Mobile Offloading Using WiFi:

Viable in VANETs? Presented by: Nan Cheng

2013.05.31

Broadband Communications Research (BBCR) Lab

Vehicular Data Offloading

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Broadband Communications Research (BBCR) Lab Smart Grid Research Group

Vehicular Data

• Multi-media services in car: audios & videos, email, other infotainment data

• Vehicle-specific data. E.g., vehicle diagnoses data: 700 Mbytes/Mo.

• Need to access Internet. • How? Nowadays CELLULAR.

Cellular data offloading (1)

• Operators of mobile cellular data networks (3G and 4G) face an uphill battle against increasing data usage and declining ARPUs

• iPhones, iPads, Android smartphones, netbooks are all tapping the mobile network for access anywhere anytime

Cellular data offloading (2)

• Cellular: – Coverage is good – Limited bandwidth (LTE-20MHz) (Low QoS, network congestion, etc.) – Prohibitive fees (Roges)

• Offload the cellular network? – Drive-thru Internet, WiFi, Femto… – Device-to-Device (D2D) communications

D2D communication

• Mobile users can communicate directly with each other instead of using CNs.

• For example, popular videos downloaded and stored temporarily in a device, and transmitted to others when requested. (Base-station assisted device-to-device communications for high-throughput wireless video networks)

Drive-thru Internet

• Use IEEE 802.11 (WiFi) technology for providing network access to mobile users in moving vehicles.

Drive-thru Internet

• Issues in Drive-thru Internet – High speed & low connection time – Low coverage level – WiFi deployment (20M APs in U.S.) – Unstable link condition – Delay and cost

“Mobile Data Offloading: How Much Can WiFi Deliver?” (TON ‘13)

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Broadband Communications Research (BBCR) Lab Smart Grid Research Group

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• This paper focuses on common mobile users, not vehicle users • WiFi offloading can be classified to “on-the-spot offloading” and

“delayed offloading”. • With only on-the-spot offloading, 65% of mobile data is offloaded

and 55% of battery power is saved. • Performance of delayed offloading depends on the level of delay

tolerance: • 100 sec: 2%-3% gain • 1 hour: 20% gain

• Important observations and conclusions

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• Use WiFi when available, otherwise use cellular. • Services with little delay (only transmission delay) • Already performed by most smartphones. • Achieve 65% data offloading and 55% energy saving

• On-the-spot offloading

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• Users choose an acceptable deadline. • Within the deadline, user wait the chance to use WiFi only. • At the deadline, the cellular network finish the transfer (undone part). • Whatever deadline is, the service is guaranteed to be done within it.

• For delay-tolerant services & applications. • Performance strongly depends on the delay. • Provide users flexible price strategies to use. • Scenarios:

• Delayed offloading (1)

Upload and archive?

At once, 3G

Go home, WiFi

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• A possible price v.s. delay curve

• Delayed offloading (2)

The philosophy behind the curve (Why is this?) - Carriers: Larger delay indicates

that more likely the service can be done through WiFi or in expect more data can be offloaded by WiFi. Then CN is better offloaded and the cost is reduced. That is why price goes down.

- User: Choose an appropriate and acceptable delay to reduce cost.

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• Authors of the paper conducted a comprehensive experiment in which 100 iPhones were tracked by a designed software.

• Data such as location, data rate, time, and WiFi/cellular status is recorded and analyzed.

• Data files are generated and uploaded to test the offloading performance.

• Key issues: • Total WiFi connectivity time • Data rate during connection • Connection/inter-connection time duration distribution • Travel length v.s. WiFi connection time

• About the experiment

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• WiFi connection - average: 70%

• WiFi connection v.s. travel length – Clues for VANETs: vehicle users

may have very little WiFi coverage time.

• Highlights in the experiment (1) – overall WiFi conection

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• Time duration for once WiFi connection/inter-connection

• Average time for once WiFi connection and inter-connection are 122 and 41 mins, respectively. (Users stay for a long time once they connect to WiFi. This may be very different in VANETs)

• Highlights in the experiment (2) – WiFi connection statistics

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• Time duration for once WiFi connection/inter-connection

• Highlights in the experiment (3) – WiFi deployment

• Conclusion: - More APs leads better performance. - Proper deployment strategy greatly

influence the performance. - How to evaluate the deployment

strategy in VANETs environment? (Discussed later)

WiFi Offloading + VANETs? Existing Works

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Broadband Communications Research (BBCR) Lab Smart Grid Research Group

Drive-thru Internet: IEEE 802.11b for “Automobile” Users

• First to evaluate the technical feasibility of providing “Drive-Through Internet”.

• Focus on transport protocol behavior • Under 200 m (diameter) AP coverage,

users’ devices in range for 12 sec.

J. Ott, D. Kutscher. Drive-thru Internet: IEEE 802.11b for Automobile Users. In Proc. of IEEE Infocom 2004.

Measurements I

• UDP: two-directional unicast with different packet sizes and intervals.

• TCP: vehicle moves in the coverage and establish a connection to the server. • Speed: 80 kmph, 120kmph • A three-phase concept

Measurement II

Measurement III

Measurement IV

A Measurement Study of Vehicular Internet Access Using In Situ WiFi Networks.

• In Situ: In position. An operation that occurs without interrupting the normal state of a system.

• A few cars move in and around Boston metropolitan area. (Urban scenario)

V. Bychkovsky, B. Hull, A. Miu, H. Balakrishnan, and S. Madden. A Measurement Study of Vehicular Internet Access Using In Situ WiFi Networks. In Proc. of ACM MobiCom 2006.

Several Conclusions • Median duration of link-layer connectivity: 13 sec. • Median connection upload bandwidth (TCP): 30

KBytes/s • Mean duration between successful associations

to APs: 75 seconds • Grassroots Wi-Fi networks are viable for a

variety of applications, particularly ones that can tolerate intermittent connectivity.

Other Papers • D. Hadaller, S. Keshav, T. Brecht, S. Agarwal. Vehicular

Opportunistic Communication: Under the Microscope. In Proc. of ACM MobiSys 2007.

• J. Eriksson, H. Balakrishnan, and S. Madden. Cabernet: Vehicular Content Delivery Using WiFi. In Proc. of ACM MobiCom 2008.

• Y. Zhuang, J. Pan, V. Viswanathan, and L. Cai, “On the Uplink MAC Performance of A Drive-Thru Internet,” IEEE Transaction on Vehicular Technology, vol. 11, no. 4, pp. 1925 – 1935, Apr. 2012.

MIT Cartel Project • CarTel is a distributed, mobile sensing and

computing system using phones and custom-built on-board telematics devices;

• Research contributions: – Traffic mitigation (for efficient transportation) – Road surface monitoring and hazard detection – Vehicular networking – Design of multiple generations of in-car OBD+GPS

hardware using only WiFi for connectivity.

This project can be found at http://cartel.csail.mit.edu/doku.php

Networking

• Cabernet: Use QuickWifi to make sure that a large portion of time is used for data transfer.

• CafNet: A delay-tolerant stack that enables mobile data muling and allows data to be sent across an intermittently connected network.

Cabernet: http://nms.lcs.mit.edu/papers/index.php?detail=184 Cafnet: http://cartel.csail.mit.edu/cafnet/

THANKS!