Simultaneous Wireless Power Transfer Research Articles

Secure Transmissions in Millimeter Wave SWIPT UAV-Based Relay Networks

In this letter, we consider secure transmissions of millimeter wave simultaneous wireless information and power transfer unmanned aerial vehicle (UAV) relay networks, where a source transmits confidential information to an energy-constrained destination on the ground with the help of a UAV-based relay in the presence of multiple independent homogeneous Poisson point process eavesdroppers. First, we derive closed-form expression of the lower bound of average secrecy rate using 3-D antenna gain model. Then, we study the secrecy rate lower bound maximization problem by optimizing the source/UAV transmit power, power splitting ratio, and UAV’s location. To solve this non-convex problem, we propose an alternate optimization algorithm by solving three sub-problems iteratively. Simulation results show that the proposed algorithm can greatly improve the average secrecy rate.

Wireless powered UAV relay communications over fluctuating two-ray fading channels

The unmanned aerial vehicle (UAV) relay has recently attracted a large amount of research interests, due to its relative ease of development to enhance cooperative communication performance when the direct link between transmitters and receivers is severely blocked. With simultaneous wireless information and power transfer, the UAV relay can harvest energy from radio frequency and prolong the network lifetime. In this paper, we use the time-switching relaying protocol for UAV energy harvesting (EH) and data forwarding. Different from prior works, the ground-to-air links are modeled as fluctuating two-ray fading channels, which provide a very good fit to the UAV relay communication. In addition, we obtain novel exact analytical expressions for the outage probability, symbol error rate and average capacity of the considered system employing decode-and-forward and amplify-and-forward protocols, respectively. Furthermore, we offer valuable insights into the impact of system and fading parameters on the performance. For example, the optimal EH time can be selected to enhance the system performance. Finally, numerical results are provided to validate the derived results.

Novel Energy-Harvesting AF Relaying Schemes With Channel Estimation Errors

Three novel structures using simultaneous wireless information and power transfer in energy-harvesting (EH) amplify-and-forward relaying are investigated in this paper. Different combinations of time-switching and power-splitting (PS) EH protocols are studied. Three dynamic schemes are proposed as channel estimation PS (CEPS), data transmission PS (DTPS), and combination PS (CPS). From source to relay in these schemes, the data packet includes three parts: channel estimation, data transmission, and EH. From relay to destination in these schemes, the data packet includes two parts: data transmission and channel estimation. Closed-form expressions for the cumulative distribution function of the end-to-end signal-to-noise ratio for the three structures are derived. Using these expressions, achievable rate and bit-error-rate are derived. Different parameters are examined. Numerical results show the optimal splitting ratio for the channel estimation, EH, and data transmission, when the packet size is fixed.

Modulation and Coding Design for Simultaneous Wireless Information and Power Transfer

In order to satisfy the power demands of IoT devices and thus extend their lifespan, radio frequency (RF) signal aided wireless power transfer (WPT) is exploited for remote charging. Carefully coordinating both the WPT and wireless information transfer (WIT) yields an emerging research trend in simultaneous wireless information and power transfer (SWIPT). However, SWIPT systems designed by assuming Gaussian distributed input signals may suffer from a substantial performance degradation in practice, when the finite alphabetical input is considered. In this article, we will provide a design guide of coding controlled SWIPT and study the modulation design in both single-user and multi-user SWIPT systems. We hope this guide may push SWIPT a step closer from theory to practice.

A Simultaneous Power and Downlink Data Transfer System With Pulse Phase Modulation

This brief presents a pulse phase modulation scheme for simultaneous wireless power and downlink data transfer system through the same inductive link. It is proved that the impact of data transfer on power transfer can be minimized when using the proposed pulse phase modulation. A prototype is built up with 1-MHz resonant frequency for power transfer. It shows that the data can be successfully transferred while achieving a data rate of 125 kb/s, which is 1/8 of carrier frequency, and a bit error rate (BER) of $4.5\boldsymbol {\times } 10^{\boldsymbol {-6}}$ . Furthermore, compared with the case without data transfer, the input powers and the output powers are almost unchanged, respectively.

An Open-Loop Double-Carrier Simultaneous Wireless Power and Data Transfer System

In this brief, an open-loop double-carrier simultaneous wireless power and data transfer system is presented. Although the system is intended for implantable biomedical microsystems, it can also be used for other low-power applications such as Internet of Things (IoT). In the proposed system, uplink data communication (from the implant to the outside of the body) is implemented by switching a capacitor on the implant site. This switching results in changing the resonance frequency between two different frequencies during different periods of time. To keep the power transfer efficiency (PTE) and the power delivered to the load (PDL) almost constant, two external power transmitters, each working at its own distinct frequency, are employed. The closed-loop control unit, which is commonly used to synchronize the timing between transmitter and receiver, is avoided to enhance the overall performance, including the data rate and efficiency, and to reduce the complexity of the system. In a proof-of-concept prototype, about 44 mW of power is transmitted to a 750 ${{\Omega }}$ resistive load over ${f_{1} = 1.93}$ MHz and $ {f_{2} = 1.44}$ MHz with an average efficiency of 39%. A data rate of 50 kb/s has also been achieved for the uplink telemetry.

Robust Optimization for Energy Efficiency in MIMO Two-Way Relay Networks With SWIPT

Energy efficiency (EE) is a key issue in energy-constrained wireless networks because of the energy scarcity. In this paper, we present the robust energy-efficient optimization design for multiple-input–multiple-output two-way relay networks with simultaneous wireless information and power transfer, where the available channel state information is considered to be imperfect. We model the channel errors by using the norm bounded model, and aim to maximize the worst-case EE by jointly designing the precoders of the sources and relay, and the power splitting ratio of the relay under the worst-case transmit power constraints at the sources and relay. To solve the robust EE optimization problem, we propose an iterative optimization algorithm based on the weighted minimum mean-square-error method, where the $\mathcal {S}$ -procedure and sign-definiteness lemma are employed to eliminate the channel errors. To balance the performance and complexity, we propose a channel diagonalization algorithm based on the generalized singular value decomposition, which has lower complexity. The effectiveness of the proposed algorithms is shown by numerical results.

Transceiver design for SWIPT multicasting MIMO relay system

Radio signals can potentially transmit wireless information and energy simultaneously, hence energy harvesting (EH) through simultaneous wireless information and power transfer (SWIPT) has been proposed for next generation wireless devices. In this paper, the joint base station and relay station transmitter design, and receiver power splitting for a downlink multiuser multiple-input-multiple-output (MU-MIMO) simultaneous wireless information and power transfer (SWIPT) system was investigated. The objective is to minimize the source and relay transmit powers by jointly optimizing the base station precoder, amplify-and-forward relay matrix, the power splitting (PS) ratio, and information decoding mobile stations (MSs) minimum mean squared error (MMSE) receivers subjected to both given mean squared error (MSE) and energy harvesting (EH) constraints. This non-convex problem can be solved by using semi-definite relaxation (SDR). Simulation results show that the proposed technique can harvest sufficient energy to provide additional powers to recharge the IoT devices.

Wireless Powered Massive Access for Cellular Internet of Things With Imperfect SIC and Nonlinear EH

In this paper, we investigate the issue of simultaneous wireless information and power transfer in the cellular Internet of Things (IoT) with a massive number of different access devices, e.g., information decoding devices, energy harvesting (EH) devices, and hybrid devices. Especially, we consider a practical scenario of the cellular IoT, where the IoT devices have a nonlinear EH receiver and perform imperfect successive interference cancellation (SIC) due to a limited capability. The benefits offered by a multiple-antenna base station are exploited to enhance the efficiency of both information transmission and power transfer. In particular, we propose to jointly optimize the spatial beam, transmit power, and power splitting ratio to alleviate the impacts of both nonlinear EH and imperfect SIC. To this end, two effective algorithms are designed from the perspectives of maximizing the weighted sum rate and minimizing the total power consumption, respectively. Finally, extensive simulation results are presented to validate the effectiveness of the proposed algorithms.

SSK-Based SWIPT With AF Relay

The performance of space shift keying (SSK) modulation using energy harvesting amplify and forward (AF) relaying is analyzed over the Rayleigh fading channel. Simultaneous wireless information and power transfer technique eliminates the need of power supply at the relay in cooperative communication. However, energy tapped from an information signal for harvesting would degrade receiver performance. At the same time, the distance between the relay and the receiver can be increased due to the power splitting-based relay with the SSK modulation. New closed-form expressions for average bit error probability (ABEP) is derived with a single AF relay and an upper bound expression for multiple relays with a direct link. Furthermore, the ABEP is analyzed for a partial relay selection operation. The numerical and computer simulation results are presented with the discussion.

Power Splitting-Based SWIPT Systems With Decoding Cost

We study optimal power splitting-based simultaneous wireless information and power transfer (PS-SWIPT) for two communication systems wherein all receiving nodes are subject to a decoding cost. First, for a point-to-point (PtP) channel, the optimal achievable rate is obtained, and then, for a two-hop half-duplex (HD) decode-and-forward (DF) relay channel, the achievable data rate is maximized. Finally, performances of the PtP system and the relay channel with DF and amplify-and-forward (AF) relaying schemes are discussed where we observe performance superiority of the DF relay channel over AF relaying and the PtP channel for sufficiently less decoding cost at the relay than the destination.

Optimum SWIPT relaying in bidirectional non‐regenerative relay networks

The authors study the optimal design of simultaneous wireless information and power transfer relaying in bidirectional non-regenerative relay networks. They consider both power splitting relaying and time switching relaying. Since there are two opposite traffic flows between two sources, they characterise the transmission rate performance by the minimum rate of two opposite traffic flows. Specifically, they first obtain closed-form expressions for the optimum power splitting and time switching coefficients to maximise the minimum transmission rate of bidirectional non-regenerative relaying. They also derive the resulting maximum transmission rate expressions. Furthermore, they consider a minimum input radio frequency (RF) power level to turn on diodes, and derive the turn-on probability of the RF energy harvesting circuit when two channels experience independent Rayleigh fading. Numerical results confirm that the authors' analyses exactly match with simulation results and that the two relaying strategies with optimum coefficients give almost the same transmission rate performance.

Max–Min Fairness Optimal Rate-Energy Trade-Off of SWIPT for Massive MIMO Downlink

Max–min fairness optimal rate-energy trade-off of simultaneous wireless information and power transfer is derived with imperfectly estimated channels at the massive multiple-input multiple-output base-station and statistical channel knowledge at the users. The optimal transmit power control coefficients, common harvested energy, and common achievable user rates are derived for time-switching and power-splitting protocols.

Improvement of SWIPT Relaying System Performance Under the Interference Environment

Based on the simultaneous wireless information and power transfer, this paper investigates an amplify-and-forward relaying system. It is assumed that the system works in an environment with the interference, and the system cannot implement the normal information transmission (IT) when the interference reaches a certain level. We analyze the system rate in this environment, and propose the scheme to improve the system rate. First, we divide the communication process of the system into two periods: the interference period (IP) and the communication period (CP). In the IP, the energy-constrained relay harvests the energy of the radio frequency signals received during this period and stores the energy into its energy storage till the interference ends. Then, in the CP, the relay allocates the energy of its energy storage to the blocks of the communication process, and the system performs the normal communication process. According to the principle of power splitting, the blocks that are allocated energy can reduce the signal stream proportion of the energy harvesting mode and increase the signal stream proportion of the IT mode. Thus the system rate is improved. We discuss two kinds of energy allocation scheme of the relay. Through strict formula derivation, we prove that the proposed average-energy-allocation (AEA) scheme can maximize the system rate. In addition, through numerical simulation, we observe the influence of the AEA scheme on the system rate, and compare the effect of with/without the AEA scheme on the system rate when changing two system parameters. The results show that the proposed AEA scheme can effectively improve the relaying system rate under the interference channel.

SWIPT Schemes for Carrier Index Differential Chaos Shift Keying Modulation: A New Look at the Inactive Carriers

In this paper, two carrier index differential chaos shift keying (CI-DCSK) with simultaneous wireless information and power transfer schemes, which integrate CI-DCSK modulation with wireless power transfer, are proposed. In the proposed schemes, based on the transmission characteristics of index modulation, the inactive carriers of CI-DCSK are exploited to deliver energy by transmitting random noise-like signals subjected to normal distribution. By applying time switching (TS) at the receiver, each frame time of the proposed schemes is divided into two intervals. Unlike usual TS-based systems, two intervals of the proposed schemes are related, where energy harvesting and decoding of the modulated bits are both operated in the second interval. Analytical bit error rate (BER) expressions over additive white Gaussian noise and multipath Rayleigh fading channels of the two schemes are derived. The expression for the parameter $\xi$ is also derived that measures the probability of self-sufficiency of these schemes. The impact of the dividing point of two intervals on BER performance of systems is also analyzed and optimized. Since the energy on the inactive carriers is adjustable, the schemes are always self-sustainable in energy supply. To provide the best performance, the ratio of energy on the inactive carriers to that on the active carriers is optimized. Simulation results show that though performances of the proposed schemes are a little worse than CI-DCSK with the same spectral efficiency, the proposed schemes are all self-sustainable.

Robust Power- and Rate-Splitting-Based Transceiver Design in <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math> </inline-formula>-User MISO SWIPT Interference Channel Under Imperfect CSIT

We investigate the rate-splitting (RS)-based robust transceiver design problem in a multi-antenna interference channel with simultaneous wireless information and power transfer under the norm-bounded errors of channel state information at transmitters. The beamforming vectors, power splitting ratios, and target common rates are jointly optimized via minimizing the total transmit power subject to the quality of service and energy harvesting requirements. The non-convex problem with infinite constraints is first transformed into finite-constraint convex one and then jointly solved by a gradient-based algorithm. The results demonstrate that the RS-based robust schemes outperform the conventional robust designs.

On the Outage Performance of SWIPT-Based Three-Step Two-Way DF Relay Networks

In this paper, we study the outage performance of simultaneous wireless information and power transfer based three-step two-way decode-and-forward relay networks, where both power-splitting (PS) and “harvest-then-forward” are employed. In particular, we derive the expressions of terminal-to-terminal (T2T) and system outage probabilities based on a Gaussian-Chebyshev quadrature approximation, and obtain the T2T and system outage capacities. The effects of various system parameters, e.g., the static power allocation ratio at the relay, symmetric PS, as well as asymmetric PS, on the outage performance of the investigated network are examined. It is shown that our derived expression for T2T outage capacity is more accurate than existing analytical results, and that the asymmetric PS achieves a higher system outage capacity than the symmetric one when the channels between the relay node and the terminal nodes have different statistic gains.

Performance Analysis of Hybrid Protocol Based AF EH Relaying over Asymmetric Fading Channels

Simultaneous wireless information and power transfer is a practicable solution to encourage energy-constrained relay nodes to cooperate with the source to transmit information to the destination. In this paper, we study the outage performance of hybrid protocol based amplify-and-forward (AF) relay networks over asymmetric fading channels, where the source-relay link and the relay-destination link are subjected to Rician fading and Rayleigh fading, respectively. In particular, we derive the lower bound of outage probability and the upper bound of outage capacity based on a high signal-to-noise ratio approximation, respectively. We further investigate the effects of various system parameters, such as the parameters of hybrid protocol, the target rate, and the Rician K-factor, on the investigated network. It is shown that a good selection of parameters of hybrid protocol is of significance to improve system capacity, and that a larger Rician factor is desirable in the investigated network.

Robust Beamforming Design for Multi-User MISO Full-Duplex SWIPT System With Channel State Information Uncertainty

A multi-user multiple-input single-output simultaneous wireless information and power transfer full-duplex system with imperfect channel state information is considered. Under the assumption that the unknown channel estimation error is within a certain range, the self-interference cannot be suppressed completely at the base station and at the multi-user nodes. The proposed design problem is formulated as maximizing the average harvested energy of multi-user nodes and maintaining the signal-to-interference-plus-noise ratio requirement, which is proved to be non-convex. Utilizing semidefinite relaxation and S-procedure methods, a convex optimization problem of optimal beamforming vector for the multi-antenna transmitter is obtained. Moreover, semidefinite relaxation is proved to be tight by showing the existence of rank-one optimal solutions. Simulation results are presented to verify the robustness and effectiveness of the proposed algorithm compared with the non-robust design.

Improved Hybrid Relaying Protocol for DF Relaying in the Presence of a Direct Link

This letter proposes an improved hybrid relaying (i-HRe) protocol for a decode-and-forward relay system in the presence of a direct link between the source and the destination. A non-linear energy harvester is equipped at the relay to facilitate simultaneous wireless information and power transfer. We formulate an optimization problem to maximize the system capacity by optimizing the parameters of the proposed i-HRe protocol, i.e., time-switching ratio and power-splitting ratio. As this problem is non-convex, we convert it into two subproblems by means of the inequality relation between the signal noise ratios of source-relay link and relay-destination link to derive the optimal solution. Simulation study verifies the fast convergence of the proposed iterative algorithm. The results show that the i-HRe protocol achieves a higher system capacity than the existing protocols.