Radio Frequency Channel Research Articles

Detection and Localization of Ultrasound Scatterers Using Convolutional Neural Networks.

Delay-and-sum (DAS) beamforming is unable to identify individual scatterers when their density is so high that their point spread functions overlap. This paper proposes a convolutional neural network (CNN)-based method to detect and localize high-density scatterers, some of which are closer than the resolution limit of delay-and-sum (DAS) beamforming. A CNN was designed to take radio frequency channel data and return non-overlapping Gaussian confidence maps. The scatterer positions were estimated from the confidence maps by identifying local maxima. On simulated test sets, the CNN method with three plane waves achieved a precision of 1.00 and a recall of 0.91. Localization uncertainties after excluding outliers were ±46 [Formula: see text] (outlier ratio: 4%) laterally and ±26 [Formula: see text] (outlier ratio: 1%) axially. To evaluate the proposed method on measured data, two phantoms containing cavities were 3-D printed and imaged. For the phantom study, the training data were modified according to the physical properties of the phantoms and a new CNN was trained. On an uniformly spaced scatterer phantom, a precision of 0.98 and a recall of 1.00 were achieved with the localization uncertainties of ±101 [Formula: see text] (outlier ratio: 1%) laterally and ±37 [Formula: see text] (outlier ratio: 1%) axially. On a randomly spaced scatterer phantom, a precision of 0.59 and a recall of 0.63 were achieved. The localization uncertainties were ±132 [Formula: see text] (outlier ratio: 0%) laterally and ±44 [Formula: see text] with a bias of 22 [Formula: see text] (outlier ratio: 0%) axially. This method can potentially be extended to detect highly concentrated microbubbles in order to shorten data acquisition times of super-resolution ultrasound imaging.

Design, Implementation, Evaluation and Application of a 32-Channel Radio Frequency Signal Generator for Thermal Magnetic Resonance Based Anti-Cancer Treatment.

Thermal Magnetic Resonance (ThermalMR) leverages radio frequency (RF)-induced heating to examine the role of temperature in biological systems and disease. To advance RF heating with multi-channel RF antenna arrays and overcome the shortcomings of current RF signal sources, this work reports on a 32-channel modular signal generator (SGPLL). The SGPLL was designed around phase-locked loop (PLL) chips and a field-programmable gate array chip. To examine the system properties, switching/settling times, accuracy of RF power level and phase shifting were characterized. Electric field manipulation was successfully demonstrated in deionized water. RF heating was conducted in a phantom setup using self-grounded bow-tie RF antennae driven by the SGPLL. Commercial signal generators limited to a lower number of RF channels were used for comparison. RF heating was evaluated with numerical temperature simulations and experimentally validated with MR thermometry. Numerical temperature simulations and heating experiments controlled by the SGPLL revealed the same RF interference patterns. Upon RF heating similar temperature changes across the phantom were observed for the SGPLL and for the commercial devices. To conclude, this work presents the first 32-channel modular signal source for RF heating. The large number of coherent RF channels, wide frequency range and accurate phase shift provided by the SGPLL form a technological basis for ThermalMR controlled hyperthermia anti-cancer treatment.

Correlation between the potential electromagnetic pollution level and the danger of COVID-19. 4G/5G/6G can be safe for people

The paper considers a hypothesis concerned the possible influence of electromagnetic pollution of the environment on the lethality rate of the population from coronavirus infection, along with other factors. The hypothesis is indirectly confirmed by the correlation between the degree of rigidity of hygienic regulations of radio frequency electromagnetic background levels for the population, which are mainly created by mobile (cellular) communication systems, and the lethality rate from COVID-19 in various countries. A special measures to ensure the safety of rapid development of technologies, systems and services for mobile communications of the fourth (4G), fifth (5G), and, by 2030, the sixth (6G) generation, associated with an increase by several orders of magnitude in the number of radiating devices, the data transmission rates over radio frequency channels and the area capacity of mobile traffic, are discussed. For quantitative analysis of these processes, a practical method of worst-case estimation of electromagnetic background level generated by these systems has been developed, verified using the results of numerous measurements of the electromagnetic background in various countries, and described in this paper. This technique is based on the use of the integrated system characteristics of wireless information services and makes it possible to justify the necessary system, technical and managerial solutions aimed at ensuring the necessary level of electromagnetic ecology of populous areas and electromagnetic safety of people in conditions of rapid advancement of 4G/5G/6G systems without affecting the quality of informational support of the population and information technologies in economy, education, healthcare and other sectors.

Transmitters for Combined Radio Over a Fiber and Outdoor Millimeter-Wave System at 25 GHz

In the modern wireless networks, millimeter-wave radio-frequency (RF) bands are becoming more attractive as they provide larger bandwidth and higher data rates than the today-used systems operating at frequencies below 6 GHz. In addition, according to the fact that coaxial cables exhibit extremely high attenuation for millimeter-wave RF signals, analog radio over fiber techniques (RoF) form a promising technology for delivering unaltered radio waveform to a remote antenna. This paper experimentally analyzes three types of RoF modulations, namely a directly modulated laser, an electro-absorption modulator, and a Mach-Zehnder Modulator. The primary focus is on the implementation of each RoF transmitter in an RoF system, such as those in 5G networks. The experimental study includes a detailed characterization of an RoF system with a 50-m long outdoor free-space RF channel operating in the frequency band of 25 GHz. Frequency response (S-parameters) and third-order nonlinear distortion are investigated in detail. Tests of EVM performance were conducted using an orthogonal frequency division multiplexing signal modulated with 16-quadrature amplitude modulation (16-QAM) with a long-term evolution signal. It is demonstrated that the transmitters studied can operate under a 13.5% EVM limit given for 16-QAM. Apart from the detailed system performance, the considerable power fluctuations in the 25 GHz free-space RF outdoor channel are reported.

Investigation of Inter-Frequency Signal Delays on Board Glonass Navigation Satellites

The problem of inter-frequency signal delays estimation of GLONASS system navigation satellites is considered. Such signal delays in the radio-frequency channel of navigation satellites are a source of instrumental error of pseudorange measuring. A method for estimating the inter-frequency signal delays is proposed, based on the calculation of the first differences of pseudorange measurements on navigation satellites, the relative angular position of which differs by no more than 1°. An experiment on estimating the inter-frequency signal delays based on the developed method was performed. The experiment is based on the use of calibrated navigation user equipment to separate errors caused by signal delays in the receiver and the navigation satellite. Furthermore, to minimize the influence of the Earth’s ionospheric layer, only those measurements that are obtained at a low value of the total electron content (TEC) are included in the processing. Pseudorange measurements from the signals of navigation satellites of the GLONASS and GPS systems were used as the initial data. The estimation results for all GLONASS orbit group satellites were compared with the form values provided as part of the navigation frame. The results of experimental studies were analyzed and the standard deviations of the delays of GLONASS orbit group were obtained. To confirm the adequacy of the results, the internal convergence of the results was verified and the error of the developed method for estimating the inter-frequency delays of navigation satellites was determined.

Exploiting the RSSI Long-Term Data of a WSN for the RF Channel Modeling in EPS Environments.

In this paper, we propose a methodology to use the received signal strength indicator (RSSI) available by the protocol stack of an installed Wireless Sensor Network (WSN) at an electric-power-system environment (EPS) as a tool for obtaining the characteristic of its communication channel. Thereby, it is possible to optimize the settings and configuration of the network after its deployment, which is usually run empirically without any previous knowledge of the channel. A study case of a hydroelectric power plant is presented, where measurements recorded over a two-month period were analyzed and treated to obtain the large-scale characteristics of the radiofrequency channel at 2.4 GHz. In addition, we showed that instantaneous RSSI data can also be used to detect specific issues in the network, such as repetitive patterns in the transmitted power level of the nodes, and information about its environment, such as the presence of external sources of electromagnetic interference. As a result, we demonstrate the practical use of the RSSI long-term data generated by the WSN for its own performance optimization and the detection of particular events in an EPS or any similar industrial environment.

Radio-optical line for SCADA systems with relay

Hybrid optical-radio communication systems provide high-speed access within the “last mile” and can act as highly reliable broadband channels of SCADA software and hardware systems. They use optical channels as the main communication lines, and radio channels as backup, since the transmission quality of atmospheric optical channels is largely determined by weather conditions. To reduce the effect of atmospheric turbulence, it is proposed to use the option of spatial diversity with line-of-sight channels and containing a repeater. When the signal-to-noise ratio decreases in the optical channel below the selected threshold, switching to the radio link is to be performed. The paper provides the results of modeling the operation of a hybrid radio-optical line in SCADA systems, in which a new switching system for optical and radio-frequency channels using a repeater is proposed. The dependences of the outage probability of the optical channel and the system as a whole are obtained.

Symbol error probability evaluation for PSK modulation schemes in generalized non‐Gaussian noise channels

SummaryThe average symbol error probability (ASEP) performance over the faded radio frequency (RF) link when the noise is additive in nature and has generalized Laplacian distribution is evaluated in this paper. The additive white generalized Laplacian noise (AWGLN) distribution can model different impulsive and non‐Gaussian noise environments often encountered in practice and provides a robust alternative to Gaussian distribution. A new expression for evaluating the exact symbol error probability over a multilevel M‐ary PSK‐modulated AWGLN channel is derived. Based on the obtained expression, the ASEP for the single‐hop RF link that models the shadowing and fading conditions over the RF channel by a generalized –K (GK) distribution is derived. Further, the error performance of a decode‐and‐forward relayed and GK‐distributed two‐hop RF link is discussed, and the results are validated through numerical plots.

IP-Based Cooperative Services Using ATSC 3.0 Broadcast and Broadband

This paper presents Internet protocol (IP)-based convergence of broadcast and broadband networks using Advanced Television Systems Committee (ATSC) 3.0–the next generation terrestrial broadcasting standard. In the broadcast network, the combination of Layered Division Multiplexing (LDM) and Scalable High Efficiency Video Codec (SHVC) is used, enabling efficient use of spectrum when mobile and fixed services are intended in a single radio frequency (RF) channel. The proposed use case of IP-based convergence is that a service is largely consumed through the high power high tower (HPHT) based broadcast network, and then alternative streams are requested via unicast for areas where broadcast signals are not receivable. The implementation details of broadcast and broadband convergence include MPEG Media Transport (MMT)/Real-time Objective delivery over Unidirectional Transport (ROUTE) description for broadcast useand Dynamic Adaptive Streaming over HTTP (DASH) for broadband use. To achieve seamless convergence between broadcast and broadband, transmission and reception systems based on ATSC 3.0 are hardware-developed and their implementation details are described. The proposed IP-based convergence use case of ATSC 3.0 broadcast and broadband is verified in a real-field environment using a public cellular network.

Wideband Dual-Channel Photonic RF Repeater Based on Polarization Division Multiplexing Modulation and Polarization Control

Radio frequency (RF) repeaters are often used in satellite communication, wireless wideband communication, and electronic warfare systems for signal receiving, forwarding, and processing. Due to frequency-dependent microwave devices, conventional electrical RF repeaters have limited bandwidth and are susceptible to electromagnetic interference. In this article, a dual-channel photonic RF repeater using a polarization-division multiplexing dual-parallel Mach–Zehnder modulator is proposed. The RF repeater is built entirely using optical methods and does not require any frequency-dependent equipment, thus enabling high operating frequency and large operating bandwidth. The modulator is used to perform frequency conversion on the received uplink/downlink RF signals, and the followed polarization controller and the balanced photodetector realize switching of the uplink and downlink RF channels. In the experiment, wide operating bandwidth (1–20 GHz), low channel crosstalk (>33 dB), and a large spurious-free dynamic range (106 dB·Hz2/3) for the RF repeater are obtained. Also, the channel switching of 16 quadrature amplitude modulation (QAM) RF signals with 200 Mbps data rate is demonstrated, while the adjacent channel power ratio (ACPR), demodulated constellation diagrams, and the error vector magnitude (EVM) are evaluated.

Q-Learning Based Two-Timescale Power Allocation for Multi-Homing Hybrid RF/VLC Networks

This letter investigates hybrid networks composed of a radio frequency (RF) access point (AP) and multiple visible light communication (VLC) APs. We consider mobile multi-homing users that can aggregate resources from both RF and VLC APs. In hybrid RF/VLC networks, RF channel gains vary faster than VLC channels due to small scale fading. By leveraging multi-agent Q-learning to interact with the dynamics of wireless environments, we develop an online two-timescale power allocation strategy that optimizes the transmit powers at the RF and VLC APs to ensure quality-of-service satisfaction. Simulation results demonstrate the effectiveness of the proposed Q-learning based strategy.

A Compact and Cost-Effective BLE Beacon With Multiprotocol and Dynamic Content Advertising for IoT Application

Bluetooth low-energy (BLE) beacons have been used in a variety of IoT applications. This article proposes a compact and cost-effective BLE beacon, which only uses a 2.4-GHz Gaussian frequency-shift keying (GFSK) transceiver and an ultralow power 8-bit 16-MHz microcontroller unit (MCU). The minimum requirements and the data processing procedure for commonly used GFSK transceivers to generate the BLE-compatible advertising packages are also provided in this article. Benefited from the compact architecture and the simple generation procedure, the BLE-compatible packages can be directly controlled to broadcast at any given radio frequency (RF) channel or time. Based on the flexible characteristics of our proposed beacon, the multiprotocol and dynamic content advertising are developed in this article. With the help of multiprotocol and dynamic content advertising, the proposed beacons can be used to provide more sophisticated services. Since the broadcast channels and time are freely controlled, the proposed BLE beacons are also very suitable for anti-collision applications with custom-defined channels and time intervals. The experimental results show that the proposed beacon can broadcast BLE-compatible protocol data units (PDUs) at a minimum interval of about 1 ms. The measured average current is about 51 uA when the advertising interval is 800 ms. Different protocols and dynamic content PDUs generated by the proposed beacon can be properly received by BLE-enabled devices, proving that they are fully compatible with the BLE specification. The measured bit rate of the proposed beacon in dynamic content advertising is about 198.4 kb/s.

Secure Cooperative Transmission for Mixed RF/FSO Spectrum Sharing Networks

This paper is concerned with the secrecy rate based optimization problems in a mixed radio frequency (RF) / free space optical (FSO) spectrum sharing network, wherein multiple single-antenna secondary users (SUs) are connected to a decode and forward (DF) single-antenna relay through RF links and the relay is connected with the secondary destination through an FSO link. The RF and FSO channels are assumed to follow Rayleigh and Gamma-Gamma distributions with the effect of pointing errors, respectively. The three schemes, i.e., direct transmission, single-user cooperative jamming and multi-user cooperative beamforming jamming, are proposed to improve the physical-layer information security in the presence of a single-antenna eavesdropper. The mutual interference between the primary and secondary networks is considered. The problems are to jointly optimize the SU transmit power and jamming power for the best secrecy performance under both the RF and FSO dominant cases. Such problems are nonconvex. The Dinkelbach approach is adopted to solve the optimization in the direct transmission and single-user cooperative jamming schemes and a two-level optimization approach with semi-definite relaxation (SDR) is applied to obtain the solution for the multi-user cooperative beamforming scheme. Moreover, the SDR optimality is proved by Karush-Kuhn-Tucker conditions analysis. Simulation results are provided, and the results show that the proposed multi-user cooperative beamforming jamming can attain the higher achievable secrecy rate than the zero-forcing beamforming scheme and other two suboptimal designs.

Dynamic 1 H-MRS for detection of 13 C-labeled glucose metabolism in the human brain at 3T.

In 2004, Boumezbeur et al proposed a simple yet powerful approach to detect the metabolism of 13 C-enriched substrates in the brain. Their approach consisted of dynamic 1 H-MRS, without a 13 C radiofrequency (RF) channel, and its successful application was demonstrated in monkeys. Since then, this promising method has yet to be applied rigorously in humans. In this study, we revisit the use of dynamic 1 H-MRS to measure the metabolism of 13 C-enriched substrates and demonstrate its application in the human brain. In healthy participants, 1 H-MRS data were acquired dynamically before and following a bolus infusion of [1-13 C] glucose. Data were acquired on a 3T clinical MRI scanner using a short-TE SPECIAL sequence, with regions of interest in both anterior and posterior cingulate cortex. Using simulated basis spectra to model signal changes in both 12 C-bonded and 13 C-coupled resonances, the acquired spectra were fit in LCModel to obtain labeling time courses for glutmate and glutamine at both C4 and C3 positions. Presence of the 13 C label was clearly detectable, owing to the pronounced effect of heteronuclear (13 C-1 H) scalar coupling on the observed 1 H spectra. A decrease in signal from 12 C-bonded protons and an increase in signal from 13 C-coupled protons were observed. The fractional enrichment of Glu-C4, (Glu+Gln)-C4, and (Glu+Gln)-C3 at 30 minutes following infusion of [1-13 C] glucose was similar in both regions: 11% to 13%, 9% to 12% and 3% to 5%, respectively. These preliminary results confirm the feasibility of the use of dynamic 1 H-MRS to monitor 13 C labeling in the human brain, without a 13 C RF channel.

Modelling and Prediction of Mobile Service Channel Power Density for RF Energy Harvesting

Ambient radio frequency (RF) energy harvesting could provide power for perpetual battery-less operation without placement constrain. Nonetheless, the highly varying power levels of ambient RF channels often keep harvesting circuits working with low efficiency. To design optimal RF energy harvesters with high efficiency, it is critical to model and predict the channel power density. In this letter, we derived a statistic model based on kernel density estimation for the power density of mobile service channels. This model matches well with the measurement results. We have also developed a power density prediction method for mobile service channels based on the moving average. It enables accurate and effective prediction. The prediction method is simple for implementation in hardware.

Boosting the resolution of low-field [Formula: see text] relaxation experiments on intrinsically disordered proteins with triple-resonance NMR.

Improving our understanding of nanosecond motions in disordered proteins requires the enhanced sampling of the spectral density function obtained from relaxation at low magnetic fields. High-resolution relaxometry and two-field NMR measurements of relaxation have, so far, only been based on the recording of one- or two-dimensional spectra, which provide insufficient resolution for challenging disordered proteins. Here, we introduce a 3D-HNCO-based two-field NMR experiment for measurements of protein backbone [Formula: see text] amide longitudinal relaxation rates. The experiment provides accurate longitudinal relaxation rates at low field (0.33 T in our case) preserving the resolution and sensitivity typical for high-field NMR spectroscopy. Radiofrequency pulses applied on six different radiofrequency channels are used to manipulate the spin system at both fields. The experiment was demonstrated on the C-terminal domain of [Formula: see text] subunit of RNA polymerase from Bacillus subtilis, a protein with highly repetitive amino-acid sequence and very low dispersion of backbone chemical shifts.

Ergodic Sum Rate Analysis of UAV-Based Relay Networks With Mixed RF-FSO Channels

Unmanned aerial vehicle (UAV)-based communications is a promising new technology that can add a wide range of new capabilities to the current network infrastructure. Given the flexibility, cost-efficiency, and convenient use of UAVs, they can be deployed as temporary base stations (BSs) for on-demand situations like BS overloading or natural disasters. In this work, a UAV-based communication system with radio frequency (RF) access links to the mobile users (MUs) and a free-space optical (FSO) backhaul link to the ground station (GS) is considered. In particular, the RF and FSO channels in this network depend on the UAV’s positioning and (in)stability. The relative position of the UAV with respect to the MUs impacts the likelihood of a line-of-sight (LOS) connection in the RF link and the instability of the hovering UAV affects the quality of the FSO channel. Thus, taking these effects into account, we analyze the end-to-end system performance of networks employing UAVs as buffer-aided (BA) and non-buffer-aided (non-BA) relays in terms of the ergodic sum rate. Simulation results validate the accuracy of the proposed analytical derivations and reveal the benefits of buffering for compensation of the random fluctuations caused by the UAV’s instability. Our simulations also show that the ergodic sum rate of both BA and non-BA UAV-based relays can be enhanced considerably by optimizing the positioning of the UAV. We further study the impact of the MU density and the weather conditions on the end-to-end system performance.

Impact of Atmospheric Turbulence, Pointing Error, and Traffic Pattern on the Performance of Cognitive Hybrid FSO/RF System

Atmospheric turbulence conditions and mis-alignment in the free space optical (FSO) link are prime factors which necessitate the requirement of a back up radio frequency (RF) link to improve the link availability of the FSO systems. However, the utilization of this back-up RF link is limited. The RF channel which is meant chiefly as a back-up resource in case of FSO link failure, can be utilized more efficiently. In this work, it is attempted to improve the utilization of this RF resource. A second FSO link is converted to a Cognitive Hybrid FSO/RF link by accessing the already existing RF in the cognitive interweave mode. RF utilization factor is a measure of the efficiency with which the two FSO links utilize the same RF resource. The system performance is evaluated on the basis of RF utilization, outage probability and bit error rate (BER) under atmospheric turbulence and mis-alignment. Further, the impact of data traffic characteristics on system performance has been investigated. Closed form expressions for RF utilization, outage probability and BER have been derived for various traffic conditions. The analytical results have been verified through simulations. Results indicate improved system performance and better overall utilization of the RF resource.

Multi-Band Notched Antennas for UWB Applications

A compact ultra-wideband circular monopole antennas with single, dual, triple and quad-band rejection characteristics are proposed in this paper. The antenna units are designed using RT/DUROID substrate with permittivity 2.2 and all are fed through a coplanar waveguide (CPW). In the proposed antennas splitted concentric rings (SCR) are used to achieve band rejection characteristics. The proposed antennas will reject the existing WLAN (Wireless Local Area Network), WiMAX (World Wide Interoperability for Microwave Access), X-band downlink satellite communication and radio-frequency channel arrangements for fixed wireless systems to avoid interference. Simulations are carried out using CST Wave Studio Suite 2016. Antenna performance parameters like return loss, VSWR, radiation pattern and gain are evaluated for all the antenna units. The antenna units having dimensions of 30×23×1.57 mm3 are fabricated and tested. The simulated and tested results are compared and reported. These antenna units provide good gain and a larger bandwidth over the frequency range 3–11.6 GHz.

Key-Free Authentication Protocol Against Subverted Indoor Smart Devices for Smart Home

Smart homes are an increasingly common concept, particularly in technologically advanced countries. In these settings, the smart devices [also commonly referred to as the Internet of Things (IoT) devices] typically communicate via the radio frequency (RF) channel. In such an open communication channel, key establishment protocols are used to generate a session key between the command senders and the command receivers. The commands or messages are then encrypted using the session key. However, not all the smart home devices have sufficient computational capability to generate and store session keys. Therefore, in this article, we construct a communication protocol using the home limited channel (HLC). The protocol constructed in this article takes into account the existence of malicious indoor smart devices and the need to defend against such malicious indoor smart devices.