Performance Of Radio Frequency Research Articles

Secrecy Performance Analysis of Hybrid RF/VLC Dual-Hop Relaying Systems

In this article, the secrecy performance of a hybrid radio frequency (RF)/visible light communication (VLC) system is studied. In this hybrid system, the source node (i.e., Alice) transmits information to the relay node via the outdoor RF link. Nakagami-m fading and path loss are considered for the RF link. The relay node includes an outdoor component and an indoor component, which are connected by using a wired medium. The outdoor component receives and recovers information by using the decode-and-forward (DF) relaying scheme and then transmits it to the indoor component. The indoor component then converts the received electrical signal into an optical signal by using a light-emitting diode. A legitimate receiver (i.e., Bob) deployed on the floor receives the optical signal. An eavesdropper (i.e., Eve) deployed in the RF or VLC link wiretaps the confidential information. In this study, we use the secrecy outage probability (SOP) and the probability of strictly positive secrecy capacity (SPSC) to evaluate the system performance. We then obtain the closed-form expression for a lower bound on the SOP and an exact closed-form expression for the probability of SPSC when the RF and VLC links are wiretapped, respectively. Numerical results are presented to validate the accuracy of our derivations. We further discuss the effects of the noise standard deviation, the equivalent threshold of the signal-to-noise ratio, and the floor radius on the system secrecy performance when the VLC link is eavesdropped upon. For the case when the RF link is eavesdropped upon, the impacts of the distance between Alice and the relay, the path loss exponent, the fading factor, and the distance between Alice and Eve on secrecy performance are also provided.

Physical layer security analysis of a dual-hop hybrid RF-VLC system

Abstract In this paper, we investigate the secrecy performance of a dual-hop hybrid radio frequency–visible light communication (RF–VLC) system in which we consider a single source antenna (S) transmitting data signals via RF channel through decode and forward (DF) relay (R) toward an authorized receiving antenna (D) at the destination via VLC channel. In this system, we assume that the eavesdropper (E) attempts to eavesdrop the RF channel (S,R) during transmission of the signal. The relay decodes the incoming RF signal into corresponding optical signal and retransmits toward destination via VLC channel (R,D). The RF and VLC channels of the hybrid system are modelled using generalized-K fading distribution and generalized Lambertian radiant intensity distribution respectively. Also the receiver is assumed to be mobile and its mobility is defined by random waypoint (RWP) model. The channels statistics are used to derive the exact analytical expressions for average secrecy capacity and intercept probability in terms of Meijer’s G-function. The derived closed form analytical expressions are the efficient tool to illustrate the impact of variation in different channel parameters on the secrecy performance, namely, shadowing parameters of RF channel, field of view (FOV), semiangle, and the order of Lambertian emission of the VLC channel. Further, numerical analysis is carried out to support the mathematical analysis of the RF–VLC hybrid system.

Performance Analysis of Hybrid Radio Frequency and Free Space Optical Communication Networks with Cooperative Spectrum Sharing

This paper investigates the impact of cooperative spectrum sharing policy on the performance of hybrid radio frequency and free space optical wireless communication networks, where primary users and secondary users develop a band of the same spectrum resource. The radio frequency links obey Nakagami-m distribution with arbitrary fading parameter m, while the free space optical link follows gamma-gamma distributed atmospheric turbulence with nonzero pointing error. Because the secondary users access the spectrum band without payment, their behavior needs to be restricted. Specifically, the power of the secondary users is dominated by the tolerable threshold of the primary users. Considering both heterodyne and intensity modulation/direct detection strategies in optical receiver, the performance of optical relaying networks is completely different from that of traditional networks. With the help of bivariable Fox’s H function, new expressions for cumulative distribution function of equivalent signal to noise ratio at destination, probability density function, outage probability, ergodic capacity and symbol error probability are built in closed forms.

Recent Progress in Radio-Frequency Sensing Platforms with Graphene/Graphene Oxide for Wireless Health Care System

In the past decade, graphene has been widely researched to improve or overcome the performance of conventional radio-frequency (RF) nanodevices and circuits. In recent years, novel RF bio and gas sensors based on graphene and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), have emerged as new RF sensing platforms using a wireless remote system. Although the sensing schemes are still immature, this review focuses on the recent trends and advances of graphene and GO (rGO)-based RF bio and gas sensors for a real-time and continuous wireless health care system.

RF wave propagation simulation for ICRF antenna in EAST

ABSTRACT The propagation performance of radiofrequency (RF) waves excited by ICRF antenna in plasma has a great influence on the coupling effect. In this paper, the propagation characteristics of fast wave (FW) and slow wave (SW) under tokamak experimental condition are calculated, and the influence of angular frequency w 0, antenna power spectrum k// and tokamak total magnetic field B 0 is illustrated based on the typical operating parameters in EAST. By applying perfect matched layer (PML) boundary processing method to simulate single-pass absorption and using finite element method (FEM) to solve Maxwell equations in frequency domain, the propagation and coupling simulation of RF waves in cold plasma for EAST ICRF antenna in B-window were carried out to obtain the polarization characteristics of fields and the relationship between the coupling impedance and the gap length from antenna to the FW cut-off layer. The analysis results in this paper provide useful reference and guidance for the study of propagation coupling of ICRF waves in EAST and other magnetic confined fusion devices.

On outage analysis of nonlinear radio frequency energy harvesting based cooperative communication in cognitive radio network

AbstractThe aim of this article is to investigate the outage performance of nonlinear radio frequency (RF) energy harvesting (EH) enabled decode‐and‐forward relay assisted cognitive radio network. Here, secondary transmitter (ST) can access the licensed spectrum of primary users (PUs) to send its message toward the secondary receiver and at the same time, it can support the primary communication by performing like a relay node. ST can harvest the energy from the received RF signal of primary transmitter to execute its necessary activities. The closed‐form expressions of PU and secondary user outage are derived to measure the end‐to‐end reliability of the system. The accuracy of derived expressions are also validated through the observation of simulation results. In addition to that, the performance of nonlinear EH model is also compared with respect to linear EH model.

Influence of Microcracks on Silver/Polydimethylsiloxane-Based Flexible Microstrip Transmission Lines

Microcrack is commonly seen as a defect in materials that affects the performance of flexible radio frequency (RF) devices. Here, we investigate the influence of microcracks on the RF characteristics of flexible microstrip by stretching flexible microstrip that is based on polydimethylsiloxane (PDMS) substrate and an Ag microparticles/PDMS (AgMP/PDMS) composite conductor. The RF characteristics of the microstrip were monitored with a variety of tensile displacements. An equivalent circuit model of the microstrip with microcracks was proposed to reveal the mechanisms. The fitting results matched the actual measurement well. In addition, the morphology of the microcracks was characterized by SEM and the direct-current (DC) resistance was monitored. The results show that the changes in equivalent circuit element parameters (R, L, C) are due to the change in the conductive pathways, which affect the transmission and reflection of the RF signals.

Desafíos de confiabilidad en dispositivos y circuitos nano-electrónicos de radiofrecuencia

Las tecnologías de integración de circuitos nanoelectrónicos basadas en silicio se acercan al límite de su evolución. La introducción de nuevos materiales para los dispositivos de efecto de campo, incluyendo óxidos de alta constante dieléctrica y semiconductores de alta movilidad, presenta enorme potencial para la próxima generación de componentes nanoelectrónicos, en donde uno de los principales desafíos a afrontar es su confiabilidad. A su vez, el impacto de la degradación de los óxidos delgados a nivel de circuitos complejos cobra gran importancia a medida que las aplicaciones se vuelven más complejas y sus condiciones de trabajo más exigentes. En este trabajo se presenta una recolección de algunos resultados obtenidos en el área de confiabilidad con una visión integral del problema, proponiendo explicaciones físicas de la degradación en dispositivos nanoelectrónicos novedosos y generando estrategias para garantizar el desempeño de circuitos de radiofrecuencia frente al envejecimiento.

A Survey on Reconfigurable Microstrip Filter–Antenna Integration: Recent Developments and Challenges

Reconfigurable and tunable radio frequency (RF) and microwave (MW) components have become exciting topics for many researchers and design engineers in recent years. Reconfigurable microstrip filter–antenna combinations have been studied in the literature to handle multifunctional tasks for wireless communication systems. Using such devices can reduce the need for many RF components and minimize the cost of the whole wireless system, since the changes in the performance of these applications are achieved using electronic tuning techniques. However, with the rapid development of current fourth-generation (4G) and fifth-generation (5G) applications, compact and reconfigurable structures with a wide tuning range are in high demand. However, meeting these requirements comes with some challenges, namely the increased design complexity and system size. Accordingly, this paper aims to discuss these challenges and review the recent developments in the design techniques used for reconfigurable filters and antennas, as well as their integration. Various designs for different applications are studied and investigated in terms of their geometrical structures and operational performance. This paper begins with an introduction to microstrip filters, antennas, and filtering antennas (filtennas). Then, performance comparisons between the key and essential structures for these aspects are presented and discussed. Furthermore, a comparison between several RF reconfiguration techniques, current challenges, and future developments is presented and discussed in this review. Among several reconfigurable structures, the most efficient designs with the best attractive features are addressed and highlighted in this paper to improve the performance of RF and MW front end systems.

On the Effect of Interference and Misalignment Error in Mixed RF/FSO Systems Over Generalized Fading Channels

In this paper, the end-to-end performance of a mixed radio frequency (RF)/free space optical (FSO) affected by co-channel interference (CCI), is studied. We consider that the RF link experiences $\eta -\mu $ fading and the FSO link is subjected to atmospheric turbulence, which is modeled by the $\alpha -\mu $ distribution. Also, the statistics of the FSO link is presented for the case of zero and non-zero boresight pointing errors. Furthermore, we assume intensity modulation with direct detection (IM/DD) and coherent demodulation. In particular, we present a closed-form expression for the probability density function of the FSO link, which is then used to obtain a closed-form and an asymptotic expression for the outage probability. In order to quantify the system performance, we utilize this asymptotic result to yield the system’s coding gain and diversity order. Moreover, we have presented analytical expressions for the average bit error rate (BER) and ergodic capacity for the system design. In order to gain more insights, high signal-to-noise ratio (SNR) approximations expressions for the BER and ergodic capacity, are also derived. Finally, the analytical results presented in the paper are validated through computer simulations.

Distributed Degenerate Band Edge Oscillator

We propose a new class of oscillators by engineering the dispersion of two-coupled periodic waveguides to exhibit a degenerate band edge (DBE). The DBE is an exceptional point of degeneracy (EPD) of order four, i.e., representing the coalescence of four eigenmodes of a waveguide system without loss and gain. We present a distributed DBE oscillator realized in periodic coupled transmission lines with a unique mode selection scheme that leads to a stable single-frequency oscillation, even in the presence of load variation. The DBE oscillator potentially leads to a boost of the efficiency and performance of radio frequency (RF) sources, due to the unique features associated with the EPD concept. This class of oscillators is promising for improving discrete-distributed coherent sources and can be extended to radiating structures to achieve a new class of active integrated antenna arrays.

Efficient strategy to optimize key devices positions in large-scale RF mesh networks

RF Mesh technology is currently one of the most used in North America for smart grid communications where reputable companies such as Itron and Landys&Gyr are setting up their smart meters with RF Mesh radios. The overall performance of radio frequency (RF) Mesh network communications depends in high measure on the positions of key devices in RF Mesh network such as routers and collectors. With this in mind, we have designed a strategy to optimize jointly the positions of the key devices of RF Mesh network such as routers and collectors to achieve the highest possible connectivity between different components of RF Mesh network. Furthermore, for a big amount of meters, the proposed strategy process becomes unfeasible in terms of processing time. For that, we have applied an optimized prepartitioning methodology on the proposed strategy that leads to vastly accelerate our proposed strategy to more than 13 times for Montreal dataset with a negligible effect on quality of service (QoS) parameters.

Outage and throughput performance of a multihop network with an adaptive power splitting-based energy harvesting

ABSTRACT In this letter, throughput performance of radio frequency (RF) energy harvesting-based multihop decode forward relay network with a novel adaptive harvesting scheme is proposed and performance is investigated. In the proposed adaptive power splitting scheme, the power splitting factors are adjusted dynamically to achieve the maximum end to end signal-to-noise ratio (SNR) by equalising the SNR at all nodes. The statistics of variation of power splitting factors of each node are reported. The simulation results show that the performance of the proposed scheme outperformed in comparison with the conventional scheme in terms of throughput and outage probability.

Filtenna Designs for Radio-Frequency Front-End Systems: A structural-oriented review

Wireless communication has witnessed rapid developments in the last few decades. To further improve the performance of wireless radio-frequency (RF) systems, emphasis has been given to designing multifunctional modules. The front end of RF systems includes transmitting/receiving antennas integrated with bandpass filters (BPFs). These integrated units are commonly known as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">filtering antennas</i> or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">filtennas</i> . The techniques related to designing filtennas have been continuously upgraded in the last couple of years. However, different design constraints are encountered during filtenna implementation, which can be better described in terms of frequency selectivity, bandwidth, high gain, radiation efficiency, polarization, and so on. Therefore, an extensive review has been carried out on integrated filtering antenna structures that were introduced during the last decade. The objective of the article is to present an overview of various approaches adopted to deal with different design challenges. The authors hope that this review exercise will be helpful for RF engineers to get a better understanding on filtenna designs and will encourage young researchers who would like to work in this domain.

Photonic Generation of Dual-Chirp Microwave Waveforms Based on a Tunable Optoelectronic Oscillator

We propose a photonic scheme to generate dual-chirp microwave waveforms based on a widely tunable optoelectronic oscillator (OEO) using a dual-polarization dual-drive Mach-Zehnder modulator (DP-DDMZM). The upper DDMZM is properly biased to serve as a phase modulator and further constructs OEO loop to generate radio frequency (RF). The lower DDMZM injected by the combination of the RF and a single-chirp signal is utilized to generate a dual-chirp microwave waveform with an arbitrarily tunable central frequency. The RF from the OEO replaces external millimeter-wave source in our scheme, which improves the phase noise performance of RF in high-frequency range, alleviates the complexity of the system, and increases the possibility of integration. Dual-chirp microwave waveforms centered at 10 GHz with a bandwidths of 0.4 GHz and 1 GHz, and centered at 15 GHz with a bandwidth of 0.4 GHz are successfully generated. The proposed scheme is theoretically analyzed and experimentally demonstrated.

A performance of radio frequency and signal strength of LoRa with BME280 sensor

LoRa is a Radio Frequency module that can send packet data up to 3 km in FSPL.LoRa has 3 different Frequency Radios i.e, 915 MHz, 868 MHz, and 433 MHz. LoRa testing is based on different distances, BME280 provides Barometric Pressure, Temperature, and Humidity data. An analysis from the results of the Received Signal Strength to the distance (m) to the farthest point to prove and provide QoS data from LoRa 915 MHz. Sensor nodes are built using ADR and Automatic sleep mode algorithms. Communication systems between nodes are built dynamic sensor nodes in mesh networking. Monitoring signal transferring on the 915 MHz Frequency waveform is carried out using the Textronix Spectrum analyzer. Based on the BME280 Data packet transmission from the LoRa 915 MHz Transmitter to the Receiver Receiver at a distance of 100m is -84 dBm and at a distance of 500m is -107 dBm. The LoRa Internet Gateway has 2 types of settings, i.e, application, and gateway, this setting is to find out the location of the gateway with longitude and latitude. Furthermore, the gateway holds Sensor data from the End node, while the Application Server displays sensor data in the form of Graphics in realtime.

Co-operative RF-UWOC link performance over hyperbolic tangent log-normal distribution channel with pointing errors

In this paper, we have proposed an analytic model and determined the outage probability and average bit error rate (BER) performance of a co-operative radio frequency − underwater wireless optical communication (RF−UWOC) system. In recent years, UWOC has attracted attention as a useful enabler of underwater activities such as climate and ocean monitoring, surveillance, ocean exploration, underwater wireless optical sensor networks (UWOSN) and internet of underwater things (IoUT) because of its high speed, ease of deployability and wide bandwidth availability which is free of licensing fees. The proposed co-operative RF–UWOC system is designed to establish a connection between an underwater vehicle inside the ocean to a terrestrial ground station using decode−forward and amplify−forward relays. The RF link between the terrestrial ground station to relay is modeled as a Rayleigh distributed channel. The UWOC link between the relay to the underwater vehicle is modeled as being perturbed by the hyperbolic tangent log-normal (HTLN) distribution. To the best of our knowledge, it is for the first time that the perturbations due to weak oceanic turbulence have been modeled using HTLN distribution. This distribution is a member of the class of log-normal distributions derived from hyperbolic tangent distribution. Novel closed-form expressions have been derived for the outage probability and average BER for various modulation techniques that can be employed in this system. The analytical results are evaluated and validated with Monte-Carlo simulations in the presence and absence of pointing errors. The results show that the impact of pointing errors in the RF-UWOC system is to impose an additional SNR penalty of at-least 10 dB to obtain a BER of 10−6 when compared with the system operating without pointing errors.

Integrated Tunable Magnetoelectric RF Inductors

A great challenge in power/RF electronics has been achieving integrated magnetic inductors with high quality factor ( $Q$ -factor) and high inductance density at gigahertz frequencies. In this article, integrated solenoid magnetoelectric inductors based on FeGaB/Al2O3 multilayer as the magnetic core are designed to operate at high gigahertz frequencies, high $Q$ -factor, and inductance tunability. A high self-resonant frequency of >3 GHz with a flat inductance of 1.4 nH and a peak $Q$ -factor of ~32.7 has been achieved within a wide operating frequency ranging from 0.3 to 3 GHz with magnetic annealing treatment to enhance the inductance density and $Q$ -factor. Two different inductance-tuning methods are tested. For magnetic field tuning, an external magnetic field from 0 to 500 Oe is applied to achieve an inductance tunability $\Delta {\mathbf {L}/\mathbf {L}} _{\mathbf {min}}$ of ~69.2%. Voltage tuning is also tested based on the magnetoelectric coupling between FeGaB/Al2O3 multilayer and ferroelectric slab achieving a maximum tunability of 191% with a flat inductance within the operating frequency. Such a high $Q$ -factor and high inductance density together with giant electrical tunability will greatly improve the integration level and performance of tunable radio frequency integrated circuits while reducing their power consumption and cost.

First in-vivo human imaging at 10.5T: Imaging the body at 447 MHz.

To investigate the feasibility of imaging the human torso and to evaluate the performance of several radiofrequency (RF) management strategies at 10.5T. Healthy volunteers were imaged on a 10.5T whole-body scanner in multiple target anatomies, including the prostate, hip, kidney, liver, and heart. Phase-only shimming and spoke pulses were used to demonstrate their performance in managing the inhomogeneity present at 447 MHz. Imaging protocols included both qualitative and quantitative acquisitions to show the feasibility of imaging with different contrasts. High-quality images were acquired and demonstrated excellent overall contrast and signal-to-noise ratio. The experimental results matched well with predictions and suggested good translational capabilities of the RF management strategies previously developed at 7T. Phase-only shimming provided increased efficiency, but showed pronounced limitations in homogeneity, demonstrating the need for the increased degrees of freedom made possible through single- and multispoke RF pulse design. The first in-vivo human imaging was successfully performed at 10.5T using previously developed RF management strategies. Further improvement in RF coils, transmit chain, and full integration of parallel transmit functionality are needed to fully realize the benefits of 10.5T.

On Secure Mixed RF-FSO Decode-and-Forward Relaying Systems With Energy Harvesting

In this article, we study the security performance of a mixed radio frequency (RF)-free space optical (FSO) decode-and-forward (DF) relaying system with the simultaneous wireless information and power transfer (SWIPT) technology. The RF channels experience Nakagami- $m$ fading and the FSO channel suffers Malaga turbulence and pointing errors. More precisely, we derive analytical closed-form expressions for the average secrecy capacity and the secrecy outage probability to investigate the security performance of the proposed mixed RF-FSO communication framework with energy harvesting technology.