Cross-Layer Optimized Video Streaming Over Wireless Multihop Mesh Networks

1. Yiannis Andreopoulos et al.IEEE JSAC’06November 2006 Cross-Layer Optimized Video Streaming Over Wireless Multihop Mesh Networks 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 802.11 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 • 4. For each path pi • 5. For each link li,j of path pi • 6. For each modulation strategy m(li,j) • 7. Calculate eli,j(Lv), epi (Lv), dqueue(li,j) • 8. Calculate Tpimax • 9. Evaluate the end-to-end cross-layer optimization • 10. Compare with previous best choice • 11. 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