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

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

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

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

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

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

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

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

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

11. Factors selection test Tx 15 sec silence

12. Factors affecting throughput :RSSI

13. Effect of our transmission rate on others RSSI 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 We select the least interference channel dynamically Channel interference metric Channel interference metric where C i is the interference metric of channel i, N ip, N iq are the number of other packets captured at node p and q on channel i in a 120s window. where C i is the interference metric of channel i, N ip, N iq are the number of other packets captured at node p and q on channel i in a 120s window. Selected channel j, s.t. Selected channel j, s.t.

17. Experiment: Process Send a 3MB file using each scheme Send a 3MB file using each scheme 15s pause interval in between each transfer 15s pause interval in between each transfer Repeat Repeat SRD 15 sec silence 120 sec query window

18. Background Traffic

19. Results: Dynamic v. Static

20. Results: Dynamic v. Random

21. Results: Random v. Static

22. Channels picked

23. Results: Summary SchemeDynamicStaticRandom Avg Rate 4042 kbps 2100 kbps 2742 kbps Average Transfer Time (3MB) 6.08s11.7s8.96s

24. Effect of channel switching time t d = Tx time on dynamic channel t s = Tx time on static channel t c = Time to change r d = Rate on dynamic channel r s = Rate on static channel f = Size of file Our implementation

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

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