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Low Latency Broadcast in Multirate Wireless Mesh Networks Chun Tung Chou, Archan Misra, Junaid Qadir Keon Jang 2007. 10. 18
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Outline Introduction Impact of Multirate Links on Efficient Broadcasting Problem Formulation Heuristic Algorithm Simulation and Performance Study Conclusion
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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
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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
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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?
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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
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Case 1: 1 Transmit / 1 Node 51234 400m 1Mbps 400m 1Mbps 400m 1Mbps 100m 11Mbps 1 -> (2,5)2 -> 33 -> 4 0112233 Time
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Case 2: Allow multiple transmit 51234 400m 1Mbps 400m 1Mbps 400m 1Mbps 100m 11Mbps 1 -> 2 2 -> 3 3 -> 4 1 -> 5 012231 Time
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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!
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Heuristic Algorithm 3 Stages ▫Broadcasting Tree Construction ▫Multicast Grouping ▫Scheduling Transmissions s 1 2 2 2
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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
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Multicast Grouping Algorithm a->b, 1 a->c, 8 a c b 8 1...... 20 30...... 31 Time 1 +Max(8+20,30) ----------------- 31
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Multicast Grouping Algorithm(cont’d) a->(b,c) 8 a c b 8 8...... 20 30...... 38 Time 8 +Max(20,30) ----------------- 38
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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
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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
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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
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Normalized Latency Single Transmission Case
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Normalized Throughput Single Transmission Case
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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
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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
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