Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Resource allocation in WiMAX relay networks(Montana State University - Bozeman, College of Engineering, 2010) Wan, Shen; Chairperson, Graduate Committee: Jian TangWiMAX is a promising wireless technology to provide high-speed, reliable communications in large areas. Relay stations can be deployed in a WiMAX network to extend its coverage and improve its capacity. Orthogonal Frequency Division Multiplexing Access (OFDMA) enables better channel utilization and exploits the benefits of channel diversity and user diversity. A smart adaptive antenna provides multiple Degrees of Freedom (DOFs) for intended communications and interference suppression, which results in more efficient spatial reuse and higher throughput. In this dissertation, we discuss how to combine those aforementioned technologies in a WiMAX relay network (WRN), and study the routing, scheduling, channel assignment, and antenna DOF assignment problems. It has been shown by previous research that the performance of wireless scheduling algorithms usually depends on the interference degree. Therefore, we study the interference degree in WiMAX networks and show that it is at most 4 in any 2-hop WRN and at most 14 in any general WiMAX network. Next, we consider routing and scheduling in WRN with smart antennas. We formally define the Interference-aware Tree Construction Problem (ITCP) for routing, which offers full consideration for interference impact and DOF availability. We then present an algorithm to optimally solve it in polynomial time. As for scheduling, we first present a polynomial-time, optimal algorithm for a special case in which the number of DOFs in each node is large enough to suppress all potential secondary interference. An effective algorithm is then presented for the general case. We also study a scheduling problem for throughput maximization in OFDMA-based WRN with consideration for multi-user diversity, channel diversity and spacial reuse. We present a Mixed Integer Linear Programming (MILP) formulation to provide optimum solutions. Furthermore, we show that both the simple greedy algorithm and our proposed weighted-degree based greedy algorithm have approximation ratio of 1/5 for 2-hop WRN and 1/15 for any WiMAX networks. In addition, we present 3 other efficient algorithms, namely, the maximum weighted independent set (MWIS) algorithm, the sequential knapsack algorithm and the LP rounding algorithm. Extensive simulations are conducted to evaluate the performance of all proposed algorithms.Item Topology control and interference aware resource allocation algorithms using directional antenna for QoS (802.16e) performance in multi-hop wireless networks(Montana State University - Bozeman, College of Engineering, 2010) Annavarapu, Vishwanath; Chairperson, Graduate Committee: Jian TangIn recent years, there has been a lot of research work being done on the wireless networking using Directional antennas. But not many approached the issue together with resource allocation and channel assignment in multi-channel multi-radio networks, especially in multi-hop WiMAX (802.16e) networks. This work also explores the implementation of Directional antenna for communication in mobile scenario where the nodes move either in specified trajectory or randomly. The overall goal of this research is to work towards improving the wireless communication and proposing solutions for some existing issues. The methods of topology control algorithms for maximizing the minimum link capacity and then a different approach to balance the network load should be one of the few pieces of work in this regard. Implementation of these proposed methods have improved the network performance in aspects like throughput, delay, network capacity, interference, traffic congestion and network balance. The major issues that determine the performance of wireless networks include traffic congestion, interference, signal quality, Quality of Service (QoS), mobility issues like handover. These issues for a multi-hop WiMAX scenario that would possibly emerge in future were studied and solution were suggested and tested. Large numbers of WiMAX scenarios of different sizes with different type of applications, models, devices, resources and methodologies have been simulated and various aspects like mobility, QoS, interference control, traffic congestion and network balance have been studied. During the course of research, various wireless communication issues have been addressed by providing feasible to optimal solutions; new designs and methodologies for the WiMAX models is being incorporated to induce useful functionalities; communication models, antennas and other devices and technically enhanced. Also, the QoS in WiMAX networks hasn't been studied much; our research work includes simulation and detailed analysis of various service classes in different conditions and scenarios for WiMAX multi-hop networks.