School of Computing Science Simon Fraser University, Canada

Mohamed Hefeeda 1

School of Computing ScienceSimon Fraser University, Canada

Video Streaming over Cooperative Wireless Networks

Mohamed Hefeeda(Joint work with Yi Liu)

22 February 2010

Mohamed Hefeeda

Motivations

Video streaming to mobile devices is getting popular- High demand from users- Phones have enough network and processing capacity - Business opportunity for content providers (different peak

viewing hours)

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Mohamed Hefeeda

Mobile Video Streaming Either Unicast (e.g., 3G cell networks):

- On-demand, but limited capacity for serving videos

Or Broadcast (dedicated networks)- Known as Mobile TV- Supports large-scale users- Offers many video streams (TV Channels)- The focus of this paper

Example broadcast networks- DVB-H (Digital Video Broadcast-Handheld)- MediaFLO (Forward Link Only)- CMMB (China Mobile Multimedia Broadcasting)

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Mohamed Hefeeda

Mobile Video Broadcast

Base station broadcasts multiple video streams to mobile devices over WMAN (Wireless Metropolitan Area Network)

Base Station

WMAN

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Mohamed Hefeeda

Research Problems Considered

Energy consumption of mobile devices- Battery powered- Video consumes substantial energy short viewing time

Channel switching delay- Delay until user starts viewing the stream- Important QoE parameter for users

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Base station broadcasts in bursts to save energy user has to wait for a burst Tradeoff: Saving energy introduces delay

Energy Saving—Switching Delay Tradeoff

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Our Goal

Saving more energy for mobile devices

AND

Reducing channel switching delay

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Our Approach

Use cooperation among mobile devices to benefit all - Cooperation achieved over wireless LAN (WLAN)

Why?- Energy per bit in WLAN is lower than in WMAN- Faster transmission in WLAN- WLANs widely deployed, most phones have them

- Streams can be obtained quickly over WLAN very short switching delay

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Mohamed Hefeeda

Overview

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Mohamed Hefeeda

Our Contributions

Distributed algorithm to elect devices and manage data transmission- Simple, efficient, and motivates truthful cooperation

Quantitative analysis of the cooperative system- To show the gain with different parameters

Implementation in real mobile TV testbed- Proof of concept

Empirical results show:- Substantial energy savings (up to 70% gain) AND- Switching delay almost eliminated (up to 98% reduction)

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Mohamed Hefeeda

System Design: High-Level

Mobiles receiving same TV channel form group 1 on-duty node is elected:

- Receives data from base station over WMAN,- relays it to others in the group over WLAN,- and serves it immediately to new joiners - Broadcasts ON-DUTY messages

- On-duty period is one WMAN burst cycle (few seconds)

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Mohamed Hefeeda

System Design: High-Level

K backup nodes are elected:- Each has a different timer- If on-duty node fails, one will become on-duty- Receive data from WMAN, and store it

N-k-1 nodes are off-duty- Received data from on-duty node over WLAN- WMAN interface is off

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Mohamed Hefeeda

System Design: High-Level

Election:- Nodes maintain Contribution list with N entries- Entry n is total amount of data relayed by node n- Node computes other nodes’ contributions based on actual data

received - Node with least contribution becomes on-duty- Next k nodes become backup- In case of tie, node with oldest joining time is chosen

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Mohamed Hefeeda

Handling Network Dynamics Device Join:

- A join message sent to the on-duty device. On-duty replies with burst data and contribution list

Device Leave: - If backup or off-duty device leave: LEAVE message sent to on-duty

device- If on-duty device leave: LEAVE message broadcast to the group, one

backup device takes over the on-duty role

Device Failure: - If backup or off-duty device fail: No harm, will be detected in next

cycle- If on-duty device fail: No more ON-DUTY message broadcast, can be

detected by backup devices, then one backup device takes the on-duty role

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Mohamed Hefeeda

Time Synchronization

Time offset contained in the header of burst data packets

No extra clock synchronization algorithm needed

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Analysis Results

Compute energy saving gain, and number of needed nodes for cooperation As function of energy consumption values of WMAN

and WLAN and their transmission rates

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Evaluation in Mobile TV (DVB-H) Testbed

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Experimental Setup

We implemented our algorithm in PC with USB DVB-H receivers (4 in total)

We setup an 8 MHz radio channel to broadcast four 5-minute long TV programs coded at 250 kbps.

We used the QPSK modulation scheme together with the convolution coding rate at 2/3 and guard interval at 1/8.

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Mohamed Hefeeda

Energy Saving Gain

In theory, saving about 33%

In experiment, saving about 29%

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Mohamed Hefeeda

Energy consumption of one mobile device

On-duty mode spend 23% more

Backup mode spend 8% more

Off-duty mode save 75%

One device takesturns to be indifferent mode

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Evaluation in Simulation

Trace-drive simulation- Increase number of nodes, exercise wide range of parameters

Used actual MPEG-TS transport streams (obtained from Nokia)

Used actual power consumption values from chip data sheets

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Potential energy saving gain in simulator

Only 3 devices needed to outperform current systems

Saving up to 70% with 30 devices

Saving about 21% with3 devices

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Channel Switching Delay

Reduce channelswitching delayby up to 98%

From up to 700 msec to at most13 msec

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Energy saving gain under network dynamics

Survives a sudden loss of 90% devices

Energy hit of 51%under 90% failure

Quickly adapts to network dynamics

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Standard deviation of contribution is less than 0.6 MB

Total contributionvalue in the orderof hundred MBs

Load Distribution

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Conclusions

Proposed video streaming over cooperative WMAN and WLAN networks

Real implementation, simulation, and analytic analysis show that the proposed system improves energy saving and switching delay concurrently

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Mohamed Hefeeda

Thank You!

Questions??

More info at:

http://nsl.cs.sfu.ca/

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