Transcript Wireless Communications Research Overview

TTT4160-1
Mobile Communications
Professor Geir E. Øien
IET, NTNU
Outline
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Course Info and background
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Course Syllabus
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Wireless History and Trends
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Wireless Vision for the Future
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Technical Challenges
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Current Wireless Systems
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Emerging Wireless Systems
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Spectrum Regulation
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Standardization
Course Information:
People
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Lecturer:
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Prof. Geir E. Øien, room C349, Elektroblokk C. Tlf: 94315. Mail:
[email protected].
Teaching Assistants:
Sébastien de la Kethulle de Ryhove, room C351b, Elektroblokk C. Tlf: 96977.
Mail: [email protected].
 Changmian Wang, room C351b, Elektroblokk C. Tlf: 93670. Mail:
[email protected].
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Course Information, cont’d
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Prerequisites: TTT4125 Information theory, coding
and compression + TTT4130 Digital
Communications (or foreign equivalents)
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Required Textbook:
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Wireless Communications, by Prof. Andrea J. Goldsmith
(Cambridge University Press, available at Tapir bookstore)
Class Homepage:
http://www.iet.ntnu.no/courses/ttt4160/
 NB website not yet updated...!
Course Background
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This course is partly based on a course which
has been developed and taught repeatedly by
Professor Andrea Goldsmith (textbook author)
at Stanford University in the past decade.
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Presentation will be partly based on material
from the Stanford course (credits to Prof.
Homayoun Hashemi for some of the slides).
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Supplements from locally developed course and
guest lecturers.
Course Information,
continued
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Exercises:
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One compulsory “midterm” exercise, the rest voluntary
Mostly written exercises, but possibly also some in Matlab later
Exercises will be assigned during lectures, and are due next Monday
before 12 am for those who want their answers checked by the T.A.
No exercise assigned today: first on Monday, January 15th.
Help from teaching assistant will be given in EL4, Tuesdays 16.15 18.00 (first on January 16th).
Exercise sessions (except first): Combination of review of last
week’s exercise + help with the current week’s.
Exam: Written exam, 09.00 - 13.00, Saturday, June 2nd, 2007
Grading: A - F scale, based on final exam only
Tentative Course Syllabus
Overview of Wireless Communications (Ch. 1) 8/1-07
 Path Loss and Shadowing (Ch. 2) 15/1-07
 Statistical Fading Models (Ch. 3) 22/1-07
 Capacity of Wireless Channels (Ch. 4.1 - 4.3.1) 29/1-07
 Digital Modulation and its Performance (Ch. 5+6) 5/2-07 + 12/2-07 + 19/2-07
 Adaptive Modulation (Ch. 9.1 - 9.4) 12/3-07
 Diversity (Ch. 7.1 - 7.3) 19/3-07
 Spread Spectrum (Ch. 13) 26/3-07 + 16/4-07
 Cellular Systems and Infrastructure-Based Wireless Networks (Ch. 15) 23/4-07
 The GSM System (guest lecture by Dr. Magne Pettersen, Teleplan) 30/4-07
NOTE 1: A more detailed syllabus will be handed out towards the end of the
course.
NOTE 2: Most of the rest of the book will be covered by the in-depth module
(skall-emne) “Kommunikasjons- og kodingsteori for trådløse kanaler”, fall
2007.
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Wireless (Pre-)History
• ”Pre-historic” times: smoke signals, bonfires, lighthouses, torches
• 1895: first radio transmission (Marconi, Isle of Wight, 18 mile distance)
• 1915: Wireless voice transmission established between San Francisco
and New York
• 1945: Arthur C. Clarke(sci-fi writer) suggests geostationary satellites
• 1946: Public mobile telephony introduced in 25 US cities
• 1947: Invention of cellular concept (AT&T)
• 1957: First deployed communication satellite (Sputnik, Soviet Union)
• 1963: First deployed geostationary satellite (NASA)
• 1971: First packet-based radio network (ALOHANET, Univ. of Hawaii)
• 1983: First analog cellular system deployed (Chicago)
• 1985: Unlicensed frequency bands first authorized for WLAN use
• Ca. 1990: First digital cellular systems (”2G”)
• 2000 - now: Standardization of 3rd generation mobile communication
systems, WLANs, WPANs, sensor network radios,...
Wireless History, cont’d
First Mobile Radio Telephone 1924
Pre-Cellular Wireless
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One highly-elevated, high-powered
antenna in a large service area
Small number of channels (few users)
 Analog transmission, inefficient use of
spectrum (no frequency reuse)
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Very low capacity, power-inefficient
The Cellular Concept
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Basic Principles:
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Frequency Re-use
Cell Splitting
Qu ickTime™ and a
TIFF (Uncompressed) de compressor
are nee ded to see this pic ture.
(First proposed by D. H.
Ring at Bell Laboratories,
NJ, USA in 1947.)
Cellular - Implementation
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Cellular - Implementation
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
NB: Not ”entirely wireless” since
base stations are connected by
wired network!
Cellular Systems:
Re-use channels to maximize capacity
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Geographic regions are divided into cells
Frequencies/timeslots/codes reused at spatially separated locations.
NB: Co-channel interference (between same-color cells below).
Base stations/MTSOs (Mobile Telephone Switching Offices)
coordinate handoff and control functions
Shrinking cell size increases capacity - but also networking burden..
BASE
STATION
MTSO
Cellular Phone Networks
San Francisco
BS
PSTN: Public Service
Telephone Network
BS
Internet
MTSO
PSTN
New York
MTSO
BS
The Wireless Revolution
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Cellular is the fastest growing sector of communication industry
(exponential growth since 1982, with over 2 billion users worldwide
today)
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Modern-day “generations” of wireless (pre-cellular: 0G):
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First Generation (1G - ex. NMT, ca. 1982 - ): Analog 25 or 30 KHz FM,
voice only, mostly vehicular communications.
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Second Generation (2G - ex. GSM, ca. 1993 - ): Narrowband TDMA
and CDMA, voice and low bit-rate data, portable units.
2.5G - 2.75G: Enhancements to 2G network for increased data
transmission capabilities (ex. GPRS + EDGE, ca. 2000 - ).
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Third Generation (3G - UMTS/IMT-2000, ca. 2002 - ): Wideband
TDMA and CDMA, voice and high bit-rate data, portable units
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4th Generation (4G/B3G, ca. 2010 - ?): ???... Heterogeneous network of
several interacting systems/networks, not one dedicated network;
diverse, advanced, adaptive air interfaces, protocols, and resource
allocation mechanisms; multitude of services including high-capacity
multimedia)
World Telecom Statistics
Qu ickTime™ and a
TIFF (Uncompressed) decompressor
are nee ded to see this picture .
Crossover happened in May 2002...!
World Cellular Subscribers by
Technology - as of June 2006
2.41 Billion Cellular Customers Worldwide
GSM/UMTS totals 82.3% of this (GSM dominates)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
(PDC: Personal Digital Cellular)
World Cellular Subscriber
Distribution as of June 2006
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
GSM Growth - 1993 to June 2006
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Exciting Developments
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Internet and laptop use exploding
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Wireless LANs and PANs growing rapidly
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Huge cell phone popularity worldwide
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Emerging systems such as Bluetooth, UWB,
Zigbee, and WiMAX opening new doors
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Military and security wireless needs
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Important interdisciplinary applications
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Sensor networks
Future Wireless Networks
(The Wireless Vision)
Ubiquitous Communication Among People and Devices
Wireless Internet access
Nth generation Cellular
Wireless Ad Hoc Networks
Sensor Networks
Wireless Entertainment
Smart Homes/Spaces
Automated Highways
All this and more…
• Hard Delay Constraints
• Hard Energy Constraints
Design Challenges
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The wireless channel is a difficult and capacity-limited
broadcast communications medium!
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Traffic patterns, user locations, and network conditions
are constantly changing...
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Traffic is nonstationary, both in space and in time
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Energy and delay constraints change design principles
across all layers of the protocol stack (points towards
cross-layer design)
Evolution of Current
Systems
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Wireless systems today
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Next Generation
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2G + 2.5G Cellular: ~30-70 Kb/s.
WLANs: ~10 Mb/s.
2.75G + 3G Cellular: ~300 Kb/s.
WLANs: ~70 Mb/s.
Technology Enhancements
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Hardware: Better batteries. Better circuits/processors. Cooptimization with transmission schemes.
Link: Antennas, modulation, coding, adaptivity, DSP, BW.
Network: Dynamic resource allocation. Mobility support.
3G: ITU-developed,
UMTS/IMT-2000
Global
Satellite
Suburban
Macrocell
Urban
Microcell
Basic Terminal
PDA Terminal
Audio/Visual Terminal
In-Building
Picocell
Future Generations
Rate
4G
802.11b WLAN
3G
Other Tradeoffs:
Rate vs. Coverage
Rate vs. Delay
Rate vs. Cost
Rate vs. Energy
2G
2G Cellular
Mobility
Still: Fundamental Design Breakthroughs Needed
Current Wireless Systems
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Cellular Systems
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Wireless LANs (802.11a/b/g, Wi-Fi)
Satellite Systems
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Paging Systems
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Bluetooth
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Ultrawideband radios (UWB)
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Zigbee/802.15.4 radios
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WiMAX (802.16)
Wireless Local Area
Networks (WLANs)
01011011
0101
1011
Internet
Access
Point
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WLANs connect “local” computers (~100 m range)
Breaks data into packets
Channel access is shared (random access)
Backbone Internet provides best-effort service
 Poor performance in some app’s (e.g. video)
Wireless LAN Standards (Wi-Fi)
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802.11b (Current Generation)
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802.11a (Emerging Generation)
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Standard for 2.4GHz ISM band (bw 80 MHz)
Frequency hopped spread spectrum
1.6-10 Mbps, 500 ft range
Standard for 5GHz NII band (bw 300 MHz)
OFDM with time division
20-70 Mbps, variable range
Similar to HiperLAN in Europe
802.11g (New Standard)
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Standard in both 2.4 GHz and 5 GHz bands
OFDM (multicarrier modulation)
Speeds up to 54 Mbps
In future
all WLAN
cards will
have all 3
standards...
Satellite Systems
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Cover very large areas
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Different orbit heights
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Optimized for one-way transmission:
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GEOs (39000 Km) via MEOs to LEOs (2000 Km)
Trade-off between coverage, rate, and power budget!
Radio (e.g. DAB) and movie (SatTV) broadcasting
Most two-way systems struggling or bankrupt...
(Too) expensive alternative to terrestrial systems
 (But: a few ambitious systems on the horizon)
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Paging Systems (Personsøk)
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Broad coverage for (very) short messaging
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Message broadcast from all base stations
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Simple terminals
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Optimized for 1-way transmission
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Answer-back is hard
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Overtaken by cellular
Bluetooth
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“Cable replacement” RF technology (low cost)
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Short range (10 m, extendable to 100 m)
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2.4 GHz ISM band (crowded!)
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1 Data (700 Kbps) + 3 voice channels
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Widely supported by telecommunications, PC, and
consumer electronics companies
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Few applications beyond cable replacement!
8C32810.61-Cimini-7/98
UltraWideband Radio (UWB)
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Impulse radio: sends pulses of tens of picoseconds (10-12) to
nanoseconds (10-9) - duty cycle of only a fraction of a percent
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Uses a lot of bandwidth (order of GHz)
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Low probability of detection by others + beneficial
interference properties: low transmit power (density) spread
over wide bandwidth
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This also results in short range.
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But : Excellent positioning (ranging) capability + potential of
high data rates
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Multipath highly resolvable: both good and bad
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Can use e.g. OFDM or equalization to get around multipath problem.
Why is UWB interesting?
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Unique Location and Positioning properties
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Low Power CMOS transmitters
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Very high data rates possible (although low spectral
efficiency) - 500 Mbps at ~10 feet range under current regulations
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7.5 Ghz of “free spectrum” in the U.S.
1
 100
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cm accuracy possible
times lower than Bluetooth for same range/data rate
FCC (Federal Communications Commission) recently legalized UWB
for commercial use in the US
Spectrum allocation overlays existing users, but allowed power level is
very low, to minimize interference
“Moore’s Law Radio”
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Data rate scales with the shorter pulse widths made possible with ever
faster CMOS circuits
IEEE 802.15.4/ZigBee radios
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Low-Rate WPAN (Wireless Personal Area Network) - for
communications < 30 meters.
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Data rates of 20, 40, 250 kbps
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Star topology or peer-to-peer operation, up to 255
devices/nodes per network
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Support for low-latency devices
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CSMA-CA (carrier sense multiple access with collision
avoidance) channel access
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Very low power consumption: targets sensor networks
(battery-driven nodes, lifetime maximization)
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Frequency of operation in ISM bands
WiMAX: Worldwide Interoperability for
Microwave Access
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Standards-based (PHY layer: IEEE 802.16 Wireless MAN
family/ETSI HiperMAN) technology, enabling delivery of ”last mile”
(outdoor) wireless broadband access, as an alternative to cable and
DSL (MAN = Metropolitan Area Network). Several bands possible.
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OFDM-based adaptive modulation, 256 subchannels. TDM(A)-based.
Antenna diversity/MIMO capability. Advanced coding + HARQ.
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Fixed, nomadic, portable, and mobile wireless broadband connectivity
without the need for direct line-of-sight (LOS) to base station.
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In a typical cell radius deployment of 3 to 10 kms, expected to deliver
capacities of up to 40 Mbps per channel, for fixed and portable access.
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Mobile network deployments are expected to provide up to 15 Mbps of
capacity within a typical cell radius deployment of up to 3 kms.
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WiMAX technology already has been incorporated in some notebook
computers and PDAs. Potentially important part of 4G?
Data rate
100 Mbit/sec
10 Mbit/sec
1 Mbit/sec
100 kbits/sec
UWB
802.11g
802.11b
3G
802.11a
Bluetooth
ZigBee
ZigBee
10 kbits/sec UWB
0 GHz 1GHz 2 GHz 3 GHz 4 GHz 5 GHz 6 GHz
Frequencies occupied
Range
10 km
3G
1 km
100 m
10 m
802.11a
802.11b,g
ZigBee
UWB
Bluetooth
ZigBee
UWB
1m
0 GHz 1GHz 2 GHz 3 GHz 4 GHz 5 GHz 6 GHz
Power Dissipation
10 W
3G
1W
100 mW
802.11bg
802.11a
Bluetooth
UWB
ZigBee
10 mW
ZigBee
UWB
1 mW
0 GHz 1GHz 2 GHz 3 GHz 4 GHz 5 GHz 6 GHz
Emerging Systems
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Ad hoc wireless networks
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Sensor networks
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Distributed control networks
Ad-Hoc Networks
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Peer-to-peer communications.
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No backbone infrastructure (no base stations).
I.e. “Truly wireless”!
Routing can be multihop.
Topology is dynamic in time; networks self-organize.
No centralized cooordination.
Fully connected, even with different link SINRs (signal-tointerference plus noise ratios)
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Design Issues
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Ad-hoc networks provide a flexible network infrastructure
for many emerging applications.
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The capacity of such networks is however yet generally
unknown (hot research topic).
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Transmission, access, and routing strategies for ad-hoc
networks are generally also still ad-hoc...
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Cross-layer design critical and very challenging.
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Energy constraints impose interesting design tradeoffs for
communication and networking (nodes typically batterydriven).
Sensor Networks
Energy is the driving constraint
typically powered by nonrechargeable
batteries.
 Data (sensor measurements) flow to one centralized
location (sink node, data fusion center).
 Low per-node rates - but up to 100,000 nodes.
 Sensor data highly correlated in time and space.
 Nodes can cooperate in transmission, reception,
 Nodes
Energy-Constrained Nodes
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Each node can only send a finite number of bits.
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Short-range networks must consider transmit,
circuit, and processing energy - jointly.
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Transmit energy minimized by maximizing bit time
Circuit energy consumption increases with bit time
Introduces a delay versus energy tradeoff for each bit!
Most sophisticated transmission techniques not
necessarily most energy-efficient!
Sleep modes save energy - but complicate networking.
Changes everything about the network design:
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Bit allocation must be optimized across all protocols.
Delay vs. throughput vs. node/network lifetime tradeoffs.
Optimization of node cooperation.
Spectrum Regulation
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Spectrum is a limited natural resource used by many.
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The worldwide radio spectrum is controlled by ITU-R (International
Telecommunications Union)
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In Europe, by ETSI (European Telecommunications Standardization
Institute).
In the US, by FCC (Federal Communications Commission; commercial) and
OSM (Office of Spectral Management; defense).
In Norway, by Post- og teletilsynet (PT).
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Spectrum can be auctioned, paid fixed price for, or “given away” (unlicensed
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bands).
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Some spectrum typically set aside for universal use.
Regulation, although necessary, can also stunt innovation, cause economic
disasters, and delay system rollout... (cf. UMTS spectrum auctions in Europe)
Standards
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Interacting systems require standardization (compatibility,
interoperability)
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Typically: Companies want their own systems adopted as standard!
 Alternatively: try for “de-facto” standards
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Worldwide standards determined by ITU-T (International
Telecommunications Union)
In Europe, by ETSI (European Telecommunications Standardization
Institute)
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In the US by TIA (Telecommunications Industry Association)
 IEEE standards often adopted (also worldwide)
 Process fraught with inefficiencies and interest conflicts...
Standards for current systems are summarized in Appendix D in the
textbook.
Main Points
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The wireless vision for the future encompasses many exciting
systems and applications
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Technical challenges transcend across all layers of the system
design.
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Cross-layer design is emerging as a key theme in wireless.
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Existing and emerging systems provide excellent quality for certain
applications, but poor interoperability.
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Standards and spectral allocation heavily impact the evolution of
wireless technology.
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This course will however focus on basic technology issues related to
and relevant for current and upcoming wireless systems.