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Non-orthogonal multiple access (NOMA) enables the concurrent transmission of numerous user signals, ameliorating spectral efficiency by superimposing these signals. NOMA users utilize energy harvesting to efficiently utilize available energy sources. The energy harvesting process is non-linear in general. Additionally, innumerable antennas are used at the NOMA transmitter and power source to facilitate efficient energy transfer and information transmission with antenna selection (AS). Also, wireless channels cause path loss, fading, and shadowing effects, which directly influence harvested energy and communication reliability. Accordingly, the work assesses the outage performance and throughput of NOMA, examining realistic aspects like non-linear energy harvesting (nlEH), AS, multiple antennas, and κ - μ shadowed fading. The findings indicate a considerable performance degradation due to nlEH. Moreover, appropriate parameter selection is crucial for preventing complete outages in NOMA networks and achieving optimal performance. In addition, the performance of NOMA networks meliorates with an accreting number of antennas. Furthermore, the AS criterion dramatically impacts performance difference between NOMA users. [ABSTRACT FROM AUTHOR]

This paper studies a multiuser multiple-input multiple-output simultaneous wireless information and power transfer cognitive radio system with the aid of an active intelligent reflecting surface (IRS). Considering the scenario that nonlinear energy harvesting models and power splitting (PS) protocols are adopted at energy receivers and that channel state information (CSI) imperfections of the channels to the primary users (PUs) are taken into consideration, we aim at designing the secondary base station (SBS) transmit precoding matrices, the IRS reflection coefficient matrix, and the secondary user (SU) PS ratios. The design objective is to maximize the system sum-rate (SR) under the transmit power constraints at the SBS, amplification power constraints at the IRS, amplitude constraints on IRS reflection elements, robust interference power (IP) constraints at the PUs, and minimum harvested energy constraints at the SUs. The formulated optimization problem is intractable to directly solve since the design variables are nonlinearly coupled, the objective function and constraints are highly nonconvex, and robust IP constraints are semi-infinite. To tackle the mathematical challenges, we derive the amenable surrogate functions and constraints while to handle the semi-infinite robust IP constraints, we transform them into linear matrix inequalities. Then, to find optimized solutions to the considered design problem, we exploit alternating optimization frames to derive an efficient iterative algorithm (IA). The convergence and computational complexity of the developed IA are shown. Simulation results illustrate the performance gains of the designed problem and robustness of IP constraints against CSI imperfections. Additionally, the numerical results show that the active IRS-aided systems exhibit superior SR performance over the passive IRS-aided systems. [ABSTRACT FROM AUTHOR]

Aiming at a cognitive radio network (CRN) consisting of a pair of primary users and M pairs of secondary users, the secondary throughput maximization for CRN based on the non-linear energy harvesting model was studied.Specifically, in the case of considering secondary transmitter (ST) circuit power, the secondary throughput maximization (STM) problem with primary users’ throughput demands was first modeled as a non-linear optimization problem and then transformed into a convex optimization problem.Finally, a low-complexity algorithm combining the golden section and dichotomy was proposed.By applying this low-complexity algorithm, the optimal time allocation of the primary transmitter (PT)’s energy transmission and secondary users’ information transmission, and the optimal transmission power of PT were obtained.In addition, for the case of neglecting the ST circuit power, the convex property of the STM problem was first proved, and then a more efficient algorithm was designed to solve it.The simulation results show that compared with the equal time allocation method and the link gain priority method, the proposed design algorithm significantly improves the throughput of secondary users.

Copyright of Telecommunications Science is the property of Beijing Xintong Media Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work investigates the performance of a laser-powered unmanned aerial vehicle (UAV) based hybrid wireless network consisting of a UAV-mounted base station (UAV-BS), cellular user, a low-power IoT user, and a secondary IoT network consisting of a group of multiple IoT devices. Communication among these devices takes place in two different phases. In the first phase of transmission, UAV-BS fulfills its power requirements by harvesting power from a distributed laser charging-based laser power transfer and uses non-orthogonal multiple access (NOMA) signaling to transmit the information to both the users. Further, in the second phase of transmission, the IoT user harvests power using power-splitting (PS) protocol and uses it to communicate with the selected IoT device, selected using a signal to interference-plus-noise ratio based selection strategy from the secondary IoT network, while the cellular user transmits uplink information to UAV-BS. We discuss the effect of non-linear energy harvesting on the performance of secondary IoT network and UAV-BS. Next, we analyze the performance of the proposed system by deriving the closed-form expressions of the outage probabilities, throughput, and ergodic capacity of both the users, the secondary IoT network, and UAV-BS. Furthermore, we find the optimal values of power coefficient and target rates that maximize the throughput of the IoT user while attaining a desired throughput for the cellular user. We also demonstrate that a judicious choice of the power allocation coefficient is essential in order to maximize the sum throughput of the system and hence the energy efficiency. Simulation results verify the accuracy of derived expressions and validate the effectiveness of proposed algorithms.

Energy Harvesting strategies coupled with the improvement of electronics and the progressive reduction of power requirements have been widely recognized as fundamental to enable self-powered (or autonomous) devices. Among all the potential energy sources, kinetic energy stemming from mechanical vibrations has been particularly extensively investigated for EH purposes due to its characteristics of heterogeneity and ubiquity. To exploit such energy sources, a suitable coupling mechanism to convert vibrations into electric charge is required; it must take into account the wide frequency bandwidth of mechanical vibrations as encountered in everyday scenarios. This review offers an overview of linear vs. non-linear strategies for EH, with a specific focus on different approaches to implement efficient coupling mechanisms; the performances of the specific solutions covered in this work are discussed.

We focus on the rate-optimal design of Wireless Powered Relay Networks (WPRNs) and propose a new cooperative communication scheme. Our scheme employs multiple wireless powered Amplify and Forward (AF) relays and relay selection and combines Time Splitting (TS), with Antenna Switching (AS) and Self Energy Recycling (SER). It consists of an initial Wireless Power Transfer (WPT) subframe, followed by a cooperative transmission subframe, during which one antenna is used for Energy Harvesting (EH) and SER and the remaining ones are used for data reception and data forwarding. For this scheme, we present solutions to the problems of 1) rate-optimal beamforming (BF) design, 2) rate-optimal, joint Harvesting Antenna Selection (HAS), BF design, and WPT subframe duration determination. Our solutions build on a generic piecewise linear EH model, which allows us to closely approximate the characteristics of different non linear EH measurements and models, by selecting the number of piecewise linear components and their parameters. In addition, we consider a realistic power consumption model at the relays that accounts for both transmit and circuit power consumption. Moreover, our BF solution is optimal and requires solving a set of simple optimization problems, where the solution of each one of them can be found in a simple closed form. Thus, it is characterized by low implementation complexity, and avoids sophisticated iterative optimization methods. To the best of our knowledge, this work is the first one to introduce a scheme, which combines TS, AS, and SER principles and exploits realistic EH and power consumption models at the relays. Finally, we assess the performance of our scheme over fading channels and find that it outperforms existing solutions that use the same hardware. [ABSTRACT FROM AUTHOR]

This paper studies the simultaneous wireless information and power transfer multi-antenna network with heterogeneous users and intelligent reflecting surface (IRS). Information decoding (ID) users, energy harvesting (EH) users, and power-splitting (PS) hybrid users require data and energy at the same time from the base station (BS) in the assistance of IRS. In the system model, the IRS reflects the incoming signal at each element by collaboratively adjusting phase shift to enhance the received signal at the users. In addition, the PS users exploit the PS circuit structure to simultaneously decode information and harvest energy via PS ratios. The target is to maximize the total PS-EH harvested power at PS and EH users with the non-linear EH model and limitation of BS transmit power while satisfying the signal-to-interference-plus-noise ratio requirements at ID and PS users. The information vectors at the BS, phase-shift vector at the IRS, and PS ratios at the hybrid users are jointly optimized by alternating optimization, semidefinite relaxation, sequential parametric convex approximation, and Gaussian randomization methods in the challenging non-convex problem. The numerical experiments present the convergence and effectiveness of the proposed algorithm. For certain parameters, the proposed IRS-assisted method enhances 17.65% total harvested power than the No-IRS one. [ABSTRACT FROM AUTHOR]

In this article, we investigate a multi-user multiple-input-single-output full-duplex system with simultaneous wireless information and power transfer under the non-linear energy harvesting model, where channel state information is imperfect. Since the channel estimation error is considered in our proposed system, the self-interference cannot be canceled perfectly. For such a system, a robust optimization problem that maximizes the minimum average total harvested power by jointly optimizing the uplink and downlink beamforming matrices is formulated. As the problem is non-linear and non-convex under channel estimation errors, a novel Newton method based iterative optimization algorithm is proposed to solve it efficiently. In each iteration, the semidefinite relaxation technique and S-Procedure method are applied to obtain the optimal beamforming vectors, which are proved to be optimal solutions with rank-one. Simulation results reveal that the proposed robust design can achieve better system performance than the non-robust scheme, both of which are based on the non-linear energy harvesting model.

In this paper, a novel intelligent reflecting surface (IRS)-assisted wireless powered communication network (WPCN) architecture is proposed for power-constrained Internet-of-Things (IoT) smart devices, where IRS is exploited to improve the performance of WPCN under imperfect channel state information (CSI). We formulate a hybrid access point (HAP) transmit energy minimization problem by jointly optimizing time allocation, HAP energy beamforming, receiving beamforming, user transmit power allocation, IRS energy reflection coefficient and information reflection coefficient under the imperfect CSI and non-linear energy harvesting model. On account of the high coupling of optimization variables, the formulated problem is a non-convex optimization problem that is difficult to solve directly. To address the above-mentioned challenging problem, alternating optimization (AO) technique is applied to decouple the optimization variables to solve the problem. Specifically, through AO, time allocation, HAP energy beamforming, receiving beamforming, user transmit power allocation, IRS energy reflection coefficient and information reflection coefficient are divided into three sub-problems to be solved alternately. The difference-of-convex (DC) programming is used to solve the non-convex rank-one constraint in solving IRS energy reflection coefficient and information reflection coefficient. Numerical simulations verify the superiority of the proposed optimization algorithm in decreasing HAP transmit energy compared with other benchmark schemes. [ABSTRACT FROM AUTHOR]

Wireless power transfer is considered as a novel solution for energy harvesting in wireless communication networks. In this paper, the system performance of the non-linear energy harvesting based power splitting relaying in the full-duplex relaying sensor network is investigated. We considered the system model network with one source, one destination, and one relay node in both the amplify-and-forward and decode-and-forward modes. The closed-form expressions of the system outage (OP) are analysed and derived for verifying system performance. Then, the correctness of the OP closed-form expression is verified by using the Monte Carlo simulation. Furthermore, the influence of the primary system parameters on the system OP is suggested and investigated. The research results indicated that the simulation curves and the analytical curves overlapped, verifying the correctness of the analytical expressions.

In order to enhance system energy efficiency, bidirectional link resource allocation strategy in GFDM-based multiuser SWIPT systems is proposed. In the downlink channel, each SWIPT user applies power splitting (PS) receiver structure in information decoding (ID) and non-linear energy harvesting (EH). In the uplink channel, information transmission power is originated from the harvested energy. An optimization problem is constructed to maximize weighted sum ID achievable rates in the downlink and uplink channels via bidirectional link power allocation as well as subcarriers and subsymbols scheduling. To solve this non-convex optimization problem, Lagrange duality method, sub-gradient-based method and greedy algorithm are adopted respectively. Simulation results show that the proposed strategy is superior to the fixed subcarrier scheme regardless of the weighting coefficients. It is superior to the heuristic algorithm in larger weighting coefficients scenario. [ABSTRACT FROM AUTHOR]

A reconfigurable intelligent surface (RIS)-assisted wireless communication system with non-linear energy harvesting (EH) and ultra-reliable low-latency constraints is considered for its possible applications in industrial automation. A distant data-center (DC) communicates with the multiple destination machines with the help of a full-duplex (FD) server machine (SM) and RIS. Assuming the deficiency of enough transmission power at the FD-SM, the SM is considered in the near vicinity of the destinations in the industry to forward the data received from the distant DC. The reception at SM is assisted by the RIS and a non-linear hybrid power-time splitting (PTS) based EH receiver architecture is adopted to extend the lifespan of SM, thus increasing network lifetime. The scheduling of multiple destinations is done by SM based on the considered selection criteria namely, random (RND) scheduling, absolute (ABS) channel-power-based (CPB) scheduling and normalized (NRM) CPB scheduling. The end-to-end performance of the considered FD RIS-assisted network is analyzed, and the expressions for the block error rate (BLER) for all scheduling schemes are derived. Moreover, the effects of number of RIS elements, packet size, channel uses on the system performance are analyzed for the considered ultra-reliable and low-latency communication (URLLC) network. The scheduling fairness of all the scheduling schemes is also analyzed to study the performance-fairness trade-off. The derived analytical results are verified through Monte-Carlo simulations. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) is an effective way to prolong the lifetime of the energy-constraint networks. In this paper, we investigate a wireless powered cooperative non-orthogonal multiple access (WP-CNOMA) system, consisting of a power beacon (PB), an information transmitter (S), multiple relays (R) and two information receiving devices with near device D1 and far device D2. We assume both S and R are energy-constraint and there is no direct link between S and D2. With the help of PB, S and R can harvest energy from it to restart the communication for WP-CNOMA network. For such a system, low-complexity but effective relay and antenna selection schemes are applied. To characterize the performance, outage probabilities and average throughput are derived for linear and non-linear energy harvesting (EH) models, respectively. Moreover, to maximize the average throughput, invoking the unimodal feature for average throughput with respect to the EH time, we find the optimal EH time via Golden section search method. Simulation results validate the accuracy of analytical results, and reveal the performance gain for our system over the benchmark schemes. Also, it can be seen that the non-linear EH model shows different outage behaviors from the linear one. On the other hand, considering the practical application and to improve the performance, the optimization for a simple WP-CNOMA system with single-antenna PB and single relay is also investigated, in which we aim to maximize the minimum throughput by jointly optimizing EH time and power allocation. A low-complexity analytical method is developed to find the max-min rate. Numerical results show that through optimization, the system performance can be improved significantly.

In this article, we investigate the performance of a piece-wise linear model of energy harvesting-based multiuser overlay spectrum sharing system. Herein, an energy-constrained secondary node acts as a cooperative relay to assist the information transmission between a primary transmitter and multiple primary receivers. In return for the cooperation, the secondary node enjoys access to the primary user's spectrum for its own information transfer. Specifically, by employing a time-switching based receiver, the secondary node harvests energy from the received radio-frequency signal of primary transmitter during a dedicated energy harvesting phase. In the subsequent information transfer phase, the secondary node splits the harvested power to forward the primary data as well as its own information intended for another secondary user. We analyze the impact of decoding primary's information at the secondary receiver on the performance of secondary network. Importantly, we propose an improved energy harvesting-based relaying scheme which makes an efficient use of available degrees of freedom and thereby enhances the performance of both primary and secondary networks significantly. For this analytical framework, we derive the expressions of outage probability for primary and secondary networks. Numerical and simulation results are obtained to extract various useful insights and to validate our theoretical developments.

This paper considers a max-min rate optimization problem with practical non-linear energy harvesting (NLEH) in which a multi-antenna hybrid access point transfers power to the devices via energy beamforming (BF), followed by the devices sending their data simultaneously by consuming the harvested energy. Using a sigmoid NLEH model with sensitivity, we tackle the joint energy BF and time allocation problem in two steps by solving the NLEH-aware energy BF problem for given time allocation and then solving the convex time allocation problem formulated with the aforementioned energy BF solution. We propose several iterative methods to solve the non-convex energy BF problem with and without approximation of the NLEH function. In addition, we present an asymptotic energy BF problem for a large-antenna system that can be solved at low complexity. The results show that the algorithms developed with a simple NLEH approximation provide almost the same performance with the algorithms developed with the exact NLEH function. Furthermore, the sensitivity region of the NLEH should be considered more carefully than the saturation region in the max-min rate optimization problem.

This paper investigates the relationship among the traffic throughput, statistical data latency requirement and system configurations in a wireless powered multimedia communication system. Firstly, a system model is built up with considerations of two operation modes and practical non-linear energy harvesting process. Based on the system model, the effective capacity of the considered system is derived based on the wireless charging parameter and fix data transmission rate. Then, the latency violation provability is studied by jointly taking effective capacity, traffic arrival and maximum tolerable data latency into account. Thereafter, the traffic maximization problem is transformed to the effective capacity maximization problem. Furthermore, We propose an optimal solution and a near-optimal solution to find out the system configurations of wireless charging time and transmission rate. Simulation results verify the accuracy of the near-optimal solution and also shed light on the operation mode selection in the considered system.

Mobile-edge computing (MEC) and wireless power transfer are technologies that can assist in the implementation of next generation wireless networks, which will deploy a large number of computational and energy limited devices. In this letter, we consider a point-to-point MEC system, where the device harvests energy from the access point’s (AP’s) transmitted signal to power the offloading and/or the local computation of a task. By taking into account the non-linearities of energy harvesting, we provide analytical expressions for the probability of successful computation and for the average number of successfully computed bits. Our results show that a hybrid scheme of partial offloading and local computation is not always efficient. In particular, the decision to offload and/or compute locally, depends on the system’s parameters such as the distance to the AP and the number of bits that need to be computed. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel hybrid user pairing (HUP) scheme in multiuser multiple-input single-output non-orthogonal multiple access networks with simultaneous wireless information and power transfer. In this system, two information users with distinct channel conditions are optimally paired while energy users perform energy harvesting (EH) under non-linearity of the EH circuits. We consider the problem of jointly optimizing user pairing and power allocation to maximize the overall spectral efficiency (SE) and energy efficiency (EE) subject to user-specific quality-of-service and harvested power requirements. A new paradigm for the EE-EH trade-off is then proposed to achieve a good balance of network power consumption. Such design problems are formulated as the maximization of non-concave functions subject to the class of mixed-integer non-convex constraints, which are very challenging to solve optimally. To address these challenges, we first relax binary pairing variables to be continuous and transform the design problems into equivalent non-convex ones, but with more tractable forms. We then develop low-complexity iterative algorithms to improve the objectives and converge to a local optimum by means of the inner approximation framework. Simulation results show the convergence of proposed algorithms and the SE and EE improvements of the proposed HUP scheme over state-of-the-art designs. In addition, the effects of key parameters such as the number of antennas and dynamic power at the BS, target data rates, and energy threshold, on the system performance are evaluated to show the effectiveness of the proposed schemes in balancing resource utilization. [ABSTRACT FROM AUTHOR]

Wirelessly-powered sensor networks (WPSNs) are becoming increasingly important in different monitoring applications. We consider a WPSN where a multiple-antenna base station, which is dedicated for energy transmission, sends pilot signals to estimate the channel state information and consequently shapes the energy beams toward the sensor nodes. Given a fixed energy budget at the base station, in this paper, we investigate the novel problem of optimally allocating the power for the channel estimation and for the energy transmission. We formulate this non-convex optimization problem for general channel estimation and beamforming schemes that satisfy some qualification conditions. We provide a new solution approach and a performance analysis in terms of optimality and complexity. We also present a closed-form solution for the case where the channels are estimated based on a least square channel estimation and a maximum ratio transmit beamforming scheme. The analysis and simulations indicate a significant gain in terms of the network sensing rate, compared to the fixed power allocation, and the importance of improving the channel estimation efficiency. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Signal Processing is the property of Journal of Signal Processing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper considers a cognitive small cell network, where one cognitive base station (CBS) transmits information to the cognitive user and energy to the energy harvesting receivers (EHRs). The Markov channel model is exploited to characterize the state change of the macrocell base station. The spectrum sensing time, the spectrum sensing interval, and the beamforming matrixes of the CBS are jointly optimized to achieve three goals: the maximization of the CBS throughput, the minimization of the energy cost of the CBS, and the minimization of the interferences to the macrocell users (MUEs). These objectives are optimized subject to the interference constraints of the MUEs, the secrecy rate constraint, the transmit power constraint of the CBS, and the energy harvesting constraints of the EHRs. The formulated problems are challenging non-convex and difficult to solve. A 1-D line search method and semidefinite relaxation-based algorithm is proposed to solve these problems. It is proved that the optimal solution can be obtained under some conditions. If the conditions are not satisfied, Gaussian randomization procedure is used to obtain the suboptimal solutions. Simulation results verify our theoretical findings and demonstrate the effectiveness of the proposed resource allocation scheme.

The design of energy harvesting (EH) scheme is one of important issues in energy-constrained relaying networks. Since most of the existing EH schemes assume a linear EH model, which cannot capture the properties of EH circuits, the EH schemes dedicated for a practical EH model should be redesigned. Based on the time switching (TS) and power splitting (PS) receiver architectures, we study two EH schemes, namely, PS scheme and TS scheme, in an amplify-and-forward (AF) energy-constrained relaying network under a non-linear EH model. Two problems are formulated to maximize the achievable throughput based on the instantaneous channel state information by optimizing the PS ratio and TS ratio, respectively. The solutions for both EH schemes are obtained. Numerical results are presented to show that the designed EH schemes based on the non-linear EH model are able to achieve a higher throughput than those based on the existing linear model. It is found that employing a non-linear energy harvester instead of the linear one into AF relaying network, and the PS scheme still outperforms the TS scheme in general.

In wireless power transfer (WPT)-assisted relaying systems, spectral efficiency (SE) of source-relay link plays a dominant role in system SE performance due to the limited transmission power at the WPT-aided relay. In this paper, we propose a novel protocol for a downlink orthogonal frequency division multiple access (OFDMA) system with a WPT-aided relay operating in full-duplex (FD) decode-and-forward (DF) mode, where the time slot durations of the source-relay and relay-users hops are designed to be dynamic, to enhance the utilization of degrees of freedom and hence the system SE. In particular, a multiple-input and signal-output (MISO) source-relay channel is considered to satisfy the stringent sensitivity of the energy harvesting (EH) circuit at the relay, while a single-input and single-output (SISO) relay-user channel is considered to alleviate the power consumption at the relay node. Taking into account the non-linearity of EH efficiency, a near-optimal iteration-based dynamic WPT-aided FD relaying (A-FR) algorithm is developed by jointly optimizing the time slot durations, subcarriers, and transmission power at the source and the relay. Furthermore, self-interference generated at the relay is utilized as a vital energy source rather than being canceled, which increases substantially the total energy harvested at the FD relay. We also reveal some implicit characteristics of the considered WPT-aided FD relaying system through intensive discussions. Simulation results confirm that the proposed A-FR achieves a significant enhancement in terms of SE with different relay's locations and the number of users, compared to the conventional symmetric WPT-aided FD relaying (S-FR) and the time-switching-based WPT-aided FD relaying (TS-FR) benchmarks. [ABSTRACT FROM AUTHOR]

This paper studies joint source and relay beamforming for a wireless powered downlink multirelay multiuser network. Considering nonlinear energy harvesting and imperfect channel state information, we aim to minimize the total transmit power at the base station by jointly optimizing the source beamforming and the relay beamforming weights under the energy causality constraints at the relays and the signal-to-noise ratio constraints at the users. The formulated problem is highly nonconvex, and thus, it is difficult to solve. To solve the problem, we first transform it into a worst-case optimization, and then, an iterative algorithm is developed to solve this worst-case optimization. Numerical results show the advantage of the proposed robust scheme. [ABSTRACT FROM AUTHOR]

This paper investigates the optimal power minimization design of simultaneous wireless information and power transfer systems under non-linear energy harvesting (EH) model, where a multi-antenna hybrid access point (H-AP) simultaneously transmits information and power to multiple heterogeneous users, such as information-energy receivers (IERs), information receivers (IRs), and ERs. Power splitting (PS) receiver architecture is adopted at all IERs. In order to achieve green system design, an optimization problem is formulated to minimize the transmit power of H-AP subject to the required signal-to-interference-plusnoise ratios (SINRs) constraints at IERs and IRs, and the harvested energy constrains at IERs and ERs, by jointly optimizing the beamforming vector at H-AP and the PS ratios at IERs. Since the problem is nonconvex and the employ of the non-linear EH model makes it more difficult to solve, the semidefinite relaxation and variable substitutions are used to handle it. For some cases, we theoretically prove that the globe optimal solution can be guaranteed by using our method, and for rest cases, we discuss its optimality via simulations. Numerical results show that although the traditional linear EH model is feasible for the practical EH circuits in some cases, the corresponding system consumes more transmit power than that under the non-linear model EH. Moreover, the effects of the numbers of users, the required SINRs, and the harvested energy on the system transmit power are also discussed.

In this paper, we study the outage and throughput performance for the simultaneous wireless information and power transfer (SWIPT) cooperative decode-and-forward (DF) communication systems. The hybrid receiver that uses both time switching (TS) and power splitting (PS) methods for energy harvesting (EH) and information decoding (ID), and the piece-wise linear EH model that captures the non-linear input-output characteristic of the EH circuit, are considered. We present exact analytical expressions of the outage probability (OP) and throughput, which are expressed as single definite integral on finite interval and can be easily evaluated, for the systems in Rayleigh fading channel. For further simplicity of calculation, we derive novel and closed-form approximate expressions of the OP and throughput. The impact of different system parameters on the system performance is investigated. Numerical results show the high accuracy of the proposed closed-form approximate expressions especially in the region of higher signal-to-noise ratio (SNR). It is also shown that the system performance is greatly overestimated when the ideal linear EH model is used instead of the practical non-linear EH model. A different result to the non-hybrid receiver with both linear EH model and non-linear EH model that there exists an optimal location to minimize the OP for the hybrid receiving relay node with non-linear EH model is also demonstrated.

This paper studies the secure communication of a non-orthogonal multiple-access (NOMA) relaying system in the presence of an eavesdropper in which the NOMA communication between a source and two users is assisted by an energy-harvesting (EH) relay. The relay extracts a part of its received signal strength using a power-splitting (PS) policy then harvests energy using a non-linear EH (NLEH) circuit. A friendly jammer sends jamming signals to help secure communication. The jammer is exploited as an additional energy source. A store-and-transmit (SaT) scheme which allows the EH relay to perform energy storing and information transmitting is proposed. For performance evaluation, the closed-form expressions for three metrics, secrecy outage probability (SOP), average achievable secrecy rate (AASR) and average stored energy (ASE) are derived. These results enable studies on the effects of various system parameters, such as NOMA power-allocation factors, target secrecy rates, jammer’s location, and relay’s power levels, on the system performance.

In this letter, a cooperative cognitive radio network, in presence of an eavesdropper, is considered that operates in a frame structure comprising of energy harvesting, spectrum sensing and cooperation or opportunistic data transmission. The objective is to maximize the sum secondary throughput under the constraints of sensing reliability, harvesting energy causality, primary user cooperation data rate, secondary data outage, sum and individual secondary secrecy outage. Results show a gain in sum throughput ~25.43% over the existing work. [ABSTRACT FROM AUTHOR]

A vibro-impact mechanical system comprising of a ball moving freely between two dielectric membranes located at a certain distance from each other is studied. The system generates electricity when the ball moving due ambient vibrations impacts one of the membranes. The energy harvesting principle of the proposed system is explained and then used to formulate a numerical model for estimating the system output voltage. The dynamic behavior and output performance of the system are thoroughly studied under a harmonic excitation, as well as different initial conditions and various values of the restitution coefficient of the membranes. The delivered research results are useful for selecting the system parameters to achieve its optimal output performance in a realistic vibrational environment. Potential application of the proposed system for energy harvesting from car engine vibrations is presented. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) and non-orthogonal multiple access (NOMA) have been deemed two promising technologies due to their potential to achieve high spectral efficiency and massive connectivity. This paper studies a multiple-input single-output NOMA CR network relying on simultaneous wireless information and power transfer conceived for supporting a massive population of power limited battery-driven devices. In contrast to most of the existing works, which use an ideally linear energy harvesting model, this study applies a more practical non-linear energy harvesting model. In order to improve the security of the primary network, an artificial-noise-aided cooperative jamming scheme is proposed. The artificial-noise-aided beamforming design problems are investigated subject to the practical secrecy rate and energy harvesting constraints. Specifically, the transmission power minimization problems are formulated under both perfect channel state information (CSI) and the bounded CSI error model. The problems formulated are non-convex, hence they are challenging to solve. A pair of algorithms either using semidefinite relaxation (SDR) or a cost function are proposed for solving these problems. Our simulation results show that the proposed cooperative jamming scheme succeeds in establishing secure communications and NOMA is capable of outperforming the conventional orthogonal multiple access in terms of its power efficiency. Finally, we demonstrate that the cost function algorithm outperforms the SDR-based algorithm. [ABSTRACT FROM AUTHOR]

The research trend for harvesting energy from the ambient vibration sources has moved from using a linear resonant generator to a non-linear generator in order to improve on the performance of a linear generator; for example, the relatively small bandwidth, intolerance to mistune and the suitability of the device for low-frequency applications. This article presents experimental results to illustrate the dynamic behaviour of a dual-mode non-linear energy-harvesting device operating in hardening and bi-stable modes under harmonic excitation. The device is able to change from one mode to another by altering the negative magnetic stiffness by adjusting the separation gap between the magnets and the iron core. Results for the device operating in both modes are presented. They show that there is a larger bandwidth for the device operating in the hardening mode compared to the equivalent linear device. However, the maximum power transfer theory is less applicable for the hardening mode due to occurrence of the maximum power at different frequencies, which depends on the non-linearity and the damping in the system. The results for the bi-stable mode show that the device is insensitive to a range of excitation frequencies depending upon the input level, damping and non-linearity. [ABSTRACT FROM PUBLISHER]

In this paper, a novel bidirectional backscatter-aided transmission protocol is proposed for wireless powered distributed wearable measurement networks, where we consider channel detection, backscatter-aided wireless power transfer (WPT) and backscatter-aided information transfer. First, the channel detection phase is allocated for both the AP and sensors to get the knowledge of channel state information (CSI) at the beginning of each time block. In the backscatter-aided WPT phase, all sensors harvest radio frequency (RF) energy by converting RF signals from the AP with time-division-multiple-access (TDMA). Finally, the backscatter-aided information transfer phase is allocated to sensors for transmitting their independent information to the AP by TDMA and the harvested energy at each sensor is consumed in this phase. The signals from/to a sensor to/from the AP will be reflected by all other sensors and the optimal reflection coefficient at helping sensors can be calculated according to CSI. Considering fairness among sensors, we maximize sum throughput with energy harvesting constraints and max–min throughput by jointly optimizing the time allocation and the reflection coefficients. Sum and max–min throughput maximization problems are formulated as two convex optimization problems. A low-complexity algorithm is designed to obtain optimal solutions of sum throughput maximization problem with the fairness constraint, and the optimal solutions for max–min throughput maximization are derived as closed-form expressions. Numerical results illustrate the effectiveness of the proposed protocol. [Display omitted] • A novel bidirectional backscatter-aided transmission protocol is proposed. • Sum and max–min throughput maximization problems with fairness constraints are investigated. • The optimal solutions for sum and max–min throughput maximization are obtained. [ABSTRACT FROM AUTHOR]

In this paper, the physical layer security is investigated in a dual-hop wireless communication scenario, where an energy-constrained relay not only assists the source-to-destination information transmission, but also acts as a potential eavesdropper wiretapping the source information. We take into account both antenna mode switching and destination selection for the amplify and forward relaying network. The untrusted relay (UR) is equipped with two antennas, where one antenna that maximizes the source-to-relay channel gain will be selected for reception and the other one is exploited to forward the processed information. Moreover, the N th best destination is considered as the legitimate destination, which aims to achieve a better secrecy rate. Specially, in general signal-to-noise ratio regime, a low-complexity Gaussian Q-function is introduced to derive the exact closed-form expression of ergodic secrecy rate (ESR). In addition, when the UR works in a non-linear energy harvesting mode, the achievable secrecy rate maximization problem is formulated and solved by an alternative optimization method. The simulation results reveal the correctness of the theoretical derivation and also proves that much higher secrecy performance can be achieved by the proposed scheme than other benchmark schemes. [ABSTRACT FROM AUTHOR]

In this paper, the optimization of downlink beamforming vectors, uplink transmission power, and power-splitting factors is investigated for a secure two-way SWIPT network in the presence of a hidden eavesdropper and non-linear energy harvesting circuits over both perfect and imperfect channels. The eavesdropper is inactive, so its channel information is not available at the base stations (BSs). The purpose of artificial noise is to create downlink interference with the hidden eavesdropper as much as possible, while satisfying the quality of service for two-way communications. For perfect downlink channels, the semidefinite relaxation (SDR) technique is exploited, and the optimal matrices are proven to satisfy rank-1 conditions, thus providing the optimal beamforming vectors. For imperfect downlink channel state information, we propose an iterative algorithm with a penalty function to obtain the approximate rank-1 matrices. On uplink, we attain the optimal transmission power for users receiving maximum ratio transmission beamforming at the BSs. Eventually, the numerical experiments show the superiority of the proposed scheme, compared to a conventional scheme, in terms of signal-to-interference-plus-noise ratio at the eavesdropper. [ABSTRACT FROM AUTHOR]

In this paper, we study the outage and throughput performance for the simultaneous wireless information and power transfer (SWIPT) cooperative decode-and-forward (DF) communication systems. The hybrid receiver that uses both time switching (TS) and power splitting (PS) methods for energy harvesting (EH) and information decoding (ID), and the piece-wise linear EH model that captures the non-linear input-output characteristic of the EH circuit, are considered. We present exact analytical expressions of the outage probability (OP) and throughput, which are expressed as single definite integral on finite interval and can be easily evaluated, for the systems in Rayleigh fading channel. For further simplicity of calculation, we derive novel and closed-form approximate expressions of the OP and throughput. The impact of different system parameters on the system performance is investigated. Numerical results show the high accuracy of the proposed closed-form approximate expressions especially in the region of higher signal-to-noise ratio (SNR). It is also shown that the system performance is greatly overestimated when the ideal linear EH model is used instead of the practical non-linear EH model. A different result to the non-hybrid receiver with both linear EH model and non-linear EH model that there exists an optimal location to minimize the OP for the hybrid receiving relay node with non-linear EH model is also demonstrated. [ABSTRACT FROM AUTHOR]

This paper studies the secure communication of a non-orthogonal multiple-access (NOMA) relaying system in the presence of an eavesdropper in which the NOMA communication between a source and two users is assisted by an energy-harvesting (EH) relay. The relay extracts a part of its received signal strength using a power-splitting (PS) policy then harvests energy using a non-linear EH (NLEH) circuit. A friendly jammer sends jamming signals to help secure communication. The jammer is exploited as an additional energy source. A store-and-transmit (SaT) scheme which allows the EH relay to perform energy storing and information transmitting is proposed. For performance evaluation, the closed-form expressions for three metrics, secrecy outage probability (SOP), average achievable secrecy rate (AASR) and average stored energy (ASE) are derived. These results enable studies on the effects of various system parameters, such as NOMA power-allocation factors, target secrecy rates, jammer's location, and relay's power levels, on the system performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]