School of Computing Science Simon Fraser University Canada
- Slides: 27
School of Computing Science Simon Fraser University, Canada Video Streaming over Cooperative Wireless Networks Mohamed Hefeeda (Joint work with Yi Liu) 22 February 2010 Mohamed Hefeeda 1
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) Mohamed Hefeeda 2
Mobile Video Streaming § Either Unicast (e. g. , 3 G 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) - Media. FLO (Forward Link Only) - CMMB (China Mobile Multimedia Broadcasting) Mohamed Hefeeda 3
Mobile Video Broadcast § Base station broadcasts multiple video streams to mobile devices over WMAN (Wireless Metropolitan Area Network) WMAN Base Station Mohamed Hefeeda 4
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 Qo. E parameter for users Mohamed Hefeeda 5
Energy Saving—Switching Delay Tradeoff § Base station broadcasts in bursts to save energy § user has to wait for a burst § Tradeoff: Saving energy introduces delay Mohamed Hefeeda 6
Our Goal § Saving more energy for mobile devices AND § Reducing channel switching delay Mohamed Hefeeda 7
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 Mohamed Hefeeda 8
Overview Mohamed Hefeeda 9
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) Mohamed Hefeeda 10
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) Mohamed Hefeeda 11
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 Mohamed Hefeeda 12
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 Mohamed Hefeeda 13
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 Mohamed Hefeeda 14
Time Synchronization § Time offset contained in the header of burst data packets § No extra clock synchronization algorithm needed Mohamed Hefeeda 15
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 Mohamed Hefeeda 16
Evaluation in Mobile TV (DVB-H) Testbed Mohamed Hefeeda 17
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. Mohamed Hefeeda 18
Energy Saving Gain § In theory, saving about 33% § In experiment, saving about 29% Mohamed Hefeeda 19
Energy consumption of one mobile device § On-duty mode spend 23% more § Backup mode spend 8% more § Off-duty mode save 75% § One device takes turns to be in different mode Mohamed Hefeeda 20
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 Mohamed Hefeeda 21
Potential energy saving gain in simulator § Only 3 devices needed to outperform current systems § Saving up to 70% with 30 devices § Saving about 21% with 3 devices Mohamed Hefeeda 22
Channel Switching Delay § Reduce channel switching delay by up to 98% § From up to 700 msec to at most 13 msec Mohamed Hefeeda 23
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 Mohamed Hefeeda 24
Load Distribution § Standard deviation of contribution is less than 0. 6 MB § Total contribution value in the order of hundred MBs Mohamed Hefeeda 25
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 Mohamed Hefeeda 26
Thank You! Questions? ? § More info at: http: //nsl. cs. sfu. ca/ Mohamed Hefeeda 27
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