1. No Time to Countdown: Migrating Backoff to the Frequency Domain Souvik Sen, Romit Roy Choudhury, Srihari Nelakuditi - Twohsien 2012.3.5

2. What’s the problem? http://revolutionwifi.blogspot.com/2010/07/wireless-qos-part-1-background_7048.html

3. Main Idea Time Domain Backoff Frequency Domain Backoff

4. Outline Architecture and Design – Single collision domain – Multiple collision domains – Coping with misdetection due to fading – Batched transmissions – Discussion Implementation and Evaluation – USRP/GNURadio prototype – Trace based performance evaluation Conclusion

5. Single Collision Domain

6. win

7. Single Collision Domain

8. !?

9. Multiple Collision Domains

10. Coping with Misdetection due to Fading

11. Batched Transmissions Batched size = 3

12. Discussion Self-signal is strong

13. Discussion Not tightly time synchronized – Back2F : 16.4μs – 802.11: 9~135μs High density

14. Outline Architecture and Design – Single collision domain – Multiple collision domains – Coping with misdetection due to fading – Batched transmissions – Discussion Implementation and Evaluation – USRP/GNURadio prototype – Trace based performance evaluation Conclusion

15. USRP/GNURadio Prototype Detection accuracy 64 pt FFT 128 pt FFT 256 pt FFT 97%

16. USRP/GNURadio Prototype Impact of noise and interference Without interference With 10 dB interference

17. Trace Based Performance Evaluation Throughput gain Back2F consistently outperforms 802.11 across all scenarios Improve around 5%

18. Trace Based Performance Evaluation Traffic type Skype Small packet size (Backoff overhead are fixed)

19. Trace Based Performance Evaluation Fairness Jain’s fairness index

20. Trace Based Performance Evaluation Impact of channel fading

21. Trace Based Performance Evaluation Dense network

22. Outline Architecture and Design – Single collision domain – Multiple collision domains – Coping with misdetection due to fading – Batched transmissions – Discussion Implementation and Evaluation – USRP/GNURadio prototype – Trace based performance evaluation Conclusion

23. Migrate protocol operations from the time to the frequency domain. Nearly instantaneous contention resolution method.