Cognitive Radios for Open Access to Spectrum Narayan

Cognitive Radios for Open Access to Spectrum Narayan Mandayam Christopher Rose Predrag Spasojevic Roy Yates (in partnership with Lucent Technologies) Rutgers University www. winlab. rutgers. edu Email: narayan@winlab. rutgers. edu

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 802. 11 vs. 3 G • 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

Spectrum Policy Server (SPS) 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 Spectrum Policy Server www. spectrum. net Internet WLAN operator A AP 1 Access Point (AP 2) Etiquette Protocol AP 1: type, loc, freq, pwr AP 2: type, loc, freq, pwr BT MN: type, loc, freq, pwr WLAN operator B Master Node Ad-hoc Bluetooth Piconet Wide-area Cellular data service

SPS Methodology • New users get an SPS address – Analogous to DHCP SPS • Users send activity traces to SPS server • SPS maintains database of activity traces 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?

Incentives for Forwarding? • 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 ? Fostering Cooperation Through “Bribery”

A Microeconomic Framework for Enabling Forwarding: Pricing & Reimbursement • Nodes control their: – – – to Transmit powers Forwarding Preferences Destination Preferences maximize bits/Joule • The network controls: – Pricing Coefficient – Reimbursement Coefficient: to maximize its revenue

Two User-One Access Point Example 10 19 Aggregate bits/Joule, no reimbursement. Horizontal Trajectory 10 18 ACCESS POINT 10 Radio tower POSITIONS OF USER 1 IN HORIZONTAL GEOMETRY 5 m 5 m 10 10 m 10 -5 m - USER 2 (POTENTIAL FORWARDER) USER 1(NONFORWARDER) 10 17 16 15 14 0 1 2 3 4 5 6 user 2 distance • Incentives forwarding works when nodes tend to “cluster” • The aggregate bits/Joule in network is higher • Network revenue is also higher 7

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 Chan. Nels Symmetric -10 d. B Interference High (30 d. B) SNR

Signal Space Game 1. 0 5. 7 2. 2 5. 0 2. 2 5. 7 2. 0 2. 2 5. 7 5. 0 5. 7 2. 2 1. 0

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 • Capacity performance – Information rates, spectral efficiency, BER, FER, outage Efficiency • Cost performance – Hardware complexity – Software complexity • Emulation of large-scale networks of cognitive radios – ORBIT Testbed – Emergent behavior Hardware Complexity Agile radio Spectrum server Protocol Complexity Pricing collaboration Cognitive protocols Coded cooperation