Time Switching-based Relaying Research Articles

Throughput Maximization for the Full-Duplex Two-Way Relay System with Energy Harvesting

The full-duplex technique can improve the transmission capacity of the communication systems, and energy harvesting (EH) is a promising operation to prolong the lifespan of a wireless node by utilizing the radio-frequency signals. In this paper, the throughput performance of a full-duplex two-way energy EH capable relay system is investigated. In particular, a practical EH protocol, named the time-switching-based relaying (TSR) protocol, is used for EH and the decode-and-forward (DF) policy for information transmission. The outage probability is successfully obtained, and the corresponding system throughput for TSR protocol can be derived by it. The derived throughput is a function of different system parameters, including the time-switching (TS) ratio, power allocation ratio, and the length of the communication time slot. Meanwhile, the throughput is used to characterize a joint time and power allocation scheme for the system, and we aim to find the optimal time and power allocation to achieve the optimal throughput. Due to the existence of three variables and the integral form of throughput expression, an optimization for the throughput is difficult. However, a modified simulated annealing-based search (SABS) algorithm can be used to optimize the throughput. The modified SABS algorithm overcomes being highly impacted by the initial point, and derives the optimal solution fast. Simulation results show that the analytical throughput expression is related with the TS ratio, power allocation ratio, and the length of the communication time slot. The analytical curve of the throughput matches with the simulated one well, which shows that the obtained analytical system throughput for the TSR protocol is valid. Meanwhile, the proposed modified SABS algorithm could be used to derive accurate throughput when SNR is higher than 10 dB.

Secrecy performance analysis of amplify-and-forward relay cooperative networks with simultaneous wireless information and power transfer

Simultaneous wireless information and power transfer (SWIPT) is a promising technology to enhance the power constraint issue in the wireless networks. In this paper, we investigate the secrecy performance of a selective cooperative relaying network with an energy harvesting (EH) technique, in which a source terminal communicates with a legitimate user at the destination terminal through N amplify-and-forward (AF) relays in the presence of multiple eavesdroppers. The relays deploy SWIPT with power splitting-based relaying (PSR) and time switching-based relaying (TSR) protocols to harvest energy. We present closed-form expressions for the secrecy performance metrics, consisting of the probability of non-zero secrecy capacity, the secrecy outage probability, and the average secrecy capacity to evaluate the physical layer security (PLS) of the system. Using the mathematical expressions, we obtain numerical results under the parameters of the system. These results demonstrate that using relay selection can significantly improve the secrecy performance of the system. Moreover, we compare the cooperative relay system without SWIPT and the system with SWIPT. It is observed that depending on the distance of eavesdroppers from the relays and the destination, the system based on SWIPT may achieve a better PLS than the system without SWIPT. Finally, we provide Monte-Carlo simulation results to confirm the validity of our analysis.

Joint Time Allocation for Wireless Energy Harvesting Decode-and-Forward Relay-Based IoT Networks With Rechargeable and Nonrechargeable Batteries

This article considers a one-way decode-and-forward (DF) relay-based Internet-of-Things (IoT) network consisting of a source, a relay, and a destination in wireless energy harvesting (EH) and information transmission (IT) using the time switching-based relaying (TSR) protocol. The one-way DF relay network using the TSR protocol consists of some time slots. This article proposes the time allocation scheme for maximizing the achievable data rate under the total block time constraint. It is assumed that the relay is considered the IoT device used for long periods of time without battery replacement and it is equipped with both nonrechargeable and rechargeable batteries. Based on the supplied power by the nonrechargeable battery, the proposed scheme determines whether or not to harvest energy and operates two alternate time allocation schemes. Since the proposed scheme is based on the closed-form expressions, it provides low complexity. Numerical results show that the achievable data rate of the proposed time allocation scheme is greater than that of the fixed time allocation scheme.

Secrecy Outage Minimization for Wireless-Powered Relay Networks With Destination-Assisted Cooperative Jamming

To solve security vulnerability and energy scarcity problems in relay, we propose two secure relaying protocols, power splitting-based relaying (PSR) and time switching-based relaying (TSR), in a wireless-powered relay network with destination-assisted cooperative jamming. In these protocols, the relay adaptively controls the amount of energy harvested from the received signals using PS or TS policy, considering information leakage to the eavesdropper. We first prove the convexity of the secrecy outage probability with respect to the PS ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> ) and TS ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> ), and then derive the closed-form expressions of the optimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> for minimizing secrecy outage under the signal-to-noise ratio (SNR) assumption. Numerical results reveal that the proposed PSR and TSR protocols using the derived <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> can achieve near-optimal performance in terms of secrecy outage. It is observed that the optimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> do not depend on the eavesdropping channels in a high SNR regime such that the near-optimal secrecy outage can be achieved practically without knowledge of the eavesdropper location. Furthermore, intensive simulations reveal that it is advantageous to allocate more power to energy harvesting for PSR, whereas more time to signal processing for TSR to minimize secrecy outage.

Power splitting versus time switching based cooperative relaying protocols for SWIPT in NOMA systems

Non-orthogonal multiple access (NOMA) along with wireless power transfer have recently been adapted to cooperative communications for 5G and beyond wireless networks. This paper investigates NOMA based cooperative relaying wireless-powered networks (CRWPNs) where, decode-and-forward (DF) relaying and successive interference cancellation are both employed at a wireless-powered intermediate node. For simultaneous wireless information and power transfer (SWIPT), power-splitting relaying (PSR) and time switching-based relaying (TSR) protocols are considered in the NOMA based CRWPN. As a result, the combination of cooperative relaying power domain NOMA network and PSR and TSR protocols is proposed in this paper. The outage performance and ergodic rate of both protocols are analysed for evaluation of the impacts of energy harvesting (EH) time, EH efficiency, power splitting ratio, source data rate, and the distance between the nodes. In addition, two delay limited transmission (DLT) and delay tolerant transmission (DTT) modes are considered in this network model to investigate the throughput and ergodic rate of the system according to the source transmission rate. It is shown that the cooperative relaying NOMA (CRNOMA) scheme achieves a lower outage probability when compared to the conventional orthogonal multiple access (OMA) schemes. Additionally, the PSR outperforms the TSR in both low and high signal-to-noise ratio (SNR) regions in terms of throughput, ergodic rate and energy efficiency. For instance, the outage probability of CRNOMA for both PSR and TSR in SNR range of from -10 dB to +20 dB (i.e. a low SNR region) decreases gradually but not linearly. However, in SNR range of from +20 dB to +40 dB (i.e. a high SNR region), the outage probability of CRNOMA for both PSR and TSR decreases quickly. Furthermore, the energy efficiency is shown to be considerably enhanced with the employment of EH for CRNOMA. Finally, the impacts of the distance between the nodes on the performance and a comparison between two scenarios of having and without having direct links are evaluated.

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.

Performance Analysis of an Energy-Harvesting IoT System Using a UAV Friendly Jammer and NOMA Under Cooperative Attack

In this article, we consider the information leakage and outage probabilities of a multiple-input single-output (MISO) energy-harvesting (EH) Internet of Things (IoT) system in which a multiantenna ground base station (GBS) transmits messages to legitimate IoT destinations (LIDs) with the help of IoT relays (IRs) using non-orthogonal multiple access (NOMA) in the presence of a malicious jammer (MJ) and eavesdroppers (EAVs). The communication protocol is separated into two phases. In the EH phase, the IRs harvest energy from a power beacon (PB). In the information transmission (IT) phase, the communication process is further divided into two subphases: 1) The GBS broadcasts signals to the IRs using NOMA. Simultaneously, the MJ sends interfering signals to attack the IRs while the EAVs steal the confidential signals from the GBS, in a process called a cooperative attack. On the other hand, to protect the legitimate communication, an unmanned aerial vehicle (UAV) is used as a friendly jammer to defend against the EAVs. 2) A selected IR employs the time-switching-based relaying (TSR) technique to forward the received signal to the LIDs using NOMA. Similar to the first subphase, the LIDs are subjected to a cooperative attack, and the UAV attacks the EAVs in return. The secrecy performance of this communication protocol is characterized by deriving expressions for the information leakage probabilities (ILPs) for the LIDs' signals. A UAV altitude optimization algorithm is also proposed to achieve the best possible secrecy performance. Furthermore, we evaluate the system performance by deriving closed-form expressions for the outage probabilities (OPs). Accordingly, an algorithm is proposed to guarantee both the secrecy and system performance (in terms of the ILPs and OPs). Monte Carlo simulations are presented to verify our analytical results.

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.

Joint design of beamforming and time switching/power splitting for wireless-powered multi-antenna dual-relay network

In this paper, we consider a wireless-powered dual-relay network consisting of one multi-antenna source, two single-antenna energy-constrained relays and one single-antenna destination without direct source to destination link. In order to establish the communication flow, the energy-constrained relays harvest energy from the radio frequency transmitted by the source firstly, then exploit the harvested energy to forward the source information to the destination based on distributed space time coding (DSTC). Under this network architecture, three decode-and-forward (DF) technique-based relaying protocols, i.e., time switching-based relaying (TSR) protocol, power splitting-based relaying (PSR) protocol, and hybrid relaying (HR) protocol, are considered to drive the energy transfer and information transmission. To maximize the network throughput, the joint design for the optimal energy and information beamforming vectors employed at the source, the optimal time switching, and power splitting ratios under these three protocols are investigated and solved efficiently by employing simple sequential optimization approach or alternating optimization approach. Simulations are conducted to show the superior performance achieved by our proposed scheme. Moreover, we find that the TSR protocol outperforms the PSR protocol in the low signal-to-noise ratio (SNR) region, while the latter outperforms the former in the high SNR region. And the HR protocol achieves the best performance in any SNR region. At the same time, the effect of the relays’ locations on the throughput performance of these three protocols is also investigated.

Impact of fixed power allocation in wireless energy harvesting NOMA networks

SummaryThe time switching‐based relaying (TSR) scheme is considered in energy harvesting protocol to implement with its advantage to nonorthogonal multiple access (NOMA) system. In particular, decode‐and‐forward (DF) mode is proposed to employ in relay to forward signal to serve two far NOMA users. There are two main metrics including outage probability and ergodic rate, which are derived in exact expressions with respect to varying performance under impacts of energy harvesting fractions. To evaluate system performance, outage event and related capacity are illustrated, and we tailor performance gap among two NOMA users and such gap can be controlled by selecting of appropriate power allocation factors assigned for each user to obtain optimal performance. By examining node arrangement, target rates and varying transmit signal to noise ratio (SNR), it can be further achieved performance in several situations of such NOMA. As important result, the considered NOMA system outperforms than the conventional multiple access scheme, and this expected result is confirmed in numerical result and theoretical results. We also explore impacts of transmit power at source, noise power, the other key parameters of energy harvesting scheme to exhibit outage, and ergodic performance. Simulation results are presented to corroborate the proposed methodology.

Non-Linear EH Relaying in Delay-Transmission Mode over n-µ Fading Channels

Energy harvesting is a technique to harvest energy from RF (radio frequency) waves. The RF signals have the ability to convey energy and information concurrently. The EH in coop-erative relaying systems may increase the capacity and coverage of wireless networks. In this work, we study a dual-hop (two-hop) relaying. This system has three nodes: a source, a relay, and a destination. The source and destination have multiple antennas. We account a non-linear EH model and TSR (time-switching-based relaying) protocol at the single-antenna relay node. We evaluate the system performance over η−µ fading channels. With a saturation threshold, a non-linear EH receiver restrains the harvested power. In the TSR protocol, the relay changes mode between the EH and information processing, by which a fraction of time is used with each process. The fading model η−µ incorporates some fading models as notable cases, viz., Nakagami- m, One-sided Gaussian, Nakagami-q (Hoyt), and Rayleigh. The system performance is analyzed in terms of the average capacity and throughput for different saturation threshold power levels, divers antennas arrangements, and different parameter values of η and µ.

Adaptive Wireless-Powered Relaying Schemes With Cooperative Jamming for Two-Hop Secure Communication

A two-hop relay network is considered, in which an eavesdropper can overhear the relaying signal. To prevent the eavesdropper from decoding this signal, a destination transmits a jamming noise while a source transmits the data signal to the relay. At the same time, the relay can harvest energy from both the source signal and the jamming noise, and use this harvested energy to forward the received signal to the destination. In such a wireless-powered relay system with cooperative jamming, we propose two adaptive relaying schemes based on power splitting and time switching techniques. In the proposed power splitting-based relaying (PSR) and time switching-based relaying (TSR) schemes, the relay controls the power splitting ratio ( ${\rho }$ ) and time switching ratio ( ${\alpha }$ ), respectively, in order to achieve a balance between signal processing and energy harvesting. We find analytically the optimal values of ${\rho }$ and ${\alpha }$ in each scheme to maximize the secrecy capacity under the assumption of high signal-to-noise ratio (SNR). Interestingly, although the eavesdropper’s channel state information (CSI) is used in the derivation of the optimal control parameters ( ${\rho }$ and ${\alpha }$ ), they are shown not to be affected by the eavesdropper’s CSI in a high SNR regime. This implies that the proposed schemes can be effective even for practical environments where there is no eavesdropper’s CSI. Furthermore, simulation results show that they well coincide with the exact solutions in practical environments even though the closed-form solutions are obtained with a high SNR assumption. Moreover, the comparisons of PSR and TSR in various scenarios show that the two relaying schemes have complementary performances depending on the network conditions. Specifically, PSR achieves greater secrecy capacity than TSR when the channel condition is unfavorable to the eavesdropper for wiretapping.

Performance of cognitive relay network with energy harvesting relay under imperfect CSI

SummaryThis paper evaluates the performance of an underlay cognitive relay network under imperfect channel state information (CSI) where a secondary user (SU) transmits using a secondary relay (SR) based on decode and forward scheme. The outage probability (OP) of SU is investigated in a scenario where the decode and forward relay harvests energy from radio frequency signal of SU. The relay uses a fraction of time for harvesting in time switching–based relaying (TSR) while a fraction of received power is used for harvesting in power splitting–based relaying (PSR) scheme. The SU and relay control their transmit power using a scaling factor, based on CSI of the interfering links (ie, links from SU transmitter and SR to the primary user [PU] receiver) to protect the quality of service of PU. The available CSI at the SU and SR are imperfect due to practical limitation. Analytical expressions of the OP are derived for TSR‐ and PSR‐based schemes. The impact of harvesting time, power splitting ratio, imperfect CSI, PU outage constraint and interference threshold on the OP of the SU network, and average transmit power of SR is indicated. Further, the impact of multiple SRs is also shown.

An Instantaneous Transmission Mode Analysis in Energy Harvesting for Half-Duplex and Full-Duplex Relaying Network

Energy harvesting (EH) based on surrounding radio frequency (RF) has lastly become advanced approach to prolong the lifetime of the wireless networks. This paper deals with energy harvesting architecture of the half duplex and the full duplex relaying networks. By applying time switching based relaying (TSR) protocol and Amplify-and-Forward (AF) scheme, we derive the closed-form expression of the instantaneous throughput and then compare instantaneous throughput of two networks. An important result can be seen clearly that the time fraction, the position of relay, noise at relay, energy conversion factor as well as target rate in TSR impact on their throughput. Finally, numerical results show an efficient relaying strategy in half -duplex and full duplex cooperative networks.

Performance of Amplify-and-Forward Relaying with Wireless Power Transfer over Dissimilar Channels

Relaying transmission is a promising approach for enhancing the performance of wireless networks, meanwhile wireless power transfer is an emerging solution for prolonging the lifetime of energy constrained relay nodes. In this framework, the amplify-and-forward (AF) relay network consisting of a power transfer and information source, an energy constrained relay and a destination over dissimilar fading channels is taken into account. First, the relay employs the time switching-based relaying (TSR) protocol to harvest energy from the source. Accordingly, the relay supports the source transmits information to the destination. By utilizing the statistical characteristics of signal-to-noise ratio (SNR), the closed-form expressions of outage probability (OP) and average symbol error probability (ASEP) are derived. By means of the obtained result of OP, we also investigate throughput of the system for delay-limited transmission mode. Moreover, we accordingly evaluate the analysis in details and assess the performance of the considered system in various system parameters, such as energy harvesting time, energy harvesting efficiency, and relay location. Finally, Monte-Carlo simulation is also contributed to confirm the correctness of the analytical results. DOI: http://dx.doi.org/10.5755/j01.eee.21.5.13331

Wireless Information and Energy Transfer for Two-Hop Non-Regenerative MIMO-OFDM Relay Networks

This paper investigates the simultaneous wireless information and energy transfer for the non-regenerative multipleinput multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) relaying system. By considering two practical receiver architectures, we present two protocols, time switchingbased relaying (TSR) and power splitting-based relaying (PSR). To explore the system performance limit, we formulate two optimization problems to maximize the end-to-end achievable information rate with the full channel state information (CSI) assumption. Since both problems are non-convex and have no known solution method, we firstly derive some explicit results by theoretical analysis and then design effective algorithms for them. Numerical results show that the performances of both protocols are greatly affected by the relay position. Specifically, PSR and TSR show very different behaviors to the variation of relay position. The achievable information rate of PSR monotonically decreases when the relay moves from the source towards the destination, but for TSR, the performance is relatively worse when the relay is placed in the middle of the source and the destination. This is the first time to observe such a phenomenon. In addition, it is also shown that PSR always outperforms TSR in such a MIMO-OFDM relaying system. Moreover, the effect of the number of antennas and the number of subcarriers are also discussed.

Relaying Protocols for Wireless Energy Harvesting and Information Processing

An emerging solution for prolonging the lifetime of energy constrained relay nodes in wireless networks is to avail the ambient radio-frequency (RF) signal and to simultaneously harvest energy and process information. In this paper, an amplify-and-forward (AF) relaying network is considered, where an energy constrained relay node harvests energy from the received RF signal and uses that harvested energy to forward the source information to the destination. Based on the time switching and power splitting receiver architectures, two relaying protocols, namely, i) time switching-based relaying (TSR) protocol and ii) power splitting-based relaying (PSR) protocol are proposed to enable energy harvesting and information processing at the relay. In order to determine the throughput, analytical expressions for the outage probability and the ergodic capacity are derived for delay-limited and delay-tolerant transmission modes, respectively. The numerical analysis provides practical insights into the effect of various system parameters, such as energy harvesting time, power splitting ratio, source transmission rate, source to relay distance, noise power, and energy harvesting efficiency, on the performance of wireless energy harvesting and information processing using AF relay nodes. In particular, the TSR protocol outperforms the PSR protocol in terms of throughput at relatively low signal-to-noise-ratios and high transmission rate.