Wireless mesh network (WMN) is a strong candidate for the next generation wireless network. A WMN is made up with three types of entities: Internet Gateways (IGWs), mesh routers (MRs), and mesh clients (MCs). IGWs provide interfaces to both the Internet and MRs. MRs together with IGWs form a mesh backbone by interconnecting each other via multi-hop wireless links. MCs access the Internet by setting up connections with MRs. The placement of three entities is one of the fundamental issues that could greatly affect the performance of a WMN. Positioning technique in WMNs aims at optimizing the positions of these nodes to improve network performance and could be further categorized into: IGW placement, MR placement and MC association.
The first part of this dissertation introduces our work over MR placement. MR placement is a strategy that determines the minimal number and positions of MRs that satisfies various constraints such as network coverage, connectivity, Internet traffic demand, etc., for a given network area to be covered by a WMN. Some MR placement strategies may also indicate the appropriate number of interfaces each MR needs as well. A systematic MR placement is the first important step for establishing a WMN with desired network performance efficiently. Our study starts from modeling and formulating the MR placement problem. Then, we analyze the problem in an ideal homogeneous network model, which is characterized by single IGW, identical transmission rate, and MRs could be positioned anywhere in the network region. Hence, we extend the discussion into a more realistic constraint network model: MRs can only be placed in the pre-decided candidate positions; traffic demands is non-uniformly distributed. Furthermore, we deepen our study by taking into accounts the nature of multiple transmission ranges/rates of commercial MRs. We propose a heuristic placement algorithm called ILSearch, which considers both multiple transmission rates and co-channel interference in the constraint network with multiple IGWs. In addition, we develop a virtual force based algorithm: VFPlace, to place MRs in a special constraint network where only candidate areas, rather than specific positions, are known in advance. The numeric results shows the correctness and effectives of our analytical models and proposed algorithms.
The second part of this dissertation presents our work about MC association. MC association strategy targets at helping MCs choose best MRs to establish the connections in the limited space and time. MC association can influence the performance of a WMN to a large extent since it determines how well the mesh backbone, i.e., the associated MRs, can serve MCs. MR's capability for serving MCs varies dynamically due to the changing channel condition, traffic load, and other network parameters. Mobile MCs should attach to MRs that are able to provide best service so as to maximize their own performance. But the determination procedure is constrained by time and space, which makes MCs only able to check partial MRs of the WMN. We map MC association problem as the modified secretary problem. Then, we propose three probabilistic strategies to enhance the possibility that MCs choose the best MRs: opportunistic association, conservative association, and hybrid association. Both statistical analysis and simulations show the conservative strategy outperforms the other two.