DozyAP: Power-Efficient Wi-Fi Tethering Speaker - Utk

wheatprisonMobile - Wireless

Dec 10, 2013 (3 years and 10 months ago)

129 views

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

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


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


Wi
-
Fi

Cellular

up to 54Mbps for 802.11a/g

up to 600Mbps for 802.11n

up to 2Mbps for 3G

Up to 100Mbps for LTE 4G

Many opportunities SoftAP could and should sleep !

9


Two way hand
-
shake protocol


Sleep request


Sleep response



SoftAP sleeps only if receiving sleep response


Sleep Request
-
Response
Protocol

Ethernet Header
(
type
=
0
xffff
)
Type
Sequence
Number
Sleep Duration
The Sleep “Request
-
Response” Protocol
0
x
1
:
sleep request
0
x
2
:
sleep response
t
0

t
1

idle > threshold

t
2

t
3

sleep

any buffered

data

Yes

No

any delayed

data

Yes

No

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)


extra delay

sleep

Pkt
i

Pkt
i+1

sleep

sleep

Pkt
i

Pkt
i+1

Pkt
i

Pkt
i+1

sleep

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

Firmware

Kernel & Drivers

Proprietary & closed source

DozyAP, power saving up to 3
3%

Applications

Firmware

Kernel & Drivers

DozyAP, power saving up to 80%

Current

Future

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