A Bandwidth Scheduling Algorithm Based on Minimum Interference Traffic in Mesh Mode

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 BS SSs New SS broadcast MSH-NENT MSH-NENT MSH-NCFG MSH-NCFG connect one as its response node MSH-NENT Finish the process

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.) BS SSs MSH-CSCF (broadcast) Forward to SSs Maintain a routing tree MSH-CSCH (Request message) Determine the amount of granted resources for each link MSH-CSCH (Grant message)

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. Bui(j) : the bandwidth which node i was assigned in frame j of uplinks. Bdi(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. Cj: 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. 3 7 4 6 0 1 2 5 Proposed Scheduling Algorithm-Construction of Routing tree • Interference model Link Range UL4,7 DL4,7 UL0,4 DL0,3 UL0,3 DL0,4 BS UL0,1 DL0,2 DL0,1 UL0,2 UL1,5 UL1,5 DL1,5 DL1,5 Figure 2. Interference model of routing tree

15. 0 i j k Proposed Scheduling Algorithm-Construction of Routing tree • When node i communicates with node j, it can calculate the total interference traffic ISi, j : {UIx,y} :the collection of links that ULx,y interferes {DIx,y} :the collection of links that DLx,y interferes PSk : the total interference traffic which the path impacts

16. 3 7 4 6 0 1 2 5 Proposed Scheduling Algorithm-Construction of Routing tree • example PS8=IS2,8+PS2 8 PS8=IS5,8+PS5 new

17. Proposed Scheduling Algorithm-Construction of Routing tree -reconstruct • Network flow changes with time, therefore PSkof 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 -reconstruct • Process 1 0 BS r optimal response node j select PSj leaf node i PSi PSi’= ISj,i + PSj (excludes the traffic that SSi generated)  k : the time that every link in Pi

19. Proposed Scheduling Algorithm-Construction of Routing tree -reconstruct • Process 2 • If the difference between PSiand PS’iis 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.