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

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

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

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

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

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

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

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

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

Put Together: How LC Impacts NC? 10 University of Minnesota Shuai ICNP’ 14 Network Coding Step1: Coding Step1: CodingStep2:Transmit e.g., Opportunistic listening, encoding Send out with one coded pkt Low Link Correlation High Link Correlation Conclusion: there exists a tradeoff between the coding opportunity and transmit efficiency.

Our Solution – Key Idea 11 University of Minnesota Shuai ICNP’ 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.

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

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

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

15 Applications – Metric Embedding Network Coding Protocol Packet Reception Information LinkIndependence Transmission Cost Estimation 1/LQ LinkCorrelation Correlated Coding Metric University of Minnesota Shuai ICNP’ 14

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

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

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

Testbed Environment 19 University of Minnesota Shuai ICNP’ : Lab : Open Office : Outdoor : University Building

Evaluation Number of Transmissions 20 University of Minnesota Shuai ICNP’ 14 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 testbed testbed

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

Conclusion 1.We introduce link correlation to NC, and find that the previous link independence assumption overestimates the true diversity benefit. 2.We propose a correlated coding metric to help network designers decide when to use network coding. 3.The experiments results on one testbed, and three testbeds show that with our design, coding operations are reduced while the transmission efficiency is improved by 30% ~50%. 22 University of Minnesota Shuai ICNP’ 14

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