Self-energy Recycling Research Articles

Full-Duplex With Self-Energy Recycling in the RF Powered Multi-Antenna Relay Channels

In this letter, we address the beamforming in full-duplex self-energy recycling relay system, where an amplify-and-forward relay delivers the source message to the destination in a single time slot while recycling a portion of its RF energy through energy harvesting. The signal received at the realy is divided into two circuits, one for the full-duplex relaying and the other for the energy harvesting. The beamforming vectors and the power division ratio at the relay are optimized to maximize the harvested energy while maintaining a certain reception quality threshold at the destination. Simulation results show various advantages and trade-offs of the proposed system.

Relay selection based on energy harvesting in two-way full-duplex relay networks

In this paper, the time switching (TS) relay protocol and the self-energy recycling (SER) relay protocol are integrated into a two-way full-duplex (FD) relay network. For the proposed TS FD relay protocol, the joint optimization of the TS factor and the relay selection (RS) problem is proposed, where the relay nodes switch between energy harvesting (EH) and FD information relaying in different phases. To remove the self-interference (SI) operation at the relay nodes, a novel FD transmission protocol suitable for the two-way relay system is proposed, in which the relay nodes can recycle the SI as part of energy. Then two relay selection schemes are proposed to improve the outage probability and the sum rate of the two-way relay networks. Besides, the proposed RS schemes and two FD relay protocols can improve the performance metrics and solve the power constraint of the relay node. Simulation results show that the proposed two RS schemes for two-way FD relay networks can improve the output performance than traditional schemes.

Robust Optimum and Near-Optimum Beamformers for Decode-and-Forward Full-Duplex Multi-Antenna Relay With Self-Energy Recycling

In this paper, we consider the full-duplex decode-and-forward wireless-powered relaying system, which employs energy harvesting protocol with power splitting. The robust joint optimum relay transmit beamformer and power splitting factor are obtained for the quality of service (QoS)-aware problem for the first time in the literature. The optimum solution is found by analyzing the Karush–Kuhn–Tucker conditions, thanks to the effective reformulation of the problem in an equivalent and simplified manner. In addition, the signal-to-interference-plus-noise ratio (SINR) maximization problem is investigated in order to find the robust optimum solution. The simulation results verify the optimality of the proposed method compared with the sub-optimum one which is presented by Zhao et al. . In the next part of this paper, the considered system is generalized by employing multiple receive antennas at the relay. Both QoS-aware and SINR maximization problems are considered. The near-optimum relay transmit and receive beamformers as well as power splitting factor are found by optimizing the variables alternately. First, transmit beamformer and power splitting factor are found optimally for a given initial receive beamformer. Then, the optimum receive beamformer is obtained. Relay with multiple-receive antennas is shown to perform better than the single receive antenna relay in terms of SINR and transmission power.

Resource Allocation for Secure Wireless Powered Integrated Multicast and Unicast Services With Full Duplex Self-Energy Recycling

This paper investigates a secure wireless-powered integrated service system with full-duplex self-energy recycling. Specifically, an energy-constrained information transmitter (IT), powered by a power station (PS) in a wireless fashion, broadcasts two types of services to all users: a multicast service intended for all users and a confidential unicast service subscribed to by only one user while protecting it from any other unsubscribed users and an eavesdropper. Our goal is to jointly design the optimal input covariance matrices for the energy beamforming, the multicast service, the confidential unicast service, and the artificial noises from the PS and the IT, such that the secrecy-multicast rate region (SMRR) is maximized subject to the transmit power constraints. Due to the non-convexity of the SMRR maximization (SMRRM) problem, we employ a semidefinite programming-based two-level approach to solve this problem and find all of its Pareto optimal points. In addition, we extend the SMRRM problem to the imperfect channel-state information case, where a worst-case SMRRM formulation is investigated. Moreover, we exploit the optimized transmission strategies for the confidential service and energy transfer by analyzing their own rank-one profile. Finally, numerical results are provided to validate our proposed schemes.

Secrecy Transmission for Self-Energy Recycling Untrusted Relay Networks With Imperfect Channel State Information

For the self-energy recycling (SER) untrusted relay network, a two-phase destination-based jamming (DBJ) protocol is proposed, in which the destination transmits the jamming signal to reduce the received SNR of the untrusted relay node in the first phase and the relay node operated in full-duplex (FD) mode for simultaneous energy transfer and information relaying in the second phase. In addition, the loopback interference (LI) generated by FD relay node can be reused as part of energy. To satisfy some practical application scenarios, we consider the imperfect channel estimation error at the destination. Considering the total power constraint and the quality of service (QoS) requirement at the destination, the secrecy rate maximization problem is formulated by optimizing the transmission power of source and destination. However, the formulated problem is non-convex and difficult to solve directly. To cope with this difficulty, an iterative power allocation algorithm is proposed. The key idea of the proposed algorithm first integrates the non-convex constraint into the objective function by the exact penalty method. Then the difference of convex functions (DC) programming can be utilized to convert the non-convex objective function into the approximate convex function and the sub-optimal transmission power of source and destination can be obtained by the traditional convex programming. Simulation results show the superiority security performance of the proposed scheme with the traditional schemes.

A full-duplex SWIPT system with self-energy recycling to minimize energy consumption

In simultaneous wireless information and power transfer system (SWIPT), additional resource allocation for power transfer degrades system performance. Therefore, how to allocate power and time to data transmission and energy transfer is very important for the performance of time switching-based SWTPT system. In this paper, we propose a time switching-based full-duplex SWIPT system combined with self-energy recycling since self-interference harvesting is more efficient than simultaneous data transmission if the magnitude of self-interference is sufficiently large. Proposed system has additional self-energy recycling phases compared to the conventional time switching-based full-duplex SWIPT system. Considering the limitation of maximum transmission power, proposed system is optimized transmission time as well as power. For the validity of the proposed system, we show the bi-convexity of proposed system and propose an iterative algorithm for optimization of proposed system. In simulations, we compare proposed system with the half-duplex system without simultaneous data transmission phase and the full-duplex system without self-energy recycling phase. Simulation results show proposed system consume less energy than the conventional systems.

Secure Transmission and Self-Energy Recycling With Partial Eavesdropper CSI

This paper focuses on the secure transmission of wireless-powered relay systems with imperfect eavesdropper channel state information (ECSI). For efficient energy transfer and information relaying, a novel two-phase protocol is proposed, in which the relay operates in full-duplex (FD) mode to achieve simultaneous wireless power and information transmission. Compared with those existing protocols, the proposed design possesses two main advantages: 1) it fully exploits the available hardware resource (antenna element) of relay and can offer higher secrecy rate; 2) it enables self-energy recycling (S-ER) at relay, in which the loopback interference (LI) generated by FD operation is harvested and reused for information relaying. To maximize the worst-case secrecy rate (WCSR) through jointly designing the source and relay beamformers coupled with the power allocation ratio, an optimization problem is formulated. This formulated problem is proved to be non-convex and the challenge to solve it is how to concurrently solve out the beamformers and the power allocation ratio. To cope with this difficulty, an alternative approach is proposed by converting the original problem into three subproblems. By solving these subproblems iteratively, the closed form solutions of robust beamformers and power allocation ratio for the original problem are achieved. Simulations are done and results reveal that the proposed S-ER based secure transmission scheme outperforms the traditional time-switching based relaying (TSR) scheme at a maximum WCSR gain of 80%.Results also demonstrate that the WCSR performance of the scheme reusing idle antennas for information reception is much better than that of schemes exploiting only one receive antenna.

Is Self-Interference in Full-Duplex Communications a Foe or a Friend?

This paper studies the potential of harvesting energy from the self-interference of a full-duplex base station. The base station is equipped with a self-interference cancellation switch, which is turned-off for a fraction of the transmission period for harvesting the energy from the self-interference that arises due to the downlink transmission. For the remaining transmission period, the switch is on such that the uplink transmission takes place simultaneously with the downlink transmission. A novel energy-efficiency maximization problem is formulated for the joint design of downlink beamformers, uplink power allocations and transmission time-splitting factor. The optimization problem is nonconvex, and hence, a rapidly converging iterative algorithm is proposed by employing the successive convex approximation approach. Numerical simulation results show significant improvement in the energy-efficiency by allowing self-energy recycling.

Secure transmission for multi-antenna wireless powered communication with co-channel interference and self-energy recycling

In this paper, we investigate secure transmission resource allocation problem for multi-antenna wireless powered communication networks (WPCNs) where a full-duplex (FD) wireless device (WD) sends confidential signals to an information receiver (IR), and an energy transmitter (ET) is employed to provide radio energy to the FD WD and to jam the multiple eavesdroppers at the same time. In order to improve energy efficiency, the FD WD also collects energy from its own loop interference signals. The energy FD WD harvested is supplied to its information transmission in the same time slot. We aim to maximize the achievable secrecy rate at the IR by designing the transmit covariances of the WD and ET under the energy harvesting constraint of WD and transmit power constraints of WD and ET, respectively. Firstly, we consider perfect channel state information (CSI) of all links. Due to the non-convexity of the optimization problem, we propose a two-level optimization algorithm, the inner level optimization problem is a semi-definite programming (SDP) problem and the outer level optimization problem is a single-variable optimization problem. The optimal solution is derived and the sufficient condition to ensure that transmit beamforming having rank-one structure is also provided. Then, we consider robust secure transmit scheme design where the CSI uncertainties are molded by the worst-case model, and S-procedure and its extension are employed to transform the semi-infinite constraint problem into finite constraint problem. Similarly, the optimal robust solution and the sufficient condition to ensure that robust transmit beamforming is optimal are provided. Simulation results demonstrate the effectiveness of our proposed strategies.

Optimum QoS-Aware Beamformer Design for Full-Duplex Relay With Self-Energy Recycling

In this letter, we introduce quality of service-aware beamformer design for full-duplex wireless-powered relay with self-energy recycling. In the first phase of communication, the information signal is transmitted from the source to the relay. In the second phase, the relay forwards this signal using beamforming while it harvests energy via self recycling and from the source. The aim is to satisfy the signal-to-noise ratio requirement of the destination with minimum transmission power from the relay’s own battery. A closed-form solution for the optimum relay beamformer is derived and the feasibility conditions are obtained. The effects of different system parameters on the relay’s performance are discussed in the simulation results.

Full-Duplex User Relaying for NOMA System With Self-Energy Recycling

This paper proposes a self-energy recycling full-duplex cooperative non-orthogonal multiple access (SRF-NOMA) system, where a nearby user can be employed as a decode-and-forward, amplify-and-forward, and quantize-map-forward relay with self-energy recycling protocol to assist a distant user. The relay harvests energy from dedicated energy signal sent by a base station, while it reuses energy from loop self-interference (LI) signal. To characterize the performance of the system proposed, new expressions of exact and asymptotic outage probabilities for two users are derived. Based on analytical results, the diversity orders achieved by the nearby and distant user are one and two, respectively. We confirm that the diversity orders of the distant user are obtained with direct link and relaying link, since the energy from LI is harvested for information transmission at the relay. Numerical results are presented to validate the accuracy of the derived results and demonstrate that: 1) when the DF or AF protocol is employed, the outage behavior of the SRF-NOMA system is superior to orthogonal multiple access; 2) in the high signal-to-noise ratio region, DF relay in the SRF-NOMA system is capable of enhancing the outage performance compared to AF relay; and 3) the distant user in the SRF-NOMA system with QMF relay is able to obtain a better performance than that of DF and AF relays.

Robust Secure Beamforming for Wireless Powered Full-Duplex Systems With Self-Energy Recycling

In this paper, we study a multiuser wireless powered communication system, where an energy-constrained full-duplex information transmitter (IT), powered by wireless energy from a dedicated energy transmitter (ET), intends to send confidential information to the information receiver (IR) in the presence of multiple idle users that could be the potential eavesdroppers. In the practical scenario of imperfect channel state information and assuming that the idle users need to harvest energy from the ET, we aim to maximize the worst-case secrecy rate at the IR by jointly optimizing the transmit covariance matrix at the ET as well as the information beamforming and artificial noise covariance at the IT, subject to their individual transmit power constraints and the minimum required power transferred to the idle users. We employ the semidefinite relaxation (SDR) and extended S -procedure approaches to transform the original nonconvex optimization problem into convex problem, which can be efficiently solved by solving a sequence of semidefinite programs. Furthermore, we show that the SDR is tight since there always exists a rank-one optimal solution. For performance comparison, two heuristic schemes for ease of implementation are also developed. Numerical results are presented to show the effectiveness of our proposed schemes.

Multi-Antenna Beamforming Techniques in Full-Duplex and Self-Energy Recycling Systems: Opportunities and Challenges

Full-duplex technique is considered as an essential component of the coming 5G wireless systems. Since the SI from its transmit antennas dominates over the signal received from remote sites, the suppression of SI is the first priority challenge in the design of FD systems, and thus combinations of analog SI cancellation with radio frequency domain approaches are considered. Applying BF techniques with multiple antennas on top of these combined approaches can further strengthen the SI suppression capability so that wireless systems can enjoy the benefit from FD operation without much concern on SI. However, various factors affect the design of BF in FD networks, and hence they provide a set of research challenges. Also, S-ER is an alternative way of utilizing SI in FD networks, where the RF radiation from a node is reused as an energy source. In this article, we go through these opportunities and challenges along with a survey of technical results developed so far in regard to the BF for handling the SI of FD systems. We look at various network models, the strategies for handling the SI, relay protocols, and antenna structure to see how these provide technical challenges for the BF design.

Decode‐and‐forward relaying with full‐duplex wireless information and power transfer

In this study, the authors consider a decode-and-forward (DF) relaying protocol with full-duplex wireless information and power transfer, and investigate its outage performance. In this protocol, a cooperative relay can transmit the information to the destination and harvest the energy from the source simultaneously. Thus, part of the energy used by the relay can be recycled through the self-loop channel that exists in the relay's full-duplex operation. An approximated expression for the outage probability is derived under the scenario where the self-loop channel is fading, and then the authors derive an exact closed-form expression for the outage probability under a scenario where the self-loop channel is non-fading. Moreover, to optimise the outage performance, a power allocation scheme is also provided. The authors analyse the effect of self-loop channel on the outage performance, and show that, benefiting from the full-duplex operation and self-energy recycling, the considered protocol is superior to the existing power splitting-based and time switching-based DF relaying protocols, in terms of outage performance. Simulations are provided to validate the authors' results.

Spatial-Modulation-Based Wireless-Powered Communication for Achievable Rate Enhancement

In this letter, we propose to utilize spatial modulation (SM) at the wireless device (WD) in a wireless-powered communication (WPC) system for information transmission (IT) by mapping information to the active antenna indices, so that the remaining antennas can be dedicated to energy harvesting (EH) simultaneously. Consequently, the proposed scheme enjoys the advantages of improved system achievable rate (AR), simultaneous EH and IT, and self-energy recycling (SE-R) while requiring no backhaul links between the WD and the information receiver. Numerical results verify the AR enhancement of the proposed scheme with a Gaussian input over the existing time switching-based WPC protocol, the antenna selection-based WPC protocol, and SE-R without SM.

Secure Beamforming for Full-Duplex Wireless Powered Communication Systems With Self-Energy Recycling

In this letter, we study a novel multi-antenna wireless powered communication (WPC) system consisting of an energy source (ES), a full-duplex self-energy recycling information source (IS), an information receiver (IR), and an energy receiver (ER) (potential eavesdropper). The energy-constrained IS, powered by ES, sends the confidential information to IR over the wiretap channel. Our goal is to maximize the secrecy rate for IR by jointly optimizing the energy and information beamforming vectors, under the constraints of the transmit power at ES and IS and the harvested energy at ER. To solve the formulated non-convex problem, a partial Lagrange dual method coupled with two-stage optimization method is proposed, which derives the optimal solution in semi-closed form. Numerical results show the superiority of our proposed design compared with the existing schemes.

Self-Energy Recycling for RF Powered Multi-Antenna Relay Channels

We investigate self-energy recycling (S-ER)-based RF powered multi-antenna relay channels (RCs) for the coverage extension in sensor networks or small cells. In the S-ER-based RF powered RC, the power used at the relay station for data transmission depends only on the energy from the access point and the recycled energy from its own transmission. We propose an optimal beamforming scheme with associated protocols and study their behaviors for both cases of downlink only and joint up–down link. Strategies for the power allocation between data transmission and RF powering are provided and a comparison with the conventional RF powered RC is made. For the proposed power allocation strategies, the performance of the conventional RC is achieved by the proposed RF powered RC only when infinite RF power is available. A high value of S-ER helps the proposed systems to reach the performance of conventional relay systems. In the joint up–down link protocol, we show that the up–down rate region can simply be constructed with easy power allocation strategy.

Beamforming optimisation in energy harvesting cooperative full‐duplex networks with self‐energy recycling protocol

This study considers the problem of beamforming optimisation in an amplify-and-forward relaying cooperative network, in which the relay node harvests the energy from the radio-frequency signal. Based on the self-energy recycling relay protocol, the authors study the beamforming optimisation problem. The formulated problem aims to maximise the achievable rate subject to the available transmitted power at the relay node. The authors develop a semidefinite programming (SDP) relaxation method to solve the proposed problem. They also use SDP and the full search to solve the beamforming optimisation based on a time-switching relaying protocol as a benchmark. The simulation results are presented to verify that the self-energy recycling protocol achieves a significant rate gain compared with the time-switching relaying protocol and the power-splitting relaying protocol.

Secure Communications in the Presence of a Buffer-Aided Wireless-Powered Relay With Self-Energy Recycling

We consider a relay-assisted wireless network, where the energy-harvesting buffer-aided relay node is powered by radio-frequency signals from a source node wishing to communicate with its destination. We propose two secure cooperative protocols for a network composed of a source node equipped with a data buffer communicating with its destination in the presence of a buffer-aided relay node and an eavesdropper. Our proposed protocols are designed based on the channel state information and the buffer state information at the source and relay nodes. The burstiness of data at the source node queue (buffer) and the energy recycling process at the relay are taken into account in our analysis. In addition, we take the decoding and signal processing circuit power consumption constraints into consideration. For the limiting case of an infinite-size battery at the relay, we derive a sufficient condition for the energy queue to saturate. Our numerical results demonstrate the throughput gains of our proposed protocols.

Weighted Sum Transmit Power Minimization for Full-Duplex System With SWIPT and Self-Energy Recycling

This correspondence considers a full-duplex (FD) point-to-point system consisting of one multi-antenna full-duplex access point (FD-AP) and one two-antenna full-duplex mobile station (FD-MS). We adopt simultaneous wireless information and power transfer (SWIPT) scheme and apply the self-energy recycling at FD-MS. In order to minimize the weighted sum transmit power, we jointly design the transmit beamforming vector of FD-AP, the receive power splitting (PS) ratio of FD-MS, as well as the transmit power value of FD-MS. Since the original problem is non-convex, we apply semidefinite relaxation (SDR) and obtain a new convex problem. We further prove that both problems have exactly the same solutions. Finally, simulations are provided to verify our analysis, and the comparison with a half-duplex (HD) system demonstrates the significant performance gain from self-energy recycling.