Cognitive Radios for Open Access to Spectrum Narayan Mandayam Christopher Rose Predrag Spasojevic Roy Yates (in partnership with Lucent Technologies) Rutgers University

Project Motivation Triumph 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 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 environments The Answer? “Cognitive Radios”

Cognitive Radios for Enabling Open Access POOF! 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 Server Internet-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) AP1 WLAN operator A WLAN operator B Ad-hoc Bluetooth Piconet Wide-area Cellular data service Spectrum Policy Server AP1: type, loc, freq, pwr AP2: type, loc, freq, pwr BT MN: type, loc, freq, pwr Master Node Etiquette Protocol 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 Preferences to maximize bits/Joule The network controls: –Pricing Coefficient –Reimbursement Coefficient: to maximize its revenue

Horizontal Trajectory Radio tower 5 m10 m -5 m - USER 2 (POTENTIAL FORWARDER) USER 1(NON- FORWARDER) ACCESS POINT 5 m POSITIONS OF USER 1 IN HORIZONTAL GEOMETRY Incentives for forwarding works when nodes tend to “cluster” The aggregate bits/Joule in network is higher Network revenue is also higher Aggregate bits/Joule Aggregate bits/Joule, no reimbursement. Two User-One Access Point Example user 2 distance

What You Learned in Kindergarten The 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 Power 2 Orthogonal ChanNels Symmetric -10dB Interference High (30dB) SNR

Signal Space Game

Preliminary Results If 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 Hardware Complexity Efficiency Protocol Complexity Pricing collaboration Spectrum server Agile radio 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