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 accuracy64 pt FFT 128 pt FFT

256 pt FFT

97%

USRP/GNURadio Prototype

• Impact of noise and interference

Without interference

With 10 dBinterference

Trace Based Performance Evaluation

• Throughput gain

Back2F consistently outperforms 802.11 across all scenarios

Improve around 5%

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 contention resolution method.