1. Yiannis Andreopoulos et al. IEEE JSAC’06 November 2006
Cross-Layer Optimized Video Streaming Over Wireless Multihop Mesh Networks
Yiannis Andreopoulos et al. IEEE JSAC’06 November 2006
Yoonchan Choi
Advanced Networking Lab
Nov 27, 2007

2. Outline Introduction Proposed Integrated Cross-Layer Video Streaming
Problem Formulation
Video Streaming Optimization
Experimental Results
Conclusion

3. Introduction Existing protocols for wireless multihop mesh networks
Desired to reduce deployment costs and increase interoperability
Has significant challenges in the optimization of each layer strategies
For efficient video transmission across wireless mesh networks
Current multihop video streaming
Not consider the protection techniques
Optimize the video transport using purely end-to-end metrics
Integrated video streaming paradigm
Enables cross-layer interaction across the protocol stack and across the multiple hops

4. Introduction
Real-time transmission of an video bitstream across a multihop wireless network
What is the video quality improvement?
If an integrated cross-layer strategy is performed
What is the performance?
Using only limited & localized information vs. global & complete information
Optimization framework jointly determines per packet
1) optimal modulation at the PHY
2) optimal retry limit at the MAC
3) optimal path to the receiver
4) application-layer optimized packet scheduling

5. Integrated Cross-Layer Video Streaming
Simple topology with three hops
h1 : original video source / hN : destination node
gij : allocated bandwidth for the video traffic
eij : error rate observed on the link
dijqueue : corresponding delay due to the video queue
Video packets are lost due to the experienced BER and delays incurred in the transmission

6. Integrated Cross-Layer Video Streaming
More complex topologies with seven hops

7. Integrated Cross-Layer Video Streaming
More complex topologies with seven hops

8. Integrated Cross-Layer Video Streaming
Wireless Multihop Mesh Topology Specification
Connectivity structure
pi : connectivity vector (1 ≤ i ≤ M)
li,j : particular wireless link (1 ≤ j < ρitotal)
ρitotal – 1 : total number of links participating in the network path pi

9. Integrated Cross-Layer Video Streaming
Link and Path Parameter Specification
Guaranteed bandwidth g(li,j)
Provided by each link at the application layer
Depends on the provided physical-layer rate Rphy(li,j)
tTXOP(li,j) : transmission opportunity duration
: MAC service data unit (MSDU) size
tSI(li,j) : specified duration of the service interval
Rphy(li,j) : physical-layer rate
Toverhead : duration of the required overheads

10. Integrated Cross-Layer Video Streaming
Link and Path Parameter Specification
Probability of error for the transmission of MSDU v of size LV bits
Probability of error for the packet transmission in path pi
Transmission delay for path pi

11. Integrated Cross-Layer Video Streaming
Link and Path Parameter Specification
Average number of transmissions over path pi until the packet is successfully transmitted, or the retransmission limit is reached
End-to-end expected delay for the transmission of an MSDU of size Lv through pi

12. Integrated Cross-Layer Video Streaming
Application and Network-Layer Parameter Specification
Queuing delay depends on
MSDUs from a particular flow that are scheduled for transmission via the link of interest at the moment when MSDU v arrives
Queue output rate

13. Problem Formulation End-to-end cross-layer optimization determines
Chosen path (routing)
Maximum MAC retry limit
Chosen modulation at the PHY layer
where

14. Problem Formulation Two constraints
Problem constraint can be expressed for each MSDU v
Timing constraint set from HCCA scheduling
The tightest bound for the maximum retry limit

15. Video Streaming Optimization
End-to-End Optimization
Proposed optimization algorithm
1. For each node that has non-expired MSDUs in its queue
2. Extract the network connectivity structure
3. For the MSDU v existing at output of the queue of the sender node
For each path pi
For each link li,j of path pi
For each modulation strategy m(li,j)
Calculate eli,j (Lv), epi (Lv), dqueue(li,j)
Calculate Tpimax
Evaluate the end-to-end cross-layer optimization
Compare with previous best choice
Schedule the MSDU according to the established {pi, Tpimax, m(li,j)}

16. Video Streaming Optimization
Optimization under a certain horizon of network information
Algorithm for cross-layer optimization under an estimation-based framework
1. The optimal modulation parameters are estimated only once per link during the optimization of the first MSDU
2. The optimal modulation parameters remain constant throughout the remaining MSDUs
3. Per MSDU, the expected physical layer rate and guaranteed bandwidth per link are estimated and the error for each path is estimated
4. the maximum retry limit and the average number of retries are established
5. For each node, the link that maximizes is selected

17. Experimental Results
Average PSNR results for video streaming

18. Experimental Results
Percentage of losses for each packet distortion-reduction class

19. Conclusion
The integrated cross-layer solution appears to provide significant improvement over other optimized solution
The utilization of network information appears to be of paramount importance for the overall video quality at the receiver hop

20. Thank you