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DozyAP: Power-Efficient Wi-Fi Tethering

DozyAP: Power-Efficient Wi-Fi Tethering. Speaker Hao Han College of William & Mary 3/22/2013. W&M Graduate Research Symposium 2013. Outline. Motivation Design Evaluation Conclusion. What is Wi-Fi Tethering. Sharing a cellular data connection via Wi-Fi

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DozyAP: Power-Efficient Wi-Fi Tethering

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  1. DozyAP: Power-Efficient Wi-Fi Tethering Speaker Hao Han College of William & Mary 3/22/2013 W&M Graduate Research Symposium 2013

  2. Outline • Motivation • Design • Evaluation • Conclusion

  3. What is Wi-Fi Tethering Sharing a cellular data connection via Wi-Fi An Internet-capable mobile phone acts as a Soft Access Point (SoftAP) Also known as “Mobile Hotspot” soft access point (a.k.a., mobile hotspot)

  4. Wi-Fi Tethering is Desirable Widely supported on mainstream mobile phones Built-in feature on iOS (v4.3+), Android (v2.2+) and Windows Phone (v7.5+) Other third-party tethering tools Reasons Cellular data network coverage is ubiquitous People usually own multiple devices but only one data plan

  5. Wi-Fi Tethering is a "Battery Killer" Nexus One (Android) HTC HD7 (WP) iPhone 4 (iOS) • Even when idle, battery life is reduced from days to hours • Practical usage will draw battery morequickly

  6. Power Saving for Wi-Fi Tethering is Demanded Old wisdom: APs are externally powered Not true for smartphones working in Wi-Fi tethering DozyAP: Power-Efficient Wi-Fi Tethering Goals reduce power consumption of Wi-Fi tethering Retain good user experience Key idea Put a Wi-Fi interface to sleep when network is idle Challenges Avoid packet loss Reduce network latency

  7. Contributions • First work to study the power efficiency of Wi-Fi tethering for SoftAPs • Solution without underlying support • First working system on commercial smartphones

  8. Sources of Idle Time • Network traffic is bursty and idle for most of time • Speed discrepancy between cellular and Wi-Fi Many opportunities SoftAP could and should sleep !

  9. Yes Yes No No Sleep Request-Response Protocol • Two way hand-shake protocol • Sleep request • Sleep response • SoftAP sleeps only if receiving sleep response data t0 idle > threshold sleep request t1 t2 sleep response sleep data t3 sleep request any buffered data any delayed data data sleep response SoftAP Client

  10. Two-stage Adaptive Sleep Algorithm How long to sleep? Wake up as few times as possible (more energy saving) Wake up shortly before next packet arrives (less extra delay) sleep Pkt i Pkt i Pkt i+1 Pkt i+1 sleep sleep sleep Pkt i+1 Pkt i extra delay

  11. Evaluation • Allow Wi-Fi interface sleep for up to 88% of the total time • Reduce power consumption by up to 33% • Only increase network latency by less than 5.1%

  12. Potential to Save More Power Applications Current Kernel & Drivers DozyAP, power saving up to 33% Firmware Proprietary & closed source Applications Kernel & Drivers Future Firmware DozyAP, power saving up to 80%

  13. Conclusion • Study the characteristics of Wi-Fi tethering • Propose DozyAP with two protocols • Sleep request-response protocol • Two-stage adaptive sleep algorithm • Implement DozyAP on commercial smartphones • Extensive evaluation

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