PERFORMANCE ANALYSIS IN WIRELESS POWERED D2D- AIDED NON-ORTHOGONAL MULTIPLE ACCESS NETWORKS

This paper examine how to integrate energy harvesting (EH) to non-orthogonal multiple access (NOMA) networks. Recently, device-to-device (D2D) underlaying licensed network is introduced as novel transmission mode to perform two nearby user equipment units (UEs) communicating directly without signal processing through the nearest base station (BS). By wireless power transfer, they can be further operational to D2D communications in which a UE may harvest energy from RF signal of dedicated power beacons (PB) to help EH assisted UEs communicate with each other or assist these UEs to communicate with the BS. In particular, we investigate outage and throughput performance in a scenario of D2D communications powered by RF signal where one UE may help other two UEs to exchange information with optimal throughput

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

Hybrid satellite-terrestrial relay network: proposed model and application of power splitting multiple access

The development of hybrid satellite-terrestrial relay networks (HSTRNs) is one of the driving forces for revolutionizing satellite communications in the modern era. Although there are many unique features of conventional satellite networks, their evolution pace is much slower than the terrestrial wireless networks. As a result, it is becoming more important to use HSTRNs for the seamless integration of terrestrial cellular and satellite communications. With this intent, this paper provides a comprehensive performance evaluation of HSTRNs employing non-orthogonal multiple access technique. The terrestrial relay is considered to be wireless-powered and harvests energy from the radio signal of the satellite. For the sake of comparison, both amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols are considered. Subsequently, the closed-form expressions of outage probabilities and ergodic capacities are derived for each relaying protocol. Extensive simulations are performed to verify the accuracy of the obtained closed-form expressions. The results provided in this work characterize the outage and capacity performance of such a HSTRN.publishe

Power splitting versus time switching based cooperative relaying protocols for SWIPT in NOMA systems

Non-orthogonal multiple access (NOMA) along with wireless power transfer have recently been adapted to cooperative communications for 5G and beyond wireless networks. This paper investigates NOMA based cooperative relaying wireless- powered networks (CRWPNs) where, decode-and-forward (DF) relaying and successive interference cancellation are both employed at a wireless-powered intermediate node. For simultaneous wireless information and power transfer (SWIPT), power-splitting relaying (PSR) and time switching-based relaying (TSR) protocols are considered in the NOMA based CRWPN. As a result, the combination of cooperative relaying power domain NOMA network and PSR and TSR protocols is proposed in this paper. The outage performance and ergodic rate of both protocols are analysed for evaluation of the impacts of energy harvesting (EH) time, EH efficiency, power splitting ratio, source data rate, and the distance between the nodes. In addition, two delay limited transmission (DLT) and delay tolerant transmission (DTT) modes are considered in this network model to investigate the throughput and ergodic rate of the system according to the source transmission rate. It is shown that the cooperative relaying NOMA (CRNOMA) scheme achieves a lower outage probability when compared to the conventional orthogonal multiple access (OMA) schemes. Additionally, the PSR outperforms the TSR in both low and high signal-to-noise ratio (SNR) regions in terms of throughput, ergodic rate and energy efficiency. For instance, the outage probability of CRNOMA for both PSR and TSR in SNR range of from -10 dB to +20 dB (i.e. a low SNR region) decreases gradually but not linearly. However, in SNR range of from +20 dB to +40 dB (i.e. a high SNR region), the outage probability of CRNOMA for both PSR and TSR decreases quickly. Furthermore, the energy efficiency is shown to be considerably enhanced with the employment of EH for CRNOMA. Finally, the impacts of the distance between the nodes on the performance and a comparison between two scenarios of having and without having direct links are evaluated

Enabling non-linear energy harvesting in power domain based multiple access in relaying networks: Outage and ergodic capacity performance analysis

The Power Domain-based Multiple Access (PDMA) scheme is considered as one kind of Non-Orthogonal Multiple Access (NOMA) in green communications and can support energy-limited devices by employing wireless power transfer. Such a technique is known as a lifetime-expanding solution for operations in future access policy, especially in the deployment of power-constrained relays for a three-node dual-hop system. In particular, PDMA and energy harvesting are considered as two communication concepts, which are jointly investigated in this paper. However, the dual-hop relaying network system is a popular model assuming an ideal linear energy harvesting circuit, as in recent works, while the practical system situation motivates us to concentrate on another protocol, namely non-linear energy harvesting. As important results, a closed-form formula of outage probability and ergodic capacity is studied under a practical non-linear energy harvesting model. To explore the optimal system performance in terms of outage probability and ergodic capacity, several main parameters including the energy harvesting coefficients, position allocation of each node, power allocation factors, and transmit signal-to-noise ratio (SNR) are jointly considered. To provide insights into the performance, the approximate expressions for the ergodic capacity are given. By matching analytical and Monte Carlo simulations, the correctness of this framework can be examined. With the observation of the simulation results, the figures also show that the performance of energy harvesting-aware PDMA systems under the proposed model can satisfy the requirements in real PDMA applications.Web of Science87art. no. 81