Simultaneous Wireless Power Transfer Research Articles

Optimal coordinated beamforming with artificial noise for secure SWIPT in multi-cell networks

This paper investigates the multi-cell coordinated beamforming (MCBF) design for secure simultaneous wireless information and power transfer (SWIPT) in both centralized and distributed manners. In each cell, one transmitter serves multiple information receivers (IRs) and energy receivers (ERs) with the non-linear energy harvesting (EH) model. Meanwhile, several eavesdroppers (Eves) intend to intercept the confidential information transmitted for IRs. To achieve a secure transmission, the artificial noise (AN) is embedded in the transmit signals of each transmitter. The proposed design is formulated into a power-minimization problem to guarantee the IRs’ information and ERs’ energy requirements while avoiding the information being intercepted by Eves. Since the problem is non-convex and not easy to solve, a solution method based on semi-definition relaxation (SDR) is proposed and the global optimum is proved to be guaranteed with full channel state information (CSI). We further present a distributed AN-aided MCBF for the system by using alternating direction method of multipliers (ADMM), with which each transmitter is able to calculate its own beamforming vectors and AN covariance matrix based on its local CSI. Simulation results show that our proposed distributed design converges to the global optimum obtained by the centralized one. It is also shown that by employing AN, the total required power of the system is reduced and the effect of AN on the system performance decreases with increment of transmit antennas. Compared with traditional linear EH model, optimizing the system under the non-linear EH one avoids false output power at the ERs and saves power at the transmitter.

An Analysis of the Optimum Node Density for Simultaneous Wireless Information and Power Transfer in Ad Hoc Networks

This paper investigates simultaneous wireless information and power transfer (SWIPT) in the ad hoc network, where access points (APs) with multiple antennas can transfer energy as well as information using a common spectrum resource. The receiving nodes decode the incoming information data (information decoding, ID) and/or harvest the RF energy (energy harvesting, EH), where two different receiving node architectures—time switching (TS) and power splitting (PS)—are considered. By using a stochastic geometry approach, we aim to analyze the transmission capacity and the harvested energy per unit area as performance measures of the SWIPT in the ad hoc network. From the analytical results, we can derive the optimal node densities of ID nodes and EH nodes for TS architectures and, furthermore, optimize the power splitting ratio jointly with the node density for the PS architectures such that the harvested energy per unit area is maximized when the target transmission capacity is given. The proposed node density optimization gives us a useful insight into the design of SWIPT-based ad hoc network, where we can show how densely the APs/nodes can be deployed in a given area and furthermore, find that the ad hoc network with PS receiving nodes outperforms that with TS receiving nodes for a large target transmission capacity, and vice versa.

Incomplete CSI Based Resource Optimization in SWIPT Enabled Heterogeneous Networks: A Non-Cooperative Game Theoretic Approach

Heterogeneous small cell network with energy harvesting is a promising technique in the next generation mobile communications. However, the cross tier and co-tier co-channel interference can be severe due to the spectrum sharing in inter tier and intra tier of a heterogeneous small cell network. This paper investigates the problem of power allocation and subchannel assignment with the consideration of cross tier/co-tier interference mitigation, energy harvesting, and incomplete channel state information. The power allocation problem in heterogeneous small cell network is modeled as a non-cooperative game by introducing a time-varying cross tier/co-tier interference pricing with simultaneous wireless information and power transfer. Subchannel allocation is modeled as a non-cooperative potential game by minimizing the total interferences experienced by users on each subchannel. Iterative algorithms of power optimization and subchannel allocation are proposed to obtain the Nash equilibrium points. Simulation results are presented to verify the effectiveness of the proposed algorithms in the heterogeneous small cell network.

Optimal Beamforming Design for Simultaneous Wireless Information and Power Transfer in Sustainable Cloud-RAN

In this paper, a joint beamforming design for energy-throughput tradeoff is investigated in a sustainable cloud radio access network, where multiple remote radio heads powered by independent renewable energy sources collaboratively transmit wireless information and energy to the data receiver and the energy receiver simultaneously. To explore the optimal joint beamforming design for both time-invariant and time-varying channels, first, optimization problems are formulated to maximize the throughput of the data receiver while charging the energy receiver with sufficient radio-frequency energy over a finite time horizon. Then, the formulated non-convex optimization problems are relaxed into a convex form and shown to be upper bounded by the optimal value of the relaxed problem. This upper bound can be further proved to be tight as the optimal solution to the relaxed problem is rank one. Moreover, motivated by the derived optimal solution, an efficient online joint beamforming algorithm is proposed for practical implementation. Finally, extensive simulations are performed to verify the superiority of the proposed joint beamforming strategies to other beamforming designs.

Robust Downlink Beamforming for Multiuser SWIPT Systems with Imperfect CSI

A multiuser multiple-input-single-output simultaneous wireless information and power transfer downlink system with imperfect channel is considered. This paper maximizes the worst-case harvested energy of all users and maintains the signal-to-interference and noise ratio requirement. The unknown channel estimate error is assumed within a certain range. Under the assumption, beamforming vector optimization is formulated as a semi-definite programming problem transformed by S-Procedure method. Using semidefinite relaxation technique, an optimal beamforming vector is obtained for the multi-antenna transmitter. The robustness and effectiveness of our proposed algorithm are provided by the simulation results compared with the non-robust design.

Simultaneous Wireless Information and Power Transfer in Multi-antenna Systems

In this paper, we provide a comprehensive literature survey on simultaneous wireless information and power transfer (SWIPT) in multi-antenna systems. We first review recent contributions on the theory analysis of SWIPT from information theoretic standpoint and introduce the tradeoff between information transfer and power transfer under various settings. Then, we focus on the utilization of multi-antenna techniques to solve existing problems of SWIPT. Contributions on the implementation aspects of multi-antenna SWIPT are summarized. The performance of SWIPT is evaluated by different metrics, therefore, we review the works on dynamic SWIPT optimization based on objective function using multi-antenna techniques. In addition, the implementation of SWIPT brings up secure issue. Thus, we summarize recent works on secure SWIPT. Finally, we present researches combining SWIPT with state-of-the-art techniques due to potential application in different scenarios.

Performance Study for SWIPT Cooperative Communication Systems in Shadowed Nakagami Fading Channels

In this paper, we investigate the performance of simultaneous wireless information and power transfer cooperative amplify-and-forward communication systems in shadowed Nakagami-m fading channels. Both coherent and non-coherent modulations, namely, binary phase-shift keying (BPSK) and binary differential phase-shift keying (BDPSK) are considered. We propose closed-form expressions of the moment generating function and the probability density function for the received signal-to-noise ratio of the cooperative link. Based on this, we further derive the average bit-error-rate and the outage probability expressions for the systems with both BPSK and BDPSK modulations. All of these expressions are given in closedform except one in single integral that can be easily evaluated using numerical integration methods. Numerical results are used to confirm the validity of the proposed analytical results. It is shown that the performance of the systems is more susceptible to the fading parameter m than to the shadowing level σs and does not change much with the power splitting ratio.

Performance of SWIPT for AF MIMO Relay Systems With Direct Link

A simultaneous wireless information and power transfer scheme for amplify-and-forward relay systems with a direct source–receiver link is investigated. According to the minimum-mean-square-error criterion, we formulate a joint beamforming problem under an energy harvesting constraint at the receiver plus transmitting power constraints at source and relay. Using an iterative algorithm, the non-convex problem is decoupled into two subproblems. A successive convex approximation method with iterative algorithm is designed for obtaining the local optimum. Assuming that $\mathbf {M}_{s}\leq {\mathbf {min}(\mathbf {N}, \mathbf {M}_{d})}$ , we propose a simplified measure using singular value decomposition and generalized singular value decomposition techniques. Numerical results for the number of iterations and bit error rate are carried out to evaluate the performance of the three different schemes.

Both Worst-Case and Chance-Constrained Robust Secure SWIPT in MISO Interference Channels

This paper addresses robust designs of secure simultaneous wireless information and power transfer for multiple-input single-output (MISO) multiuser systems. By using a bounded uncertainty model for the channel state information (CSI) from transmitters to legitimate receivers and under the assumption of only available statistic knowledge of the CSI to eavesdroppers, we consider the robust designs with both worst-case and chance-constrained optimizations. To jointly optimize transmit beamforming vectors and power splitting factors, we formulate three problems aiming at minimizing the system power, maximizing the sum secrecy rate, and maximizing the minimal secrecy rate, respectively, subject to both energy harvesting and secrecy outage constraints. These problems are intractable in their original forms due to the CSI models and their non-convexity. To reach computationally efficient solutions, we first rewrite the original problems by semi-definite relaxation, then transform the CSI uncertainty related constraints by S-procedure, and finally approximate the non-convex constraints by the first-order Taylor expansion. By the reformulations, we present iterative successive convex approximation algorithm for approaching the optimized solutions. Simulation results under various setups of system parameters are provided to examine the system performance and validate the effectiveness of the proposed schemes.

Space-Time Signal Optimization for SWIPT: Linear Versus Nonlinear Energy Harvesting Model

In simultaneous wireless information and power transfer systems, optimization of transmit signals is critical to system performance. Although the optimization problem can be efficiently solved under a linear energy harvesting model, the obtained solution may not work well in practice, since the energy harvester contains nonlinear elements, such as diodes. On the other hand, while a nonlinear model can be used to capture the dynamics of energy harvesting circuits, it introduces additional complexity at the optimization stage. Specifically, under a nonlinear model, traditional convex optimization is not applicable, since the energy harvesting function is fractional. To address this challenge, this letter first derives an optimal solution for static channels by introducing pseudo-inverse of the nonlinear model. Then, an iterative algorithm that converges to a sub-optimal solution is proposed for time varying channels. With the developed methods, the performance-complexity tradeoff between linear and nonlinear models is illustrated.

Simultaneous Wireless Information and Power Transfer in Cellular Two-Way Relay Networks With Massive MIMO

In this paper, we study an energy-harvesting cellular two-way relay network with massive multiple-input multiple-output, where multiple energy-harvesting mobile stations (MSs) communicate with a base station (BS) via an energy-harvesting relay station (RS). A signal space alignment (SSA) based simultaneous wireless information and power transfer (SWIPT) protocol is proposed for efficient energy harvesting and information exchange. We analyze the performance of the proposed SSA-SWIPT scheme, and derive closed-form expressions for the asymptotic signal-to-interference-plus-noise ratios and the achievable sum-rate when the numbers of antennas at the BS and the RS go large simultaneously. We also investigate the optimal power splitting ratios at the RS and the MSs to maximize the achievable sum-rate. Numerical results are provided to verify the analysis and it is shown that employing massive antennas can improve the efficiencies of wireless energy harvesting and information transmission.

Energy Efficiency Optimization for OFDM Based 5G Wireless Networks With Simultaneous Wireless Information and Power Transfer

In 5G wireless networks, the system capacity and the number of users will be significantly increased. However, the energy consumed for the communication will also be increased, which results in low system energy efficiency. Simultaneous wireless information and power transfer (SWIPT) can enable the user to perform energy harvesting from the radio-frequency signals parallel with the information decoding, which can effectively improve the system energy efficiency. In this paper, we study the energy efficiency optimization problem for the orthogonal frequency-division multiplexing-based 5G wireless networks with SWIPT, in which the subcarrier and power allocation are jointly optimized to maximize the system energy efficiency for single user and multiple user cases. For those two cases, through mathematical transforming, we use the Dinkelbach iterative method and the Lagrange dual method to solve the non-convex energy efficiency optimization problem. Simulation results show that compared with other algorithms, our proposed algorithm can achieve higher energy efficiency.

Optimal Power Splitting for Simultaneous Wireless Information and Power Transfer in Amplify-and-Forward Multiple-Relay Systems

In this paper, we investigate simultaneous wireless information and power transfer (SWIPT) amplify-and-forward relay systems, in which multiple relay nodes support communication between a source node and a destination node. Relay node transceivers are equipped with radio frequency energy harvesters for a power source to retransmit the signals from the source to the destination node. Both the power splitting (PS) ratio and adaptive power control are jointly optimized for SWIPT multiple-relay systems. We prove that the optimal power allocation strategy in our joint solution is to fully use the harvested power, which is contrary to conventional non-SWIPT multiple-relay systems. Based on this result, we propose an optimal centralized PS scheme and suboptimal distributed PS methods. Simulation results demonstrate that the proposed schemes outperform the naive PS schemes in terms of the average rate and the bit-error rate.

Decentralized Robust Transceiver Designs for MISO SWIPT Interference Channel

This paper considers a $K$ -user multiple-input single-output interference channel for simultaneous wireless information and power transfer, where each multi-antenna transmitter serves a single-antenna receiver per user pair. All receivers perform simultaneously information processing and energy harvesting (EH) based on the receive power-splitting (PS) architectures. Assuming imperfect channel state information (CSI) at the transmitters, we develop a near-optimal robust transceiver design scheme that minimizes the total transmission power under the worst-case signal-to-interference-plus-noise ratio (SINR) and EH constraints at the receivers, by jointly optimizing transmit beamforming and receive PS ratio per receiver. When the CSI uncertainties are bounded by ellipsoidal regions, it is shown that the worst-case SINR and EH constraints per receiver can be recast into quadratic matrix inequality forms. Leveraging semidefinite relaxation technique, the intended robust beamforming and PS (BFPS) problem can be relaxed as a tractable (centralized) semidefinite program. More importantly, relying on the state-of-the-art alternating direction method of multipliers in convex optimization, we propose a decentralized algorithm capable of computing the robust BFPS scheme with local CSI and limited information exchange among the transmitters. It is shown that the proposed decentralized algorithm is guaranteed to converge to the centralized solution. Numerical results are provided to demonstrate the merits of the proposed approaches.

Notice of Violation of IEEE Publication Principles: Robust Secure Precoding Design for MIMO SWIPT System With Bounded Channel Uncertainties

In this paper, we investigate the worst-case robust secure precoding design for simultaneous wireless information and power transfer in multiple-input-multiple-output wiretap system, which consists of one transmitter, one information receiver, and one energy receiver. By treating the ER as potential eavesdropper, we aim to maximize the worst-case secrecy rate by designing the transmit precoding matrix. This is a typical non-convex optimal design while the channel state information uncertainties make this problem harder to handle, thus we propose a new method to obtain the solution. Specifically, instead of approximating the logarithmic determinant as a trace, we propose to linearize the two log-det terms. After linearization, epigraph reformulation is used to deal with the bounded channel uncertainties. Then, an alternating optimization method is utilized to solve the reformulated problem. After obtaining the precoding matrix, we derive the worst-case secrecy rate by solving another optimal problem with respect to the channel uncertainty. Numerical results validate the performance of our proposed design.

Performance Analysis of DF/AF Cooperative MISO Wireless Sensor Networks With NOMA and SWIPT Over Nakagami-<inline-formula> <tex-math notation="LaTeX">$m$ </tex-math> </inline-formula> Fading

In this paper, we investigate downlink cooperative multiple-input single-output wireless sensor networks with the nonorthogonal multiple access technique and simultaneous wireless information and power transfer over Nakagami- $m$ fading. Specifically, the considered network includes a multiantenna sink node, an energy-limited relay cluster, a high-priority sensor node (SN) cluster, and a low-priority SN cluster. Prior to transmission, a transmit antenna, a relay, a high-priority SN, and a low-priority SN are selected. In this paper, we propose three antenna-relay-destination selection schemes, i.e., sink node-high-priority, sink node-relay, and sink node-low-priority. In each proposed scheme, we consider two relaying strategies, i.e., decode-and-forward and amplify-and-forward, and then, we derive the corresponding closed-form expressions of outage probability at the selected SNs. In addition, we introduce two algorithms: 1) the power-splitting ratio optimization algorithm and 2) the best antenna-relay-destination selection determination algorithm. Finally, we utilize the Monte Carlo simulations to verify our analytical results.

Performance Analysis for BDPSK Modulated SWIPT Cooperative Systems With Nonlinear Energy Harvesting Model

In this paper, we investigate the performance of simultaneous wireless information and power transfer cooperative amplify-and-forward communication systems with binary differential phase-shift keying modulation. The piece-wise linear energy harvesting (EH) model that captures the nonlinear input-output characteristic of the EH circuit is considered. We derive a novel and closed-form expression of the probability density function (PDF) for the harvested power of the nonlinear EH receiver. Based on this, we further derive the expressions for the PDF of the received signal-to-noise ratio of the cooperative link and the average bit-error-rate of the systems. Numerical results confirm the validity of the proposed analytical results. It is shown that the system performance is significantly overestimated when the ideal linear EH model is used in the place of the practical nonlinear EH model. An opposite result to the linear EH model that the system performance is monotonically improved with the increase of the distance between the location of the relay node and the source node is also demonstrated.

Achieving Green Transmission With Energy Harvesting Based Cooperative Communication

The cooperative communication with simultaneous wireless information and power transfer can provide a potential solution to meet the demands of next-generation green transmission. In this paper, we consider a cooperative system where each user has the capability of energy harvesting (EH) from the radio frequency and relays the data of other users. Our target is to minimize the overall energy consumption while satisfying the quality of service constraints of each user in terms of minimum required data rate. The time division scheme is adopted for data transmission and relaying while power splitting protocol is used at each node to receive information and energy, concurrently. We optimize the transmit power for data and relay transmission at each node and find the optimal time sharing for user cooperation. Unfortunately, under the decode and forward relaying the complex primal problem is not convex. Thus, we first re-formulate the problem into standard optimization and then transform to a convex problem. We solve the problem through duality theory and derive the closed form solution of the primal variables. Further, we consider the cooperative communication without EH and non-cooperative transmission with EH, and then optimal solutions are obtained from similar techniques. Finally, simulation results are provided where the performance of the proposed solutions is compared with the non-optimized cooperation time and without EH models.

Integrated Data and Energy Communication Network: A Comprehensive Survey

In order to satisfy the power thirst of communication devices in the imminent fifth generation era, wireless charging techniques have attracted much attention both from the academic and industrial communities. Although the inductive coupling and magnetic resonance-based charging techniques are indeed capable of supplying energy in a wireless manner, they tend to restrict the freedom of movement. By contrast, radio frequency (RF) signals are capable of supplying energy over distances, which are gradually inclining closer to our ultimate goal-charging anytime and anywhere. Furthermore, transmitters capable of emitting RF signals have been widely deployed, such as TV towers, cellular base stations, and Wi-Fi access points. This communication infrastructure may indeed be employed also for wireless energy transfer (WET). Therefore, no extra investment in dedicated WET infrastructure is required. However, allowing RF signal-based WET may impair the wireless information transfer (WIT) operating in the same spectrum. Hence, it is crucial to coordinate and balance WET and WIT for simultaneous wireless information and power transfer, which evolves to integrated data and energy communication networks (IDENs). To this end, a ubiquitous IDEN architecture is introduced by summarizing its natural heterogeneity and by synthesizing a diverse range of integrated WET and WIT scenarios. Then the inherent relationship between WET and WIT is revealed from an information theoretical perspective, which is followed by the critical appraisal of the hardware enabling techniques extracting energy from RF signals. Furthermore, the transceiver design, resource allocation, and user scheduling as well as networking aspects are elaborated on. In a nutshell, this treatise can be used as a handbook for researchers and engineers, who are interested in enriching their knowledge base of IDENs and in putting this vision into practice.

Multi-Objective Resource Allocation in a NOMA Cognitive Radio Network With a Practical Non-Linear Energy Harvesting Model

Cognitive radio and non-orthogonal multiple access are promising for alleviating the severe spectral scarcity problem encountered by the next generation wireless communication systems. In this paper, in order to improve energy efficiency and spectral efficiency, a non-orthogonal multiple access cognitive radio network with simultaneous wireless information and power transfer is studied under a practical non-linear energy harvesting model. A multi-objective resource optimization problem is formulated for maximizing the harvesting power of each energy harvesting receiver. This problem is non-convex and challenging to solve. A weighted Tchebycheff method is applied to solve the formulated problem. It is shown that the performance achieved under the non-linear energy harvesting model is better than that obtained under the linear energy harvesting model.