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Dynamic channel allocation in wireless ad-hoc networks

Dynamic channel allocation in wireless ad-hoc networks. Anup Tapadia Liang Chen Shaan Mahbubani. Background. 802.11 networks have experienced a tremendous growth in last few years Access points work on a single static channel Contention & congestion

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Dynamic channel allocation in wireless ad-hoc networks

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  1. Dynamic channel allocation in wireless ad-hoc networks Anup Tapadia Liang Chen Shaan Mahbubani

  2. Background • 802.11 networks have experienced a tremendous growth in last few years • Access points work on a single static channel • Contention & congestion • Low throughput due to inefficient channel allocation • Presence of other interfering networks impacts performance

  3. Channel variations Traffic on Thursday 26th April at Calit2 6th floor

  4. CogNet testbed setup at Calit2 CogNet is supported by NSF SGER-CogNet

  5. CalNode • Seokris 4521 • Linux 2.6 • Iperf • Monitor Card • Atheros w/ Mad Wifi • Data Card • Prism 2.5 802.11b • Wired to UCSD network

  6. What may affect the channel performance? • Interfering 802.11 Traffic • Packet count • 802.11 Rate • RSSI • Other interference • Bluetooth • Cordless phones • Microwaves Our Focus

  7. Challenge • How do we select the channel that permits maximum throughput in an ad-hoc network ?

  8. AP Towards Nodes Connection Stub iwlib WiFi NIC WiFi NIC Channel Controller (Java & C++) SQL Query Decision Logic CogNet DB Channel Switcher Iperf Test Scheduler

  9. AP AP AP AP Connection Stub Connection Stub Connection Stub Connection Stub iwlib iwlib iwlib iwlib WiFi NIC WiFi NIC WiFi NIC WiFi NIC WiFi NIC WiFi NIC WiFi NIC WiFi NIC Software Architecture Channel Controller Decision Logic Channel Switcher

  10. Channel Switch Channel Controller Decision Logic Channel Switcher Channel Switch Message Channel Switch Message Connection Stub Connection Stub iwlib iwlib 802.11 Driver 802.11 Driver Switch Channel Switch Channel Probe 802.11 H/W 802.11 H/W Reply

  11. Factors selection test Tx Tx Tx 15 sec silence 15 sec silence

  12. Factors affecting throughput :RSSI

  13. Effect of our transmission rate on others RSSI

  14. Factors affecting throughput : Rate

  15. Factors affecting throughput :Packets

  16. Channel Selection Algorithm • We select the least interference channel dynamically • Channel interference metric where Ci is the interference metric of channel i, Nip, Niq are the number of other packets captured at node p and q on channel i in a 120s window. • Selected channel j, s.t.

  17. 120 sec query window S R D 15 sec silence 15 sec silence Experiment: Process • Send a 3MB file using each scheme • 15s pause interval in betweeneach transfer • Repeat

  18. Background Traffic

  19. Results: Dynamic v. Static

  20. Results: Dynamic v. Random

  21. Results: Random v. Static

  22. Channels picked

  23. Results: Summary

  24. Effect of channel switching time Our implementation td = Tx time on dynamic channel ts = Tx time on static channel tc = Time to change rd = Rate on dynamic channel rs = Rate on static channel f = Size of file

  25. Future work • Multi hop links • More complex allocation schemes • Finer data granularity and patterns • Improve channel switching time • Effect of frequency of channel switching

  26. Conclusions • Dynamic performed better than Static and Random • Static on a free channel provides upper bound on Dynamic performance; improvements come when static channel is loaded (channel usage varies over time)

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