Time Switching Ratio Research Articles

Physical layer security in wireless sensors networks: secrecy outage probability analysis

ABSTRACT The secrecy performance of wireless networks powered up by a dedicated power beacon (PB) is addressed in this work. Particularly, the closed-form expression of the secrecy outage probability (SOP) under the presence of multiple eavesdroppers is given. The considered networks are asymmetric since there are multiple eavesdroppers but only a single legitimate receiver. As a consequence, two wiretap schemes are employed, namely, non-colluding and colluding schemes, to take advantage of multiple eavesdroppers. To draw insights from the derived framework, the asymptotic framework of the SOP under the high transmit power regime is also provided. Next, Monte Carlo simulations are provided to validate the theoretical foundations of the proposed approach. Our findings show that by increasing the transmit power from −10 dB to 30 dB, the SOP ameliorates almost a thousand times. Additionally, the SOP is a monotonic decreasing function with a time-switching ratio. We also make comparisons with work in the literature in which the full-duplex relay is employed to help the legitimate link. Numerical results illustrate that the proposed network outperforms those described in the literature. Particularly, through reliance on the setup, the SOP under the proposed system is better than those of the literature by about twofold.

Performance analysis of energy harvesting‐enabled relay networks in κ‐μ fading channels

AbstractIn this paper, we investigate the performance of an energy harvesting (EH)‐enabled multiple relay network operating over generalized ‐ fading channels. Our approach involves utilizing a partial relay selection strategy and employing an amplify and forward relay protocol for efficient EH from RF signals. Additionally, we integrate a selection combining scheme at the receiver to combine both direct and relaying path signals. In our research, we first obtain the exact closed‐form expression of the cumulative distribution function (CDF) for the system under investigation. Subsequently, we derive expressions for the outage probability (OP) and the moment generating function (MGF) using the derived CDF expression. Furthermore, with the assistance of a CDF‐based approach, we derive closed‐form expressions for the average symbol error rate (ASER) for coherent quadrature amplitude modulation (QAM) schemes, including rectangular QAM (RQAM) and hexagonal QAM (HQAM). We also analyze the ASER expression for non‐coherent frequency shift keying (NCFSK), leveraging the derived MGF expression. To gain valuable insights into the performance of EH‐enabled multiple relay networks, we assess the asymptotic expression of the OP. The outcomes indicate how the behavior of the system is affected by various factors such as time switching ratio, channel fading components, number of relays, and the distance between nodes. To corroborate the accuracy of the analytical findings, Monte Carlo simulations are executed.

Nanographene‐Based Metal‐Organic Framework Thin Films: Optimized Packing and Efficient Electron‐Hole Separation Yielding Efficient Photodetector

AbstractOrganic semiconductors, specifically polycyclic aromatic chromophores like pentacene, coronene, and nanographenes (hexa‐peri‐hexabenzocoronene, HBC), are often utilized in optoelectronic applications due to their intriguing single‐molecule properties. However, the integration of these aromatic compounds into optoelectronic devices frequently encounters significant obstacles, primarily due to the unpredictable and challenging control over the structure and morphology of their condensed phase. Rather than resorting to chemical modifications or advanced thin‐film manufacturing methods such as chemical vapor deposition, the so‐called metal‐organic framework (MOF) approach is employed to create a highly photoresponsive, nanographene‐based thin film employing a layer‐by‐layer, liquid‐phase epitaxy method. It is demonstrated that the novel Cu‐HBC MOF thin film exhibits excellent photoresponsive behavior under ultraviolet illumination, including a fast response time (˂ 0.02 s) and high current switching ratio (≈104), which significantly outperforms an isostructural MOF Zn‐HBC. Furthermore, it is demonstrated that the metal nodes inside the MOF can be used to enhance the photoresponse by efficient exciton splitting.

Multi-Dimensional Resource Allocation for Throughput Maximization in CRIoT with SWIPT

To solve the power supply problem of battery-limited Internet of Things devices (IoDs) and the spectrum scarcity problem, simultaneous wireless information and power transfer (SWIPT) and cognitive radio (CR) technology were integrated into the Internet of Things (IoT) network to build a cognitive radio IoT (CRIoT) with SWIPT. In this network, secondary users (SUs) could adaptively switch between spectrum sensing, SWIPT, and information transmission to improve the total throughput. To solve the complicated multi-dimensional resource allocation problem in CRIoT with SWIPT, we propose a multi-dimensional resource allocation algorithm for maximizing the total throughput. Three-dimensional resources were jointly optimized, which are time resource (the duration of each process), power resource (the transmit power and the power splitting ratio of each node), and spectrum resource, under some constraints, such as maximum transmit power constraint and maximum permissible interference constraint. To solve this intractable mixed-integer nonlinear program (MINLP) problem, firstly, the sensing task assignment for cooperative spectrum sensing (CSS) was obtained by using a greedy sensing algorithm. Secondly, the original problem was transformed into a convex problem via some transformations with fixed-power splitting ratio and time switching. The Lagrange dual method and subgradient method were adopted to obtain the optimal power and channel allocation. Then, a one-dimensional search algorithm was used to obtain the optimal power splitting ratio and the time switching ratio. Finally, a heuristic algorithm was adopted to obtain the optimal sensing duration. The simulation results show that the proposed algorithm can achieve higher total system throughput than other benchmark algorithms, such as a greedy algorithm, an average algorithm, and the Kuhn–Munkres (KM) algorithm.

Physical Layer Security in Two-Way SWIPT Relay Networks with Imperfect CSI and a Friendly Jammer.

In this paper, the security of two-way relay communications in the presence of a passive eavesdropper is investigated. Two users communicate via a relay that depends solely on energy harvesting to amplify and forward the received signals. Time switching is employed at the relay to harvest energy and obtain user information. A friendly jammer is utilized to hinder the eavesdropping from wiretapping the information signal. The eavesdropper employs maximal ratio combining and selection combining to improve the signal-to-noise ratio of the wiretapped signals. Geometric programming (GP) is used to maximize the secrecy capacity of the system by jointly optimizing the time switching ratio of the relay and transmit power of the two users and jammer. The impact of imperfect channel state information at the eavesdropper for the links between the eavesdropper and the other nodes is determined. Further, the secrecy capacity when the jamming signal is not perfectly cancelled at the relay is examined. The secrecy capacity is shown to be greater with a jammer compared to the case without a jammer. The effect of the relay, jammer, and eavesdropper locations on the secrecy capacity is also studied. It is shown that the secrecy capacity is greatest when the relay is at the midpoint between the users. The closer the jammer is to the eavesdropper, the higher the secrecy capacity as the shorter distance decreases the signal-to-noise ratio of the jammer.

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.

On the ASER performance of RF energy harvesting multiple relay networks

We present the average symbol error rate (ASER) of quadrature amplitude modulation (QAM) for radio frequency energy harvesting assisted dual-hop multiple amplify-and-forward (AF) relay network. In this relaying network, partial relay selection scheme is employed to select best relay among multiple relays, while selection combining is considered at destination to combine the signals coming from the direct path and the relaying path. In particular, we derive the exact ASER expressions of rectangular QAM (RQAM), hexagonal QAM and cross QAM schemes for the considered systems over independent and non-identically distributed Nakagami-m fading channels using cumulative distribution function method. Moreover, the asymptotic ASER expression of RQAM is determined to examine the system’s diversity order. Further, to verify the correctness of derived expressions, numerically evaluated results are compared with Monte Carlo simulations. Furthermore, the effects of fading parameter, number of relay, time switching ratio, and large scale fading are studied on the ASER performance.

Intelligent Reflecting Surface assisted RF Energy Harvesting Mobile Edge Computing NOMA Networks: Performance Analysis and Optimization

In this paper, we focus on the performance analysis and optimization of an RF energy harvesting (EH) mobile edge computing (MEC) network by the assistance of the intelligent reflecting surface (IRS) and non-orthogonal multiple access (NOMA) schemes. Specifically, a pair of users harvest RF energy from a hybrid access point (HAP) and offloads their tasks to the MEC server at HAP through wireless links by employing an IRS-aided and uplink NOMA scheme. To evaluate the performance of this proposed system, the closed-form expressions of successful computation and energy transfer efficiency probabilities are derived. We further formulate a multi-objective optimization problem and propose an algorithm to find the optimal energy harvesting time switching ratio value to achieve the best performance, namely SENSGA-II. Moreover, the impacts of the network parameters are provided to draw helpful insight into the system performance. Finally, the Monte-Carlo simulation results are shown to confirm the correctness of our analysis. The results have shown that the deployment of IRS can improve the performance of this considered RF EH NOMA system by increasing the number of reflecting elements.

Learning-Based Optimization of Wireless-Powered Two-Way Interference Channels With Imperfect CSI

In this paper, we consider wireless-powered two-way communication in an N-user interference channel with imperfect channel state information (CSI). In the system considered, the receivers harvest energy and receive information simultaneously from data signals sent by transmitters using a time switching (TS) policy, before transmitting response signals back to the transmitters in a subsequent phase using the harvested energy. We aim to find the resource allocation that allows the transmit power and TS ratio to be determined jointly to maximize the sum rate of the response links whilst guaranteeing a predetermined rate requirement for each data link, even in the presence of errors in the estimated CSI. To deal with the non-convexity of our optimization problem, we first introduce a gradient algorithm with a barrier function that finds suboptimal solutions heuristically. Moreover, to overcome the limitations of the gradient algorithm, e.g., its high computational complexity and vulnerability to channel error, we devise a robust strategy for resource allocation based on deep learning, in which artificially distorted CSI is fed into the deep neural network (DNN) during training to compensate for the incompleteness of the derived solutions caused by channel error. The performances of the considered schemes are examined through simulations, in which the proposed DNN scheme achieves a near-optimal performance with respect to the sum rate of the response links and outage probability under imperfect CSI, which validates its usefulness and robustness.

Achievable Rate Maximization for Multi-Relay AF Cooperative SWIPT Systems with a Nonlinear EH Model.

In this paper, the maximization of the achievable information rate is proposed for the multi-relay amplify-and-forward cooperative simultaneous wireless information and power transfer communication systems, where the nonlinear characteristic of the energy harvesting (EH) circuits is taken into account for the receivers of the relay nodes. The time switching (TS) and power splitting (PS) schemes are considered for the EH receivers and the achievable rate maximization problems are formulated as convex and non-convex optimization problems, respectively. The optimal TS and PS ratios for the relay nodes along with the maximum achievable rates for the system are obtained, respectively, by solving the optimal problems with efficient algorithms. The asymptotic maximum achievable rates at low and high input signal-to-noise ratios (SNRs) for both the PS and TS schemes are also analyzed. It is demonstrated that the PS scheme is more susceptible to the variation of the relays’ location and the channel parameters than TS scheme, whereas the TS scheme is more susceptible to the mismatch of the resource allocation than PS scheme. Specifically, compared to the linear EH model, the nonlinear EH model achieves significant performance gain for the TS scheme, whereas inconspicuous performance improvement is achieved for the PS scheme.

Cooperative NOMA-Enabled SWIPT IoT Networks With Imperfect SIC: Performance Analysis and Deep Learning Evaluation

In this article, we propose a cooperative nonorthogonal multiple access (NOMA)-enabled simultaneous wireless information and power transfer (SWIPT) Internet of Things (IoT) networks, where one information source harvests energy from a multiantennas power beacon (PB) to serve two IoT users via the help of multiple energy-limited relay nodes. To improve the performance of far IoT user, we propose reactive and proactive relay selection protocols together with time-power energy harvesting mechanism under imperfect successive interference cancellation. Closed-form expressions for the outage probability (OP), throughput, and energy efficiency (EE) of the proposed system are obtained, from which the asymptotic analysis for the throughput is also carried out. To further enhance the system performance, we propose a low-complexity method to optimize the outage and throughput performance subject to power allocation, time, and power splitting parameters. Toward real-time configurations in IoT networks, we design a deep learning framework for the sum-throughput and EE predictions with low computation complexity and high accuracy. The influences of antennas setting at PB, time-switching ratio, power-splitting ratio, power allocation factor, and the number of relays on the system OP, throughput, and EE are evaluated and discussed along with numerical results.

Performance Analysis and Optimization for IoT Mobile Edge Computing Networks With RF Energy Harvesting and UAV Relaying

This paper studies unmanned aerial vehicle (UAV)-aided nonorthogonal multiple access (NOMA)-based mobile-edge computing (MEC) in Internet of Things (IoT) systems in which the uav acts as a relay (UR). Specifically, we consider a scenario with two clusters IoT devices (IDs) (i.e., a high-priority cluster IA and a low-priority cluster IB) with limited resources, so these IDs cannot compute their tasks and must offload them to a base station (BS) through a UR. We propose a protocol named time switching - radio frequency (RF) energy harvesting (EH) UR NOMA (TS-REUN), which is divided into 5 phases. By applying the TS-REUN protocol, the IDs in the two clusters and the UR harvest RF energy from the broadcast signal of the power beacons (PB). Then, the IDs offload their tasks to the MEC server located at the BS. After server processing, the IDs receive the calculation results from the BS via the UR. The effects of both imperfect channel state information (ICSI) and imperfect successive interference cancellation (ISIC) on the REUN-based mec (REUN-MEC) are taken into account. To evaluate the performance of the system, we derive closed-form expressions for the successful computation probability (SCP) and energy consumption probability (ECP) in the Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathfrak {m}$ </tex-math></inline-formula> fading channel. Moreover, we propose an optimization problem formulation that maximizes the SCP by optimizing the position and the height of the UR and the time switching ratio (TSR). The problem was addressed by employing an algorithm based on particle swarm optimization (PSO). In addition, the Monte Carlo simulation results confirmed the accuracy of our analysis based on system performance simulations with various system parameters, such as the number of antennas at the BS, the number of IDs in each cluster, the TSR, and the position and the height of the UR.

Hybrid protocol for wireless-powered untrusted relay networks with imperfect channel reciprocity

This work investigates the security issue of the energy-constrained untrusted relay network with imperfect channel reciprocity, where the relay without the built-in power supply can only scavenge energy from radio-frequency signals radiated by the source and destination. A hybrid power-splitting (PS)- and time-switching (TS)-based relaying (HPTR) protocol is presented to improve the degraded secrecy performance due to the incomplete self-interference cancellation at the destination. To evaluate the secrecy throughput (ST) of the studied system, the analytical expression of the secrecy outage probability under the delay-limited transmission mode and the closed-form lower bound of the ergodic secrecy capacity under delay-tolerant transmission mode are derived. Both linear and nonlinear models for the energy harvester at the relay are compared. The optimal PS and TS ratios are evaluated numerically. The theoretical derivations are validated by numerical results, revealing that the residual jamming has a negative effect on the secrecy performance of untrusted relay networks, which can be alleviated by the HPTR protocol. Besides, we compare the ST performance of the HPTR protocol with that of the PS and TS relaying schemes, and the results show that the HPTR protocol outperforms both PS and TS relaying protocols in terms of the ST.

On the optimal energy efficiency and spectral efficiency trade-off of CF massive MIMO SWIPT system

Energy efficiency is a key requirement for future network design, and user-centric (UC) cell-free (CF) massive multi-input multi-output (MIMO) networks can achieve over ten times the energy efficiency. Based on this, this paper studies a CF MIMO simultaneous wireless information and power transmission system and proposes a UC access point (AP) selection method and a trade-off performance optimization scheme for spectral efficiency and energy efficiency. In this system, users have both energy recovery and information transmission functions. According to the difference between the interference in the energy harvesting and information transmission process, a flexible AP selection scheme is designed. Blindly pursuing high spectral efficiency will result in waste of resources. This paper proposes an evaluation index that takes into account both energy efficiency and spectral efficiency, analyses the trade-off between energy efficiency and spectral efficiency, and jointly optimizes the AP selection scheme and the uplink (UL) and downlink (DL) time switching ratio to maximize the trade-off performance. Then, the non-convex problem is converted to a geometric planning problem to solve. The simulation results show that by implementing a suitable AP selection scheme and UL and DL time allocation, the information processing scheme on the AP side has a slight loss in spectral efficiency, but the energy efficiency is close to the performance of global processing on the central processing unit.

Combining RF energy harvesting and cooperative communications for low-power wide-area systems

This paper presents the combination of energy harvesting (EH) at the wireless sensor and cooperative communications for low-power wide-area (LPWA) systems. Firstly, the Internet of Things sensor harvests the energy from the power beacon with multiple transmit antennas via radio frequency signals and then uses the harvested energy to transmit signals to multiple gateways with multiple receive antennas. Then, the cooperative communications is applied at the server based on the gateway outputs. By mathematical analysis, we derive the exact closed-form expressions of outage probabilities (OPs), throughput, and symbol error probabilities (SEPs) of the EH-LPWA system over Nakagami-m fading channel in the cases without and with cooperative communications. Our expressions can be considered as the first results applying EH for LPWA systems with mathematical analysis. Then, we obtain the optimal value of the time switching ratio that minimizes the OPs and SEPs and maximizes the throughput of the considered EH-LPWA system. Numerical results have clarified that, the distances, path loss exponent, and data transmission rate have a strong impact on the OPs, throughput, and SEPs. Particularly, using a half of transmission blocks for EH can maximize the system performance. Moreover, when the number of transmit antennas at power beacon is equal to the number of receive antennas at gateways, the system performance can be improved significantly. Finally, the accuracy of the obtained expressions is demonstrated via Monte-Carlo simulations.

Transmit antenna selection – An effective method for improving the performance of spatial modulation full-duplex relay networks with wireless energy harvesting

Full-duplex (FD) communications have been proved as an inevitable techniques to obtain high quality of service in modern wireless communications. In this paper, an integrated communication scheme using spatial modulation (SM) with transmit antenna selection (TAS) and wireless energy harvesting (EH) is proposed to enhance the overall spectral efficiency and diversity order of full-duplex relaying (FDR) networks as well as to overcome the battery shortage problem at the intermediate relay nodes. The performance of this EH-SM-FDR system is investigated thoroughly by deriving the exact-form expressions of the outage probability (OP) and network throughput. The impact of residual self-interference (RSI) at FD relay and the EH time-switching ratio is also analyzed, from which the optimal value of EH time-switching ratio to minimize the OP and maximize the network throughput of the system is obtained. It is recommended from our analysis that more receive antennas should be equipped at the relay than at the destination to achieve better OP performance. This analysis also recommends best suitable data transmission rate depending on the source transmit power to reach lowest OP and highest throughput. Finally, Monte Carlo simulations are conducted to validate all analytical results.

Relay Selection for Security Improvement in Cognitive Radio Networks with Energy Harvesting

This paper selects an unlicensed relay among available self‐powered relays to not only remain but also secure information transmission from an unlicensed source to an unlicensed destination. The relays harvest energy in signals of the unlicensed source and the licensed transmitter. Then, they spend the harvested energy for their relaying operation. Conditioned on the licensed outage restriction, the peak transmission power restriction, Rayleigh fading, and the licensed interference, the current paper proposes an exact closed‐form formula of the secrecy outage probability to quickly evaluate the secrecy performance of the proposed relay selection method in cognitive radio networks with energy harvesting. The proposed formula is corroborated by computer simulations. Several results illustrate the effectiveness of the relay selection in securing information transmission. Additionally, the security capability is saturated at large peak transmission powers or large preset outage probabilities of licensed users. Furthermore, the security capability depends on many specifications among which the power splitting ratio, the relays’ positions, and the time switching ratio can be optimally selected to obtain the best security performance.

Secrecy Rate Maximization in Virtual-MIMO Enabled SWIPT for 5G Centric IoT Applications

In 5G centric sensors-enabled Internet of Things (IoT) applications, virtual multiple-input multiple-output (V-MIMO) technique has witnessed significant attention as physical layer security enabler. In IoT, physical layer security is potential due to the vulnerability of wireless broadcasting in low computation capability and limited power source of the sensor nodes. In this regard, this article presents a secure and energy efficient V-MIMO enabled simultaneous wireless information and power transfer framework. The security framework uses beamforming and cooperative jamming signal to maximize the secrecy rate of the IoT systems. An optimization problem is formulated by collectively optimizing the beamforming vector, power splitting ratio, and time switching ratio. Since the maximization problem is nonconvex, to find solution of the problem an iterative algorithm is presented, which inherently uses the penalty function to find the solution. It is evident from simulation results that the secrecy rate optimization of the proposed framework is better as compared to the state-of-the-art techniques considering various metrics.

Outage and throughput analysis of power-beacon assisted nonlinear energy harvesting NOMA multi-user relay system over Nakagami-m fading channels

This paper considers a non-orthogonal multiple access (NOMA) multi-user relay system where both source and relay harvest the energy from a power beacon (PB) equipped with multiple antennas and use this harvested energy to transmit signals to several users. Realistic nonlinear energy harvesting models are applied, and time switching protocols are adopted at source and relay. We successfully derive the exact closed-form expressions of the outage probability and throughput of the system over Nakagami-m fading channels. Then, we use Monte-Carlo simulations to validate the correctness of these derived mathematical expressions. Numerical results show that a higher saturated power threshold of the nonlinear energy harvester results in lower outage probability and higher throughput. Moreover, the optimal time switching ratio that maximizes the throughput is smaller than the optimal time switching ratio that minimizes the outage probability.

Cooperative Physical Layer Security Transmission Scheme Based on Energy Harvesting

Energy harvesting (EH) is introduced into the physical layer security transmission of wireless sensor networks. It takes the energy efficiency and security into account simultaneously. To improve the physical layer security of the cooperative wireless sensor network, an EH-based physical layer security transmission scheme called multi-relay time switching (MRTS) is proposed in this paper. In the multi-source single-destination network with eavesdroppers, multiple relay nodes with time switching (TS) protocol convert the received signals into energy and information according to the time slots, and the converted energy is used to amplify and forward the received information. The research shows the optimal time switching ratio, under which the maximum secrecy capacity is achievable with the optimal converted energy. The results prove that under the same conditions, the secure transmission scheme based on MRTS is better than power splitting-based relaying (PSR) scheme when the total power of sources is limited.