Correlated Coding: Efficient Network Coding under Unreliable Wireless Links

1. Correlated Coding: Efficient Network Coding under Unreliable Wireless Links Shuai Wang, Song Min Kim, Zhimeng Yin, and Tian He University of Minnesota ICNP 2014 24st Oct 2013

2. Network Coding (NC) Network coding has the potential to Improve the network performance. Widely used coding technologies: Opportunistic Coding Linear Network Coding University of Minnesota Shuai Wang @ ICNP’ 14 2

3. Existing Problems & This Paper Existing Problems - Community’s concern: Use network coding or not? Our Solutions focus on the key factor – Link Correlation: Help network designers decide whether to apply NC. University of Minnesota Shuai Wang @ ICNP’ 14

4. Unrealistic Assumption and Modeling Assumptions in existing protocol designs, e.g., 1/LQ in COPE and MORE: Wireless transmissions are independent. Does the assumption reflect the real situation? University of Minnesota Shuai Wang @ ICNP’ 14

5. Wireless Links are Correlated! 802.11 Testbed: 1 AP 6 Laptops 100 Packets Empirical Trace Synthetic Independent Trace University of Minnesota Shuai Wang @ ICNP’ 14

6. Wireless Links are Correlated! 802.15.4 Testbed: 1 Source node 6 Receivers 100 Packets Empirical Trace Synthetic Independent Trace University of Minnesota Shuai Wang @ ICNP’ 14

7. How Link Correlation Impacts NC? NetworkCoding Step1: Coding Step2: Transmit Send out with coded packets e.g., Opportunistic listening, encoding University of Minnesota Shuai Wang @ ICNP’ 14

8. How LC Impacts Step 1 - “Coding”? Impact of link correlation on the “Coding” procedure: Coding Scenario Non-Coding Scenario Sub-Conclusion 1: the “Coding” procedure prefers low link correlation (i.e., high diversity). University of Minnesota Shuai Wang @ ICNP’ 14

9. How LC Impacts Step 2 - “Transmit”？ Impact of link correlation on the “Transmit” procedure: (a) Low Correlated: Link quality: 0.8 # of coded pkts need to be retransmitted: 4 (b) High Correlated: Link quality: 0.7 # of codedpkts need to be retransmitted: 3 Sub-Conclusion 2: the “Transmit” procedure prefers high link correlation (i.e., low diversity). . University of Minnesota Shuai Wang @ ICNP’ 14

10. Put Together: How LC Impacts NC? NetworkCoding Step1: Coding Step2:Transmit High Link Correlation Low Link Correlation Send out with one coded pkt e.g., Opportunistic listening, encoding Conclusion: there exists a tradeoff between the coding opportunity and transmit efficiency. University of Minnesota Shuai Wang @ ICNP’ 14

11. Our Solution – Key Idea 1. Decompose Network Coding into two steps: (i) Coding, and (ii) Transmit. 2. Use the link correlation model to quantify the potential cost of Coding and Transmit separately. 3. Provide unified Correlated Coding metrics. University of Minnesota Shuai Wang @ ICNP’ 14

12. The Solution Quantify the potential cost of Step 1 - “Coding”: Physical Meaning: The number of packets needs to be sent in the output queue after Network Coding. Wo/ NC: W/ NC: University of Minnesota Shuai Wang @ ICNP’ 14 12

13. The Solution Quantify the potential cost of Step 2 - “Transmit”: … details in the paper! Physical Meaning: is the expected transmissions to reliably broadcast one packet under link correlation. University of Minnesota Shuai Wang @ ICNP’ 14 13

14. The Solution The unified Correlated Coding Metric: No. of Coded Pkts Per Pkt Transmit Cost Physical Meaning: the per-receiver transmission cost to reliably broadcast one packet to K receivers University of Minnesota Shuai Wang @ ICNP’ 14 14

15. Applications – Metric Embedding Network Coding Protocol Link Independence Link Correlation Correlated Coding Metric 1/LQ Transmission Cost Estimation Packet Reception Information University of Minnesota Shuai Wang @ ICNP’ 14

16. Applications – An Example Switch/Hub AP AP Correlated Coding Metric University of Minnesota Shuai Wang @ ICNP’ 14

17. Supported Protocols • Integrated Protocols: • Unicast: 1). ZigBee 2). OLSR 3). ETX • Broadcast: 4). Spanning Tree 5). Forwarding Node Cluster 6). Partial Dominating Pruning • Multicast: 7). Flexible Multicast Service University of Minnesota Shuai Wang @ ICNP’ 14

18. Compared Protocols and Performance Metric • Compared Protocols: • Protocols W/O NC • Protocols W/ Coding Aware Design • Protocols W/ Correlated Coding Metric • Performance Metric: • Number of Transmissions • Number of Coding Operations University of Minnesota Shuai Wang @ ICNP’ 14

19. Testbed Environment 802.15.4: Open Office 802.15.4: Lab 802.15.4: Outdoor 802.11: University Building Shuai Wang @ ICNP’ 14 University of Minnesota 19

20. Evaluation 802.15.4 testbed 802.11testbed Compared with the protocol wo/ NC, w/ NC, w/ Coding aware design, the correlated coding design saves about 60%, 40%, and 25% of the transmissions. • Number of Transmissions University of Minnesota Shuai Wang @ ICNP’ 14

21. Evaluation Compared to coding aware protocols, the number of coding operations is reduced while the transmission efficiency is improved! • Number of Coding Operations University of Minnesota Shuai Wang @ ICNP’ 14

22. Conclusion We introduce link correlation to NC, and find that the previous link independence assumption overestimates the true diversity benefit. We propose a correlated coding metric to help network designers decide when to use network coding. The experiments results on one 802.11 testbed, and three 802.15.4 testbeds show that with our design, coding operations are reduced while the transmission efficiency is improved by 30% ~50%. University of Minnesota Shuai Wang @ ICNP’ 14

23. Thank you! Q&A University of Minnesota Shuai Wang @ ICNP’ 14