Capacity and Coverage Analysis for Multihop Relay-Enhanced WiMAX Networks

WiMAX (IEEE 802.16) has emerged as a promising radio access technology for providing high speed broadband connectivity to subscribers over large geographic regions. New enhancements allow deployments of relay stations (RSs) that can extend the coverage of the base station (BS), increase cell capacity, or both. This thesis studies the impact of deploying RSs on both capacity and coverage aspects. It consists of the following five main parts.;In the first part, the focus is on enhancing the cell capacity, and considering the placements of RSs that maximize the cell capacity. We then provide a closed-form approximation for the optimal location of an RS inside a cell. A numerical analysis of a number of case studies validates the closed-form approximation. The numerical results show that the closed-form approximation is reasonably accurate.;The second part focuses on deploying RSs for the purpose of coverage extension and studies the issue of fairness in such networks. We evaluate the performance of well-known fairness schemes such as max-min and proportional fairness. We also introduce a new fairness scheme, named subsection fairness that can achieve better throughput than traditional fairness schemes by maximizing bandwidth utilization. We evaluate the performance of each fairness scheme in terms of cell throughput and fairness.;In the third part, we propose an optimal scheduling scheme that maximizes cell throughput while preserving fairness among active subscriber stations (SSs), and compare its performance with two different resource allocation schemes, namely, the orthogonal and overlapped schemes in terms of cell throughput and outage performance. The orthogonal scheme minimizes interference by not allowing frequency reuse, however it can lead to lower throughput performance, whereas the overlapped scheme can achieve higher throughput by employing frequency reuse but the outage rate is also increased due to interference. Our numerical results show that the proposed optimal scheme can achieve more throughput than the orthogonal scheme, while maintaining the fairness and lower outage performance of the orthogonal one.;The fourth part focuses on cost-effective coverage extension. We explore how deploying RSs affects the cost and throughput of the network. We evaluate the performance of the network with RSs by varying parameters such as the number of active SSs in a cell, position of the RSs, and the number of RSs. Through simulation and numerical analysis, we make several fundamental observations about cost-effective coverage extension in such networks.;In the last part, we propose a hybrid resource allocation scheme by combining the advantages of the orthogonal and overlapped schemes. In this hybrid scheme frequencies are reused and outage is avoided by minimizing interference while preserving low time complexity. We evaluate the performance of the proposed hybrid scheme by comparing it with the optimal scheduling scheme as well as the orthogonal and overlapped schemes, in terms of cell throughput, outage rate, and computation time. The numerical results show that the computational time of the proposed hybrid scheme is significantly less than the optimal scheme at the expense of minimal throughput degradation and without an increase in outage rate.