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Title Spectrum and Power Efficient Multimedia Transmissions in OFDMA Wireless Networks
Degree Ph.D.
Author Richard O. Afolabi
Advisor Kiseon Kim
Graduation Date 2015.02.25 File
    Date 2017-03-06 10:44

Radio spectrum is a scarce resource. The overwhelming demands for high data rates and the need to support large number of users with flexible quality of service (QoS) requirements implies a large number of heterogenous future wireless devices must compete for the limited system resources. Since there is no substitute for intelligent deployment and utilization of finite resources, the idea of multimedia multicasting has emerged as an aggressive solution to increasing spectrum utilization through resource sharing and optimization. Multicasting allows users within close proximity and/or requiring similar multimedia contents to form groups and share allocated system resources. Multimedia Broadcast Multicast Services (MBMS) together with Orthogonal Frequency Division Multiple Access (OFDMA) and advanced dynamic resource allocation (MDRA) techniques have emerged as aggressive solutions to increasing spectrum utilization through resource sharing and optimization. However, at the heart of MDRA are several fundamental problems that require careful investigations.

In this dissertation, we examine the multicast technology stack from its fundamentals, to identify its limitations, challenges and alternative techniques to mitigate the limiting behaviour. We partition this dissertation into three parts. First part serves as a coagulator, solidifying and presenting an insightful view of the current state-of-the-art on existing MDRA algorithms. We explain the main ideas, features, optimality, complexities and main weaknesses of existing MDRA algorithms. Second part capitalizes on the limitation impose by a fundamental assumption in conventional multimedia multicasting and proposes a novel, high-performance multicasting scheme. The final part presents a QoS-aware MDRA algorithm and investigate the performance of the conventional multicasting with the limiting assumption, comparing it with the high-performance multicasting scheme propose in part two under different metrics. 

First, we develop a multi-dimensional taxonomy classifying existing MDRA algorithms into different meaningful classifications. Based on their group formation concepts, we characterize multicasting into single-rate or multi-rate techniques and identify the strengths and several challenges confronting each category. The main idea here is to provide an authoritative taxonomy that connects several disparate existing works together while noting their weaknesses.

In the second part, we propose, design, analyze and evaluate a novel spectrum and power efficient transmission scheme for MBMS with the goal of ensuring a more spectrally-efficient multimedia transmission using the amortized weighted averaging (AWG) of users SNR. We develop mathematical and computational model for the system using ordered statistics of exponential and uniform distribution and derive statistics for the density function, distribution function and moment generating function. We then apply the modelling results to study the performance of wireless multicasting over Rayleigh fading channels. More specifically, we obtain the outage probability, reliability function and mean capacities for broadcast and multicast systems. We show the trade-off in terms of the average mean capacity.

In the third part, we present a technique based on the statistical approximations of the AWG of users SNR to evaluate spectrum and power allocation in MBMS. We propose a suboptimal multicast resource allocation algorithm using memoization with stochastic rounding (MSR) and evaluated its system-level performance. Through analytical results presented in this dissertation, we show that contrary to popular opinion in existing MBMS scheme, it is possible to systematically exploit the users channel perception and prevent system saturation as we admit more users into the system. The proposed AWG scheme is reliable, avoid outage and is more efficient than existing multicasting techniques especially in the low SNR region.

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