No Time to Countdown: Migrating Backoff to the Frequency Domain

1. No Time to Countdown: Migrating Backoff to the Frequency Domain SouvikSen,Romit Roy Choudhury,SrihariNelakuditi - 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. Single Collision Domain win

7. Single Collision Domain

8. Single Collision Domain !?

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 128 pt FFT 64 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 Improve around 5% Back2F consistently outperforms 802.11 across all scenarios

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