CorLayer: A Transparent Link Correlation Layer for Energy Efficient Broadcast

1. CorLayer: A Transparent Link Correlation Layer for Energy Efficient Broadcast Shuai Wang, Song Min Kim, Yunhuai Liu, Guang Tan, and Tian He University of Minnesota MobiCom 2013 1st Oct 2013

2. The Need for Broadcast Operation Wireless communication essentially occurs in a broadcast medium. Global Time Sync Code Dissemination Routing Discovery Data Collection University of Minnesota Shuai Wang @ MobiCom’ 13

3. The Need for Broadcast Operation Multi-path Routing Advanced designs exploit the benefit from broadcast nature. Opportunistic Forwarding Network Coding University of Minnesota Shuai Wang @ MobiCom’ 13

4. Motivation Despite the fact that wireless communication essentially occurs in a broadcast medium with concurrent receptions Existing research predominately examine separate statistics for individual links (channel) or path: ETX, PPR, LQI, RSSI Little research has been done to investigate the joint statistics involving concurrent wireless links (e.g. broadcast) Because of the legacy assumption of link independence University of Minnesota Shuai Wang @ MobiCom’ 13

5. Legacy Assumption N1 S N2 i.e., Packet loss at N2 is independent of packet loss at N1. It is assumed that wireless reception among concurrent links are independent due to multipath induced fading. University of Minnesota Shuai Wang @ MobiCom’ 13

6. Unfortunately…. Legacy assumption no longer holds well because packet loss due to the coexistence of wireless networks University of Minnesota Shuai Wang @ MobiCom’ 13

7. The co-existence of ZigBee and Wi-Fi University of Minnesota Shuai Wang @ MobiCom’ 13

8. The co-existence of ZigBee and Wi-Fi Wireless spectrum becomes crowded: 802.11b, 802.11g, and 802.15.4 all use the 2.4 GHz ISM band. 25dB difference 11 19 Interference becomes the major cause of pack loss instead of fading University of Minnesota University of Minnesota Shuai Wang @ MobiCom’ 13

9. Explosive Growth of Wi-Fi 1100% Wi-Fi Hotspots in U.S. University of Minnesota University of Minnesota Shuai Wang @ MobiCom’ 13

10. Increasing Cross-Network Interference Interference leads to correlated packet loss: Two receivers' PRR The concurrent noise increase University of Minnesota University of Minnesota Shuai Wang @ MobiCom’ 13

11. Furthermore, Correlated Shadow Fading Closely located devices may suffer correlated lose since wireless signals suffer shadow fading when obstacles appear in the propagation path of the radio waves. University of Minnesota Shuai Wang @ MobiCom’ 13

12. Furthermore, Correlated Shadow Fading Appearance of Obstacles Closely Located Two receivers' PRR The concurrent RSSI reduction University of Minnesota University of Minnesota Shuai Wang @ MobiCom’ 13

13. Wireless links are correlated! 1 Source node 9 Receivers 100 Packets Synthetic Independent Trace Empirical Trace University of Minnesota University of Minnesota Shuai Wang @ MobiCom’ 13

14. How Link Correlation Affects Broadcast？ (a) Negative Correlated: Link quality: 0.8 # of packets need to be retransmitted: 4 (b) Positive Correlated: Link quality: 0.7 # of packets need to be retransmitted: 3 In order to accurately estimate the broadcast performance, we MUST consider link correlation. University of Minnesota Shuai Wang @ MobiCom’ 13

15. Theoretical Analysis Transmissions due to Link Quality Reduced transmissions by Link Correlation Ki(u) is a subset of N(u) with size i, where N(u) is node u’s one-hop neighbor set. : the probability that all nodes in K(u) successfully receive a packet. . The expected number of transmissions : University of Minnesota Shuai Wang @ MobiCom’ 13

16. The Property of Property 1: Special Case – when links are independent: Property 2: The higher the link correlation - The fewer the transmissions - University of Minnesota Shuai Wang @ MobiCom’ 13 16

17. Link Blacklisting for Better Correlation Empirical Study: Blacklisting leads to a significant reduction in transmission! 2.4 4.5 The average number of transmissions before blacklisting is mainly concentrated around 4.5 and it's 2.4 after blacklisting. University of Minnesota Shuai Wang @ MobiCom’ 13

18. CorLayer:Goals Broadcast Protocols Updated Logical Topology CorLayer Original Physical Topology Neighbor Discovery • Goals: Design a supporting layer by blacklisting low correlated links to help upper layer protocols save transmissions. University of Minnesota Shuai Wang @ MobiCom’ 13

19. CorLayer:Challenges • How to guarantee the network connectivity when blacklisting is executed? • A localized light-weight algorithm for connectivity check. • How to blacklist links thus the updated topology can benefit the upper layer broadcast protocols? • Assess the cost of covering one-hop neighbors, taking link correlation into consideration. University of Minnesota Shuai Wang @ MobiCom’ 13

20. CorLayer:Design – Connectivity Check Key Idea – link blacklisting requires the existence of an alternative path. W U V Asynchronously Blacklisting – two-phase locking is used to avoid a race condition. University of Minnesota Shuai Wang @ MobiCom’ 13

21. CorLayer:Design – Link Blacklisting Key Idea - Triangular Blacklisting Rule: blacklisting a link if the source node could take fewer transmissions via an alternative path. y W z U V x University of Minnesota Shuai Wang @ MobiCom’ 13

22. CorLayer:Design – Link Blacklisting Key Idea - Triangular Blacklisting Rule: blacklisting a link if the source node could take fewer transmissions via an alternative path. Cost for 1st Hop Cost for 2nd Hop W W W Direct Broadcast U V U V U V x x University of Minnesota Shuai Wang @ MobiCom’ 13

23. Evaluation Testbed Settings Shuai Wang @ MobiCom’ 13 University of Minnesota 23

24. Supported Protocols (1/2) • Integrated Protocols: • Tree based: 1). S-Tree: A. Juttneret al. Mobile Networks and Application’05 2). C-Tree: K. Alzoubiet al. HICSS’02 • Cluster based: 3). Cluster: J. Wu et al. Wireless Communication and Mobile Computing’03 4). Intermediate: J. Wu et al. Telecommunication Systems’01 5). Clustering: I. Stojmenovicet al. TPDS’02 6). P-Clustering: T. J. Kwon et al. SIGCOMM’02 • Multiple point relay: 7). MPR: A. Qayyumet al. HICSS’02 8 – 9). Min-id MPR, MPRCDS: C. Adjihet al.INRIA-Rapport’02 University of Minnesota Shuai Wang @ MobiCom’ 13

25. Supported Protocols (2/2) Extensive evaluation with 16 protocols run on 3 testbeds! • Integrated Protocols: • Pruning based: 10-11). SP, DP: H. Lim et al. Computer Communications Journal’01 12-13). PDP, TDP: W. Lou et al. TMC’02 14). RNG: J. Cartignyet al. IJFCS’03 • Location based: 15). CCH: M. T. Sun et al. CS-NMC’05 • Network Coding: 16). COPE: S. Kattiet al. SIGCOMM’06 16). CODEB: E. L. Li et al. INFOCOM’07 • Evaluation Metrics: • The total number of transmissions needed to deliver one packet to all the nodes in the network. University of Minnesota Shuai Wang @ MobiCom’ 13

26. Evaluation On average, CorLayer reduces transmissions by 47%! 49% 52% 48% 36% 38% 39% • Main Performance Results University of Minnesota Shuai Wang @ MobiCom’ 13

27. Evaluation R_: CorLayer Saves “R_”50%Transmissions! WL_: CorLayer Saves “WL_” 20% Transmissions! MPR Cluster Pruning Network Coding • Impact of blacklisting rules • R_: Random Blacklisting; • WL_: Worst Link Blacklisting; • CorLayer_: Our Design; University of Minnesota Shuai Wang @ MobiCom’ 13

28. Conclusion • We have presented CorLayer, a link correlation-based layer that enhances the energy efficiency of reliable broadcasting. • We integrated CorLayer transparently with sixteen state-of-the-art broadcast algorithms and evaluated the design on three real-world multi-hop testbeds. • The results indicate that with CorLayer, reliable broadcast avoids unnecessary transmissions caused by wireless links that are less positively correlated. University of Minnesota Shuai Wang @ MobiCom’ 13

29. Thank you! Q&A University of Minnesota Shuai Wang @ MobiCom’ 13