Time-switching Relaying Research Articles

Secrecy Performance Analysis of Energy Harvesting Untrusted Relay Networks with Hardware Impairments

In this work, we focus on the issue of secure communication in energy harvesting untrusted relay networks taking into account the impact of hardware impairments, where an energy‐constrained relay, powered by received radio frequency signals, attempts to decode sensitive data from the source without authorization. To achieve secure communication, we employ destination‐assisted jamming to prevent the untrusted relay from decoding sensitive data while serving as a useful energy source. We derive the interception probability (IP), connection outage probability (COP), and effective secrecy throughput (EST) in closed form for time switching relaying (TSR) strategy. Subsequently, we conduct an asymptotic analysis in the high signal‐to‐noise ratio (SNR) regime to provide practical insights into how various system parameters affect security, reliability, and efficiency, including time switching factor and the level of hardware impairments. Our findings demonstrate that the presence of hardware impairments improves security performance but compromises reliability performance, which does more harm than good.

SWIPT-Based Cooperative NOMA for Two-Way Relay Communications: PSR versus TSR

Spectrum and energy efficiency with simultaneous wireless information and power transfer (SWIPT) to prolong the lifetime of power-constrained wireless devices in cooperative relaying nonorthogonal multiple access (CR-NOMA) has received great attention in the last decade. This paper investigates a two-way relay channel in a CR-NOMA system where two users exchange data with the assistance of a relay. Power-splitting relaying (PSR) and time-switching relaying (TSR) protocols are employed at the relay to harvest RF energy and process information from two users. We firstly derive the exact expressions of outage probability (OP) and system throughput (ST). The impacts of signal quality, energy coefficients, the distance of the nodes, and the data rate of two users on these performance metrics are then evaluated through several system settings to reflect practical network scenarios. It is shown that the OP and ST of the TSR are superior to that of the PSR protocol. Specifically, numerical results indicate that a higher throughput of up to 8% can be achieved with the TSR when compared to the PSR. It is further revealed that the OP and ST of the PSR are strongly affected by energy harvesting (EH) coefficients, while the performance obtained with the TSR is nearly independent of the EH capability at the relay.

Outage and Throughput Analysis of Full-Duplex Cooperative NOMA System With Energy Harvesting

This paper investigates the outage and throughput performance of full duplex (FD) cooperative relaying (CR) based non-orthogonal multiple access system (NOMA) with energy harvesting (EH) i.e., FD-CR-EH-NOMA system. We consider a network scenario, where the base station (BS) serves two downlink users, with the near user configured as a FD relay to deliver messages to the far user. We derive analytical expressions for the outage probabilities experienced by the users and the system outage probability of FD-CR-EH-NOMA network under time switching relaying (TSR) protocol in the presence/absence of direct link from BS to the far user. Assuming imperfect successive interference cancellation (i-SIC), we derive analytical expressions for (i) optimal power allocation (OPA) factor at the BS and (ii) optimal time switching (OTS) factor at the relay that independently minimizes the system outage probability. Further, we use the alternating optimization technique to determine the jointly optimal power allocation and time switching factors that minimize the system outage probability. Furthermore, we determine the OTS factor that maximizes the asymptotic throughput of the system in the delay-limited transmission mode. With the help of numerical and simulation investigations, we show that the system outage and throughput of the considered network improve significantly under the proposed schemes.

Outage probability analysis for hybrid TSR-PSR based SWIPT systems over log-normal fading channels

Employing simultaneous information and power transfer (SWIPT) technology in cooperative relaying networks has drawn considerable attention from the research community. We can find several studies that focus on Rayleigh and Nakagami-m fading channels, which are used to model outdoor scenarios. Differing itself from several existing studies, this study is conducted in the context of indoor scenario modelled by log-normal fading channels. Specifically, we investigate a so-called hybrid time switching relaying (TSR)-power splitting relaying (PSR) protocol in an energy-constrained cooperative amplify-and-forward (AF) relaying network. We evaluate the system performance with outage probability (OP) by analytically expressing and simulating it with Monte Carlo method. The impact of power-splitting (PS), time-switching (TS) and signal-to-noise ratio (SNR) on the OP was as well investigated. Subsequently, the system performance of TSR, PSR and hybrid TSR-PSR schemes were compared. The simulation results are relatively accurate because they align well with the theory.

Performance Estimation of Sustainable Smart Farming with Blockchain Technology

Sustainable smart agriculture with increase in signal to interference or signal to noise ratio (SIR/SNR) for selection of best relay is discussed in a wireless blockchain based network. The overall communication throughput (OCT), power splitting relaying (PSR), time switching relaying (TSR) and transmission success rate (TRS) are also derived during the selection of best relay performance with and without interference. The performance of OCT, PSR, TSR and TRS increases with the increase in the number of potential relay nodes as seen in the results of derivation. The accuracy of the theoretical values are validated by numerical simulations.

Performance Analysis of Underlay Cognitive Radio System with Self-Sustainable Relay and Statistical CSI

The relentlessly increasing number of small-sized devices with limited powering and computational capabilities requires the adoption of new approaches to spectrum access. In this paper, we analyze an underlay cooperative cognitive wireless system based on available statistical channel state information (CSI) that is applicable to the cognitive system with limited computational resources due to its low complexity. We considered the scenario where the primary and the cognitive network coexist in the same spectrum band, under the constraints of interference threshold and maximal tolerable outage permitted by the primary user. The communication in the secondary decode-and-forward (DF) relaying system is established via a self-sustainable relay, which harvests energy from both cognitive and primary transmitters. The closed-form expressions for the outage probability of the cognitive network are derived, which are valid for both time-switching relaying (TSR) and power-splitting relaying (PSR) protocols. We analyze the influence of both cognitive and primary systems as well as the impact of channel parameters on the cognitive system outage performance. The derived analytical results are corroborated by an independent simulation method.

A Hybrid Protocol for SWIPT in Cooperative Networks

A promising technology for addressing network lifetime and energy bottlenecks in wireless networks is the Simultaneous Wireless Information and Power Transfer (SWIPT). In this paper, a Hybrid Time switching and Power splitting-based Relaying (HTPR) protocol for SWIPT in an Amplify-and-Forward (AF) network is proposed. The network consists of a source, relay, and destination in which the relay performs Energy Harvesting (EH) from the source signal and uses the harvested energy to transmit the signal to the destination. A direct link exists between the source and destination, and the signals from the source and relay are combined by the Maximum Ratio Combining (MRC) method at the destination. Closed-form expressions for outage probability are derived under delay-limited transmission to determine the achievable throughput at the destination in different transmission schemes. For a constant data rate, HTPR protocol with uniform and optimal EH ratios are considered for throughput maximization. To solve the optimization problem, the convex optimization technique Lagrange multiplier method and Karush-Kuhn-Tucker (KKT) conditions are used. Results show that the HTPR protocol has higher throughput than other SWIPT protocols at relatively high Signal-to-Noise Ratio (SNR).

Performance Analysis for Exact and Upper Bound Capacity in DF Energy Harvesting Full-Duplex with Hybrid TPSR Protocol

In this paper, we investigate the full-duplex (FD) decode-and-forward (DF) cooperative relaying system, whereas the relay node can harvest energy from radiofrequency (RF) signals of the source and then utilize the harvested energy to transfer the information to the destination. Specifically, a hybrid time-power switching-based relaying method is adopted, which leverages the benefits of time-switching relaying (TSR) and power-splitting relaying (PSR) protocols. While energy harvesting (EH) helps to reduce the limited energy at the relay, full-duplex is one of the most important techniques to enhance the spectrum efficiency by its capacity of transmitting and receiving signals simultaneously. Based on the proposed system model, the performance of the proposed relaying system in terms of the ergodic capacity (EC) is analyzed. Specifically, we derive the exact closed form for upper bound EC by applying some special function mathematics. Then, the Monte Carlo simulations are performed to validate the mathematical analysis and numerical results.

A Multi-Objective Target-Oriented Cooperative MAC Protocol for Wireless Ad-hoc Networks With Energy Harvesting

In this paper, we present a cross layer cooperative medium access control (CMAC) protocol with energy harvesting (EH) capability. The small energy capacity and size of wireless nodes pose a great challenge to the longevity of wireless networks due to the cost of ensuring a reliable communication link between transmitting nodes characterized by path-loss, shadowing and fading effects. Besides, the inability of existing CMAC protocols to exhibit multi-objective target orientation limits their adaptation to the dynamic network requirements. To address this problem, we propose a protocol that harnesses the radio frequency (RF) EH in the physical layer to enhance the throughput, end to end delay, energy efficiency and network lifetime of energy constraint wireless networks. This ensures that beneficial cooperation is achieved in fairness and multi-objective target-oriented protocol. We then investigate the performance of deploying a selective time-switching relaying (TSR) and power-splitting relaying (PSR) schemes in the MAC layer stack for a decode-and-forward (DF) reactive relaying distributed network. In addition, the quality of service requirement, outage probability, and network lifetime optimization techniques, respectively were utilized for optimal power allocation. Also, we propose a distributed and adaptive relay selection algorithm to select the best helper node that improves the network performance and balance the network energy consumption. The results of simulation show that a multi-objective target orientation can be achieved by the proposed EH-CMAC protocol and outperforms EAP-CMAC protocol with respect to throughput, end to end delay, network lifetime and energy efficiency.

Energy Efficient Buffer-Aided Transmission Scheme in Wireless Powered Cooperative NOMA Relay Network

In this paper, we consider a wireless powered cooperative non-orthogonal multiple access (NOMA) relay network, in which one source is supposed to send independent messages to two users with the assistance of one energy-constrained relay that harvests energy from the source. Firstly, we study the minimum power consumption at the source node to fulfill the least required transmission rates by two users in both time switching relaying (TSR) strategy and power splitting relaying (PSR) one. Secondly, when the relay is provisioned with data buffer and energy storage, the long-term average power consumption minimization problem is formulated to take into account of the data and energy queue causality, peak transmit power constraint, and transmission mode selection. By using Lyapunov optimization framework, a novel buffer-aided transmission scheme (BATS) is proposed to asymptotically approach the optimal solution. Our analysis shows that, the PSR outperforms the TSR in terms of the realized energy efficiency, and BATS can be utilized to further improve the energy efficiency. It is disclosed that, there is an inherent trade-off between the long-term power consumption and the average queuing delay. In addition, larger user rates or less power consumption can be realized if a larger delay can be tolerated.

Optimum Design of Energy Harvesting Relay for Two-Way Decode-and-Forward Relay Networks Under Max–Min and Max-Sum Criterions

We study the optimum design of an energy harvesting relay for two-way decode-and-forward (DF) relay networks. In the networks, the relay harvests energy as well as decodes information using the received signal from two sources with power splitting relaying (PSR) and time switching relaying (TSR) strategies. Since the two-way relay network has two opposite traffic flows, it can be considered as a special case of multi-user systems. Applying the max–min criterion for fairness and max-sum criterion for maximum resource utilization, we optimize the operations of the energy harvesting relay. Specifically, considering the transmission rate constraints of individual hops, we derive optimum power splitting coefficients and optimum time switching coefficients, respectively, for PSR-based and TSR-based networks under both criterions, and analytically calculate the resulting maximum transmission rates. Numerical results confirm that our analyses exactly match with exhaustive search simulations. The obtained optimum coefficients are given in closed-form, therefore, they can be easily adopted in simple two-way relay networks with limited computational power such as sensor/Internet of Things (IoT) networks and can help two-way DF relay networks.

Optimization of Links With a Battery-Assisted Time-Switching Wireless Energy Harvesting Relay

In this paper, we analyze the performance of a two-hop network in which a multiantenna source communicates with a single-antenna destination through a decode-and-forward single-antenna energy harvesting (EH) relay. We assume a novel practical system framework in which the EH relay has the option of augmenting the wireless energy harvested by drawing energy from a supplementary battery, thereby improving link performance. Assuming use of the time-switching relaying (TSR) EH protocol, the outage and throughput performance are analyzed. We optimize the fraction of time devoted to EH (the TSR parameter) so as to maximize throughput for fixed supplementary battery energy. We also optimize the TSR parameter to minimize supplementary battery energy consumption for target throughput performance. We further show that exploiting second-hop channel knowledge at the relay can dramatically reduce the energy drawn from the supplementary battery. These insights are of fundamental importance to system designers. Simulation results validate the derived analytical expressions and corroborate our findings.

Performance analysis of downlink NOMA–EH relaying network in the presence of residual transmit RF hardware impairments

In this paper, we investigate the effects of residual-transmit radio-frequency impairments on the downlink non-orthogonal multiple access system with perfect successive interference cancellation using an energy-harvesting (EH) relay in which nodes in the network are equipped with a single antenna. The source node communicates with two users with the help of the amplify-and-forward EH relay node. In addition, both the power-splitting relaying (PSR) and time-switching relaying (TSR) protocols are examined. To evaluate the performance of the proposed system, closed-form expressions of the outage performance and the available throughput are derived over Rayleigh fading channels. Moreover, the accuracy of analytical results is verified by a Monte Carlo simulation. The results show the effects of various parameters, such as power allocation factors, the relay node location, data rate, transmit hardware impairment level, and power allocation factors on the outage performance ($${\mathcal {OP}}$$) and throughput with two users for both PSR and TSR architectures in the presence of hardware impairments. Furthermore, these results are compared with performance of orthogonal multiple access (OMA) EH relaying system.

Performance of EH Protocols in Two-Hop Networks With a Battery-Assisted EH Relay

In this paper, we compare the performance of time-switching relaying (TSR) and power-splitting relaying (PSR) protocols in two-hop networks with a battery-assisted energy-harvesting (EH) amplify-and-forward relay. In this battery-assisted relay framework, the EH relay augments the harvested energy with energy drawn from a battery. Using expressions derived for throughput and average battery energy consumption, we investigate maximization of throughput for given battery energy availability per time slot and minimization of battery energy consumption for target throughput requirement. When only statistical channel knowledge is available, PSR results in better throughput performance at practical signal-to-noise ratios. However, in the typical low battery energy and low target throughput regime, it is TSR that is more battery energy efficient. When second-hop instantaneous channel knowledge is available, we observe dramatical energy savings that increases lifetime of nodes. Simulation results are presented to demonstrate accuracy of the derived expressions.

On the Performance of Wireless Powered Cognitive Relay Network With Interference Alignment

In this paper, a two-hop decode-and-forward wireless powered relaying cognitive radio network with interference alignment over Rayleigh fading channels is investigated. The energy-constrained secondary relay node harvests energy from both the information and interference signals. Then, the harvested energy is used by the relay to forward the information signal from the source to the destination node. By applying beamforming matrices to primary and secondary networks, the performance metrics, such as outage probability, capacity, and bit error rate are studied under perfect and imperfect channel state information scenarios for both power-splitting relaying (PSR) and time-switching relaying (TSR) protocols. In addition, the optimal network performance is achieved by calculating the optimal energy harvesting time-switching and power-splitting coefficients. Finally, closed-form expressions for the outage probability of primary and secondary users are derived. Monte Carlo simulation results corroborate the analytical ones and show that the PSR technique outperforms TSR in the considered system model.

An efficient time-switching relaying protocol for multiuser cognitive radio relay networks with SWIPT

In this paper, we propose a new time-switching relaying (TSR) protocol for multi-destination dual-hop underlay cognitive radio relay networks with simultaneous wireless information and power transfer (SWIPT) technique. The proposed protocol maintains the same receiver complexity of the conventional TSR protocol with the ability for implementing both of them using the same hardware. We study the performance of the proposed TSR protocol and compare it with the conventional TSR and power-splitting relaying (PSR) protocols. Unified analytical expression is derived for the outage probability, in addition to studying the performance at high signal-to-noise ratio (SNR) values where unified approximate and simple expressions for the outage probability are provided. The results show that the proposed TSR protocol outperforms the conventional TSR protocol in terms of outage probability. Also, findings illustrate that applying the SWIPT technique in multi-destination underlay cognitive relay networks results in a unity diversity order. In contrast to conventional relaying networks, results show that the best location for the relay node in SWIPT relay networks is either near the source or the destinations, but not in between.

Performance Analysis of General Hybrid TSR-PSR Energy Harvesting Protocol for Amplify-and-Forward Half-Duplex Relaying Networks

In this paper, we propose a hybrid protocol for energy harvesting in wireless relay networks, which combines the benefits of both time-switching relaying (TSR) and power-splitting relaying (PSR), which are two main protocols for energy harvesting. In TSR, a dedicated harvesting time in each time slot is allocated for energy harvesting, while the remaining time is used for information transmission. In PSR, a portion of received power is split for energy harvesting. TSR can simplify the hardware compared to PSR, but reduce the throughput or achievable rate of the system. Specifically, we conduct a rigorous analysis to derive the closed-form formulas for performance factors of the system. We deliver the analysis results for various transmission modes: instantaneous transmission, delay-limited transmission, and delay-tolerant transmission, which are different from each other on the availability of statistical information about the channels between source and relay nodes. The results are also confirmed by Monte Carlo simulation. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

A Novel Time-Switching Relaying Protocol for Multi-user Relay Networks with SWIPT

In this paper, we propose a new time-switching relaying (TSR) protocol for dual-hop relay networks with simultaneous wireless information and power transfer (SWIPT) technique. The proposed protocol maintains the same receiver complexity of the conventional TSR protocol with the ability for implementing them using the same hardware. We study the performance of the proposed TSR protocol and compare it with the conventional TSR and power-splitting relaying protocols. Unified analytical expressions are derived for the outage probability, achievable throughput, and the ergodic channel capacity, in addition to studying the performance at high signal-to-noise ratio values where a unified approximate expression for the outage probability and expressions for the diversity order and coding gain are provided. The results show that the proposed TSR protocol outperforms the conventional TSR protocol in terms of outage probability and throughput. Also, findings illustrate that applying the SWIPT technique in multi-destination relay networks results in a unity diversity order. In contrast to conventional relaying networks, results show that the best location for the relay node in SWIPT relay networks is either near the source or the destinations but not in between.

Hybrid protocol for wireless energy harvesting network over log‐normal fading channel

In a wireless energy harvesting network with an energy-constrained decode and forward relay node, the authors propose a hybrid protocol (HP) which is a combination of power splitting relaying (PSR) and time switching relaying (TSR). The authors derive the analytical outage probability expressions of the HP over log-normal fading channel. The numerical results show that the HP scheme significantly outperforms the PSR and TSR schemes in terms of outage probability performance.

RF Energy Harvesting with Multiple Sources in Wireless Mesh Network

Energy harvesting (EH) module for wireless sensor network has become a promising feature to prolong the conventional battery inside the devices. This emerging technology is gaining interest from sensor manufacturers as well as academicians across the globe. The concept of employing EH module must be cost effective and practical. In such, the use of EH module type besides RF is more realistic due to the size of the scavenger module, the availability of the resources and conversion efficiency. Most of the oil and gas plants have some drawbacks in scavenging RF from surrounding (i.e. router, Wi-Fi, base station, cell phone) due to its placement in remote area and thus limited energy sources could be a threat in this application. Multiple sources, including co-channel interference (CCI) in any constraint nodes is a feasible way of scavenging several wastes from ambient RF energy via wireless mesh topology. In this paper, a 3-node decode-and-forward (DF) model is proposed where the relay node is subject to an energy constraint. Multiple primary sources and CCI are added in the system model known as Multiple-Source and Single-Relay (MSSR). A mathematical model is derived in Time Switching Relaying (TSR) and Power Splitting Relaying (PSR) schemes to obtain an average system throughput at a destination. Numerical simulation with respect to the average throughput and EH ratio was performed and compared with the Single-Source and Single-Relay (SSSR) and ideal receiver. By applying multiple sources and CCI as an energy enhancement at the constraint node, the optimal value of EH ratio for TSR can be reduced significantly by 10% as compared to the ideal receiver whereas the optimal value of EH ratio for PSR is outweigh TSR in terms of overall system throughput.