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

What’s the problem?

http://revolutionwifi.blogspot.com/2010/07/wireless-qos-part-1-background_7048.html

Main Idea Time Domain Backoff Frequency Domain Backoff

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

Single Collision Domain

Single Collision Domain win

Single Collision Domain

Single Collision Domain

!?

Multiple Collision Domains

Coping with Misdetection due to Fading

Batched Transmissions Batched size = 3

Discussion • Self-signal is strong

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

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

USRP/GNURadio Prototype • Detection accuracy

64 pt FFT 128 pt FFT 256 pt FFT 97%

USRP/GNURadio Prototype • Impact of noise and interference

Without interference With 10 dB interference

Trace Based Performance Evaluation • Throughput gain Improve around 5%

Back2F consistently outperforms 802.11 across all scenarios

Trace Based Performance Evaluation • Traffic type

Skype

Small packet size (Backoff overhead are fixed)

Trace Based Performance Evaluation • Fairness Jain’s fairness index

Trace Based Performance Evaluation • Impact of channel fading

Trace Based Performance Evaluation • Dense network

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

Conclusion • • Migrate protocol operations from the time to the frequency domain.

Nearly instantaneous method.

contention resolution