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Channel Assignment Strategies for Multiradio Wireless Mesh Networks

Channel Assignment Strategies for Multiradio Wireless Mesh Networks. Issues and Solutions. Outline. Introduction Channel Assignment (CA) and Taxonomy MesTic Performance Review. Introduction. Wireless Mesh Networks (WMN) Highly flexible High bandwidth backhaul connectivity

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Channel Assignment Strategies for Multiradio Wireless Mesh Networks

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  1. Channel Assignment Strategies forMultiradio Wireless Mesh Networks Issues and Solutions

  2. Outline • Introduction • Channel Assignment (CA) and Taxonomy • MesTic • Performance Review

  3. Introduction • Wireless Mesh Networks (WMN) • Highly flexible • High bandwidth backhaul connectivity • Extending WiFi coverage • Typically configured to operate on single channel, single radio • Lower capacity due to the interference from adjacent nodes How to Solve this issue ?

  4. Introduction (cnt’d) • Proposed Solutions: • Modified MAC • Directional Antennas • Channel switching on single radio • Requires tight time sync. • Multiple Radio • Assign non-overlapping channels to different Radios • Cheap, off-the-shelf equipment • Provide different spatio-temoporal diversity of radios Infeasible Efficient channel Assignment problem rises !

  5. Outline • Introduction • Channel Assignment (CA) and Taxonomy • MesTic • Performance Review

  6. Channel Assignment (CA) • Efficient Channel Assignment is a key issue • Guarantees network connectivity • Mitigates the adverse effects of interference There is always a Trade-off Between Maximizing Connectivity and Minimizing the Interference

  7. Review the CA Taxonomy • Divided in three main categories: • Depending on the frequency with which the CA scheme is modified. • Fixed: CA is almost constant • Hybrid: Fixed on some interfaces and dynamic on the others • Dynamic: channels are continuously updated.

  8. Fixed CA • Common Channel Assignment (CCA) [Kyasanur05]: • The radio interfaces of each node are all assigned the same set of channels. • Gain and Loss ? • Varying Channel Assignment (VCA): • Interfaces of different nodes may be assigned different sets of channels. • Network Partition and topology changes.

  9. VCA Centralized Channel Assignment. Topology Control Approach Connected Low Interference Channel Assignment (CLICA) [Marina09]: Calculates priority for CA based on topology using: Connectivity Graph Conflict Graph Override in case of inflexibility Traffic independent approach • Traffic mainly directed toward gateway [Raniwala04] • First, estimate the total expected load on each link (from flow) • Second, CA algorithm visits each link (in decreasing order of load) and assigns a channel • Since it does not visit each node once, it may cause ripple effect.

  10. Dynamic Channel Assignment (DCA) • Allow any interface to be assigned to any channel • Requires Coordination • A pre-determined rendezvous channel • Slotted Seeded Channel Hopping (SSCH) [Bahl06] • Each node changes channel synchronously in a pseudo-random sequence • Pitfall: Channel Switching Delay

  11. Hybrid Channel Assignment • Fixed channel for some interfaces • Generally can be used for control and data • Common • Varying • Are attractive because of simple coordination • Link Layer protocol for Interface Assignment (LLP) [Kyasanur05] • Fixed for long intervals • Switchable interfaces for short intervals • Interference-Aware Channel Assignment (IACA) [Raniwala04] • One radio on each node to operate on a default common channel • Ensures common network connectivity • Provides alternate fallback routes • Avoids flow disruption

  12. Outline • Introduction • Channel Assignment (CA) and Taxonomy • MesTic • Performance Review

  13. MesTIC • Mesh based Traffic and Interference Aware Channel Assignment [Skali07] • Author’s new channel assignment • Improves aggregate throughput of the network, • Takes into account, traffic and interference • Fixed , rank-based centralized algorithm • Fixed, so no switching delay. • Visits every node once • no ripple effect • Rank is based on link traffic, topology and number of interfaces • Topological connectivity using common default channel on a separate radio • Prevent flow disruption

  14. Proposed Algorithm • Calculate Rank(node) • Determines priority in CA phase • Depends on aggregate traffic at the node • Distance of the node from gateway • Number of radio Interfaces Rationale ?

  15. Outline • Introduction • Channel Assignment (CA) and Taxonomy • MesTic • Performance Review

  16. Working Principle • After Calculating Rank • Algorithm traverses the mesh network in decreasing order of Rank • Assigns channels to radios • b is the gateway node • Three channels and two interfaces

  17. Performance Study • Developed using NS-2 • 5x5 grid topology • Each node potentially could communicate with 4 neighbors • Randomly generated traffic profile between [0-3] Mbps. • CBR UDP • Three radios for 12 nonoverlapping channels • Ran for 100s on DSR

  18. Summary • MesTiC is a fixe centralized algorithm • Takes into account, traffic load and channel interfereance • Does not have ripple effect (difference with C-HYA) • Ensures connectivity by default radio

  19. Algorithm Review • This algorithm in general provides a good load balancing, however it is not scalable for dynamic traffic changes • This algorithm needs to have a priori traffic matrix • The algorithm is not scalable as new nodes may be introduced to the network

  20. Questions?

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