Energy Constrained Relay Node Research Articles

Energy-efficient two-way full-duplex relay transmission strategy with SWIPT and direct links

In this paper, we improve networks’ spectral efficiency (SE), extend networks’ lifetime, and maximize networks’ energy efficiency (EE) of two-way full-duplex (FD) relay networks. Firstly, to improve networks’ SE and to extend networks’ lifetime simultaneously, we design a two-way FD relay transmission strategy with simultaneous wireless information and power transfer and direct links (DLs). The designed transmission strategy can complete a bidirectional communication in only one time slot with the exists of DLs and the energy-constrained relay node. With the designed transmission strategy, we further give the characteristics of relay amplification factor, the analysis of the designed transmission strategy, and the EE analysis of traditional half-duplex two-way amplify-and-forward relaying. Secondly, to maximize networks’ EE, we present both the EE maximization problems and analyses of the designed transmission strategy with equal power allocation and optimal power allocation. To solve the EE maximization problems, we further propose the alternating optimal algorithm and give complexity analysis of the algorithm. Simulations show that our designed transmission strategy can improve the SE and EE of the networks.

System Outage Probability of PS-SWIPT Enabled Two-Way AF Relaying With Hardware Impairments

In this paper, we investigate the system outage probability of a simultaneous wireless information, and power transfer (SWIPT) based two-way amplify-and-forward (AF) relay network, where transceiver hardware impairments (HIs) are considered. The energy-constrained relay node processes the received signals based on a power splitting protocol, and the two terminals employ a selection combining (SC) scheme to exploit the signals from the direct and relaying links. Assuming independent but non-identically distributed Nakagami-m fading channels, we derive the system outage probability in a closed-form, which enables us to identify two crucial ceiling effects on the system outage probability caused by HIs in the high data rate regions, i.e., relay cooperation ceiling (RCC) and overall system ceiling (OSC). Specifically, the RCC prevents the relaying link from participating in cooperative communications, while the OSC leaves the overall system in outage. Furthermore, we derive the achievable diversity gain of the considered network, which shows that the diversity gain equals either the shape parameter of the direct link or zero. Computer simulations are provided to validate the correctness of our analytical results, and study the effects of various system parameters on the system outage performance and the optimal power splitting ratio, as well as the energy efficiency.

Performance of SWIPT for Full-Duplex Relay System With Co-Channel Interference

In this correspondence, we study the outage performance for the simultaneous wireless information and power transfer (SWIPT) full-duplex relay system. The energy-constrained relay node is subject to the co-channel interference (CCI). Although the interference deteriorates the system performance, it can also provide additional energy for harvesting at the relay. Hence, in order to quantify the impact of CCI for the energy harvesting system, a closed-form and asymptotic expression of the system outage performance is derived for the power splitting (PS) based relay. Moreover, with the aid of the approximated outage analysis, we obtain a simple expression for the optimal PS ratio. Simulation results are provided to validate the accuracy of our analysis.

SWIPT in multi-hop amplify-and-forward wireless sensor networks

ABSTRACTEnergy harvesting (EH) is an eminent solution to perpetuate the lifetime of energy-constrained relay nodes in wireless sensor networks (WSNs). This paper considers a multi-hop amplify-and-forward (AF) network in which relay nodes with EH capability harvest energy inherent in the source transmitted radio frequency (RF) signal and use the harvested energy for signal transmission. Based on the time switching and power splitting EH receiver designs, we have examined the performance of, (i) time switching based relaying (TSR) and (ii) power splitting based relaying (PSR) protocols in multi-hop AF network, with throughput as the figure of merit. The numerical analysis reveals that, PSR outperforms TSR at high signal-to-noise ratio (SNR) whereas TSR outperforms PSR at low SNR, in multi-hop AF-WSNs with energy harvesting.

Outage performance analysis of wireless energy harvesting‐based two‐unicast networks

In the study, a wireless energy harvesting-based two-unicast network is proposed. The proposed model consists of two source–destination pairs, in which two source nodes transmit information to their respective destination nodes via the help of the same relay node. Each transmission can be divided into two time slots each with the same time duration. In the first time slot, two source nodes transmit the signals to their opposite destination nodes, and the energy-constrained relay node harvests energy using the power splitting relaying protocol. In the second time slot, adopting the amplify-and-forward mode, the relay node forwards the mixed signals to two destination nodes and each destination node can subtract the signal of another destination, which is received in the first time slot, and obtain its own signal. The performances of the proposed scheme are evaluated in terms of outage probability and throughput. Numerical results corroborate the derived analytical expressions and show that the proposed scheme nearly doubles the maximal throughput compared with the conventional one.

Energy Efficiency Optimization for SWIPT-Enabled Cooperative Relay Networks in the Presence of Interfering Transmitter

Recently, energy harvesting via radio frequency (RF) signals has gained significant attention from academe and industry as a suitable solution to powering energy constrained relay nodes in cooperative networks. The ability to maximize the energy efficiency of such cooperative networks is still a critical issue because an inefficient cooperative network can affect certain requirements for the system quality of service (QoS). In this letter, we study the energy efficiency performance of a simultaneous wireless information and power transfer (SWIPT)-enabled cooperative relay network in the presence of an interfering transmitter (IT). The SWIPT-enabled relay network is subjected to interference, which affects the quality of the signal received at both the relay node and the destination node. We consider two scenarios: 1) when the RF energy that the relay can harvest from the interference signal is assumed to be negligible and 2) when the relay harvests the RF energy from both the source and the IT transmissions. We derived the optimal transmitted source’s power for each scenario and obtained the suboptimal power splitting and energy consumed factors by running extensive simulations. Then, we proposed a new energy-saving power splitting relaying (ES-PSR) protocol.

Power‐splitting relaying protocol for wireless energy harvesting and information processing in NOMA systems

Non-orthogonal multiple access (NOMA) along with cooperative communications have been recognised as promising candidates for the fifth generation (5G) wireless networks and have attracted many researchers. Every networked device however has its own limited power supply. To this extent, this study investigates a power-splitting relaying (PSR) protocol for wireless energy harvesting (EH) and information processing in the NOMA systems to prolong the lifetime of the energy constrained relay nodes in wireless networks so as to avail the ambient radio-frequency (RF) signal as well as to simultaneously harvest the energy and process the information. Decode-and-forward relaying is employed at the relay node where the energy from the received RF signal is harvested and exploited to forward the information to the destination. Specifically, the outage probability and ergodic rate of the PSR protocol are derived to realise the impacts of EH time, EH efficiency, power splitting ratio, source data rate, and the distance between nodes. It is shown that an outperformance in terms of the energy efficiency is achieved with an increased EH efficiency and the employment of the NOMA when compared to the conventional orthogonal multiple access.

Simultaneous wireless information and power transfer in energy‐augmented amplify and forward cooperative cognitive networks

Simultaneous wireless information and power transfer (SWIPT) and energy harvesting (EH) have been considered as the promising technique to enhance the lifetime of energy constrained relay nodes of the amplify and forward (AF)-based cognitive wireless network. The amalgamation of cognitive and cooperative communication has emerged as a powerful method for improving spectrum utilisation. In this study, an energy-augmented AF (EAF) protocol has been proposed to enhance the throughput and minimise the outage probability of cooperative cognitive relay networks. A power splitting based SWIPT relay secondary user in the EH module harvests the energy and uses the harvested energy to forward the amplified version of the signal to the destination. System model and analytical equations have been developed for the proposed EAF protocol. Simulation results demonstrate that the proposed EAF protocol outperforms the conventional schemes in terms of capacity, outage probability and throughput.

Sum rate analysis of two‐unicast wireless energy harvesting system

The authors study the sum rate of a two-unicast wireless energy harvesting system. The system consists of two source nodes, two destination nodes and one energy constrained relay node, which only harvests energy from the signals transmitted by the source nodes for its operation. Each source node transmits the signal to its corresponding destination node via the help of the relay node. The transmission process is divided into two time slots each with the same time duration. In the first time slot, two source nodes transmit the signals to the relay node and the destination nodes, and the relay node uses the power splitting (PS) protocol for harvesting energy. In the second time slot, adopting analogue network coding, the relay node retransmits the mixed signal to the destination nodes using the harvested energy. Considering network coding noise, the analytical expressions of a near optimal adaptive PS factor that leads to a maximal sum rate is derived. Numerical results corroborate the analytical results and show the superior performance of the proposed scheme in comparison with the conventional one.

Energy Efficiency Optimization for AF Relaying with TS-SWIPT

In this paper, we focus on energy efficiency (EE) maximization for simultaneous wireless information and power transfer (SWIPT) based energy-constrained and amplify-and-forward (AF) relay networks. We adopt low-complexity time-switching (TS) protocol to realize SWIPT at the energy-constrained relay node, and formulate an EE maximization problem in which TS factor and transmit power control are needed to be jointly optimized. Since the formulated problem is non-convex and difficult to solve, we propose an algorithm combining fractional programming and alternating convex optimization to optimize TS factor and transmit power iteratively with low complexity. Simulation results are provided to demonstrate the convergence of the proposed algorithm, as well as the performance gains in terms of EE compared with other existing schemes.

System Outage Performance for Three-Step Two-Way Energy Harvesting DF Relaying

Wireless energy harvesting (WEH) has been recognized as a promising technique to prolong the lifetime of energy constrained relay nodes in wireless sensor networks. Its application and related performance study in three-step two-way decode-and-forward (DF) relay networks are of high interest but still lack sufficient study. In this paper we propose a dynamic power splitting (PS) scheme to minimize the system outage probability in a three-step two-way energy harvesting DF relay network and derive an analytical expression for the system outage probability with respect to the optimal dynamic PS ratios. In order to further improve the system outage performance, we propose an improved dynamic scheme where both the PS ratios and the power allocation ratio at the relay are dynamically adjusted according to instantaneous channel gains. The corresponding system performance with the improved dynamic scheme is also investigated. Simulation results show that our proposed schemes outperform the existing scheme in terms of the system outage performance and the improved dynamic scheme is superior to the dynamic PS scheme.

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.

Cooperative non‐orthogonal multiple access with SWIPT over Nakagami‐m fading channels

AbstractTo meet with both the energy and spectral efficiency, cooperative non‐orthogonal multiple access (NOMA) (termed as CNOMA) and simultaneous wireless information and power transfer (SWIPT) are integrated in this paper. Two different protocols such as CNOMA‐SWIPT‐PS and CNOMA‐SWIPT‐TS are proposed, by employing power‐splitting (PS) and time‐switching (TS) energy harvesting (EH) techniques, respectively. In the proposed protocols, a base station (BS) directly communicates with a NOMA near user, whereas the communication with a NOMA far user is performed with the assistance of an energy‐constrained relay node. The relay node harvests energy from the transmitted signal by the BS, employing PS or TS EH technique. We investigate ergodic sum capacity and outage probability of the proposed protocols along with analytical derivations over Nakagami‐m fading channels. Finally, the effectiveness of the proposed schemes over existing strategy and conventional multiple access is demonstrated through analysis and simulation.

An Adaptive Transmission Scheme in Cooperative Relay Networks with Energy Accumulation

We investigate a wireless-powered cooperative relay network, where an energy constrained relay node accumulates the energy harvested from radio frequency signals, and then assists source signal transmission. An adaptive cooperative transmission scheme for cooperative relay network is developed. The relay helps to transmit the source signal only if it has harvested enough energy and the channels between source and relay do not suffer from an outage. Before each transmission block, one out of two transmission modes, i.e., Half-duplex (HD) or Full-duplex (FD), is dynamically adopted based on the maximal instantaneous capacity of the system. A closed-form expression for the exact outage probability of the system with the proposed scheme is derived. Monte Carlo simulations are run to validate the accuracy of the mathematical analysis, and numerical results show that the proposed protocol outperforms the existing fixed cooperative transmission modes.

Analysis of time-switching and power-splitting protocols in wireless-powered cooperative communication system

SWIPT techniques combined with wireless cooperative communication provides a sustainable solution to extend the lifetime of the communication networks. It prolongs the battery life of wireless low-powered devices and enables additional efficiency in terms of power in wireless communications. This paper explores performance difference of two simultaneous wireless information and power transfer (SWIPT) protocols named Time-Switching (TS) and Power-Splitting (PS). Two identical decode-and-forward relaying communication networks with multiple relays are considered, where energy constrained relay nodes harvest energy from the received Radio Frequency (RF) and use harvested energy to assist information transmission between the source and the destination. All relay nodes in one network use TS protocol while the relay nodes in the other network use PS protocol. In particular, we evaluate throughput and outage probability of maximal ratio combiner (MRC) output at the destination node of both systems. In order to evaluate throughput, outage probability is derived for delay-limited transmission mode. The numerical results provide practical insight into the performance difference in various system parameters for both TS and PS protocols. Simulation results obtained depict that the TS protocol is superior to PS protocol in performance parameters, BER, Outage probability and throughput in low transmission rate. However, in higher transmission rates PS becomes superior to TS protocol, though overall performance reduce compare to lower transmission rate.

Energy efficiency maximisation in wireless powered networks with cooperative non‐orthogonal multiple access

In the 5G wireless networks, non-orthogonal multiple access (NOMA) is a promising paradigm to improve its high spectrum efficiency. This study considers applying simultaneous wireless information and power transfer (SWIPT) technique to cooperative NOMA wireless networks, where energy-constrained relay nodes harvest the ambient radio-frequency signal and use the harvested energy to forward the packets from sources to destinations. To this end, the authors first formulate the energy-efficient cooperative transmission problem for SWIPT in NOMA with imperfect channel state information. Then, by exploiting alternative optimisation and dual decomposition, they design an iterative algorithm for power allocation and power splitting (PS) to solve the non-convex optimisation problem. The authors' simulation results reveal that the proposed algorithm can converge within a few iterations and yield optimal system energy efficiency.

Performance Analysis of Wireless Powered DF Relay System Under Nakagami-$m$ Fading

In this paper, we analyze the average symbol error rate (SER) for a wireless powered three-node decode-and-forward (DF) relaying system in Nakagami- $m$ fading environment. $M$ -ary phase-shift keying modulated data at source is communicated to destination through energy-constrained relay node in three time slots. In the first slot, the signal transmitted by the source is used for energy harvesting at the relay node. Next two slots are employed for selective DF relaying, where relay transmits using the energy harvested from the source node. The source node is assumed to have a dedicated power supply. We analyze the end-to-end average SER expressions using the moment generating function based approach for two relaying scenarios: i) the direct link between the source and the destination exists and ii) the direct link is deeply faded and therefore can be ignored. The asymptotic approximations of the average SER are also obtained to determine the optimal energy allocated for each transmission. Since energy is related to the power transmitted at a node and the slot duration, the optimal energy expression can be judiciously used to optimize power and time for the corresponding slot. The effects of modulation order, relay placement, and channel conditions on the performance of the system with and without optimal resource allocation are investigated. The achievable diversity order and the throughput are also analyzed.

Energy Efficiency Maximization in Mobile Wireless Energy Harvesting Sensor Networks

In mobile wireless sensor networks (MWSNs), scavenging energy from ambient radio frequency (RF) signals is a promising solution to prolonging the lifetime of energy-constrained relay nodes. In this paper, we apply the Simultaneous Wireless Information and Power Transfer (SWIPT) technique to a MWSN where the energy harvested by relay nodes can compensate their energy consumption on data forwarding. In such a network, how to maximize system energy efficiency (bits/Joule delivered to relays) by trading off energy harvesting and data forwarding is a critical issue. To this end, we design a resource allocation (ResAll) algorithm by considering different power splitting abilities of relays under two scenarios. In the first scenario, the power received by relays is split into a continuous set of power streams with arbitrary power splitting ratios. In the second scenario, the received power is only split into a discrete set of power streams with fixed power splitting ratios. For each scenario above, we formulate the ResAll problem in a MWSN with SWIPT as a non-convex energy efficiency maximization problem. By exploiting fractional programming and dual decomposition, we further propose a cross-layer ResAll algorithm consisting of subalgorithms for rate control, power allocation, and power splitting to solve the problem efficiently and optimally. Simulation results reveal that the proposed ResAll algorithm converges within a small number of iterations, and achieves optimal system energy efficiency by balancing energy efficiency, data rate, transmit power, and power splitting ratio.

On the Performance Analysis of WPT-Based Dual-Hop AF Relaying Networks in <inline-formula> <tex-math notation="LaTeX">$\alpha$ </tex-math> </inline-formula>-<inline-formula> <tex-math notation="LaTeX">$\mu$ </tex-math> </inline-formula> Fading

In this paper, a two-hop amplify-and-forward relaying system, where an energy-constrained relay node entirely depends on the energy scavenged from the source signal, is investigated. This paper analyzes the performance of the energy-harvesting (EH) protocols, namely, ideal relaying receiver, power-splitting relaying (PSR), and time-switching relaying (TSR), over independent but not identically distributed (i.n.i.d.) $\alpha $ - $\mu $ fading channels in terms of the ergodic capacity and ergodic outage probability (OP). We derive exact unified and closed-form analytical expressions for the performance metrics with the aforementioned protocols over i.n.i.d. $\alpha $ - $\mu $ channels. Three fading scenarios, such as Weibull, Nakagami- $m$ , and Rayleigh channels, are investigated. Provided simulation and numerical results validate our analysis. It is demonstrated that the optimal EH time-switching and power-splitting factors of the corresponding TSR and PSR protocols are critical in achieving the best system performance. Finally, we analyzed the impact of the fading parameters $\alpha $ and $\mu $ on the achievable ergodic OP.

Secrecy Analysis of SWIPT-Enabled Cooperative Networks With DF HPTSR Protocol

The simultaneous wireless information and power transfer (SWIPT) technology is recently used to sustain the lifetime of energy-constrained relay nodes in wireless cooperative networks. An example to achieve this technology is the hybridized power-time splitting-based relaying (HPTSR) protocol. However, the information security aspect of wireless cooperative networks is important and needs adequate attention. In this paper, we perform the secrecy analysis of a SWIPT-enabled cooperative network with source–relay link-based decode-and-forward HPTSR protocol, which can enhance the operational lifetime of the relay nodes and the secrecy performance of the entire cooperative network. Specifically, we examine the secrecy performance of the considered network by deriving the analytical expressions for the near-optimal power splitting factor, secrecy outage probability, and secure energy efficiency of the system. All analytical results are confirmed by numerical simulations. Our results show that the SWIPT-enabled cooperative network outperforms the conventional relaying scheme-based network presented in literature at relatively high signal-to-noise ratios.