Energy Harvesting Relay Research Articles

Transmit beamformer based performance analysis and diversity gains of cell edge user in cooperative MISO-NOMA system

This paper investigates the cell-edge user’s performance in a two-user multiple-input single-output non-orthogonal multiple access (MISO-NOMA) systems using downlink beamformers for optimal power allocation. In particular, power allocation coefficients (PACs) are adjusted through beamformers so that the cell-edge user’s performance is improved in a two-user network scenario. In the proposed model, a cell-center user with strong channel conditions plays a role as an energy harvesting (EH) relay by using simultaneous wireless information and power transfer (SWIPT) protocol to assist the cell-edge user having weak channel conditions. Initially, we formulate the expressions for signal-to-interference-plus-noise ratio (SINR) at the cell-center user and signal-to-noise ratio (SNR) and SINR at the cell-edge user in terms of an indefinite quadratic form (IQF) whilst considering distinct correlation matrices for each link. Next, we achieve exact and approximate closed-form expressions for outage probability of linearly dependent and of distinct beamformers, respectively by using IQF approach. The proposed model achieves diversity gain whereas the analytical expressions are validated by simulation means.

Secrecy rate maximisation for non‐linear energy harvesting relay networks with cooperative jamming and imperfect channel state information

The secrecy performance of a wireless-powered relaying system is investigated in the presence of imperfect channel state information. To improve the system secrecy performance, the destination splits a part of power to transmit the cooperative interference signal while the source transmits confidential information to the relay. The relay is assumed to be equipped with a non-linear energy harvester and to harvest energy from the source and destination for information processing. A joint power splitting and time allocation scheme is studied to maximise the system secrecy rate. The joint optimisation problem is dealt with by the interior-point method. For the sake of comparison, the equal time allocation scheme and the equal power splitting scheme are also investigated. The numerical results verify that the proposed scheme could achieve higher secrecy rate.

Random Access-Based Reliable Uplink Communication and Power Transfer Using Dynamic Power Splitting

Large communication networks, e.g. Internet of Things (IoT), are known to be vulnerable to co-channel interference. One possibility to address this issue is the use of orthogonal multiple access (OMA) techniques. However, due to a potentially very long duty cycle, OMA is not well suited for such schemes. Instead, random medium access (RMA) appears more promising. An RMA scheme is based on transmission of short data packets with random scheduling, which is typically unknown to the receiver. The received signal, which consists of the overlapping packets, can be used for energy harvesting and powering of a relay device. Such an energy harvesting relay may utilize the energy for further information processing and uplink transmission. In this paper, we address the design of a simultaneous information and power transfer scheme based on randomly scheduled packet transmissions and reliable symbol detection. We formulate a prediction problem with the goal to maximize the harvested power for an RMA scenario. In order to solve this problem, we propose a new prediction method, which shows a significant performance improvement compared to the straightforward baseline scheme. Furthermore, we investigate the complexity of the proposed method and its vulnerability to imperfect channel state information.

On maximizing information reliability in wireless powered cooperative networks

Unpredictable nature of fading channels and difficulty in tracking channel state information pose major challenge in wireless energy harvesting communication system design. In this work, we address relay selection problem for wireless powered communication networks, where the relays harvest energy from the source radio frequency signals. A single source–destination pair is considered without a direct link. The connecting relay nodes are equipped with storage batteries of infinite size. We assume that the channel state information (CSI) on the source–relay link is available at the relay nodes. Depending on the availability of the CSI on the relay–destination link at the relay node, we propose two relay selection schemes and evaluate their outage probability. Availability of the CSI at the relay node on the relay–destination link considerably improves the performance due to additional flexibility in the relay selection mechanism. Due to absence of CSI throughout the network at the time of transmission path selection, the analysis of the problem is not tractable. Therefore, we relax our assumptions on availability of CSI and closed-form expressions of the outage probability as a function of the amount of the available harvested energy are derived for both CSI availability cases. Finally, we numerically quantify the performance for the proposed schemes and compare the outage probability for fixed and equal number of wireless powered forwarding relays.

Secure transmission for energy harvesting relay networks with the destination self-protection mechanism

In this paper, we investigate the physical layer security (PLS) of an energy harvesting (EH) cooperative network with the destination self-protection mechanism. More specifically, we consider a cooperative transmission scenario in which a source communicates with a destination through a wireless-powered relay using power splitting (PS) protocol in the presence of an eavesdropper. To degrade the wiretap channel, the destination is operated in full-duplex (FD) to achieve simultaneous information reception and jamming transmission. Taking into account the residual self-interference (SI) at the destination, the non-convex secrecy rate maximization problem is formulated to jointly optimize the PS factor and power allocation of source and destination. Due to the non-convexity of the joint optimization, a low complexity iterative algorithm based on the alternative search method and difference of convex functions (DC) programming is proposed. The original problem is first decomposed into two sub-problems with the fixed transmission power or PS factor. Since the decomposed two sub-problems are still non-convex, we utilize the DC programming to obtain the local solutions of the two sub-problems. Then the global solutions can be obtained by the alternative search method. Simulation results present that the proposed scheme has fast convergence. Comparing with other conventional schemes, the proposed scheme has the best security performance.

Finite Blocklength Non-Orthogonal Cooperative Communication Relying on SWIPT-Enabled Energy Harvesting Relays

A finite blocklength (FBL) twin-user non-orthogonal cooperative downlink system is considered, wherein a base station simultaneously communicates with the users whilst relying on simultaneous wireless information and power transfer (SWIPT) enabled energy harvesting relay. Closed-form analytical expressions are obtained for the end-to-end average block error rate (BLER) assuming potentially dissimilar Nakagami- $m$ fading links. Furthermore, asymptotic expressions are derived for the individual user’s end-to-end average BLER performance and diversity order at high signal to noise ratios (SNRs). Additionally, since, the stronger user’s signal is detected, while assuming the weaker user’s signal to be interference, an analytical bound has been obtained for characterizing the effect of this interference on the BLER performance of both users. Furthermore, a framework is developed for joint relay splitting factor and user power allocation towards end-to-end blocklength minimization under strict reliability constraints by converting the original non-convex optimization problem to a convex geometric program (GP) that can be solved efficiently. Simulation results are presented to validate the analytical expressions derived and illustrate the efficacy of the proposed scheme.

D2D communication with energy harvesting relays for disaster management

ABSTRACT In this paper, we consider a multi-hop device-to-device (D2D) communication, which enables communication from functional area (FA), where the D2D users are placed near to base station (BS) under its coverage to non-functional area (NFA). In our proposed model, random deployment as well as certain distance-dependent deployment of D2D node is considered in NFA. In case of FA, BS is transmitting information with fixed transmit power in multi-hop D2D network. In case of NFA, a D2D node harvests energy from its preceding node, and forwards the information to the successive node. Parallel best path selection (PBPS) and immediate best path selection (IBPS) strategies are considered for FA while several cases of deployment strategies based on inter-node distance is considered for NFA to reach the final destination node. A framework has been proposed for evaluating throughput, ergodic capacity and outage probability. Energy consumption in the system has been estimated via simulation. The throughput performance, ergodic capacity and the outage probability of end-to-end link (i.e. from BS to NFA) under different system parameters are evaluated.

Secure Communication in Cooperative SWIPT NOMA Systems with Non-Linear Energy Harvesting and Friendly Jamming.

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.

Cooperative privacy provisioning for energy harvesting based cognitive multi-relay networks

In order to provide privacy provisioning for the secondary information, we propose an energy harvesting based secure transmission scheme for the cognitive multi-relay networks. In the proposed scheme, two secondary relays harvest energy to power the secondary transmitter and assist the secondary secure transmission without interfere the secondary transmission. Specifically, the proposed secure transmission policy is implemented into two phases. In the first phase, the secondary transmitter transmits the secrecy information and jamming signal through the power split method. After harvesting energy from a fraction of received radio-frequency signals, one secondary relay adopts the amplify-and-forward relay protocol to assist the secondary secure transmission and the other secondary relay just forwards the new designed jamming signal to protect the secondary privacy information and degrade the jamming interference at the secondary receiver. For the proposed scheme, we first analyze the average secrecy rate, the secondary secrecy outage probability, and the ergodic secrecy rate, and derive their closed-form expressions. Following the above results, we optimally allocate the transmission power such that the secrecy rate is maximized under the secrecy outage probability constraint. For the optimization problem, an AI based simulated annealing algorithm is proposed to allocate the transmit power. Numerical results are presented to validate the performance analytical results and show the performance superiority of the proposed scheme in terms of the average secrecy rate.

Physical Layer Security for Wireless Powered Massive MIMO Decode and Forward Relay Systems with Hardware Impairments: Performance Analysis

In this paper, the issue of secrecy capacity of wireless powered massive MIMO dual hop relay system with a single antenna eavesdropper having non ideal hardware is addressed. The relay harvests energy in a proportionate manner and passes it to destination through beamforming with classical decode and forward relaying protocol. The relay has no channel state information (CSI) of passive eavesdropper but has CSI of the legitimate channel. The work presented in this paper focuses on the analysis of the difference in system performance with ideal and non ideal hardware, bounded by strict outage probability. The performance (in terms of secrecy outage capacity) is studied with hardware impairments (HWIs) defined for all network elements, i.e., source, relay, destination and passive eavesdropper. It is also observed that compared to ideal hardware, there is significant degradation in performance due to HWIs.

Energy Beamforming for Full-Duplex Wireless Powered Cooperative Communications

In this paper, we consider a full-duplex wireless powered cooperative communication network, where a source communicates with a destination via a decode-and-forward relay in a full-duplex mode. The source and relay harvest energy from the signal transmitted by a power beacon. We formulate an optimization problem to maximize the achievable rate under the transmit power constraint of the power beacon. We find an optimal energy beamforming scheme by solving the optimization problem. Moreover, we obtain a suboptimal solution with lower computational complexity. Simulation results show that the suboptimal scheme suffers little performance degradation compared with the optimal scheme.

Performance Analysis of SWIPT in Multi-hop Wireless Sensor Networks

Abstract This paper investigates the performance of simultaneous wireless information and power transfer (SWIPT) in multi-hop amplify-and-forward (AF) and decode-and-forward (DF) wireless sensor networks (WSNs). For SWIPT, conventional energy harvesting (EH) protocols: time switching based relaying (TSR) and power splitting based relaying (PSR) are used. Relays harvest energy from the source using TSR/PSR protocol to assist information transmission to the destination. We have considered both uniform and optimal EH ratios at the relays in each protocol. Using the convex optimization method - Lagrange multiplier and Karush-Kuhn-Tucker (KKT) conditions, we have optimized the EH ratios of a 3-hop network. The mathematical expressions for destination throughput are derived for the aforementioned protocols. Results show that the SWIPT-DF network has higher throughput than the SWIPT-AF network, PSR outdoes TSR at high signal-to-noise ratio (SNR) and optimal EH ratios will result in better network throughput.

Outage performance evaluation of device-to-device system with energy harvesting relay

The development of Internet of Things (IoT) devices as well as the increase of nodes in wireless networks, motivates the use of node?s cooperation for wireless system performance improvement. On the other hand, the power requirements of the increasing number of nodes leads to the need for new powering sources. In this paper we consider device-to-device (D2D) relay-assisted system, where decode-and-forward (DF) relay is not equipped with its own power supply, but it harvests energy and uses it for the data transfer to the destination node. System performance is derived for the Fisher-Snedecor F composite fading channel model and energy harvesting protocol based on time-switching scheme. The closed-form approximate expression for the outage probability is derived, that corresponds to the exact results. The impact of the channel fading and shadowing parameters and time-switching factor of energy harvesting protocol on the system performances are investigated. Numerical results are confirmed by an independent simulation method.

Joint Relay Selection, Full-Duplex and Device-to-Device Transmission in Wireless Powered NOMA Networks

This paper investigates non-orthogonal multiple access (NOMA), cooperative relaying, and energy harvesting to support device-to-device (D2D) transmission. In particular, we deploy multiple relay nodes and a cell-center D2D device which can operate in full-duplex (FD) or half-duplex (HD) mode to communicate with a cell-edge D2D device. In this context, there are two possible signal transmission paths from the base station (BS) to the far D2D user either through multiple decode-and-forward (DF) relay nodes or through a near D2D user. Consequently, we propose three schemes to support D2D-NOMA systems, namely non-energy harvesting relaying (Non-EHR), energy harvesting relaying (EHR) and quantize-map-forward relaying (QMFR) schemes. For each of the proposed schemes, closed-form expressions of the outage probabilities of both D2D users are derived. Extensive Monte-Carlo simulation results are provided to validate the derived analytical expressions. The study results show that the proposed schemes can improve the outage performance compared to conventional orthogonal multiple access (OMA) schemes. Moreover, it is shown that the Non-EHR scheme achieves the best outage performance among the three considered schemes.

Distributed Relay Selection for Energy Harvesting Systems

In this paper, we suggest a distributed relay selection (DRS) algorithm for energy harvesting (EH) systems. Each candidate relay amplifies the source packet only when its signal to noise ratio (SNR) exceeds SNR threshold γth. Relay nodes harvest energy from radio frequency (RF) signals received from the source. Both harvesting duration and SNR threshold γth are optimised to maximise the throughput. Our results are compared to opportunistic amplify and forward (OAF) and uniform relay selection (URS).

Secure resource allocation for green two‐way relay networks with mutually untrusted relay and mobile users

The authors investigate secure resource allocation for an orthogonal frequency division multiple access two-way relay network, which has several pairs of mobile users (MUs) and one energy harvesting (EH) relay. In this network, the relay is untrusted and each MU pair may also overhear the other MU pairs' confidential information. In particular, to forward information for each MU, the relay adopts power splitting technique to harvest energy from radio frequency signals emitted by each MU. For this scenario, which has hardly been considered, the joint problem of subcarrier allocation, power control, and power splitting ratio selection is formulated, with the aim to maximise the total secrecy rate of all MUs. A suboptimal algorithm with low complexity and satisfactory performance is proposed to solve the formulated non-convex problem.

Transceiver Design for SWIPT MIMO Relay Systems With Hybridized Power-Time Splitting-Based Relaying Protocol

In this paper, we investigate a dual-hop simultaneous wireless information and power transfer (SWIPT) based amplifying-and-forward (AF) multiple-input multiple-output (MIMO) relay communication system where the relay node harvests energy based on radio frequency (RF) signals transmitted from the source node through the hybridized power-time splitting-based relaying (HPTSR) protocol to forward information to the destination node. The joint optimization of the time-switching (TS) factor, source and relay precoding matrices, and the power-splitting (PS) ratio vector is proposed to maximize the mutual information (MI) between the source and destination nodes. We derive the optimal structure for the source and relay precoding matrices to simplify the transceiver optimization problem. Two algorithms based on the upper bound and lower bound of the objective function are proposed to efficiently solve the optimization problem with low computational complexity. Numerical examples demonstrate that the proposed algorithms provide a better MI performance compared with TS based and PS based energy harvesting (EH) relay systems.

Outage and Throughput Analysis of Spectrum Sharing Cognitive Radio Network Incorporating Energy Harvesting Hybrid Relay

In this paper, cooperative spectrum sharing in cognitive radio (CR) network is incorporated with multi-antenna based RF energy harvesting relays (EH). The performance has been analyzed in the presence of multiple primary users. The relays can harvest energy from source signal and interference from primary transmitter. The relays follow adaptive hybrid protocol (AHR) for forwarding the received signal from source to destination. Outage probability and achievable throughput have been analyzed using a time-splitting relaying (TSR) scheme at the destination where best relay selection (BRS) strategy is used. The outage performances of energy harvesting and non-energy harvesting model have been compared. Throughput and outage performance comparison for AF, DF and AHR have been analyzed. The effect of the number of primary users is also investigated. A trade-off is shown between the number of relays and the number of antennas to achieve the desired throughput. The results depict that the use of energy harvesting strategy in cognitive radio network can result in an energy-efficient solution for future wireless communication.

On Residual Energy Maximization in DF Cognitive Radio Networks With Multiple Eavesdroppers

This paper explores the issues of energy harvesting (EH) and multiple eavesdropping in an underlay cognitive radio network (CRN) that comprises of a secondary transmitter ( $SU_{\mathcal {T}}$ ) and destination ( $SU_{\mathcal {D}}$ ) node connected through a decode-forward (DF) relay ( $S_{\mathcal {R}}$ ). CRN is operated following a frame structure that includes three non-overlapping slots where in the first one, the relay harvests energy from the information signal of $SU_{\mathcal {T}}$ and the interference signal of primary user (PU). During the second slot, $SU_{\mathcal {T}}$ transmits data to the relay node. In the last slot, $S_{\mathcal {R}}$ forwards the same to $SU_{\mathcal {D}}$ and $SU_{\mathcal {T}}$ does EH from PU signal. Residual energy maximization is done under the constraints of energy causality for $SU_{\mathcal {T}}$ and $S_{\mathcal {R}}$ , interference to PU, secondary outage probability and secrecy outage probability. Analytical expressions of ergodic secrecy capacity and secrecy outage probability are derived for non-colluding (NCE) and colluding eavesdropping (CE) scenarios. Closed form expressions for the optimal transmit power of $SU_{\mathcal {T}}$ and $S_{\mathcal {R}}$ along with the time slot for EH are derived and their impacts on the residual energy, secondary outage probability and secrecy outage probability are analysed. Simulation results show a gain on the maximum value of the residual energy by ~8.13% for CE and ~4.72% for NCE over the existing works.

Security Performance Analysis for Best Relay Selection in Energy-Harvesting Cooperative Communication Networks

In this paper, we investigate an energy-harvesting cooperative communication network, which comprises of a source, a destination, and multiple decode-and-forward (DF) relays in the presence of multiple passive eavesdropper (Es). Es attempt to intercept confidential information transmissions from the source to destination via DF relays. In this network, all the DF relays harvest energy from radio-frequency (RF) signals of a source through time-switching receivers. In order to improve the physical layer security of energy-harvesting cooperative communication networks, we propose a best relay selection (BRS) scheme, where the “best” relay is chosen to assist the source-destination transmission. For the purpose of comparison, we consider the classic direct transmission (DT) and equal relay selection (ERS) as benchmark schemes. We derive the exact closed-form expressions of outage probability (OP) and intercept probability (IP) for the ERS and BRS schemes over Rayleigh fading channels. Besides, the security-reliability tradeoff (SRT) is analyzed as a metric to evaluate the tradeoff performance of the proposed BRS scheme. Numerical results show that the SRT of the BRS scheme consistently outperforms that of the ERS scheme, which demonstrates the advantage of our proposed scheme against eavesdroppers. Besides, it is verified that total error rate (TER) defined as the sum of OP and IP can be minimized for both the ERS and BRS schemes through changing the time allocation factor between information transmission and energy harvesting phases. Moreover, there is a best energy conversation efficiency to obtain a maximal SRT value of the ERS and BRS schemes. In addition, as the number of DF relays increases, the SRT of BRS scheme improves notably, while that of ERS scheme remains unchanged. And as the number of Es increases, the SRT of both the ERS and BRS schemes become worse.