1. © 2007 Levente Buttyán and Jean-Pierre Hubaux Security and Cooperation in Wireless Networks http://secowinet.epfl.ch/ Chapter 11: Wireless operators in shared spectrum multi-domain sensor networks; border games in cellular networks;

2. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 2/33 Chapter outline 11.1 Multi-domain sensor networks 11.2 Border games in cellular networks

3. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 3/33  Typical cooperation: help in packet forwarding  Can cooperation emerge spontaneously in multi-domain sensor networks based solely on the self-interest of the sensor operators? Multi-domain sensor networks 11.1 Multi-domain sensor networks

4. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 4/33 Simplified model  C: Cooperation D: Defection  4 possible moves:  CC – the sensor asks for help (cost 1) and helps if asked (cost 1)  CD – the sensor asks for help (cost 1) and does not help (cost 0)  DC – the sensor sends directly (cost 2  ) and helps if asked (cost 1)  DD – the sensor sends directly (cost 2  ) and does not help (cost 0) 2α2α 11 1 11 11.1 Multi-domain sensor networks 11.1.1 Simplified model

5. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 5/33 Example : CC – CD (1/6) CC – the sensor tries to get help from the other sensor and helps if the other sensor requests it CD – the sensor tries to get help but it refuses to help CCCD 11.1 Multi-domain sensor networks 11.1.1 Simplified model

6. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 6/33 Example : CC – CD (2/6) CC – the sensor tries to get help from the other sensor and helps if the other sensor requests it CD – the sensor tries to get help but it refuses to help CCD 11.1 Multi-domain sensor networks 11.1.1 Simplified model

7. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 7/33 Example : CC – CD (3/6) C failure CDCD CC – the sensor tries to get help from the other sensor and helps if the other sensor requests it CD – the sensor tries to get help but it refuses to help 11.1 Multi-domain sensor networks 11.1.1 Simplified model

8. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 8/33 Example : CC – CD (4/6) CCCDCD CC – the sensor tries to get help from the other sensor and helps if the other sensor requests it CD – the sensor tries to get help but it refuses to help 11.1 Multi-domain sensor networks 11.1.1 Simplified model

9. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 9/33 Example : CC – CD (5/6) CCD success 11.1 Multi-domain sensor networks 11.1.1 Simplified model

10. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 10/33 Example : CC – CD (6/6) CCCD Black player Cost: 2 1 for asking 1 for helping Benefit: 0 (packet dropped) Gray player Cost: 1 1 for asking Benefit: 1 (packet arrived) 11.1 Multi-domain sensor networks 11.1.1 Simplified model

11. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 11/33 2α2α 11 Cost for black Cost for grey Outcome for black (0 = failure) Outcome for grey (1 = success) The simplified model in strategic form 11.1 Multi-domain sensor networks 11.1.1 Simplified model

12. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 12/33 Reception threshold time success / failure of packet reception Sliding window of history Success (= 1) Failure (= 0) Reception threshold ρ Average of the packet reception Risk of going below threshold  adapt strategy (move to the constrained state: only DC or DD are eligible)  Reception threshold: computed and stored at each sensor node  The battery (B) level of the sensors decreases with the moves  If the battery is empty, the sensor dies 11.1 Multi-domain sensor networks 11.1.1 Simplified model

13. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 13/33 Game Theoretic Approach  The mentioned concepts describe a game  Players: network operators  Moves (unconstrained state): CC, CD, DC, DD  Moves (constrained state): DC, DD  Information sets: histories  Strategy: function that assigns a move to every possible history considering the weight threshold  Payoff = lifetime  We are searching for Nash equilibria with the highest lifetimes 11.1 Multi-domain sensor networks 11.1.1 Simplified model

14. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 14/33 Two-step Strategies B – initial battery ρ – reception threshold  – path loss exponent (  2) ε 1,2 – payoff of transient states Cooperative Nash equilibrium Non-cooperative Nash equilibrium If ρ > 1/3, then (CC/DD, CC/DD) is more desirable 11.1 Multi-domain sensor networks 11.1.1 Simplified model

15. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 15/33 Generalized Model 11.1 Multi-domain sensor networks 11.1.2 Generalized model Simplified model with the following extensions: –many sensors, random placing –minimum energy path routing –common sink / separate sink scenarios –classification of equilibria Class 0: no cooperation (no packet is relayed) Class 1: semi cooperation (some packets are relayed) Class 2: full cooperation (all packets are relayed)

16. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 16/33 Main simulation parameters ParameterValue Number of sensors per domain20 Area size100 x 100 m Reception threshold ρ 0.6 History length5 Path loss exponent2–3–4 (3) 11.1 Multi-domain sensor networks 11.1.2 Generalized model

17. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 17/33 Impact of the path loss exponent Percentage of simulationsEquilibrium classes ( 0 – no cooperation, 1 – semi cooperation, 2 – full cooperation) Value of the path loss exponent – 2 – 3 – 4 11.1 Multi-domain sensor networks 11.1.2 Generalized model

18. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 18/33 Conclusion on multi-domain sensor networks  We examined whether cooperation is possible without the usage of incentives in multi-domain sensor networks  In the simplified model, the best Nash equilibria consist of cooperative strategies  In the generalized model, the best Nash equilibria belong to the cooperative classes in most of the cases 11.1 Multi-domain sensor networks

19. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 19/33 Chapter outline 11.1 Multi-domain sensor networks 11.2 Border games in cellular networks

20. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 20/33 Motivating example 11.2 Border games in cellular networks

21. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 21/33 Introduction  spectrum licenses do not regulate access over national borders  adjust pilot power to attract more users Is there an incentive for operators to apply competitive pilot power control? 11.2 Border games in cellular networks

22. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 22/33 System model (1/2) Network:  cellular networks using CDMA –channels defined by orthogonal codes  two operators: A and B  one base station each  pilot signal power control Users:  roaming users  users uniformly distributed  select the best quality BS  selection based signal-to- interference-plus-noise ratio (SINR) 11.2 Border games in cellular networks 11.2.1 Model

23. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 23/33 System model (2/2) A B v PAPA PBPB T Av T Bw T Aw pilot signal SINR: traffic signal SINR: P i – pilot power of i – processing gain for the pilot signal – noise energy per symbol – channel gain between BS i and user v – available bandwidth – own-cell interference affecting the pilot signal – own-cell interference factor – traffic power between BS i and user v – other-to-own-cell interference factor – set of users attached to BS i 11.2 Border games in cellular networks 11.2.1 Model

24. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 24/33 Game-theoretic model  Power Control Game, G PC –players → networks operators (BSs), A and B –strategy → pilot signal power, 0W < P i < 10W, i = {A, B} –standard power, P S = 2W –payoff → profit, where is the expected income serving user v –normalized payoff difference: 11.2 Border games in cellular networks 11.2.2 Power control game

25. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 25/33 Simulation settings 11.2 Border games in cellular networks 11.2.2 Power control game

26. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 26/33 Is there a game?  only A is strategic (B uses P B = P S )  10 data users  path loss exponent, α = 2 ΔiΔi 11.2 Border games in cellular networks 11.2.2 Power control game

27. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 27/33 When both operators are strategic  10 data users  path loss exponent, α = 4 11.2 Border games in cellular networks 11.2.2 Power control game

28. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 28/33 Nash equilibria 10 data users100 data users 11.2 Border games in cellular networks 11.2.2 Power control game

29. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 29/33 Efficiency (1/2)  10 data users 11.2 Border games in cellular networks 11.2.2 Power control game

30. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 30/33 Efficiency (2/2)  100 data users 11.2 Border games in cellular networks 11.2.2 Power control game

31. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 31/33  convergence based on better-response dynamics  convergence step: 2 W Convergence to NE (1/2) P A = 6.5 W 11.2 Border games in cellular networks 11.2.3 Convergence to a Nash Equilibrium

32. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 32/33 Convergence to NE (2/2)  convergence step: 0.1 W 11.2 Border games in cellular networks 11.2.3 Convergence to a Nash Equilibrium

33. Security and Cooperation in Wireless Networks Chapter 11: Wireless operators in shared spectrum 33/33 Conclusion on border games  not only individual nodes may exhibit selfish behavior, but operators can be selfish too  example: adjusting pilot power to attract more users at national borders  the problem can be modeled as a game between the operators –the game has an efficient Nash equilibrium –there’s a simple convergence algorithm that drives the system into the Nash equilibrium 11.2 Border games in cellular networks