A Study of Access-Point Aggregation Algorithm for Elastic Wireless Local-Area Network System and Its Implementation
Md. Ezharul Islam · Institutional Repositories DataBase (IRDB) · 2016
For ubiquitous network services, wireless local-area network (WLAN) systems using wireless access-points (APs) have been deployed in many places.In these WLANs, the allocated APs are often managed independently by different groups.Then, a user host can access to multiple APs by detecting their signals, which can degrade the communication performance due to radio interferences among them.Redundant allocations of APs and overlapped WLANs also cause energy wastages and increased operational costs when a small number of hosts participate in the network.On the other hand, if many hosts participate there, the number of APs should be increased so that the sufficient communication quality is provided for each host.Thus, a WLAN system is expected to be adaptive and elastic to the traffic load in the network.In this thesis, we first present the concept of the elastic WLAN system as a solution to these problems in multiple WLAN environments.This system controls the deployed APs and the host associations to save energies, reduce interferences, and improve performances of WLANs.Then, we present an AP aggregation approach for multiple WLAN environments to aggregate deployed APs of different groups into limited ones using virtual APs.For this purpose, we formulate the AP aggregation problem as a combinatorial optimization problem and prove the NPcompleteness of its decision problem.Then, we propose its heuristic algorithm composed of five phases.We verify the effectiveness of this AP aggregation algorithm through extensive simulations using the WIMNET simulator.However, our simulations in various instances also found that 1) the minimization of active APs sometimes excessively degrades the network performance (where many hosts participate), and 2) the sequential optimization of host associations does not always reach optimal where slow links are still used.Thus, we propose two extensions of the AP aggregation algorithm 1) to ensure the minimum average throughput for any host by adding active APs and 2) to further optimize host associations by changing multiple hosts simultaneously in the host association finalization phase.The effectiveness of this extended algorithm has been verified through simulations in four network instances using the WIMNET simulator.Then, we propose another extension of the AP aggregation algorithm to deal with the mobility of hosts by considering the probability of each host to stay active.In a real network, a user host usually joins or leaves randomly, and the AP aggregation algorithm needs to consider the mobility of hosts.We also verify the effectiveness of this extension through simulations using the WIMNET simulator.After that, we present measurement results of three important indices of WLANs for the use as algorithm parameters.They include throughput, signal strength, and signal level using IEEE802.11ncommercial devices for WLANs in outdoor environments, where the distance between the transmitting and receiving nodes is changed for various signal conditions.Due to extensive deployments of WLANs, measurements and analysis of such important indices to determine their performances have become important to improve the deployments of high-speed IEEE802.11nWLANs.The results show that these indices are strongly affected by the transmisi It is my great pleasure to thank those who made this dissertation possible.I owe my deepest gratitude to my supervisor, Professor Nobuo Funabiki, who patiently gave me advices, wonderful guidance, insightful comments, helpful discussions and directions, which inspired many ideas in this thesis.He taught me how to face the problems, how to investigate them, and how to solve them.