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Bridging Theory and Practice in Wireless Networks

Bridging Theory and Practice in Wireless Networks. Speaker order : Nitin Vaidya Augustin Chaintreau Theodoros Salonidis Peter Key. (Multi-Hop) Wireless Networks: Theory and Practice. Nitin Vaidya Illinois Center for Wireless Systems University of Illinois at Urbana-Champaign.

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Bridging Theory and Practice in Wireless Networks

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  1. Bridging Theory and Practice inWireless Networks Speaker order: Nitin Vaidya Augustin Chaintreau Theodoros Salonidis Peter Key

  2. (Multi-Hop) Wireless Networks:Theory and Practice Nitin Vaidya Illinois Center for Wireless Systems University of Illinois at Urbana-Champaign

  3. Few obvious observations

  4. outgrow 1 Those who cannot learn from historyare doomed to repeat it With apologies to George Santayana

  5. Pre-History of Wireless Communications:Smoke Signals, Fires, Semaphore Relaying : Multi-hop routes (store-and-forward)

  6. Pre-History of Wireless Communications:Homing Pigeons Exploiting mobility

  7. Reusing Ideas Reasonable,but Need to Explore Better Alternatives No wired-equivalent for wireless networks No links !

  8. Physics Does Not Know Layers 2 • Layering is a convenient abstraction,not a theorem • Backpressure scheduler ( “ throughput optimal ” ) spans traditional layers 1 through 3 [Tassiulas]

  9. What You Can't Know Can Hurt You 3 • Channel state observations differentat different nodes • A stumbling block

  10. C C f(PC) MIMO C PD D D C1 B1 PC B B B B2 C0 PB C2 B0 A A P A The Vanishing Link 4 • Diversity muddles thenotion of a link Cooperation Spatial Channel

  11. Cross-Layer Protocols Applications Transport Network Better interfaces & protocols to exploit available diversity Link Most to lose Phy

  12. Layers All The Way Down Where does Phy/Link layer end ? What should or shouldn’t it do ? Picture from Wikipedia

  13. State of Wireless • Beautiful theory • Asymptotic capacity, Capacity “within a bit” • Utility optimization • Throughput optimality • Cooperative relaying , Network coding • MIMO

  14. State of Wireless • Practical protocols & deployments • Emerging wireless standards • Many MAC & routing protocols • Many (experimental) deployments • Start-ups

  15. State of Wireless Despite the large volume of activity • Theory not translated to practice adequately • Theory often ignores realities of wireless networks Greater success in cellular environments

  16. The Way Forward • Clearly, more attention to phy / theory desirable • “Cross-Layer” protocols… smarter everything (antennas, radios, protocols, …)

  17. The Way Forward • Clearly, more attention to phy / theory desirable • “Cross-Layer” protocols… smarter everything (antennas, radios, protocols, …) Why do protocols lag so far behind ?

  18. What Do We Lack ? • Funding ? • Manpower ? • Theory ? Probably none of the above

  19. What Do We Lack ?

  20. What Do We Really Lack ? Meaningful contact between • Practice • Networking Theory Comm Picture from Wikipedia

  21. Four-Point Agenda

  22. The Way Forward • Clearly, more attention to phy / theory desirable • “Cross-Layer” protocols… smarter everything (antennas, radios, protocols, people)

  23. 1. Educate BetterOurselves & Next Generation Reduce the unknownunknowns • Increase phy content in CS/CE networking courses • Awareness of phy necessary to ask better questions • Educate phy students about higher layer issues - More realism in theoretical models - Identify implications for practice

  24. 2. Fewer Research Programs • Resist narrowly targeted research programs • Avoid creating false demand for research funding • Examples ? • Sensor networks • Clean slate design • Encourage projects spanning different communities (phy-networks)

  25. 3. Fewer “Better” Conferences • Increase venues that encourage diversecommunity interactions(phy-networking , theory-applied) • More Workshops, fewer “selective” conferences • Co-located conferences

  26. 4. Greater Industry/User Feedback • What are the industry-perceived long-term challenges ? • Theoretical formulations constrained by reality

  27. Mapping BetweenTheory & PracticeCan Make Both More Worthwhile

  28. Mapping BetweenTheory & PracticeCan Make Both More Worthwhile Proof by Example

  29. Multiple Channels 26 MHz 100 MHz 200 MHz 150 MHz 915 MHz 2.45 GHz 5.25 GHz 5.8 GHz IEEE 802.11 in ISM Band

  30. Multi-Channel Environments Available spectrum Spectrum divided into channels 1 2 3 4 … c

  31. Common Assumption in Past Work • A network uses c channels • All hosts tune to all c channels at all times • Examples: * Gupta-Kumar capacity * Microsoft multi-channel mesh

  32. Capacity [Gupta-Kumar] Capacity scales linearly with channels if number of interfaces also scaled 1 1 c c capacity a

  33. 1 m Practical Scenario • A host can only be on a subset of channels • Channel switching introduces overhead c

  34. Multi-Channel Network Capacity Gupta-Kumar square-root Capacity linear Channels With fixed hardware resources

  35. capacity User Applications Multi-channel protocol channels Capacity bounds Insights on protocol design Fixed D IP Stack OS improvements Software architecture Net-X testbed F B ARP E Switchable A Channel Abstraction Module C Interface Device Driver Interface Device Driver Net-XTheory to Practice

  36. Closing the Loop

  37. capacity User Applications Multi-channel protocol channels Capacity bounds Insights on protocol design Fixed D IP Stack OS improvements Software architecture Net-X testbed F B ARP E Switchable A Channel Abstraction Module C Interface Device Driver Interface Device Driver Net-XTheory to Practice

  38. Constrained Switchability • An interface may be constrained to use only asubset of channels • Motivation: • Hardware limitations (“untuned radio” [petrovic] ) • Hardware heterogeneity (802.11b/g versus 802.11a/b/g) • Policy issues (cognitive radios)

  39. Constrained Channel Assignment Example – Random (c, f) Assignment Capacity-achieving construction requires joint routing & scheduling f = 2 c = 8

  40. More information on my research page

  41. Wrap-Up • Practice • Networking Theory Comm Picture from Wikipedia Need researchers who understand little bit of all aspects of wireless systems

  42. Thanks! www.crhc.illinois.edu / wireless

  43. Thanks! www.crhc.illinois.edu / wireless

  44. Thanks! www.crhc.illinois.edu / wireless

  45. Thanks! www.crhc.illinois.edu / wireless

  46. Insights from Analysis (1) Channel Usage • Need to balance load on channels • Local channel assignment schemes helpful in some large scale scenarios  Local mechanisms with some hints from nearby nodes

  47. Insights from Analysis (2) • Static channel allocation not optimal performance in general • Must dynamically switch channels Channel 1 B A C 2 D

  48. Insights from Analysis (3) • Small number of switchable interfaces suffice in theory • How to use a larger number of interfaces ? • Simplify protocol design • Improve peak flow throughput

  49. Channel Management • Hybrid channel assignment: Static + Dynamic A B C Fixed (ch 1) Fixed (ch 2) Fixed (ch 3) Switchable Switchable Switchable 2 1 3 2

  50. Insights from Analysis (4) • Interface bottleneck can constrain performance Interfaces as a resource in addition to spectrum, time and space

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