A Study of Access Point Allocation and Channel Assignment for Dependable Wireless Mesh Network

The rapid progress of wireless communications and the availability of lightweight, smallsize, and portable computing devices have given great impacts on our communities. These technologies have made the dream of communications at anytime and at anywhere come true. A common solution for such ubiquitous communications is the use of the wireless local area network (WLAN). WLAN has been widely studied and deployed as an access network to the Internet in many places. With the progression of WLAN, the wireless mesh network has been developed as a flexible, adaptive, and reconfigured network architecture while offering cost-effective solutions to service providers. A wireless mesh network is composed of multiple wireless routers that are connected wirelessly, in addition to wireless communications between user hosts and routers, in order to expand the coverage area that is usually limited into a small space by a single AP in a conventional WLAN. Thus, data communications between routers are usually offered by multi-hop wireless communications. Among several variations of under-studying wireless mesh networks, our research group has focused on the one that targets the Internet access service, uses only access points (APs) as wireless routers, and realizes wireless communications between APs mainly on the MAC layer using the wireless distribution system (WDS). Henceforth, we call this Wireless Internet-access Mesh NETwork as WIMNET for convenience. WIMNET consists of a number of APs and their wireless links that can cause failures easily. As a result, the dependability enhancement of WIMNET becomes a very important task for a secure access network to the Internet, where even some failures of APs and/or links may not cause the malfunction or the disconnection of WIMNET. In this thesis, we first formulate the link-fault and AP-fault dependable AP allocation problems for WIMNET, after giving the background about WIMNET and the overview of the network model used in our study, and present their algorithms by extending the existing AP allocation algorithm. We verify the effectiveness of our approach through extensive simulations using the WIMNET simulator. Three network topologies are adopted as simulated instances for evaluations. The simulation results show that a small number of additional APs are required to satisfy the dependability constraint, and the degradation of the throughput is not serious regardless of the increasing interference by increasing APs. Then, we introduce the route availability (RA) index for WIMNET to represent how many hosts can be connected with the GW on average under a gaiven set of probabilities. Four network topologies are adopted as simulated instances for evaluations. The simulation results show that the RA index is actually improved in our fault dependable AP allocations found by our algorithms, and the difference between RA indices and the corresponding simulation results is small.