Energy Harvesting Relay Research Articles

Transmission Policy of Two-Way Relay Networks With Multiple Stochastic Energy Harvesting Nodes

The online optimal transmission policy and outage performance are investigated for energy harvesting (EH) two-way relay (TWR) networks by exploiting a real-data-driven stochastic EH model. In this network, two solar-powered source nodes are both equipped with finite-sized batteries, and communicate with each other via a relay node. Two energy supply modes are studied for the relay node: fixed power (FP) or solar-powered as an EH node with a finite-sized battery. The long-term outage probability of the TWR network is optimized by adapting the transmission power of all EH nodes to the causal solar EH condition, the fading channel states and the energy storage of their batteries. Thus, the framework is formulated as a Markov decision process (MDP), and the reward function is defined as the complement of the network's conditional outage probability, whose exact closed-form is derived theoretically. Based on the MDP model, the optimal transmission policy and expected outage probability of the network are computed. In the FP relay mode, a two-dimensional (2D) on-off threshold structure of the optimal policy is revealed, and it shows the 2-D zero-action, non-conservative and power-converged properties of the power actions of the two EH source nodes. This special property indicates the transmission interaction between the two EH source nodes. Further, the outage performance limit of the network is found out to be determined by the deficiency probability of network batteries, and it reflects the impact of the EH capabilities of the two source nodes on the network performance. Moreover, in the EH relay mode, a more complicated three-dimensional on-off threshold structure of the optimal policy and the outage performance limit of the network are also derived, reflecting the impact of the EH relay on the network's power allocation and outage performance, respectively. Finally, computer simulations are demonstrated to verify the theoretical analysis.

Utility-Based Stable Matching For Large Scale EH Relay Networks With Finite-Alphabet Inputs

The computational complexity of utility optimization for a large scale energy harvesting (EH) relay network is extremely high, especially when inputting finite-alphabet signals. This paper investigates the utility optimization for large scale EH relay networks with finite-alphabet inputs by the stable matching scheme. First, we divide the nodes, which may act as a user or a relay, into multiple clusters, and perform optimization strategy within the clusters. Second, the optimal power bought from the relay node to maximize the utility of the user is derived. Then, the mutual preference matrices between the users and relays by the maximum utility criterion are established. Base on the mutual preference matrices, an improved Gale-Shapley (GS) algorithm is proposed to get a sub-optimal result. The simulation results demonstrate that the proposed algorithm can bring significant performance improvements and achieve higher energy efficiency compared with the conventional algorithms. In contrast to the exhausted Search (ES) method, it costs much less time and accomplishes an approximative utility output. Moreover, the proposed scheme incurs low signaling overhead which makes it practical to be implemented.

Optimal Resource and Power Allocation With Relay Selection for RF/RE Energy Harvesting Relay-Aided D2D Communication

Device-to-device (D2D) communication is considered as a promising technology for improving both the spectral and energy efficiencies of cellular networks by reusing the resources of conventional cellular users (CUs) for direct communication of two nearby devices in a spatial manner. When the channel between the two D2D devices is highly attenuated, it is necessary to use an intermediate relay to achieve reliable and flexible relay-aided D2D communication. In order to motivate the cooperative relays to participate, it is assumed that they can harvest energy from radio frequency (RF) signals based on the power splitting (PS) protocol as well as renewable energy (RE) sources. However, resource sharing between the cellular and relay-aided D2D links leads to mutual interference that degrades their sum rate. Considering the energy-harvesting relays (EHRs) and downlink (DL) resource sharing, this paper aims to maximize the sum rate of both the links without degrading the quality of service (QoS) requirements of all users. Our maximization problem is formulated as a mixed-integer nonlinear programming (MINLP) problem that cannot be solved in a straightforward manner. Therefore, we propose a low complexity algorithm, namely the resource and power allocation with relay selection EH-aided algorithm (RPRS-EH), which determines the reuse partners, the PS factor sub-optimal value with optimal links power allocation, and provides two different strategies for optimal relay selection. The numerical results show the behavior of the proposed algorithm under various parameters as well as its considerable performance when compared to one of the most recent algorithms in terms of the links sum rate and relay energy efficiency.

Energy harvesting two‐way relaying with antenna selection scheme

This study investigates the performance of a bidirectional/two-way relaying scheme with an energy-harvesting relay while amplify-and-forward relaying is performed. With multiple antennas at the relay, the authors propose the use of the max-min antenna selection scheme in the context of an energy harvesting scenario. They show that the proposed scheme attains diversity gain, whereby its end-to-end symbol error probability performance improves with increments in the number of energy harvesting relay antennas. For limited battery capacity at the energy harvesting node, they derive the lower bound of the outage probabilities and observe a good match between the analytical and simulated results. For this scenario, a simple power provisioning technique is proposed to optimise the end nodes' transmission powers. It is observed that the proposed technique saves significantly more transmission energy than the conventional equal power provisioning technique.

On Secure Wireless Sensor Networks With Cooperative Energy Harvesting Relaying

In this paper, we investigate the physical layer security (PLS) of a wireless sensor network (WSN) that consists of a base station (BS), multiple sensor nodes (SNs), and multiple energy-limited relays (ERs) in the presence of a passive eavesdropper (EAV). We adopt a time-switching/power-splitting (TSPS) mechanism for information transmission. The communication protocol is divided into two phases. The purpose of the first phase is to decode information, and energy harvesting (EH) is performed in accordance with the TSPS protocol. The purpose of the second phase is to transmit information to multiple destinations using the amplify-and-forward (AF) technique. In this study, we introduce a multirelay cooperative scheme (MRCS) to improve the secrecy performance. We derive analytical expressions for the secrecy outage probability (SOP) of the MRCS and that of the noncooperative relay scheme (NCRS) by using the statistical characteristics of the signal-to-noise ratio (SNR). Specifically, we propose an optimal relay selection scheme to guarantee the security of the system for the MRCS. In addition, Monte Carlo simulation results are presented to confirm the accuracy of our analysis based on simulations of the secrecy performance under various system parameters, such as the positions and number of ERs, the EH time, and the EH efficiency coefficients. Finally, the simulation results show that the secrecy performance of our MRCS is higher than that of the NCRS and the traditional cooperative relay scheme (TCRS).

Multi-Dimensional Resource Optimization for Incremental AF-OFDM Systems With RF Energy Harvesting Relay

Integrating radio frequency energy harvesting into wireless communications to support simultaneous wireless information and power transfer (SWIPT) is a promising technique to extend lifetime of energy-limited wireless cooperative networks. In this paper, multiuser resource optimization for incremental amplify-and-forward orthogonal frequency division multiplexing relaying systems with SWIPT is investigated. To maximize the overall achievable rate, multi-dimensional degrees of freedom (e.g., power allocation, subcarrier assignment, incremental policy, and power splitting ratio) are jointly optimized, subject to the transmission power as well as the quality of service constraints. The optimization problem is formulated as a mixed-integer nonlinear programming and the corresponding solution entails prohibitively high computational complexity. This motivates us to find a suboptimal solution with the aim of realizing a better tradeoff between performance and complexity. Specifically, dual decomposition and subgradient algorithm are applied to achieve this goal and the essence of our proposal is that the variables to be optimized are sequentially and iteratively derived. Finally, complexity analysis and simulation results are shown to verify the effectiveness of the proposed scheme.

Optimal System Performance in Multihop Energy Harvesting WSNs Using Cooperative NOMA and Friendly Jammers

In this paper, we investigate the system performance of multihop energy harvesting (EH) wireless sensor networks (WSNs) with imperfect channel state information (CSI) using cooperative non-orthogonal multiple access (NOMA) and friendly jammers in the presence of multiple passive eavesdroppers (EAVs). Specifically, we propose a two-phase communication protocol consisting of EH and information transmission (IT). In the first phase, relays in all clusters harvest energy from power transfer station (PTS) signals. In the first time slot of the second phase, the gateway simultaneously broadcasts information and interference signals. In the subsequent time slots, a relay acting as a friendly jammer in each cluster uses the harvested energy to send an interference signal. Simultaneously, another EH relay applies the NOMA technique to transmit the information signal according to an optimal scheduling scheme based on the maximum signal-to-interference-plus-noise ratio (SINR) of a far user (MSm) and a near user (MSn). To ensure security performance, we propose an algorithm for determining the EH time constraint for a friendly jammer. Additionally, closed-form expressions for the outage probability and throughput of the considered system are derived. Accordingly, an optimal power allocation coefficient algorithm is proposed to achieve throughput fairness for pairs of users. The results of the mathematical analysis are verified by Monte Carlo simulations. Finally, the numerical results demonstrate that the MSn scheme is recommended for guaranteeing throughput fairness for pairs of users.

Transceiver Design for Downlink SWIPT NOMA Systems With Cooperative Full-Duplex Relaying

This paper studies the application of simultaneous wireless information and power transfer (SWIPT) to downlink non-orthogonal multiple access (NOMA) system. A novel cooperative NOMA protocol for high communication reliability and user fairness is proposed, where a near NOMA user acts as a full-duplex (FD) energy-harvesting relay to help transmission from the source node S to the far NOMA user. The power splitting (PS) architecture is adopted at the relay to perform the SWIPT. The aim is to maximize the data rate of the near NOMA user while satisfying the QoS requirement of the far NOMA user and the energy causality condition of the near NOMA user. The formulated problem is a non-convex fractional programming. By jointly optimizing the power allocation factor, the PS ratio, the receiver filter, and the transmit beamforming, we propose alternative optimization (AO)-based algorithm to obtain an optimal solution. In addition, a low-complexity suboptimal scheme is proposed and the semi-closed form solution is derived to characterize the performance of our proposed design. The simulation results verify the correctness of theoretical analysis and show performance gain of our proposed protocol over the existing transmission protocols.

Secrecy Performance of CCRN with an EHAF Relay under Source and Destination Jamming

SummaryIn this paper, we investigate the secrecy performance of a cooperative cognitive radio network (CCRN) considering a single energy harvesting (EH) half‐duplex amplify and forward (AF) relay and an eavesdropper (EAV). Power is allocated to each node under cognitive constraints. Because of the absence of a direct wireless link, secondary source (SS) communicates with secondary destination (SD) in two time slots. The SD and the SS broadcast jamming signal to confuse the EAV in the first and in the second time slots, respectively. The relay harvests energy in the first time slot and amplifies and forwards the signal to SD in the second time slot. The EAV employs maximal ratio combining scheme to extract the information. We evaluate the performance in terms of secrecy outage probability (SOP) of the proposed CCRN. The approximate expression of SOP is obtained in integration form. Improvement in SOP is expected for the proposed CCRN because of the use of jamming signals. The secrecy performance of CCRN improves with increase in primary transmit power, peak transmit power of secondary nodes, channel mean power, and energy conversion efficiency but degrades with increase in threshold outage rate of primary receiver and threshold secrecy rate. A MATLAB‐based simulation framework has been developed to validate the analytical work.

Optimization of Links With a Battery-Assisted Time-Switching Wireless Energy Harvesting Relay

In this paper, we analyze the performance of a two-hop network in which a multiantenna source communicates with a single-antenna destination through a decode-and-forward single-antenna energy harvesting (EH) relay. We assume a novel practical system framework in which the EH relay has the option of augmenting the wireless energy harvested by drawing energy from a supplementary battery, thereby improving link performance. Assuming use of the time-switching relaying (TSR) EH protocol, the outage and throughput performance are analyzed. We optimize the fraction of time devoted to EH (the TSR parameter) so as to maximize throughput for fixed supplementary battery energy. We also optimize the TSR parameter to minimize supplementary battery energy consumption for target throughput performance. We further show that exploiting second-hop channel knowledge at the relay can dramatically reduce the energy drawn from the supplementary battery. These insights are of fundamental importance to system designers. Simulation results validate the derived analytical expressions and corroborate our findings.

Optimizing Wireless Powered Two-Way Communication System With EH Relays and Non-EH Relays

This correspondence paper studies joint beamforming optimization and time allocation for a wireless powered two-way hybrid-relay network. As a general relaying architecture accommodating the existing relaying architectures in the literature as two special cases, we consider the two-way communication system where both energy-harvesting (EH) relays and non-EH relays exist. We aim to maximize the minimum rate by jointly optimizing the distributed beamforming vector at the relays, the energy beamforming matrix at the non-EH relays, and the EH time allocation with the energy constraints at the relays. The formulated problem is intractable to solve because the objective function and the energy constraints are highly nonconvex. We solve the optimization problem using the successive convex approximation. Simulations demonstrate that the proposed iterative algorithm considerably outperforms any existing approaches.

Achievable Rate Region of the Buffer-Aided Two-Way Energy Harvesting Relay Network

In this paper, we investigate the buffer-aided two-way wireless energy harvesting (EH) relay network comprising two users and one relay, where two users exchange information with the help of the relay via three phases of EH, multiple-access, and broadcast . By transforming the opportunistic scheduling design problem into an equivalent convex problem, we present the adaptive design for the buffer-aided two-way EH relay network to maximize the long-term achievable rate region. To fulfill the delay sensitive transmission requirements, a delay-aware adaptive transmission (DAAT) scheduling scheme is proposed to guarantee the average end-to-end delivery delay by employing the Lyapunov optimization framework. Our analysis discloses that the average achievable rate region of the two-way wireless EH relay network can be improved when fully considering the potentials by deploying data buffer and energy storage at the relay. There exists an inherent tradeoff among the achievable sum rate, the delivery delay, and the power consumption. It is shown that, when a certain time delay is tolerable, the DAAT scheduling scheme is able to realize a rate region arbitrarily close to the achievable rate region of the buffer-aided two-way wireless EH relay network.

Secure communication with energy harvesting multiple half-duplex DF relays assisted with jamming

Physical layer security in relay based cooperative networks is a promising approach to maintain confidentiality of information. In this paper, secrecy performance of a dual hop network, with multiple energy harvesting decode and forward (DF) relays, has been analyzed where an eavesdropper also receives the information from the transmission of a selected relay. A selected DF relay harvests energy based on power splitting (PS) scheme in the first time slot. In the second time slot, the selected DF relay transmits the information as well as jamming signals, only when it has harvested sufficient power as decided by a threshold, based on the outage constraint of the network. The secrecy outage probability (SOP) under some assumed conditions, termed as a conditional SOP (CSOP), has been evaluated in closed form. Performance regarding the CSOP increases with increase in transmits power of the source, threshold outage rate, number of relay and energy conversion efficiency, whereas it decreases with an increase in threshold secrecy rate. We indicate the optimal value of PS factor for harvesting energy and the optimal value of a fraction of harvested energy devoted to information signal transmission at which the CSOP is minimum. The SOP without any condition has also been evaluated with and without jamming. The results shows that the CSOP yields better results than the SOP. It is observed that the CSOP with jamming is better than the SOP with jamming by 49.12% for 1 bits/s/Hz threshold secrecy rate and by 81.94% for a threshold secrecy rate of 0.5 bits/s/Hz, respectively at 10 dBW of the source transmits power. A MATLAB based simulation is used to verify our analytical works of the CSOP and the SOP with jamming.

Resource Management in Energy Harvesting Cooperative IoT Network under QoS Constraints.

Cooperative communication with RF energy harvesting relays has emerged as a promising technique to improve the reliability, coverage, longevity and capacity of future IoT networks. An efficient relay assignment with proper power allocation and splitting is required to satisfy the network’s QoS requirements. This work considers the resource management problem in decode and forward relay based cooperative IoT network. A realistic mathematical model is proposed for joint user admission, relay assignment, power allocation and splitting ratio selection problem. The optimization problem is a mixed integer non-linear problem (MINLP) whose objective is to maximize the overall sum rate (bps) while satisfying the practical network constraints. Further, an outer approximation algorithm is adopted which provides epsilon-optimal solution to the problem with guaranteed convergence and reasonable complexity. Simulations of the proposed solution are carried out for various network scenarios. The simulation results demonstrate that cooperative communication with diversity achieves a better admission of IoT users and increases not only their individual data rates but also the overall sum rate of an IoT network.

Performance analysis of downlink NOMA–EH relaying network in the presence of residual transmit RF hardware impairments

In this paper, we investigate the effects of residual-transmit radio-frequency impairments on the downlink non-orthogonal multiple access system with perfect successive interference cancellation using an energy-harvesting (EH) relay in which nodes in the network are equipped with a single antenna. The source node communicates with two users with the help of the amplify-and-forward EH relay node. In addition, both the power-splitting relaying (PSR) and time-switching relaying (TSR) protocols are examined. To evaluate the performance of the proposed system, closed-form expressions of the outage performance and the available throughput are derived over Rayleigh fading channels. Moreover, the accuracy of analytical results is verified by a Monte Carlo simulation. The results show the effects of various parameters, such as power allocation factors, the relay node location, data rate, transmit hardware impairment level, and power allocation factors on the outage performance ($${\mathcal {OP}}$$) and throughput with two users for both PSR and TSR architectures in the presence of hardware impairments. Furthermore, these results are compared with performance of orthogonal multiple access (OMA) EH relaying system.

A Hybrid Power Line/Wireless Dual-Hop System With Energy Harvesting Relay

This paper investigates the benefits that energy harvesting (EH) can offer to increase energy efficiency in hybrid power line/wireless data communication systems for smart grid (SG) and Internet of Things (IoT) applications. In this regard, the ergodic achievable data rates of a hybrid power line/wireless dual-hop system (H2HS) model that uses EH strategies and the amplify-and-forward protocol at the relay node are considered. Also, four approaches for performing EH in the H2HS system are discussed. Performance comparisons among the H2HS, a dual-hop power line and a dual-hop wireless systems are performed by adopting four simulation settings, covering the combinations of optimal or uniform power allocation together with colored or white additive noise at the output of the power line channel. Numerical results show that the H2HS model with the power splitting EH strategy outperforms the other models. Moreover, if the transmission power of the source node is high, then the case with additive colored noise at the received power line signal can result in higher achievable data rates in comparison to the white noise case. Overall, the H2HS system making use of an EH strategy has the potential to increase the sustainability and energy efficiency in data communications for SG and IoT applications.

Joint Beamforming Design and Time Allocation for Wireless Powered Asymmetric Two-Way Multirelay Network

This paper studies the joint beamforming design and time allocation for a two-way energy harvesting (EH) relay network, where a single-antenna base station and a single-antenna user communicate with each other through multiple-single antenna EH relay nodes, and an external multiantenna power beacon wirelessly power the relays. Unlike the existing studies that assumed the symmetric two-way relaying scenario, we assume a more practical scenario of asymmetric two-way relaying considering different traffic demands on the downlink and uplink. In this paper, we design the optimal beamforming vectors at the relays and at the power beacon jointly with the time allocation between information and EH transmissions, in the sense of maximizing the sum rate of the asymmetric information transmission under the EH constraints at the relays, and the power constraint at the power beacon. The formulated optimization problem is nonconvex, and thus, it is difficult to solve. To solve this challenging problem, we propose an iterative algorithm based on the semidefinite relaxation and the successive convex approximation techniques. Also, to reduce the computational complexity, we propose an efficient noniterative scheme based on the maximum-ratio transmission. The performance of the proposed schemes is demonstrated through simulations.

Performance of EH Protocols in Two-Hop Networks With a Battery-Assisted EH Relay

In this paper, we compare the performance of time-switching relaying (TSR) and power-splitting relaying (PSR) protocols in two-hop networks with a battery-assisted energy-harvesting (EH) amplify-and-forward relay. In this battery-assisted relay framework, the EH relay augments the harvested energy with energy drawn from a battery. Using expressions derived for throughput and average battery energy consumption, we investigate maximization of throughput for given battery energy availability per time slot and minimization of battery energy consumption for target throughput requirement. When only statistical channel knowledge is available, PSR results in better throughput performance at practical signal-to-noise ratios. However, in the typical low battery energy and low target throughput regime, it is TSR that is more battery energy efficient. When second-hop instantaneous channel knowledge is available, we observe dramatical energy savings that increases lifetime of nodes. Simulation results are presented to demonstrate accuracy of the derived expressions.

Outage Analysis and Power Allocation Optimization for Multiple Energy-Harvesting Relay System Using SWIPT

Energy harvesting (EH) combined with cooperative relying plays a promising role in future wireless communication systems. We consider a wireless multiple EH relay system. All relays are assumed to be EH nodes with simultaneous wireless and information transfer (SWIPT) capabilities, which means the relays are wirelessly powered by harvesting energy from the received signal. Each EH node separates the input RF signal into two parts which are, respectively, for EH and information transmission using the power splitting (PS) protocol. In this paper, a closed-form outage probability expression is derived for the cooperative relaying system based on the characteristic function of the system’s probability density function (PDF) with only one relay. With the approximation of the outage probability expression, three optimization problems are built to minimize the outage probability under different constraints. We use the Lagrange method and Karush–Kuhn–Tucker (KKT) condition to solve the optimization problems to jointly optimize the relay’s PS factors and the transmit power. Numerical results show that our derived expression of the outage probability is accuracy and gives insights into the effect of various system parameters on the performance of protocols. Meanwhile, compared with the no optimal condition, our proposed optimization algorithms can all offer superior performance under different system constraints.

Simultaneous Wireless Information and Power Transfer Strategies in Relaying Network With Direct Link to Maximize Throughput

In this paper, we investigate the optimal throughput performance for simultaneous wireless information and power transfer relaying network in the presence of direct link between the source and the destination. By considering the direct link, system performance can be improved when the channel condition is good from source to destination. The cooperative network consists of a source, an amplify-and-forward relay, and a destination, where the relay harvests energy from the source and then uses the harvested energy to forward information to the destination. At the destination node, the signals from the direct link and relay are combined by the maximum ratio combining (MRC) method. The time switching (TS) relaying protocol is applied to enable energy harvesting and information processing simultaneously. At the same time, we made progress on analyzing the throughput of information transmission on the basis of the MRC method with power switching (PS) relaying protocol. Additionally, adaptive-MRC protocol is proposed based on the TS and PS relaying protocols, which can choose better mode to achieve the communication. The numerical analyses provide practical insights into the effect of various system parameters, such as energy harvesting time splitting ratio, source transmission rate, distance between nodes, and noise power at the destination and the relay.