Computing and Information Systems - Theses
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ItemAn energy and spectrum efficient distributed scheduling scheme for Wireless Mesh Networks( 2013)The success of Wireless Mesh Network (WMN) applications depend on the effective energy efficiency, spectrum reuse, scalability, and robustness of scheduling schemes. However, to the best of our knowledge the available schedulers fail to address these requirements simultaneously. This thesis proposes an autonomous, scalable, and deployable scheduler for WMNs with energy efficient transceiver activation and efficient spectrum reuse. Our goals are: (i) to conserve energy for longer sustainability, (ii) to effectively reuse the radio spectrum for higher throughput, lower delay, lower packet loss, and fairness, and (iii) to ensure that the proposed solution serves common WMN applications. Our research identified three major approaches in scheduling, eight key attributes, and detailed the evolution of wireless standards for distributed schedulers. Among the solutions, pseudo random access (PRA) is expected to have the strengths of randomness for scalability and robustness, and determinism for energy efficiency and spectrum reuse. However, literature on the IEEE 802.16s election based transmission timing (EBTT) scheme - the only known standardized PRA solution - is limited in scope. We use a combination of simulations, modelling, and analysis in our research. Since the existing simulators did not support our ambitious range of investigations, we developed our own simulator which we called Election Based Pseudo Random Access (EBPRA) simulator. Moreover, we introduced two types of synthetic mesh networks as a way to decompose the complexities of WMN topologies and systematically study their effects. The benchmarking study on the EBTT against a centralised cyclic access (CCA) scheme revealed less than 50% spectrum reuse, 75% low fairness measure, and more significantly, an energy wastage of up to 90% in reception with collisions in transmissions in the EBTT. Hence we propose an enhanced pseudo random access (EPRA) scheme to mitigate the issues. The EPRA does not introduce additional overheads and can be deployed on IEEE 802.16 nodes with minor firmware modifications. Simulations on the EPRA show significant improvements in the energy efficiency where collisions are eliminated and the reception is near 100% efficient. Moreover, the spectrum reuse and fairness measures also improved. These results validated the findings of the analytical models that we derived. Finally we propose two alternative solutions to handle user data packets, namely: EPRA based single scheduler (EPRA-SS), and EPRA based dual scheduler (EPRA-DS). Since satisfying requirements of voice services means requirements for data service are met, we concentrated our investigation with voice. Through extensive simulations and multidimensional data analysis, we identified the supported ranges of network densities, traffic intensities, and buffer allocations to satisfy per hop delay and packet drop conditions. Hence, we demonstrated for the first time that near 100% energy efficiency should be possible with a distributed scheduler when our EPRA scheme is used. In addition, we have also shown improvements in spectrum reuse for better throughput, shorter delays, and better fairness. Finally, EPRA based schemes have been demonstrated as effective schedulers for user data traffic over WMN deployment scenarios fulfilling our research objectives.