Electrical and Electronic Engineering - Theses
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ItemSum-Rate Optimization in Wireless Networks( 2021)Due to technological enhancements, such as mobile TV, streaming services, smart grids and augmented reality, the need to optimize the overall network throughput becomes one of the most important aspects of communication systems. In this thesis, we analyze the resource allocation problem of four different wireless communication systems with the objective of maximizing the achievable sum-rate. From a theoretical perspective, the achievable sum-rate optimization problem is very hard to solve. As such, the challenge is to solve these non-convex and NP-hard optimization problems with an acceptable level of complexity. We first consider two full-duplex and half-duplex networks and investigate the optimality of binary power allocation. In terms of the transmit power allocation, the simple power allocation method known as the binary power allocation is known to be optimal for special wireless network structures. Therefore, we derive new, necessary and sufficient conditions that would ensure the optimality of binary power allocation for such networks. We further extend our analysis to investigate the sub-optimality associated with binary power allocation and show that the loss of achievable sum-rate due to binary power allocation is negligible. Next, we concentrate on the transmission direction control in flexible duplex networks such that the achievable sum-rate is maximized. We analyze several existing approximation techniques and their feasibility for solving the resulting NP-hard optimization problem. We also develop a novel low-cost heuristic pattern search algorithm based on the direct search of function value. For a flexible network where each node has one potential desired link, we observe that the proposed algorithm has better achievable sum-rate compared to the approximation techniques and other existing resource allocation approaches. In reality, however, a node can have more than one potential desired link. As such, transmitter and receiver scheduling becomes important in the presence of multiple desired links. Therefore, we next investigate the optimum resource allocation in terms of transmit power, link direction and transmitter/receiver selection of flexible half duplex networks when the objective is to maximize the achievable sum-rate. We prove that it is optimum for each transmitting node to only transmit to one desired receiving node and use that insight to develop a novel iterative algorithm. We observe that the proposed algorithm outperforms existing resource allocation techniques specially in denser areas where larger number of nodes are operating. Finally, we consider the achievable sum-rate optimization problem in multi-user multi-hop relay networks. We derive novel closed form expressions for the achievable rate under a single-user multi-hop relay network. We extend this investigation to multi-user network and develop a novel iterative algorithm for joint relay selection and power control with the objective of maximizing the achievable sum-rate. To obtain further insights, we extend our analysis to two-user multi-hop network and prove that optimal power allocation can be analytically obtained by considering binary power allocation for two transmitting nodes. In addition, we develop a novel low-cost relay selection technique based on the average interference estimation for the special case of multi-user dual hop relay networks.