
 Communication systems recreate transmitted
information at receiver with high fidelity
 Many different types of systems which convey
many different types of information
 Design challenges include hardware, system, and
network issues
 Focus of this class is design and performance of
analog and digital communication systems
Reading
 Carlson Ch. 1
 Proakis Ch. 1