Lecture 1:
Wireless communications systems
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 : Sa-Tu
 Classes ?
 Grading: HWs 10%, Midterm 60%,
Project 30%
 Prerequisites:
 Digital Communications
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









Overview of Wireless Communications (1)
Wireless propagation
(4)
Diversity
(6)
Narrowband/Wideband Modulation
(6)
Spread Spectrum Techniques
(4)
Multiple access techniques
(2)
Cellular concept/standards
(3)
Multiple Input/output Systems (MIMO) (4)
Wireless Networks and Resource Management
(1)
References
 David Tse and Pramod Viswanath, Fundamentals of
Wireless Communications, Cambridge University
Press, 2005
 Andrea Goldsmith, Wireless Communications ,
Cambridge University Press
 Theodore S. Rappaport, Wireless communications,
principles & practice, Prentice Hall, 1996
 A.R.S. Bahai, B.R. Saltzberg, M. Ergen, “Multi-
Carrier Digital Communications, Theory and
Applications of OFDM,” 2nd Ed., Springer 2004
 R. Peterson, R. Ziemer, D. Borth, Introduction to
Spread Spectrum Communications, Prentice Hall,
1995.
Communication systems overview
 Communication started in wireless form
 smoke/torch/flash signaling
 Modern communication goes back to Telegraph (Morse
1837)
 wireline communications
 digital
 replaced old technologies
 Telephone (Bell 1876) introduced telephony
 Analog communication
 wireline
 Radio transmission was born decades later (Marconi 1895)
 Radio technology has been growing rapidly ever since
 longer distances with better quality
 less power, and smaller, cheaper equipments
Communication Systems
 Reliable (electronic) exchange of information
 Voice, data, video, music, email, web pages, etc
 Communication Systems Today
 Radio and TV broadcasting
 Public Switched Telephone Network (voice, fax, modem)
 Computer networks (LANs, WANs, and the Internet)
 Cellular Phones
 Satellite systems (TV broadcast, voice/data , pagers)
 Bluetooth/wireless devices
 Sensor networks
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 TV bands in 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
Natural area for satellite systems is broadcasting



Now operate in 12GHz band
100s of TV and radio channels
All over the world
 Global Positioning System (GPS)


Satellite signals used to pinpoint location
Popular in cars, cell phones, and navigation devices
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 MHz bands
 Different for different countries, 5.8 also used.
 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
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
 Based on CDMA technology
 WCDMA and CDMA2000
 4G ?
Bluetooth
 Cable replacement RF technology (low cost)
 Short range (10m, extendable to 100m)
 2.4 GHz band (crowded)
 1 Data (700 Kbps) and 3 voice channels, up
to 3 Mbps
 Widely supported by telecommunications,
PC, and consumer electronics companies
 Few applications beyond cable replacement
Paging Systems
 Optimized for one-way communications
 Short messaging
 Message broadcast from all base stations
 Simple terminals
 Mostly replaced by cellular
 Similar systems
 Electronic shelf labels
Ultra wideband Radio (UWB)
 7.5 Ghz of “free spectrum” in US (underlay)
 High data rates, up to 500 Mbps
 UWB is an impulse radio: sends pulses of
tens of picoseconds(10-12) to nanoseconds
(10-9)
 Duty cycle of only a fraction of a percent
 A carrier is not necessarily needed
 Multipath highly resolvable: good and bad
 Limited commercial success to date
IEEE 802.15.4 / ZigBee Radios
 Low-Rate WPAN
 Data rates of 20, 40, 250 Kbps
 Support for large mesh networking or star
clusters
 Support for low latency devices
 CSMA-CA channel access
 Very low power consumption
 Frequency of operation in ISM bands
Wireless vision
 Information exchange between people and/or
devices, anywhere, anytime
 home applications : new intelligent devices that






interact with each other (smart homes)
connectivity between business machines; phones,
computers, servers, etc
Wireless entertainment : provide wireless access to
multi-media contents
Wireless internet access
Wireless sensor networks
Automated cars – UAVs
In-body networks
 Cannot pick a segment for success, but foresee a
bright future for the whole industry
Future systems
 We will have many different systems and standards
 Different segments have different specs
 Multimedia Requirements
Voice
Data
Video
Data rate
8-32 Kbps
1-100 Mbps
1-100 Mbps
BER
10-3
10-6
10-6
PER
< 1%
0
< 1%
Delay
< 100ms
-
<100ms
Traffic
Continuous
Bursty
Continuous
 QoS depends on the application
 Rate and delay requirements
 Requires cross layer design
Wireless evolution
Rate
802.11n
802.11b WLAN
2G
Other issues:
Coverage
Latency
Cost
Energy
4G
3G
Wimax/3G
2G Cellular
Mobility
Cross layer design
 System constrains
 Rate, delay, energy
 System optimization
 System adaptation (link, MAC, network, application)
 resource management
 Scheduling



Data prioritization
Resource reservation
Access scheduling
 Achieve robustness by using diversity
 Link diversity (antenna, channel)
 Route diversity
 Power control
Design challenges
 Wireless channels are a difficult and
capacity-limited broadcast communications
medium
 Traffic patterns, user locations, and network
conditions are constantly changing
 Applications are heterogeneous with hard
constraints that must be met by the network
 Energy and delay constraints change design
principles across all layers of the protocol
stack
Emerging technologies
 Ad hoc/mesh wireless networks
 flexible/ (robust) network infrastructure
 Indoor/outdoor
 Cellular/LAN integration
 Cooperative networks
 Maximize network capacity
 Relay nodes
 Network coding
 Cross layer design critical
Wireless sensor networks
 For data collection and distributed control
 Hard energy/delay constraint
 Each node sends only finite number of bits
 Energy/delay trade offs
 Nodes cooperate in transmission, reception, and
processing
 Optimization for node/network lifetime
 Design nodes cooperation
 Completely new framework
 Must consider TX, RX, and processing
Cognitive Radio
 Underlay
 Cognitive radios cause minimal
interference to primary users
 Interweave
 Cognitive radios find spectral holes
 Overlay
 Cognitive radios overhear and enhance
noncognitive radio transmissions
Spectrum Regulation
 Spectral Allocation by ?
 Worldwide spectrum controlled by ITU-R
 Plays a key role in communication sector growth
 Allocation strategies
 Dedicated/public band
 Auction bands
 Overlay/Underlay
 Cognitive radios
 Innovations are still needed
Summary
 The wireless vision encompasses many exciting
systems and applications
 Technical challenges in all layers of the system
 Cross-layer design emerging as a key theme in
wireless
 Existing and emerging systems provide excellent
quality for certain applications but poor
interoperability.
 Standards and spectral allocation heavily impact the
evolution of wireless technology
Reading
 Carlson Ch. 1
 Proakis Ch. 1