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Joint Scheduling and Channel Allocation in Wireless Mesh Networks

Joint Scheduling and Channel Allocation in Wireless Mesh Networks

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Joint Scheduling and Channel Allocation in Wireless Mesh Networks

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  1. Joint Scheduling and Channel Allocation in Wireless Mesh Networks Nguyen H. Tran and Choong Seon Hong Consumer Communications and Networking Conference (CCNC), 2008.

  2. Outline • Introduction • System model • Fair scheduling and Channel allocation algorithm • Performance evaluation • Conclusion

  3. Introduction • Wireless Mesh Networks (WMSs) • Routing • Scheduling • Channel allocation • Interference • Multiple radios, simultaneously • Limited number of channels available • Signal noise interference rate (SNR)

  4. System model • Network model • Network graphG(V, E) • V: the set of nodes (mesh routers) • E: the set of links • Qe(t): number of packets waiting to be transmitted on link e by the end of time slot; as queue length of e • K orthogonal channels (each node has one or more than one wireless interface cards)

  5. Interference model - physical interference model • packets along link (i, j) are correctly received when • RSSij: signal strength of node j when node i transmits to node j • ISSij: interfered signal strength from another node k also transmitting • N: white noise • Vs: the subset of nodes in V that are transmitting concurrently threshold

  6. Interference model - interference graph

  7. Conditions channel 1 channel 1 A B C • G’T = {e1, …, ek} E: certain edge set of transmissions on the same channel • A necessary condition: two links incident on the same node can not be activated simultaneously on the same channel • A sufficient condition: SNIR is above the desired threshold α • COROLLARY 1. • G’T in G(V, E) is feasible if every vertex of the corresponding interference graph G’(V’, E’) satisfies:

  8. Example of correspondinginterference graph 0.2 0.3 0.4

  9. Fair scheduling algorithm

  10. Channel allocation algorithm

  11. Example of fair scheduling and channel allocation capacity rank gateway channel 1 2 1 1-hop level channel 2 a b 2 3 channel 3 3 1 2-hop level channel 4 c f d e 1 2 4 3 4 g i j k 3 2 h 2 3 l m p 1 n o

  12. Example of fair scheduling and channel allocation transform interference queue length rank gateway e (n, o) = 0.3 e (n, o) 2 1 e (f, j) = 0.2 e (f, j) a b e (b, e) = 0.4 2 3 e (b, e) 3 1 e (gw, a) = 0.3 e (gw, a) c f d e 1 2 4 3 4 g i j k 3 2 h 2 3 l m p 1 n o

  13. Performance evaluation • Comparing with 802.11 CSMA/CA access scheme • Implemented in ns-2 • Transmission range of each node is 150m • Carrier sense range of 300m • Simulations are in the 800x800m2 area which 50 nodes are placed randomly

  14. Throughput Improvement Evaluation

  15. Fairness Evaluation

  16. Conclusion • Proposed fair scheduling and channel allocation algorithms to solve the interference problem • Improved system throughput and guarantees the fairness for all nodes

  17. Thank you