Cooperative Layered Wireless Video Multicast
Post on 12-Jan-2016
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DESCRIPTIONCooperative Layered Wireless Video Multicast. Ozgu Alay, Thanasis Korakis, Yao Wang, Elza Erkip, Shivendra Panwar. Introduction. Video multicast over wireless channels Wireless video applications are emerging Multicast is effective Wireless video multicast is still a challenging problem - PowerPoint PPT Presentation
Cooperative Layered Wireless Video MulticastOzgu Alay, Thanasis Korakis, Yao Wang, Elza Erkip, Shivendra Panwar
IntroductionVideo multicast over wireless channelsWireless video applications are emergingMulticast is effectiveWireless video multicast is still a challenging problemHigh packet loss rate Bandwidth variationsCooperation is a natural solutionHigher spatial diversityAdaptive to network conditions
Prior Work: Cooperation for Unicastphysical-layer cooperation for point-to-point video communicationSingle-layer cooperationlayered cooperationMAC-layer cooperation for point-to-point communication
Why Cooperative Multicasting ?Each receiver has different channel quality Conventional Multicast Source transmits based on furthermost receiverthe receivers with a good channel quality unnecessarily suffer and see a lower quality video .
Why Cooperative Multicasting ?Cooperative MulticastDivide all the receivers into two groups such that receivers in Group 1 have better average channel quality than Group 2Sender targets receivers with good channel quality (Group1)These receivers relay the video to other receivers (Group2) It is likely that we achieve a larger coverage area (Extended Group 2).Both groups see better quality
Received Video RatesT1T2T2T
Design VariablesNumber of relays NSustainable rates (R1, R2) or transmission ranges (r1, r2)Time partition (T1, T2)N controls the tradeoff between R2 and T2How to optimize?Maximize the average qualityAll users have same qualityGroup1 has better quality
ApproachFor a particular (r1, r2) we determine the optimum (T1, T2) and N in two steps. We first determine the user partition with a minimum number of relays. Then for this user partition, we find the optimum T1 and T2 (time scheduling) that maximizes the system performance index By repeating the above procedure for all possible (r1, r2) we find the optimum user partition and time scheduling that maximizes the performance criterion.
User PartitionGoal: Find minimum number of relays N that covers all the users
User partition is defined by (r1, r2) and the separation angle a where, N = 2p/2a
User PartitionWe define amax as the maximum angle which satisfies the constraints below,
Optimum User Partitiona is maximum when
Then, using cosine theorem
Optimum User PartitionThen N is,
And rext can be computed as
Time Scheduling and Performance MetricWe use exhaustive search over a discretizied space of feasible T1 and T2, for each candidate T1 and T2, determine Rv1 and Rv2 and correspondingly D1 and D2. Here D1(Rv1) is the distortion of Group 1 receivers and D2(Rv2) is the distortion for Group 2 receivers.
Minimum Average DistortionN1 and N2 are the number of users in Group 1 and Group 2, respectively.
Equal Distortion at all usersWe require all the receivers have the same distortion. In other words, we find the optimum user partition and time scheduling that minimizes D1(Rv1) = D2(Rv2).
Best Quality at Group 1 usersConsidering that relays are spending their own resources to help others,We find the optimum user partition and time scheduling that minimizes D1(Rv1) while guaranteeing Rv2 = bRd
Sustainable Rates vs. Distance with IEEE 802.11br1=61m, R1=11 Mbpsr2=72m, R2=5.5 Mbpsr3=100m, R3=1 Mbps
Example Scenario 802.11b based WLANUniformly distributed users within 100m radius (r=100m) Achievable rate with direct transmission to all users, Rd = 1 Mbps b=0.75Soccer 704x576 resolution240 frames
Visual Quality750 kbps ( 29.84 dB )1.178 Mbps ( 30.42 dB )
3.75 Mbps ( 33.32 dB )
ConclusionUser cooperation can improve the quality of service in video multicastEqual quality at all usersBetter quality at selected usersAll better than direct transmissionOptimization of relay selection, user partition, and transmission scheduling depends on the chosen multicast performance criterion
Along with the increase in both the bandwidth of wireless networks and computational power of wireless hand-held terminals, various wireless video applications are beginning to emerge.To provide efficient delivery among a group of users simultaneously, multicast has been used as one effective solution, as it enables delivery of popular events (such as a soccergame or headline news) to many wireless users in a bandwidth efficient manner. On the other hand, the higher packet loss ratio and bandwidth variations ofwireless channels makes video multicast over wireless networks a challenging problem.Also, I assume this is based on some assumption of transmission power, and channel conditionYou should find out these from Thanasis, in case there are questions regarding this.Should also cite a reference.