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Partially Overlapping Channels Not Considered Harmful

Partially Overlapping Channels Not Considered Harmful . Trevor Reid ECE 256. Single Channel Spatial Reuse. b. a. c. d. What else can we do?. Utilize the frequency domain We have all of this space…. Split the spectrum into Channels. Power. Frequency. But it’s not perfect.

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Partially Overlapping Channels Not Considered Harmful

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  1. Partially Overlapping Channels Not Considered Harmful Trevor Reid ECE 256

  2. Single Channel Spatial Reuse • b • a • c • d

  3. What else can we do? • Utilize the frequency domain • We have all of this space…

  4. Split the spectrum into Channels Power Frequency

  5. But it’s not perfect • Can’t get full channel capacity without an ideal band-pass filter • Instead the channels look more like… Power Frequency

  6. Aside: Band-pass Filters • Only accepts frequencies within a certain range. Everything else is rejected.

  7. Partially Overlapping Channels Frequency

  8. 802.11(b) Specifications • Operates at 2.4 GHz • Split into 11 Channels • 22 Mhz Wide • 5 Mhz Separation

  9. Looks Like This… (kind of)

  10. Why use them? • Reduce Contention • 11 partially overlapping channels reduce contention by a factor of 3.05 compared to using 3 overlapping channels.

  11. How to Model Interference • I factor: I(i,j) = Amount of overlap between i and j

  12. Which looks like this

  13. Transmission Range

  14. BER

  15. Take Away • Partially overlapping channels can reduce contention • We can model interference between two channels with an I factor • Interference falls off rapidly with channel separation • Bit Error Rate falls of rapidly with channel separation

  16. How Can We Utilize this? Eric Jimmy Not Going To Help. AP Stephanie Jason

  17. But with many APs Valentin Prof Choudhury AP2 Jason Jimmy Eric AP1 AP3 Trevor Stephanie

  18. Channel Assignment Algorithm • OBJ(T,θ) = Total interference experienced for each client. • Steps: • Evaluate OBJ(T,θ) • For each AP • Assign to channel that minimizes interference • Evaluate OBJ(T,θ) again • Stop if nothing changed, otherwise repeat.

  19. Modify For Multiple Channels • Instead of calculating interference on only the same channel find channels that interfere (using I-factor). • Add up interference at client from all interfering channels. • It just works.

  20. So does it work? Yes. By a factor of ~ 2.57

  21. Wireless Mesh Networks • Use similar approach to modify existing channel assignments algorithms. • Using partially overlapped channels shows significant improvements.

  22. So What’s the Catch? Noisy people below you Who Coordinates Channel Assignment? Starbucks linksys Free Wifi Cute Girl Upstairs linksys Me Neighbor

  23. Does this actually perform well? • We don’t know • Never actually implemented • Don’t know how effective the I-Factor model is in real world conditions.

  24. Resources • http://www.ntia.doc.gov/osmhome/allochrt.pdf • http://en.wikipedia.org/wiki/File:2.4_GHz_Wi-Fi_channels_%28802.11b,g_WLAN%29.svg • http://en.wikipedia.org/wiki/File:Bandwidth_2.svg

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