cooperative layered wireless video multicast ozgu alay, thanasis korakis, yao wang, elza erkip,...
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Cooperative Layered Wireless Video Multicast
Ozgu Alay, Thanasis Korakis, Yao Wang, Elza Erkip, Shivendra Panwar
Introduction Video multicast over wireless channels
Wireless video applications are emergingMulticast is effectiveWireless video multicast is still a
challenging problem High packet loss rate Bandwidth variations
Cooperation is a natural solutionHigher spatial diversityAdaptive to network conditions
Prior Work: Cooperation for Unicast physical-layer cooperation for point-
to-point video communicationSingle-layer cooperationlayered cooperation
MAC-layer cooperation for point-to-point communication
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 .
Why Cooperative Multicasting ?
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
Relay 1
Relay 4 AP
Relay 3
Relay 2
Group 1
Group 2
Extended Group 2
rrelay
rext
R2
,r1
,r dRd
R1
,r2C
B
A
Received Video Rates
T1 T2 T2
T
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
Approach For a particular (r1, r2) we determine the
optimum (T1, T2) and N in two steps.
1. We first determine the user partition with a minimum number of relays.
2. 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 Partition Goal: Find minimum
number of relays N that covers all the users
User partition is defined by (r1, r2) and the separation angle where,
N = 2/2
rrelay
rext
R2
,r1
, r d R d
R1
,r2C
B
A
User Partition
We define max as the maximum angle which satisfies the constraints below,
rrelay
rext
R2
,r1
, r d R d
R1
,r2C
B
A
Optimum User Partition
is maximum when
Then, using cosine theorem
r1rd
r2C
B
Amax
Optimum User Partition
Then N is,
And rext can be computed as
rrelay
rext
R2
,r1
, r d R d
R1
,r2C
B
A
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.
Minimum Average Distortion
N1 and N2 are the number of users in Group 1 and Group 2, respectively.
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).
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 = Rd
Sustainable Rates vs. Distance with IEEE 802.11b
r1=61m, R1=11 Mbps
r2=72m, R2=5.5 Mbps
r3=100m, R3=1 Mbps
r 1, R 1r 3, R 3
r 2, R 2
Example Scenario 802.11b based WLAN Uniformly distributed
users within 100m radius (r=100m)
Achievable rate with direct transmission to all users,
Rd = 1 Mbps =0.75 Soccer
704x576 resolution 240 frames
r , R
Performance
Visual Quality
750 kbps ( 29.84 dB )
1.178 Mbps ( 30.42 dB ) 3.75 Mbps ( 33.32 dB )
Conclusion
User cooperation can improve the quality of service in video multicastEqual quality at all usersBetter quality at selected usersAll better than direct transmission
Optimization of relay selection, user partition, and transmission scheduling depends on the chosen multicast performance criterion
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