Thomas Scherer (PhD Thesis)

Capacity Constraints and Enhancements in Wireless Mesh Networks

Thesis for Download: scherer_thesis.pdf

Objective of this work is the study of capacity constraints for service provision in Wireless Mesh Networks. Arbitrary wireless network topologies are considered. Hot Spots provide a certain service like Internet access, which is shared via wireless mutli-hop transmissions in the mesh network. It is studied how much bandwidth is available to the service at every node. \newline
Although service dissemination is one of the primary applications for mesh networks the scalability in terms of capacity is doubted.
The set of Hot Spots needs to provide sufficient ressources to serve the entire mesh network in a multi-hop manner. Different from wired solutions frames need to access the same physical channel several times to be send to the final destination. Therefore, one has to consider that ressources have not only to be shared among the network participants, further overhead arises due to multiple allocations of the physical channel by the same frame. Especially, for the usage of omni-directional antennas it is claimed that the bandwidth might decrease too strong.\newline
Additionally, the media access control becomes a more difficult task. Nodes need to access the channel in an appropriate manner for sharing the services fairly among the mesh nodes. The approach needs to differ from wired media access control techniques as all nodes share the same physical communication media but are not necessarily in communication range to each other. The load for routing traffic increases near to Hot Spots. Therefore, it is not sufficient to let every node access the channel in the same rate. The nearer a node is situated to a Hot Spot the more traffic is routed via it. Hence, it requires more access to the communication channel. This enhanced access shall be used to provide sufficient access to nodes at farer distances but not to utilize it for own access purposes. \newline
The overall objective is the study on whether mesh networks are a scalable solution regarding service provision. Following questions will be therefore elaborated:

• Is it possible to share a service like internet access over a wireless mesh network in a fair manner without sacrificing too much capacities?
• Are WMNs scalable? Is a possible loss of capacities bound to the size of WMNs?
• What performance can be at least expected?
• What is the best achievable performance?
• What are the influencing factors on service capacities?
• What has to be done to implement good performing WMNs if they exist?

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