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Distributed Channel Assignment in Multi-Radio 802.11 Mesh Networks

Distributed Channel Assignment in Multi-Radio 802.11 Mesh Networks Bong Jun Ko (IBM T.J. Watson Research) Vishal Misra (Columbia University) Jitendra Padhye (Microsoft Research) Dan Rubenstein (Columbia University). Wireless Mesh Networks.

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Distributed Channel Assignment in Multi-Radio 802.11 Mesh Networks

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  1. Distributed Channel Assignment in Multi-Radio 802.11 Mesh Networks Bong Jun Ko (IBM T.J. Watson Research) Vishal Misra (Columbia University) Jitendra Padhye (Microsoft Research) Dan Rubenstein (Columbia University)

  2. Wireless Mesh Networks • WMN: Multi-hop wireless network infrastructure for local/residential area networks. • Goal: better channel utilization  higher network capacity. • For scalability and adaptability, light-weight distributed solution is desirable.

  3. x Our Philosophy • Why focus on channel assignment? • Decouple channel assignment and end-to-end routing. • Routing protocols adapt to dynamic traffic load, link quality, and even channel configuration(e.g., MR-LQSR1) . • Channel assignment focuses on quickly-stabilizing channel configuration based on physical topology. • More scalable than centralized, joint-optimization approaches. • There are K channels, and assume (for now) every node can transmit and receive from all channels simultaneously. • Approach: For each node, minimize the number of other interfering nodes on the same channel. x Node x’s interference range 1. R. Draves et al., “Routing in Multi-Radio, Multi-Hop Wireless Mesh Networks”, Mobicom 2004.

  4. DistributedGreedy Channel Selection • Let each node select its own channel. • Whenever it is needed, each node changes to a channel that minimizes the number of other nodes on the same channel in the interference range. Q : Will this process converge? x x y y

  5. > (+1) (-1) DistributedGreedy Channel Selection • Let each node select its own channel. • Whenever it is needed, each node changes to a channel that minimizes the number of nodes on the same channel in the interference range. Q : Will this process converge? YES! • Proof : • N(x): # of nodes on the same channel for node x. • xN(x) decreases monotonically. x x y Local optimization improves global optimization metric – Self-stabilizing!

  6. Experience with 802.11 Mesh Networks • Practical limitations • Current 802.11 transceivers can send or receive through only one channel at a time. • Neighboring nodes need to be at the same channel. • Conflicting goals: connectivity vs better utilization. • Multi-radio stations • 1 common, default channel for all nodes • Variable channels selected by channel assignment algorithm • Links of variable channels: express way • Links of common channel: local roads

  7. Performance Evaluation • Experiments on a 14-node testbed. • A default channel from 802.11a • Variable channels from 802.11g • Interference range : 3 hops • Routing protocol : MR-LQSR (Multi-Radio Link Quality Source Routing) • Aware of multi-radio, multi-channel environment • Preference given to channel-diverse paths • Measure end-to-end throughput of multiple, concurrent TCP flows with random source-destination pairs • Compare to • samech : all nodes are assigned the same channel for additional radio • rand : each node is assigned a channel uniformly at random for additional radio

  8. Testbed

  9. Individual TCP Throughput • CDF of all TCP flow throughputs in all experiments. • Flows over longer paths benefit the most.

  10. Aggregate TCP Throughput • Measured average TCP throughput of all flows in each experiment, and took median value of 5 experiments. • 50% higher than samech / 20% higher than random.

  11. Conclusion • Developed a fully-distributed, self-stabilizing channel assignment algorithm for multi-hop wireless networks. • Experiments on multi-radio 802.11 mesh network testbed. • Our mechanism shows improvements in network throughput by 50% and 20% compared to homogeneous and random assignments, respectively. • Open Problems • Theoretical running time and bounds of the distributed greedy algorithm? • Formal time-scale decomposition in radio resource control (e.g., channel, power, rate, route control).

  12. Thank You

  13. Backup slides

  14. Other Results Channel Utilization (in %) of 802.11g channels Protocol Dynamics

  15. Dealing with Delay and Asynchrony • Solution : a 3-way handshake protocol for distributed mutual exclusive operation. • REQUEST → ACCEPT or REJECT → UPDATE or ABORT

  16. 3-way Handshake Protocol x

  17. 3-way Handshake Protocol x REQUEST REQUEST specifies: • Intended channel change • Perceived channels of other nodes

  18. 3-way Handshake Protocol x ACCEPT

  19. 3-way Handshake Protocol x UPDATE When a node ACCEPTed a REQUEST, it “freezes” its channel until corresponding response (UPDATE or ABORT) is received.

  20. 3-way Handshake Protocol y y x

  21. 3-way Handshake Protocol y x REQUEST

  22. 3-way Handshake Protocol y x REJECT

  23. 3-way Handshake Protocol y x ABORT

  24. 3-way Handshake Protocol REQUEST y x REQUEST

  25. 3-way Handshake Protocol REJECT y x ACCEPT Break ties by predefined order of nodes - if x < y, y will be accepted to change.

  26. 3-way Handshake Protocol UPDATE y x ABORT

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