1 dozyap: power-efficient wi-fi tethering speaker hao han college of william & mary 3/22/2013...
TRANSCRIPT
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DozyAP: Power-Efficient Wi-Fi Tethering
SpeakerHao Han
College of William & Mary
3/22/2013
W&M Graduate Research Symposium 2013
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Outline
Motivation Design Evaluation Conclusion
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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)
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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
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Nexus One(Android)
HTC HD7(WP)
iPhone 4(iOS)
Wi-Fi Tethering is a "Battery Killer"
Wi-Fi tethering disabled Wi-Fi tethering enabled
(idle)
Power Battery Life Power Battery Life
Nexus One 20 mW 259 hours 270 mW 19 hours
HTC HD7 32 mW 150 hours 302 mW 16 hours
iPhone 4 22 mW 247 hours 333 mW 16 hours
Even when idle, battery life is reduced from days to hours Practical usage will draw battery more quickly
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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
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Contributions
First work to study the power efficiency of Wi-Fi tethering for SoftAPs
Solution without underlying support First working system on commercial smartph
ones
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Sources of Idle Time
Network traffic is bursty and idle for most of time Speed discrepancy between cellular and Wi-Fi
Wi-Fi Cellular
up to 54Mbps for 802.11a/gup to 600Mbps for 802.11n
up to 2Mbps for 3GUp to 100Mbps for LTE 4G
Many opportunities SoftAP could and should sleep !
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Two way hand-shake protocol Sleep request Sleep response
SoftAP sleeps only if receiving sleep response
Sleep Request-Response Protocol
Ethernet Header(type = 0xffff)
TypeSequence Number
Sleep Duration
The Sleep “Request-Response” Protocol
0x1: sleep request0x2: sleep response
t0
t1
idle > threshold
t2
t3
sleep
any buffered data
YesNo
any delayeddata
YesNo
data
data
sleep request
sleep response
sleep request
sleep response data
SoftAP Client
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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)
extra delay
sleepPkt i Pkt i+1
sleep sleep
Pkt i Pkt i+1
Pkt i Pkt i+1sleep
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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%
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Potential to Save More Power
Applications
Firmware
Kernel & Drivers
Proprietary & closed source
DozyAP, power saving up to 33%
Applications
Firmware
Kernel & Drivers
DozyAP, power saving up to 80%
Cu
rren
tC
urr
ent
Fu
ture
Fu
ture
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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