Evolving Strategies for Contentious but Efficient Coexistence in Unlicensed Bands
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Transcript of Evolving Strategies for Contentious but Efficient Coexistence in Unlicensed Bands
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Evolving Strategies for Contentious but Efficient
Coexistence in Unlicensed Bands
N. Clemens C. Rose
WINLAB
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Our Problem: “survivor”
Scenario: transceivers in an unlicensed band
Transceiver Skills: ‘cognitive’ and agile
Question: can transceivers learn to get along?
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2 Orthogonal ChanNels
Equal Cross Gains (g = 0.3)
Equal Gaussian Noise Floor (N = 10-3)
System Model
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The Two-Player Game
Actions: quantized power allocation All power in channel 1 All power in channel 2 Spread equally in both channels
Radio Interaction: mutual interference Payoff: channel capacity Strategy: past outcomes govern next
action Goal: maximize average capacity
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Actions and Payoffs
1.5 1.57.2 26.9 6.9
2 7.22.9 2.92 7.2
6.9 6.97.2 21.5 1.5
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Player Strategy Structure History = two previous plays Next play = S(history)
9 action pairs per play 81 two-play histories (9X9) Strategy S(k), k=1,…,81
4 Possible values for S(.) Channel 1 Channel 2 Spread Random
Must find good S(.)
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Strategy Search
Number of Strategies: 481 Use Genetic Algorithms
Strategy string genome Compose population of strings Allow “fittest” strategies to “mate” Discard weaker strategies Repeat (until tired)
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Experiments
Start with random population Human-engineered evaluator set for comparison
Completely random strategies Squatters, hoppers, avoiders
Fitness measured against evaluator set Result:
Populations evolve effective strategies We distill essential features
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Winners’ Characteristics
Winners negotiate among themselves to achieve near-optimality
Winner (red) fares well against random strategies
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Examples of Useful Traits Segregation:
stay on your side of the fence
Self-Reliance: Push me? I push you back!
Callousness: exploit passivity
Forgiveness: to teach and to encourage cooperation
Randomize: (occasionally) to avoid repeated collision
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Schema: identifying common traits
Trait Characterization: Preference for a certain response Avoidance of a certain response
Compose a histogram of relative trait frequencies
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The Schema Skeleton
Fix the observed traits in a strategy genome Choose the remaining positions randomly The performance of this is good!
A handful of rules can define a “good” strategy!
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Conclusion
Competitive strategies for cognitive radios effective stable
Implementation fix a radio with a strategy or let radios evolve strategies in situ
Caveat need to try multi-player games
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Thank You!