cognitive radios for open access to spectrum
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Cognitive Radios for Open Access to Spectrum
Narayan MandayamChristopher Rose
Predrag SpasojevicRoy Yates
(in partnership with Lucent Technologies)
Rutgers University www.winlab.rutgers.edu
Email: narayan@winlab.rutgers.edu
Project MotivationTriumph of Technology vs. Triumph of Economics
• What everyone agrees on:– Spectrum use is inefficient– FCC licensing has yielded false scarcity
• The Spectrum Debate:– Open Access (Commons)
• [Noam, Benkler, Shepard, Reed …]• Agile wideband radios will dynamically share a commons
– Spectrum Property Rights• [Coase, Hazlett, Faulhaber+Farber] • Owners can buy/sell/trade spectrum• Flexible use, flexible technology, flexible divisibility,
transferability• A spectrum market will (by the force of economics) yield
an efficient solution
The Open Access Conundrum• Systems of end-user devices• Technology Panacea
– Spread spectrum, UWB, MIMO– Short range communications– Ad hoc multi-hop mesh networks
• Evidence: success of 802.11 vs. 3G• Minor technical rules for transceivers
– power, spreading
• Technical arguments against Open Access– Partially developed theory
• ad hoc network capacity, with/without mobility• IT relay and interference channel
– Infant technology• UWB, antenna arrays• Transmitter agility
– Technology not separable from user assumptions• Capabilities of technology vary with cooperation
Technology for Enabling Open Access?
Research themes that have emerged from adhoc/sensor networks research:
• Hierarchical Architecture wins– Capacity scaling, energy efficiency, increases
lifetimes, facilitates discovery• Cooperation wins
– Fundamental performance limits via information theoretic relay and broadcast channels
• “Global” awareness and coordination wins– Space, time and frequency awareness and
coordination beyond local measurements
Technology for Enabling Open Access?
Require radios that can :– Discover– Cooperate– Collaborate– Self-Organize into hierarchical networks
• Agility is necessary at every layer of the “protocol stack”
• But cannot yet predict environmentsThe Answer? “Cognitive Radios”
Cognitive Radios for Enabling Open AccessPOOF! Let there be cognitive radios!
(let Bryan worry about details)Then What???
• Discovery strategies for available spectrum– Algorithms and protocols for frequency selection, coordination and
cooperation• Coding strategies for efficient sharing
– Cooperative diversity and coding for increased spectrum utilization• Information strategies for efficient cooperation
– “Spectrum Servers” to advise/mediate sharing• Negotiation strategies for situations of conflict
– Pricing and game theoretic strategies to promote cooperation• Domination strategies for situations of conflict
– Spectrum warfare with agile waveforms
Internet-based Spectrum Policy ServerInternet-based Spectrum Policy Server can help to coordinate wireless networks - needs connection to Internet even under congested conditions (...low bit-rate OK)- some level of position determination needed (..coarse location OK)- spectrum coordination achieved via etiquette protocol centralized at server
Internet
Access Point(AP2)
AP1WLANoperator A
WLANoperator B
Ad-hocBluetoothPiconet
Wide-areaCellular data
service
SpectrumPolicy Server
www.spectrum.net
AP1: type, loc, freq, pwrAP2: type, loc, freq, pwrBT MN: type, loc, freq, pwr
MasterNode
EtiquetteProtocol
Spectrum Policy Server (SPS)
SPS Methodology• New users get an SPS
address– Analogous to DHCP
• Users send activity traces to SPS server
• SPS maintains database of activity traces
SPS
SPS Issues• What to measure?• Coarseness of
measurements?• Trace update frequency?• SPS database organization
to facilitate fast searching?
SPS Actions• Share wireless node
descriptors?• Coordinate comm. between
nodes?• Mediate spectrum sharing
among nodes?
• Forwarding reduces interference, saves battery life, increases coverage area
• There are two kinds of costs associated with packet forwarding:
– Power Consumption (REAL COST)
– Delay in Own Data (OPPORTUNITY COST)
• Why (and how) will autonomous nodes forward ?
Incentives for Forwarding?
Fostering Cooperation Through “Bribery”
A Microeconomic Framework for Enabling Forwarding: Pricing & Reimbursement
• Nodes control their:– Transmit powers– Forwarding Preferences– Destination
Preferencesto maximize bits/Joule
• The network controls:– Pricing Coefficient– Reimbursement
Coefficient: to maximize its
revenue
NETWORK ( ACCESS POINT )
Runs an optimization algorithm to determine the
Price for channel use
Reimbursement for forwarding
to maximize the revenue
Flow of parameters between adjacent nodes
THE USERS PLAY A NON-COOPERATIVE GAME TO MAXIMIZE THEIR UTILITIES
USER USER USER text
text
text
The network declares thepricing parameters
The network inspects therevenue as an output of
declared pricingparameters
Horizontal Trajectory
Radio tower
5 m 10 m
-5 m
-
USER 2(POTENTIAL
FORWARDER)
USER 1(NON-FORWARDER)
ACCESS POINT
5 m POSITIONS OFUSER 1 IN
HORIZONTALGEOMETRY
• Incentives for forwarding works when nodes tend to “cluster” • The aggregate bits/Joule in network is higher
• Network revenue is also higher
0 1 2 3 4 5 6 710
14
1015
1016
1017
1018
1019
Aggregate bits/JouleAggregate bits/Joule, no reimbursement.
Two User-One Access Point Example
user 2 distance
What You Learned in KindergartenThe World Is A Rough Place
• Everybody wants what they want– Greed is the norm
• The Golden Rule– Be Polite– Play Nice
• The REAL Golden Rule– Be aware of your surroundings– Develop a good left hook– Bruises are bad– Forgiveness is divine (when you have a good left
hook)
A Toy Problem
2 Users with Unit Power2 Orthogonal ChanNels
Symmetric -10dB InterferenceHigh (30dB) SNR
Signal Space Game
1.0 1.0 5.7 2.2 5.0 5.0
2.2 5.7 2.0 2.0 2.2 5.7
5.0 5.0 5.7 2.2 1.0 1.0
Preliminary ResultsIf Better Performers Survive in
Marketplace…• Adaptive Policy
– tit for tat• Even Better
– tit for tat with random start– forgiveness is divine
• Use Genetic Algorithms– evolve against chosen policies– evolve against evolving policies
Evaluation of Cognitive Approaches
HardwareComplexity
Efficiency
ProtocolComplexity
Pricing collaboration
Spectrumserver
Agileradio
Coded cooperation
Cognitive protocols
• Capacity performance– Information rates, spectral
efficiency, BER, FER, outage • Cost performance
– Hardware complexity– Software complexity
• Emulation of large-scale networks of cognitive radios – ORBIT Testbed– Emergent behavior
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