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A Master of Science thesis in Electrical Engineering by Mohammed K.Y. Aborahama entitled, “Millimeter Wave Channel Characterization for 5G Cellular Systems in the UAE at the 28 GHz Band”, submitted in May 2019. Thesis advisor is Dr. Amer S. Zakaria and thesis co-advisors Dr. Mahmoud H. Ismail Ibrahim and Dr. Mohamed El-Tarhuni. Soft and hard copy available., College of Engineering, Department of Electrical Engineering

A Master of Science thesis in Electrical Engineering by Ibtihal Mohamed Taha Ahmed entitled, “Video Streaming over D2D Networks”, submitted in April 2019. Thesis advisor is Dr. Mahmoud H. Ismail Ibrahim and thesis co-advisor is Dr. Mohamed S. Hassan. Soft and hard copy available., College of Engineering, Department of Electrical Engineering

A Master of Science thesis in Electrical Engineering by Fatema Mahmood Aseeri entitled, "Video Transmission over LTE-Unlicensed," submitted in November 2017. Thesis advisor is Dr. Mohamed Hassan and thesis co-advisor is Dr. Mahmoud H. Ismail. Soft and hard copy available., The witnessed proliferation in the demand on wireless spectrum over the past years is anticipated to lead to a bandwidth scarcity problem. The situation is further aggravated by the combined increase in the demand on the delivery of high definition multimedia content over wireless networks. Recently, it was proposed to extend the LTE operation into the unlicensed spectrum (LTE-U) in an attempt to mitigate the expected scarcity problem. However, extending the operation of LTE to the unlicensed spectrum is expected to degrade the performance of other incumbent technologies, especially WiFi. While several LTE-U channel access mechanisms for enabling the coexistence of LTE with WiFi, in the unlicensed spectrum, have been proposed and evaluated, very few addressed the problem of video streaming over LTE-U. Therefore, this thesis further explores the design of efficient LTE-U channel access mechanisms from the perspective of video streaming. Specifically, we propose two channel selection schemes for video transmission over LTE-U. The first is a static channel selection scheme in which the LTE-U user equipment (UEs) are assigned to channels based on their frame type. The second one is an adaptive channel selection scheme in which UE frames are assigned to channels based on the solution to a multi-objective optimization problem that takes into account the UE's Quality of Experience (QoE) requirements while striving to minimize the interference caused to WiFi. Simulation results show that, compared to a scheme that employs an effective channel access mechanism but assigns frames to channels randomly, our proposed QoE-based channel selection scheme achieves a considerably better performance, in terms of improving the received video quality and reducing the inter-frame delay for both LTE-U and WiFi users. These results confirm the conclusion that while extending the operation of LTE-U to the unlicensed spectrum does indeed come with great benefits for LTE networks, that extens, College of Engineering, Department of Electrical Engineering

In this paper, we introduce the exposed secondary users problem in underlay cognitive radio systems, where both the secondary-to-primary and primary-to-secondary channels have a Line-of-Sight (LoS) component. Based on a Rician model for the LoS channels, we show, analytically and numerically, that LoS interference hinders the achievable secondary user capacity when interference constraints are imposed at the primary user receiver. This is caused by the poor dynamic range of the interference channels fluctuations when a dominant LoS component exists. In order to improve the capacity of such system, we propose to use an Electronically Steerable Parasitic Array Radiator (ESPAR) antenna at the secondary terminals. An ESPAR antenna involves a single RF chain and has a reconfigurable radiation pattern that is controlled by assigning arbitrary weights to M orthonormal basis radiation patterns via altering a set of reactive loads. By viewing the orthonormal patterns as multiple virtual dumb antennas, we randomly vary their weights over time creating artificial channel fluctuations that can perfectly eliminate the undesired impact of LoS interference. This scheme is termed as Random Aerial Beamforming (RAB), and is well suited for compact and low cost mobile terminals as it uses a single RF chain. Moreover, we investigate the exposed secondary users problem in a multiuser setting, showing that LoS interference hinders multiuser interference diversity and affects the growth rate of the SU capacity as a function of the number of users. Using RAB, we show that LoS interference can actually be exploited to improve multiuser diversity by boosting the effective number of users.

We propose a novel spectrum sensing technique in cognitive radio networks that provides diversity and capacity benefits using a single antenna at the Secondary User (SU) receiver. The proposed scheme is based on a reconfigurable antenna: an antenna that is capable of altering its radiation characteristics by changing its geometric configuration. Each configuration is designated as an antenna mode or state and corresponds to a distinct channel realization. Based on an abstract model for the reconfigurable antenna, we tackle two different settings for the cognitive radio problem and present fundamental limits on the achievable diversity and throughput gains. First, we explore the "to cooperate or not to cooperate" tradeoff between the diversity and coding gains in conventional cooperative and non-cooperative spectrum sensing schemes, showing that cooperation is not always beneficial. Based on this analysis, we propose two sensing schemes based on reconfigurable antennas that we term as state switching and state selection. It is shown that each of these schemes outperform both cooperative and non-cooperative spectrum sensing under a global energy constraint. Next, we study the "sensing-throughput" trade-off, and demonstrate that using reconfigurable antennas, the optimal sensing time is reduced allowing for a longer transmission time, and consequently better throughput. Moreover, state selection can be applied to boost the capacity of SU transmission.

In this paper, we revisit energy detection-based spectrum sensing cognitive radio systems operating over generalised fading channels. In particular, we derive closed-form exact expressions as well as lowand high-signal-to-noise ratio asymptotic expansions for the misdetection probability over the Fox's H-function fading channel. The closed-form expression is given in terms of the bivariate Fox's Hfunction and subsumes most of the expressions previously presented in the literature. Also, the obtained asymptotic expressions are very easy to compute and can be used to get various performance insights. We verified, theoretically and numerically, the validity of the exact expression for important special cases previously reported in the literature, namely the Nakagami-m and the extended generalised-K (EGK) fading distributions. Numerical results also demonstrate the high accuracy of the asymptotic expansions.

In this paper, we derive closed-form exact and asymptotic expressions for the symbol error rate (SER) as well as channel capacity when communicating over the Fox's H-function fading channel. The SER expressions are obtained for numerous practically-employed modulation schemes in case of single as well as three multiple-branch diversity receivers: maximal ratio combining (MRC), equal gain combining (EGC), and selection combining (SC). The derived exact expressions are given in terms of the univariate and multivariate Fox H functions for which we provide a portable and efficient Python code. Since the Fox's H-function fading channel represents the most generalized fading model ever presented in the literature, the derived expressions subsume most of those previously presented for all the known simple and composite fading models. Moreover, easy-to-compute asymptotic expansions are provided so as to easily study the behavior of the SER and channel capacity at high values of the average signal-to-noise (SNR). The asymptotic expansions are also useful in comparing different modulation schemes and receiver diversity combiners. Numerical and simulation results are also provided to support the mathematical analysis and prove the validity of the obtained expressions.

This paper investigates the problem of video transmission over cognitive radio networks with the objective of maintaining continuous video playback while gracefully degrading the quality of the reconstructed video sequences, if needed. We focus on modeling the channel availability to secondary users, which is a major limiting factor on the continuity of the streaming process. A Markov chain model for the channels availability in an M-channels system is developed. This model is used to estimate the likelihood of transmission interruptions a secondary user might experience due to the loss of a channel to a primary user. We also propose a joint adaptive mechanism where a simple source rate control scheme is integrated with an adaptive playback approach to reduce the impact of channels relocation/unavailability on the streaming process of active secondary users. Simulations and numerical investigations demonstrate the correctness of the proposed channel model. Simulation results also indicate that instants of playback buffer starvation at the secondary user ends could be avoided only when the hybrid approach is employed.

Novel closed-form exact expressions for the capacity of the recently-introduced Fox's H-function fading channel are derived. The expressions are obtained assuming different types of adaptive transmission strategies, namely, channel inversion with fixed rate (CIFR), truncated channel inversion with fixed rate (TIFR), optimum rate adaptation with fixed power (ORA) and optimum power and rate adaptation (OPRA). The obtained expressions are versatile and can be used to evaluate the capacity for virtually any fading channel one might be interested in as a special case.