Cooperative Layered Wireless Video Multicast

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Cooperative Layered Wireless Video Multicast

• Ozgu Alay, Thanasis Korakis,
• Yao Wang, Elza Erkip, Shivendra Panwar

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Introduction

• Video multicast over wireless channels
• Wireless video applications are emerging
• Multicast is effective
• Wireless video multicast is still a challenging
  problem
• High packet loss rate
• Bandwidth variations
• Cooperation is a natural solution
• Higher spatial diversity
• Adaptive to network conditions

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Prior Work Cooperation for Unicast

• physical-layer cooperation for point-to-point
  video communication
• Single-layer cooperation
• layered cooperation
• MAC-layer cooperation for point-to-point
  communication

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Why Cooperative Multicasting ?

• Each receiver has different channel quality
• Conventional Multicast
• Source transmits based on furthermost receiver
• the receivers with a good channel quality
  unnecessarily suffer and see a lower quality
  video .

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Why Cooperative Multicasting ?

• Cooperative Multicast
• Divide all the receivers into two groups such
  that receivers in Group 1 have better average
  channel quality than Group 2
• Sender 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

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Received Video Rates
T
T1
T2
T2
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Design Variables

• Number of relays N
• Sustainable rates (R1, R2) or transmission ranges
  (r1, r2)
• Time partition (T1, T2)
• N controls the tradeoff between R2 and T2
• How to optimize?
• Maximize the average quality
• All users have same quality
• Group1 has better quality

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Approach

• For 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.

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User Partition

• Goal 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

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User Partition

• We define amax as the maximum angle which
  satisfies the constraints below,

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Optimum User Partition

• a is maximum when
• Then, using cosine theorem

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Optimum User Partition

• Then N is,
• And rext can be computed as

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Time Scheduling and Performance Metric

• We 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.

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Minimum Average Distortion

• N1 and N2 are the number of users in Group 1 and
  Group 2, respectively.

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Equal Distortion at all users

• We 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).

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Best Quality at Group 1 users

• Considering 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

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Sustainable Rates vs. Distance with IEEE 802.11b
r161m, R111 Mbps r272m, R25.5 Mbps r3100m,
R31 Mbps
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Example Scenario

• 802.11b based WLAN
• Uniformly distributed users within 100m radius
  (r100m)
• Achievable rate with direct transmission to all
  users,
• Rd 1 Mbps
• b0.75
• Soccer
• 704x576 resolution
• 240 frames

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Performance
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Visual Quality

• 750 kbps ( 29.84 dB )

1.178 Mbps ( 30.42 dB )
3.75 Mbps ( 33.32 dB )
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Conclusion

• User cooperation can improve the quality of
  service in video multicast
• Equal quality at all users
• Better quality at selected users
• All better than direct transmission
• Optimization of relay selection, user partition,
  and transmission scheduling depends on the chosen
  multicast performance criterion