Wireless Information and Power Transfer in Communication Networks: Performance Analysis and Optimal Resource Allocation

Energy harvesting is considered as a prominent solution to supply the energy demand for low-power consuming devices and sensor nodes. This approach relinquishes the requirements of wired connections and regular battery replacements. This thesis analyzes the performance of energy harvesting communication networks under various operation protocols and multiple access schemes. Furthermore, since the radio frequency signal has energy, in addition to conveying information, it is also possible to power energy harvesting component while establishing data connectivity with information-decoding component. This leads to the concept of simultaneous wireless information and power transfer. The central goal of this thesis is to conduct a performance analysis in terms of throughput and energy efficiency, and determine optimal resource allocation strategies for wireless information and power transfer. In the first part of the thesis, simultaneous transfer of information and power through wireless links to energy harvesting and information decoding components is studied considering finite alphabet inputs. The concept of non-uniform probability distribution is introduced for an arbitrary input, and mathematical formulations that relate probability distribution to the required harvested energy level are provided. In addition, impact of statistical quality of service (QoS) constraints on the overall performance is studied, and power control algorithms are provided. Next, power allocation strategies that maximize the system energy efficiency subject to peak power constraints are determined for fading multiple access channels. The impact of channel characteristics, circuit power consumption and peak power level on the node selection, i.e., activation of user equipment, and the corresponding optimal transmit power level are addressed. Initially, wireless information transfer only is considered and subsequently wireless power transfer is taken into account. Assuming energy harvesting components, two scenarios are addressed based on the receiver architecture, i.e, having separated antenna or common antenna for the information decoding and energy harvesting components. In both cases, optimal SWIPT power control policies are identified, and impact of the required harvested energy is analyzed. The second line of research in this thesis focuses on wireless-powered communication devices that operate based on harvest-then-transmit protocol. Optimal time allocation for the downlink and uplink operation interval are identified formulating throughput maximization and energy-efficiency maximization problems. In addition, the performance gain among various types of downlink-uplink operation protocols is analyzed taking into account statistical QoS constraints. Furthermore, the performance analysis of energy harvesting user equipment is extended to full-duplex wireless information and power transfer as well as cellular networks. In full-duplex operation, optimal power control policies are identified, and the significance of introducing non-zero mean component on the information-bearing signal is analyzed. Meanwhile, SINR coverage probabilities, average throughput and energy efficiency are explicitly characterized for wireless-powered cellular networks, and the impact of downlink SWIPT and uplink mmWave schemes are addressed. In the final part of the thesis, energy efficiency is considered as the performance metric, and time allocation strategies that maximize energy efficiency for wireless powered communication networks with non-orthogonal multiple access scheme are determined. Low complex algorithms are proposed based on Dinkelbach’s method. In addition, the impact of statistical QoS constraints imposed as limitations on the buffer violation probabilities is addressed

Energy-Efficient NOMA Enabled Heterogeneous Cloud Radio Access Networks

Heterogeneous cloud radio access networks (H-CRANs) are envisioned to be promising in the fifth generation (5G) wireless networks. H-CRANs enable users to enjoy diverse services with high energy efficiency, high spectral efficiency, and low-cost operation, which are achieved by using cloud computing and virtualization techniques. However, H-CRANs face many technical challenges due to massive user connectivity, increasingly severe spectrum scarcity and energy-constrained devices. These challenges may significantly decrease the quality of service of users if not properly tackled. Non-orthogonal multiple access (NOMA) schemes exploit non-orthogonal resources to provide services for multiple users and are receiving increasing attention for their potential of improving spectral and energy efficiency in 5G networks. In this article a framework for energy-efficient NOMA H-CRANs is presented. The enabling technologies for NOMA H-CRANs are surveyed. Challenges to implement these technologies and open issues are discussed. This article also presents the performance evaluation on energy efficiency of H-CRANs with NOMA.Comment: This work has been accepted by IEEE Network. Pages 18, Figure

UAV-Enabled Wireless Powered Communication Networks

Unmanned aerial vehicles (UAVs), popularly known as drones, have emerged as a promising solution for providing reliable and cost-effective wireless communications. The use of UAVs as aerial wireless power transmitters (UAV-WPT), with additional flexibility and 3D mobility, is expected to provide efficient wireless power supplies to low-power and hard-to-reach devices. Due to their adjustable altitude and mobility, efficient line-of-sight (LoS) between UAVs and ground nodes (GNs) could be established, thus mitigating signal blockage and shadowing. Based on this feature, UAVs can be good candidates to charge battery-limited or hard-to-reach devices through radio frequency (RF) wireless power transfer (WPT), which will significantly improve the wireless charging efficiency compared to conventional ground charging stations at fixed locations. Although the deployment of UAVs as wireless power transmitters is promising, it comes with many design challenges and reliability problems. For instance, the energy efficiency (EE) of UAVs requires careful consideration as it significantly impacts the performance of UAV-WPT systems. Thus, there is a need for a comprehensive framework to optimize such networks, where the devices are wirelessly powered via UAVs to enable uplink data transmission. In this thesis, we propose a detailed methodology to optimize the performance of the UAV-enabled WPT networks with different topologies and applications. We provide the required steps to be followed for most applicable networks, where specific considerations have to be considered for each case. The optimization problem's solution has two main steps; firstly, the path loss of the air-to-ground channels is minimized by optimizing the UAV position depending on the GNs' service demands. Secondly, using the optimized positioning and a closed-form expression for the EE, a resource allocation aiming to maximize EE is developed using Lagrangian optimization and gradient-descent methods. We present five different system models, which reflect different practical cases and setups considering single and multiple UAV scenarios. These models are: UAV-enabled wireless powered communications network (UAV-WPCN), UAV-enabled wireless information and power transfer network (UAV-WIPT), UAV-enabled simultaneous wireless information and power transfer network (UAV-SWIPT), multiple UAV-enabled wireless powered communications network (UAVs-WPCN), and multiple UAV-enabled simultaneous wireless information and power transfer network (UAVs-SWIPT). The results of applying the proposed scheme show significant enhancement in the EE for the non-orthogonal multiple access (NOMA) scheme compared to the orthogonal multiple access (OMA) scheme in most of the scenarios. However, the topology and distribution of the ground nodes play a vital role in figuring out the suitable access scheme to be used, where OMA or hybrid NOMA/OMA schemes could perform better