The Nominal Capacity of Wireless Mesh Network

1. The Nominal Capacity of Wireless Mesh Network 694415027 劉柏廷 電機所 J. Jun, M.L. Sichitiu, IEEE Wireless Communications, October 2003

2. Outline • Introduction of Wireless Mesh Network • Problems formulation • Determining the nominal capacity • Simulation results • Discussion • Conclusion

3. Outline • Introduction of Wireless Mesh Network • Problems formulation • Determining the nominal capacity • Simulation results • Discussion • Conclusion

4. Introduction of WMN(1/4) • WMN is an alternative technology for last-mile broadband Internet access. • Provides good reliability, market coverage and scalability, as well as low upfront investments.

5. WMN topology

6. Introduction of WMN(2/4) • Independent of the underlying radio technology. • Dynamically self-organizing and self-configuring.

7. Introduction of WMN(3/4) • Similar to ad hoc networks, each user node operates notonly as a host but also as a router. • Main difference is traffic pattern: in WMN, practically all the traffic is either to or from a gateway; while in ad hoc network, the traffic flows between arbitrary pair of nodes.

8. Introduction of WMN(4/4) • Gateway in WMNs introduces “hot spot” in the network that act as bottlenecks. • Adding more gateways will not only increase the capacity of the network but also its reliability. • Bottleneck collision domain: The geographical area that limits the overall throughput of the network.

9. Outline • Introduction of Wireless Mesh Network • Problems formulation • Determining the nominal capacity • Simulation results • Discussion • Conclusion

10. Relayed traffic and fairness • Contention between self-traffic and relayed traffic.

11. Nominal MAC layer capacity • The MAC layer capacity “B” depends on parameters: • The radio technology. • The efficiency of the considered MAC layer. • The size and distribution of the packets sent through the gateway. • The error rate of the channel. • The number of nodes.

12. Link constraints and collision domains

13. Outline • Introduction of Wireless Mesh Network • Problems formulation • Determining the nominal capacity • Simulation results • Discussion • Conclusion

14. Determining the nominal capacity (1/3) • Assumption: (1) Only one gateway in the network. (2)Infinite amount of data to be sent. (3)Absolute fairness for all nodes sending data to the same gateway. (4) The traffic is unidirectional from the nodes to the gateway.

15. Determining the nominal capacity (2/3) • Chain topology: (1) The traffic forwarded by each link. (2) Construct the collision domains. ->Bottleneck collision domain (3) 4+5+6+7+8=30；

16. Determining the nominal capacity (3/3) • Arbitrary topology:

17. Outline • Introduction of Wireless Mesh Network • Problems formulation • Determining the nominal capacity • Simulation results • Discussion • Conclusion

18. Simulation results (1/2) • Using OPNET Modeler • CBR UDP flows • Data rate: 11Mbps • Packet size: 1500bytes • Aggregate throughput: 5.1Mbps

19. Simulation results (2/2)

20. Outline • Introduction of Wireless Mesh Network • Problems formulation • Determining the nominal capacity • Simulation results • Discussion • Conclusion

21. Discussion (1/3) • For chain topology, the asymptotic throughput for each node is O(1/n), the same as wireless LAN. • For stationary network, throughput decreases as O( ). • The result is in sharp contrast to the claims of the product vendors.

22. Discussion (2/3) • The main reason is the creation of a hot spot at the gateway that throttles the throughput of each node in the network. • The available throughput improves directly proportional to the number of gateway in the network.

23. Discussion (3/3) • Simple but not powerful scheme: • For asymmetric MAC environments with bidirectional traffic and different return paths, the direction of traffic must be taken into account. • Take into account cumulative interferences from neighboring links to re-define the collision domain accurately. • Not all nodes have to active at all times. • Not all nodes have to receive an equal share of the bandwidth

24. Outline • Introduction of Wireless Mesh Network • Problems formulation • Determining the nominal capacity • Simulation results • Discussion • Conclusion

25. Conclusion • The technique can be used to achieve fairness and QoS in WMNs. • The bottleneck collision domain, which throttles the throughput of the entire network. • Extend the concept of this paper to my final project.