No Time to Countdown: Migrating Backoff to the Frequency Domain
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Transcript of No Time to Countdown: Migrating Backoff to the Frequency Domain
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.