Channel Assignment Strategies for Multiradio Wireless Mesh Networks

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?