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Lecture 1: Wireless communications systems
Aliazam Abbasfar
OutlineCourse Information and policies
Course Syllabus
Communication Systems
Design Challenges
Course InformationInstructor : Aliazam Abbasfar
[email protected] Office Hours : Sa-Tu
Classes ?
Grading: HWs 10%, Midterm 60%, Project 30%
Prerequisites: Digital Communications
Class policiesExam dates are fixed (No make-up exams)
Midterm: TBDFinal: 88/11/7
Academic honestyHW 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 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 overview
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
Communication Systems
AM radio broadcast started in 1920E. Armstrong invented super heterodyne
AM receiverFM was invented in 1933
TV broadcast Commercial TV began in London (BBC 1936)FCC authorized TV bands in 1941
Satellite broadcast servicesRapid migration to digital broadcast
Radio and TV broadcasting
Satellite types: Geosynchronous (GEO) 40,000Km Medium-earth orbit (MEO) 9000 Km Low-earth orbit (LEO) 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
Satellite systems
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
Communication networks
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
Wireless LAN overview
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
Latest standards
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 communicationsHigher capacityMore services (voice, data, paging)
So many competitorsOnly 3 standards in US!GSM is most popularMulti-mode devices
3GBased on CDMA technologyWCDMA and CDMA2000
4G ?
Cellular systems
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
Bluetooth
Optimized for one-way communicationsShort messagingMessage broadcast from all base
stationsSimple terminalsMostly replaced by cellular
Similar systemsElectronic shelf labels
Paging Systems
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 neededMultipath highly resolvable: good and bad
Limited commercial success to date
Ultra wideband Radio (UWB)
Low-Rate WPANData rates of 20, 40, 250 KbpsSupport for large mesh networking or star
clustersSupport for low latency devicesCSMA-CA channel accessVery low power consumptionFrequency of operation in ISM bands
IEEE 802.15.4 / ZigBee Radios
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
Wireless vision
We will have many different systems and standards Different segments have different specs
Multimedia Requirements
QoS depends on the application Rate and delay requirements Requires cross layer design
Future systems
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
Wireless evolution
Rate
Mobility
2G
3G
4G
802.11b WLAN
2G Cellular
Other issues:Coverage
Latency Cost Energy
802.11n
Wimax/3G
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
Cross layer design
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
Design challenges
Ad hoc/mesh wireless networks flexible/ (robust) network infrastructure Indoor/outdoor Cellular/LAN integration
Cooperative networksMaximize network capacityRelay nodesNetwork coding
Cross layer design critical
Emerging technologies
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
Wireless sensor networks
UnderlayCognitive radios cause minimal
interference to primary users
InterweaveCognitive radios find spectral holes
OverlayCognitive radios overhear and enhance
noncognitive radio transmissions
Cognitive Radio
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
Spectrum Regulation
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
Summary
ReadingCarlson Ch. 1
Proakis Ch. 1