Transcript session1
Lecture 1:
Communications systems
History
Aliazam Abbasfar
Outline
Course Information and policies
Course Syllabus
Communication Systems
Design Challenges
Course Information
Instructor : Aliazam Abbasfar
[email protected]
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
Communication systems overview
(1)
Fourier Review
Energy/Power Spectral Density
Random Processes and Signals
Transmission Media
(1)
(2)
(3)
(2)
Amplitude Modulation
Frequency Modulation
Comparison of different modulations
(6)
(4)
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
Frequency allocation needed in shared environment
Band allocation to applications
To avoid interference
Spectrum is a very valuable resource
Government regulations and policies
ITU coordinates between nations
Freq band:
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)
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
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)
GEOs
Wide coverage
Good for downlink broadcast
no good in uplink (high power)
large delay (bad for voice service)
Satellite systems
LEOs
Lower power
Smaller delay
Need many satellites
Shift towards LEOs in 1990
Global domination
Compete with cellular systems
Failed miserably (Iridium )
Big, power hungry mobile terminals
Global Positioning System (GPS)
Satellite signals used to pinpoint location
Popular in cars, cell phones, and navigation devices
Natural area for satellite systems is broadcasting
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