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Bridging the Gap: A Deterministic Model for Wireless Links David Tse Wireless Foundations U.C. Berkeley NSF Wireless Networks Workshop Aug 27, 2007 TexPoint fonts used in EMF: AAA A AA A A A A A A A
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Key Features of Wireless Channels broadcast interference high dynamic range in channel strengths between different nodes Basic PHY layer model- additive Gaussian channel:
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Gaussian Model: Basis for PHY-Layer Advances Many PHY-layer advances in past decade based on the Gaussian model. Examples: MIMO, interference cancellation, superposition coding Advances in the context of point-to-point, many- to-one, and one-to-many settings. Hard to use to reason about more complex wireless network configurations. Capacity of simple networks with single-relay or two interfering point-to-point links are open problems for eons.
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Common Channel Models for Wireless Networks 0/1 connectivity models packet collision models SINR based model: treating interference as noise These models do not capture key properties of wireless medium constrains the design of innovative communication schemes
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Bridging the Gap More research needed in model building. As an example we discuss a deterministic channel model which : captures several key aspects of the wireless medium is scalable to complex wireless networks
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Point-to-Point Link Rx observes most-significant bits of the transmitted signal. is proportional to the SNR on the dB scale.
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Broadcast user 2 user 1 Users with higher SNR see more bits of the transmitted signal. Implemented by superposition coding at the PHY layer.
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Multiple Access user 2 user 1 mod addition More significant bits of strong user observed cleanly. Collision with weak user at the less significant bits. Implemented by interference cancellation at the PHY layer.
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Application to Relay Networks What is the capacity of this network from a single source S to a single destination D?
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Max-Flow Min-Cut Theorem Theorem: where Generalization of Ford-Fulkerson Theorem for wireline networks.
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Conclusion PHY layer higher layers simple wireless channel model
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