1. A Low Interference Channel Assignment Algorithm for Wireless Mesh Networks Can Que 1,2, Xinming Zhang 1, and Shifang Dai 1 1.Department of Computer Science and Technology University of Science and Technology of China 2. Department of Computer Science City University of Hong Kong IEEE Wireless Communications, Networking and Mobile Computing, 2008. 1

2. Outline Introduction Protocol Simulation Conclusion 2

3. Introduction Motivation To avoid the hidden terminal problem within two hops. To make full use of the multiple NICs and channels in the wireless mesh networks. 3

4. Introduction Assumption Multiple non-overlapping channel Multiple network interface cards (NIC) The centralized algorithm have enough information about the topology and the traffic load of each link. 4

5. 5 How effective is the IEEE 802.11 RTS/CTS Handshake in Ad Hoc Network?? SenderReceiver

6. Combinable flows 6 Protocol Common node The RTS/CTS mechanism can always work well to avoid interference within the combinable structures.

7. Combinable flows 7 Protocol Common node If they are in the same channel, the result is always one flow can work.

8. G(V,E) V contains the nodes that have packets to send I(V,E) Two nodes are within the interference range of each other 8 Protocol

9. to find maximal independent combinable structures 9 Protocol Not interfered with each otherlargest Load / Interference- degree value

10. The NP-hardness of this problem can be proved by reducing this problem to the max independent set problem. Authors use a greedy approximation algorithm to solve this problem. 10 Protocol

11. If (the traffic load is small) Algorithm I If(the traffic load is large) Algorithm II 11 Protocol

12. Algorithm I A.Calculate the Load / Interference-degree value of each combinable structure. B. Choose the structures with the largest Load / Interference-degree value, and assign these interfaces to an unused channel. C. there remains structures not interfered by the chosen structures, then go to step B. 12 Protocol

13. Algorithm I D. If there are no more interfaces or channels available for unassigned flows, we go to the algorithm designed for the large traffic load. E. If there are still some flows unscheduled, remove the nodes have no flows, go to step A. 13 Protocol

14. Algorithm II To divide these flows into several groups. Each group has almost the same total flow load To divide time into some fixed intervals (slot) To choose flows one by one from each group at the time when we begin to make schedules for a slot To solve the starvation problem 14 Protocol

15. Group All the flows in the same group are interfered by one another, in other words, only one flow in the same group can be activated when there is only one channel available. The size of each group should be almost the same as each other. 15 Protocol

16. Group Decide how large should the group be might be a tricky issue. We use the load of the node with the maximum throughput as the size of the group. 16 Protocol

17. 17 Protocol F1 F2 F3 F5 F4 F6

18. 18 Protocol We use the load of the node with the maximum throughput as the size of the group.

19. There are 2 interfaces and 2 channels available for each node. 19 Protocol

20. 20 Protocol we choose one flow from each group, say,F1, F4, F6. The max independent set of these three flows is {F1, F6}.

21. 21 Protocol we choose one flow from each group, say,F1, F4, F6. The max independent set of these three flows is {F1, F6}.

22. 22 Protocol If one flow hasn’t been scheduled for k (k > 0) times, then the priority of this link is P K = -2 K. F4 is set to -2 K=1

23. 23 Protocol Since there are still flows and channels available, we can assign more flows in slot 1 by assigning them to channel B.

24. 24 Protocol This time {F2, F4, F6} is chosen from each group. The priority value -2 is added on F4.

25. 25 Protocol This time {F2, F4, F6} is chosen from each group. We can add F3 to F4, since they are not interfered with each other.

26. 26 Protocol This time {F2, F4, F6} is chosen from each group. The priority value of F2 and F6 are set to -2.

27. 27 Protocol The assignment step of slot 1 ends.

28. 28 Protocol Set {F2, F5, F6} is chosen as the candidate flows of slot 2,channel A. F2 and F6 are chosen this time. The priority value of F5 is set to -2.

29. 29 Protocol F5 is assigned to channel B. All the flows are scheduled, and the algorithm is ended.

30. 30 Simulation

31. 31 Simulation Number of channels for each node is set to three

32. 32 Simulation Number of NICs per node is set to four

33. 33 Conclusion The capacity issue is one of the most important problems in the wireless mesh networks. In this paper, we propose two centralized algorithms to make full use of the multiple NICs and channels in the wireless mesh networks.