1. A Bandwidth Scheduling Algorithm Based on Minimum Interference Traffic in Mesh Mode Xu-Yajing, Li-ZhiTao, Zhong-XiuFang and Xu-HuiMin International Conference on Wireless Communications, Networking and Mobile Computing, 2007. WiCom 2007. Mei-jhen Chen

2. Outline  Introduction  Overview of WiMax Mesh  Proposed Scheduling Algorithm  Simulations  Conclusion

3. Introduction   IEEE 802.16 defines two different air-interfaces: Point-to-Multi-Point (PMP) and Mesh.

4. Introduction (cont.)   Related work: (consider points) To built collision Matrix of nodes Finding a path with least links finding a path with minimal blocking nodes   These papers have not discussed the traffic of interference links which will influence on transmission efficiency in Mesh mode.   In this paper a bandwidth scheduling algorithm is proposed based on minimum interference traffic.

5. Overview of WiMax Mesh   new node joins mesh network BSSSs MSH-NENT MSH-NCFG New SS MSH-NCFG broadcast connect one as its response node MSH-NENT Finish the process MSH-NENT

6. Overview of WiMax Mesh (cont.)   Centralized scheduling BS maintains the routing tree of entire network, and controls all the channel access. If one SS wants to transmit, it has to wait the grant of BS.   Distributed scheduling SSs can communicate directly on scheduling strategies without BS’s grant.

7. Overview of WiMax Mesh (cont.)   There are two control messages in centralized scheduling: Mesh Centralized Scheduling Configuration Message (MSH-CSCF) contains the channel configuration and routing tree Mesh Centralized Scheduling Message (MSH-CSCH) contains bandwidth request and grant, and updates routing tree.

8. Overview of WiMax Mesh (cont.) BSSSs MSH-CSCF (broadcast) MSH-CSCH (Request message) MSH-CSCH (Grant message) Maintain a routing tree Forward to SSs Determine the amount of granted resources for each link

9. Proposed Scheduling Algorithm   A bandwidth scheduling algorithm based on minimum interference traffic to maximize the network throughput   Authors analyze the algorithm as following steps. Calculate every uplink and downlink traffic. Find the collection of links and then compute the total traffic of this collection. Select a path from SS to BS, and compute the whole traffic which the path impacts. Make a collision-free scheduling according to routing tree and link interference collections.

10. Proposed Scheduling Algorithm -Calculation of the links’ traffic   Wireless links in Mesh are divided into uplinks and downlinks. : the average bandwidth in every frame of uplinks which BS allocates for node i. : the average bandwidth in every frame of downlinks which BS allocates for node i. f : the index of current frame. B ui (j) : the bandwidth which node i was assigned in frame j of uplinks. B di (j) : the bandwidth which node i was assigned in frame j of downlinks. N : the number of frames.

11. Proposed Scheduling Algorithm -Calculation of the links’ traffic   The total bandwidth used by a particular node per frame is recorded in a local database.   For each frame passing, the BS updates the database by removing the least recent entry and adding the latest bandwidth usage.   BS can compute the usage of bandwidth for all the nodes.

12. Proposed Scheduling Algorithm -Calculation of the links’ traffic :the average uplink flow of every wireless link. :the average downlink flow of every wireless link. C j : the child nodes of node j. node i is the response node of node j.

13. Proposed Scheduling Algorithm -Construction of Routing tree   This algorithm is looking for a path from current node to BS, if the whole traffic which is interfered by the path is lowest, it is the optimal path.   In a single-channel TDD network, any unicast transmission follows the principle. No node may simultaneously transmit and receive data No neighbor of a sending node may receive data except receiver No neighbor of a receiving node may transmit data except sender

14. 0 1 5 6 4 2 3 7 Proposed Scheduling Algorithm -Construction of Routing tree  Interference model BS Link Range DL 4,7 UL 0,4 DL 0,4 UL 0,1 DL 0,1 UL 0,2 DL 0,2 DL 0,3 DL 1,5 UL 1,5 DL 1,5 UL 1,5 UL 0,3 UL 4,7 Figure 2. Interference model of routing tree

15. Proposed Scheduling Algorithm -Construction of Routing tree   When node i communicates with node j, it can calculate the total interference traffic IS i, j : {UI x,y } :the collection of links that UL x,y interferes {DI x,y } :the collection of links that DL x,y interferes PS k : the total interference traffic which the path impacts 0 i j k

16. Proposed Scheduling Algorithm -Construction of Routing tree  example 8 0 1 5 6 4 2 3 7 new PS 8 =IS 2,8 +PS 2 PS 8 =IS 5,8 +PS 5

17. Proposed Scheduling Algorithm -Construction of Routing tree - Proposed Scheduling Algorithm -Construction of Routing tree -reconstruct   Network flow changes with time, therefore PS k of any node k changes continuously.   To reconstruct the routing tree as the following principles: Only adjust the leaf node after finishing the communications Adjust leaf node as discerning interference traffic.

18. Proposed Scheduling Algorithm -Construction of Routing tree - Proposed Scheduling Algorithm -Construction of Routing tree -reconstruct  Process 1 i j PS i optimal response node  PS i ’= IS j,i + PS j (excludes the traffic that SS i generated)  PS j r 0 BS select k : the time that every link in P i leaf node

19. Proposed Scheduling Algorithm -Construction of Routing tree - Proposed Scheduling Algorithm -Construction of Routing tree -reconstruct  Process 2 If the difference between PS i and PS’ i is little, then small flow fluctuation will cause adjustment repeatedly. Let confidence factor M ∈ (0,1) as the threshold. Update interference traffic table and response node of current node. otherwise, continue to compute next leaf node in the interference traffic table.

20. Proposed Scheduling Algorithm -Collision-free scheduling algorithm

21. Simulations -assumptions   Assume a single channel network with no bit errors.   SSs ranges from 20 to 120.   Random topology is generated in an L*L square. n : the number of SSs d : the maximal transmission range between two nodes

22. Simulations -results

23. Conclusion   This paper proposes a bandwidth scheduling mechanism in WiMAX Mesh network based on minimum interference traffic.   It can adjust network topology with the change of flow, reduce the interference among the links, and make traffic of entire Mesh network load balance.