1. Low Latency Broadcast in Multirate Wireless Mesh Networks Chun Tung Chou, Archan Misra, Junaid Qadir Keon Jang 2007. 10. 18

2. Outline Introduction Impact of Multirate Links on Efficient Broadcasting Problem Formulation Heuristic Algorithm Simulation and Performance Study Conclusion

3. Introduction Wireless mesh network (WMN) is considered to be promising technology for suburban and urban community-based networks Two aspects of WMN research is popular ▫Use of multichannel, multi-radio mesh nodes ▫Multi-rate Mac protocols 3 12 400m 1Mbps 100m 11Mbps

4. Introduction(cont’d) How low-latency (and possibly high-throughput) network-layer broadcast can be realized? WMN broadcast applications ▫Broadcast community specific content  Neighborhood soccer game or etc. ▫Wide-are content to a group of receivers

5. Introduction(cont’d) Effect of multi-rate links on efficient broadcasting ▫Is multi-rate multicast necessary? ▫How effective it is? Choice of transmission rates in multi-rate networks ▫How many different transmission rate is needed? ▫Are some rates more efficient than others?

6. Impact of Multi-rate Link on Efficient Broadcasting Broadcast from node 1 to all the other nodes 51234 400m 1Mbps 400m 1Mbps 400m 1Mbps 100m 11Mbps

7. Case 1: 1 Transmit / 1 Node 51234 400m 1Mbps 400m 1Mbps 400m 1Mbps 100m 11Mbps 1 -> (2,5)2 -> 33 -> 4 0112233 Time

8. Case 2: Allow multiple transmit 51234 400m 1Mbps 400m 1Mbps 400m 1Mbps 100m 11Mbps 1 -> 2 2 -> 3 3 -> 4 1 -> 5 012231 Time

9. Problem Formulation Build an algorithm to minimize broadcasting latency in wireless mesh networks Assumptions ▫MAC-layer multi-rate multicast capability ▫Each node has single radio ▫Radio on all nodes are tuned to common channel ▫etc This problem is NP Hard!

10. Heuristic Algorithm 3 Stages ▫Broadcasting Tree Construction ▫Multicast Grouping ▫Scheduling Transmissions s 1 2 2 2

11. Weighted Connected Dominating-set Construction (WCDS) V = nodes N(x,y)= reachable nodes from x with rate y C = covered nodes T = tree R = transmission rates WCDS is modification of MCDS

12. Multicast Grouping Algorithm a->b, 1 a->c, 8 a c b 8 1...... 20 30...... 31 Time 1 +Max(8+20,30) ----------------- 31

13. Multicast Grouping Algorithm(cont’d) a->(b,c) 8 a c b 8 8...... 20 30...... 38 Time 8 +Max(20,30) ----------------- 38

14. Multicast Grouping Algorithm(cont’d) a->b, 1 a->c, 8 a c b 8 1...... 20 30...... 31 Time 1 +Max(8+20,30) ----------------- 31

15. Scheduling of Transmissions From WCDS and Grouping, all the multicasts transmissions(sender, recipient group) are known Scheduling determines a time that each multicast happens based on dependency and interference ▫Dependency: a node can relay only after it receives

16. Simulated Performance Studies 4 Different Tree Construction Algorithm ▫WCDS ▫BIB(author’s previous work) ▫SPT (shortest path using Dijkstra) ▫CDS (lowest transmission rate only) 100 randomly generated topologies

17. Normalized Latency Single Transmission Case

18. Normalized Throughput Single Transmission Case

19. Multiple Transmission Case Only 2 out of 100 topologies required multiple transmission Multiple may not be required in single radio and single channel case However, multi-radio and multi-channel is more likely to benefit from multiple transmission

20. Conclusion Proposed the novel concept of multi-rate link- layer multicast for network-layer broadcast Showed that exploiting multi-rate can reduce latency and increase throughput