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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)}

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

Experimental Results Average PSNR results for video streaming

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

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

Thank you