1

Spontaneous Cooperation in Future Wireless Networks ?

Márk Félegyházi

Laboratory for Computer Communications and Applications (LCA)

EPFL, Switzerland

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Future Wireless Networks

• Emerging networks– Cellular networks in a shared spectrum– Hybrid ad hoc networks (also called “Multi-hop

cellular networks”)– Small operators, community networks – Mesh networks– Cognitive radio communication– “Autonomous” ad hoc networks– Vehicular networks– Sensor and RFID networks

• Emerging properties– Centralized → Distributed– More sophisticated user devices– Self(ish)-organization

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Spontaneous Cooperation in Emerging Networks?

Power contro

l

Small op., comm. NWs

Cellular networks in a shared spectrum

Mesh networks

Hybrid ad hoc networks

Autonomous ad hoc NWs

Channel allo

catio

n

(spectr

um alloca

tion)

Channel acc

ess

Packet fo

rward

ing

…

Vehicular networks

Sensor networks

Cognitive radio communication

? ?

? ? ? ?

? ? ?

? ? ?

? ? ?

? ? ? ? ?

? ?

? ?

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Game Theory: an Appropriate Tool

Study rational behavior in wireless networks

Design enforcement mechanisms (if necessary)

↓

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Problems We Studied

Power contro

l

Small op., comm. NWs

Cellular networks in a shared spectrum

Mesh networks

Hybrid ad hoc networks

Autonomous ad hoc NWs

Channel allo

catio

n

(spectr

um alloca

tion)

Channel acc

ess

Packet fo

rward

ing

…

Vehicular networks

Sensor networks

Cognitive radio communication

? ?

? ? ? ?

? ? ?

? ? ?

? ? ?

? ? ? ? ?

? ?

? ?

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Packet forwarding in ad hoc networks

Dependency: the benefit of each source is dependent on the behavior of its forwarders

dependency loop

Corollary 2: If Theorem 3 holds for every node, it is a Nash-equilibrium.

Theorem 3 (simplified): Assuming that node i is a forwarder, its behavior will be cooperative only if it has a dependency loop with each of its sources

A B

C

Example in which Corollary 2 holds:

BUT

Simulation results → in general, Corollary 2 does not hold

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Cellular Networks in a Shared Spectrum

0

maxi

i iu

Pj ju

j

P g

N P g

• Game G = (Players, Strategy, Utility function)

• Players: operators

• Strategy: radio range of base stations

• Utility: useful coverage of their pilot signal:

coverage interferencei i i iU

2

1iu

iu

gd

where the channel gain:

• freely roaming users

• power control of the pilot signal

• users attach to the base station with the best pilot signal:

Static game – Pareto-optimal Nash equilibria

Small :

Large : A B MAX

A B MIN

r r R

r r R

Repeated game – A Nash equilibrium based on RMIN isenforceable using punishments

: maximum power range (regulator)

: minimum power range (for coverage)MAX

MIN

R

R

: sensitivity to interferencei

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References• Tutorials on game theory:

– A. Mackenzie, L. Da Silva, and W. Tranter (Editor), Game Theory for Wireless Engineers, Morgan & Claypool Publishers, 2006

– M. Félegyházi and J.-P. Hubaux, Game Theory for Wireless Networks: A Tutorial, LCA-REPORT-2006-002, April 2006

• Packet forwarding in ad hoc networks:– V. Srinivasan, P. Nuggehalli, C. Chiasserini, and R. Rao, Cooperation in

Wireless Networks, IEEE Transactions on Wireless Communications 2005

– M. Félegyházi, J. P. Hubaux, and L. Buttyán, Nash Equilibria of Packet Forwarding Strategies in Wireless Ad Hoc Networks, IEEE Transactions on Mobile Computing 2006

• Cellular networks in a shared spectrum:– M. Félegyházi and J. P. Hubaux, Wireless Operators in a Shared

Spectrum, Infocom 2006

• Textbook in preparation:– L. Buttyán and J. P. Hubaux, Security and Cooperation in Wireless

Networks, Cambridge University Press, 2007

• …

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Graduate Textbook

L. Buttyán and J. P. Hubaux

“Security and Cooperation in Wireless Networks”

Cambridge University Press, 2007

V1.0 full text available at: http://secowinet.epfl.ch (430 pages)

– Part I: Existing and upcoming wireless networks– Part II: Thwarting malicious behavior– Part III: Thwarting selfish behavior– Appendix A: Introduction to security and cryptographic functions– Appendix B: Tutorial on game theory for wireless networks

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Conclusion

• Cooperation is usually assumed → selfishness can degrade network performance

• Selfish or malicious ? → different mechanisms• In general, incentives for cooperation are needed

• Links of our group:– Speaker: http://people.epfl.ch/mark.felegyhazi

– Textbook: http://secowinet.epfl.ch

– Articles: http://winet-coop.epfl.ch