Performance Analysis and Techniques for Wireless Systems with Unmanaged and Managed Interference
Ali, Ahmed Omar Desouky
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In the past few decades, the world has witnessed enormous advances in wireless communication systems introducing unprecedented applications and services. Such advances brought the idea of Internet of Things (IoT) to life, where almost every object is interconnected to each other through the existing Internet infrastructure. This results in enormous increase in the number of wireless devices sharing the same medium and bandwidth in different networks. Consequently, interference generated by such devices is expected to increase drastically, and hence innovative techniques to mitigate such interference have to be investigated. In this dissertation, we investigate the interference in wireless communication networks. The dissertation is divided into two parts dealing with unmanaged and managed interference, respectively. In the ﬁrst part, we investigate the second order statistics of a system consisting of a single receiver with multiple antennas, a single desired user and multiple interferers. Speciﬁcally, we derive exact closed-form level-crossing rate (LCR) expressions for such a system under different spatial correlation assumptions which, to the best of our knowledge, are reported for the ﬁrst time in literature. We also derive an approximate LCR expression in the spatially uncorrelated receiver to get better insight. Moreover, we investigate the effect of the different system’s parameters on the LCR. Then, we introduce two applications where in the ﬁrst we use these new expressions to evaluate the system’s packet error rate (PER). The second application uses the derived LCR expressions in Finite-State Markov Chain (FSMC) modeling to evaluate the system’s throughput when deploying Automatic Repeat Request (ARQ). We also formulate an optimization problem where we ﬁnd the packet length maximizing the system’s throughput. In the second part of the dissertation, we deal with managed interference where we use joint transmit and receive beamforming to mitigate the interference for frequency selective fading channels. In particular, we propose exploiting the guard intervals, e.g., the cyclic preﬁx or the zero-padding intervals, to increase the degrees of freedom (DoFs) used, and consequently the sum rate of the system through applying interference alignment (IA) iterative schemes. We derive an upper bound on the number of allowable DoFs per user and evaluate the system’s sum rate and compare it with other IA schemes reported in literature. We also investigate the eﬀect of partial channel state information (CSI) on the performance of such a system and propose a robust beamforming transceiver design. We also derive an approximate expression for the system’s average sum stream rate when exploiting the guard interval in transmission in presence of CSI error. Furthermore, we attempt to address the question whether it is better to align the interference or orthogonalize the transmitted signals through investigating an uplink cellular system deploying IA in presence of CSI uncertainty. In this system, we derive closed-form lower and upper bounds and approximation for the average cell rate and use the derived expressions to determine analytically the operation regions of IA relative to orthogonal multiple access (OMA) schemes. Finally, we propose a hybrid IA/OMA transmission scheme to improve the network performance.