RF Signal Transmission Research Articles

Real‐Time Communication System Using Canonical Cortical Graph Neural Network With High‐Level Target Navigation Pigeon‐Inspired Optimization

ABSTRACTRadio‐frequency (RF) fingerprinting is an emerging technology for advanced device authentication. This work addresses the issue by improving both the algorithm and hardware to target real‐time AI processing in communication systems. Here, efficient real‐time communication system using canonical cortical graph neural network with high‐level target navigation pigeon‐inspired optimization (RCS‐CCGNN‐HTNPIO) is proposed. Initially, radio frequencies from multiple devices such as modem, TV, and mobile phone, these devices transmit RF signals, which are captured and processed via RF fingerprinting. Then, RF fingerprinting system is designed to distinguish between known signals and unknown signals. Afterwards, the canonical cortical graph neural network (CCGNN) for analyzing and identifying the specific RF fingerprint of each signal. The CCGNN evaluates the signals and categorizes them as known signal or unknown signal based on the RF fingerprint characteristics. Hence, the high‐level target navigation pigeon‐inspired optimization (HTNPIO) is used to optimize the CCGNN. The performance metrics provide a complete assessment of the system's ability to manage the demands of real‐time processing in communication networks. The RCS‐CCGNN‐HTNPIO approach attains19.21%, 26.12%, and 30.15% higher accuracy compared with existing techniques likes deep learning based multidimensional radio‐frequency fingerprinting enhancement approach for IoT device identification (DL‐RFF‐DI), embedding‐assisted attentional deep learning for real‐world RF fingerprinting of Bluetooth (ADL‐RW‐RFF), and multichannel attentive feature fusion for radio‐frequency fingerprinting (MCA‐RFF). The simulation results prove that the RCS‐CCGNN‐HTNPIO can provide a robust and adaptive solution for achieving high accuracy in next‐generation radio access networks.

Stability-enhanced RF signal transmission over long fiber-optic links

Stability-enhanced RF signal transmission over long fiber-optic links

Design of multi-frequency point, high-isolation switches for micro-channel plate data acquisition.

In order to replace the phosphor screen of a proximity-gated x-ray framing camera with a readout circuit using a time-interleaved structure, this paper carries out the design of a high-isolation RF switch. In this paper, a Metal-Oxide-Semiconductor Field Effect Tube (MOSFET) switching circuit is designed to achieve high isolation and low insertion loss at 0.5-3GHz. This solves the problem that the switching circuit cannot be turned off properly due to the parasitic capacitance of MOSFETs in the process of RF signal transmission, resulting in signal feedthrough. It also ensures that the input signal can be transmitted to the output intact when the switching circuit is turned on. High isolation is achieved by using parallel resonance to increase the voltage division and series resonance to leak the current. The switch achieves 76 dB isolation and 0.07 dB insertion loss at 1GHz frequency. Isolation is increased by adding parallel branches near the 2 and 3GHz frequency points, achieving greater than 33 dB isolation from 0.5 to 3GHz.

Design of high-efficiency circularly polarized wideband energy harvesting rectenna using characteristic mode analysis

This paper presents a compact wideband rectifier system for wireless energy harvesting. The presented rectifier system is completed in two stages. In the first stage, a crescent-shaped wideband circularly polarized antenna (CPA) is designed to receive and transmit RF signals using characteristic mode analysis (CMA). And the CPA consists of a monopole antenna at the top and a slot antenna at the bottom, which control the higher and lower operating bands, respectively. In the second stage, a wideband rectifier is designed using a HSMS-2860 Schottky diode and a three-stage matching network. The HSMS-2860 Schottky diodes improve rectification efficiency at medium-power density, and the three-stage matching network effectively increase the operating bandwidth, filter out the output RF signal, and cancel out and stabilizes the impedance. To validate the proposed rectifier system, a crescent-shaped CP receiving antenna and a rectifier operating in C-band are fabricated, and the rectification performance is measured. The measurement results indicate that the proposed rectifier system harvests RF signals on the broadside and backside of the CPA over a wide input power range (8–13 dBm input power).

Using RF Signals to Generate Indoor Maps

Generating maps of indoor environments beyond the line-of-sight finds applications in several areas such as planning, navigation, and security. While researchers have previously explored the use of RF signals to generate maps, prior work has two important limitations: (i) it requires moving the mapping setup along the entire lengths of the sides of the building, and (ii) it generates maps that are not fully connected, rather are scatter plots of locations from where some obstacles reflected the signals. Thus, prior approaches require human interpretation to locate the walls and determine how they merge. In this article, we address these limitations and propose RFMap, which generates fully connected maps, and does not require the measurement setup to be moved along the sides of the buildings. To generate the map, RFMap first transmits RF signals in many different directions and then measures the distances of different reflectors inside the building. Next, it identifies these reflectors and classifies them into various types based on the properties of the reflections. A key challenge is that RFMap does not receive reflections from all the directions due to the specular nature of the reflectors. Due to this, it only gets sparse data about the objects in the environment. To address this challenge, RFMap trains a deep generative adversarial network (GAN) to intelligently predict the missing information. At runtime, it feeds the locations and types of the detected reflectors to the trained GAN and generates complete and accurate map. We implemented RFMap using software defined radios and extensively evaluated it in several real-world environments. Our results show that RFMap generated the maps of all the buildings that we tested it on with high accuracy.

Characterization of Organic Conductive Materials as an Ecological Solution for RF Applications

The use of nonmetallic conductor materials in RF applications has recently become a highlighted issue when it comes to sustainability in the electronics industry, mainly because of the waste problems associated with heavy metals and the necessity of reducing and managing them. The replacement of metal in functional applications such as in electronics is therefore very important. Among these new materials, organic conductors are of great interest since they are, in general, biocompatible and biodegradable, allowing for the disposal of electronic devices, which reduces the negative environment impact caused by electronics waste. In this work, PEDOT:PSS and Carbon are investigated. Since these materials are available as conducting pastes or inks, the production of conducting patterns by printing techniques such as screen printing is possible, which can make the process less harmful to the environment, since it permits the use of organic substrates such as paper. In order to investigate the feasibility of these materials for RF signal transmission, screen printed PEDOT:PSS and Carbon transmission lines have been designed, fabricated and characterized. Results regarding conductivity, thickness, electric permittivity and S21 parameter are presented and will serve as a foundation for the development of further reaching applications utilizing organic materials.

Classifying UAVs With Proprietary Waveforms via Preamble Feature Extraction and Federated Learning

Small unmanned aerial vehicles (UAVs) are deployed in a number of different emerging market segments as well as for recreational hobby flying. Driven by their ubiquitous availability, a large number of manufacturers offer UAV models in different form factors, control and load carrying capacities. This paper proposes a deep learning method to detect the type/model of the UAV using the transmitted RF signals, even when these signals follow proprietary medium access protocols whose headers cannot be decoded. The main contributions are as follows: (i) We show how the preamble portion of the packet is better suited for learning subtle protocol-specific differences, instead of randomly selecting any subset of the transmitted packet, (ii) we propose a pre-processing scheme that generates cross-correlation feature maps to enhance the classification accuracy, (iii) we develop a deep convolutional neural architecture that can be trained in data collected from static scenarios and then tested in practical hovering conditions with 98.2% accuracy of UAV model classification, demonstrating robustness to channel variations, and (iv) we extend this model towards a federated learning paradigm where sensors send individually trained models back to a central controller that combines them, without any appreciable loss of accuracy. Our evaluations are performed on an 8.9 GB dataset collected from static and flying UAVs, which we also release as part of the technical contributions of the work.

Green computing in IoT: Time slotted simultaneous wireless information and power transfer

Simultaneous Wireless Information and Power Transfer (SWIPT) is an emerging field to transmit information and power in IoT network through the same RF signal. Time switching (TS) protocol is more favorable in free space communication than Power Splitting (PS) protocol when the transmitted RF signal is already weak. This is because, transmitted signal loses its power due to attenuation in free space, and using PS design receiver circuit (complex), the received weak signal is further split into two fraction for energy harvesting (EH) and information decoding (ID) simultaneously, that causes inadequacy in SWIPT system. Whereas, using TS design receiver circuit (simple) insert extra delay in the network as EH and ID operations are done in two different time domain one by one. Literature on SWIPT lacks towards cooperation between more energy harvesting in case of free space communication (TS) and critical information transmission in case of delay constraint communication (PS). In this context, this paper presents a time-slotted SWIPT (T-SWIPT) focusing on maximization of energy efficiency in the relay based sensors-enabled IoT network. It enables simultaneous energy harvesting at receiver and neighboring sensors without adding extra delay in the network. The PS ratio, transmission power allotment and energy broadcast time are jointly formulated as non-convex energy efficiency maximization problem. A solution to the problem is presented using Lagrangian dual decomposition and fractional programming. The performance evaluation shows that T-SWIPT attains optimum energy efficiency by trading off transmission power allotment, power-splitting ratio and sink broadcast time slot.

A simplified coherent-detected radio-over-fiber link with intensity and phase modulation and simple digital phase noise cancellation

Reducing the complexity and the cost is the key to introducing high-performance coherent technologies into practical radio-over-fiber (RoF) links. In this paper, we propose a coherent-detected RoF link with low-complexity optical configuration and a light digital signal processing (DSP) unit. Based on a dual-parallel Mach–Zehnder modulator (DP-MZM) at the transmitter, the amplitude and phase of a light wave are modulated to achieve spectral-efficient use of the optical source. After transmission over a single optical fiber, the modulated signals are coherent-detected at the receiver by being interfered with an independent local oscillator laser and then are demodulated digitally. Compared with other two-optical-source coherent-detected RoF links, our proposed scheme can accomplish dual-channel RF signal transmission albeit with halved optical configuration. Additionally, the DSP algorithm to get rid of the laser phase fluctuation between two lasers is simple and efficient. An experimental demonstration is done. Two 16-QAM microwave vector signals at the same symbol rate of 50 Msymbol/s are transmitted over 25-km single mode fiber (SMF) and the error vector magnitudes (EVMs) of 3.15% and 3.53% are obtained respectively. To explore its potential, two 64-QAM microwave vector signals are transported with similar conditions and the measured EVMs are 4.05% and 5.88%, respectively.

Avoiding RF Isolators: Reflectionless Microwave Bandpass Filtering Components for Advanced RF Front Ends

RF/microwave bandpass filters (BPFs) are fundamental components in high-frequency RF transceivers. On the transmitter side, they limit the transmitted RF signal bandwidth by suppressing out-of-band spurious signals and intermodulation products, which are primarily generated by the nonlinear active stages and can affect other RF systems. On the other hand, in the receiver, they reject out-of-band interfering/jamming signals and noise. Whereas a large variety of microwave BPFs have been proposed in the technical literature for multiple technologies (e.g., [1] and [2]), most of these BPF devices achieve their filtering functionality by means of the frequency-selective power reflection processing of the RF input signal. This means that those RF signals allocated within the operational bandwidth of the BPF are transmitted to the output terminal (with some tolerable added in-band loss and reflective-type filter, hence decreasing the mixer conversion gain.

EHLinQ: Distributed Scheduler for D2D Communication With RF Energy Harvesting

In this paper, we study distributed scheduling for a device-to-device (D2D) communication system with radio frequency energy harvesting (RF-EH) in which D2D devices can harvest energy using the ambient RF signals from other transmitting D2D devices. In the system, due to RF-EH, the effects of link scheduling for each D2D link on the system performance, i.e., average sum rate and average total harvested energy, become much more complicated compared with conventional D2D communication without RF-EH. To address such complicated effects in a distributed manner, we study a centralized optimal link scheduling algorithm, which aims at maximizing the weighted sum of average sum rate and average total harvested energy, while satisfying the quality of service (QoS) requirements of D2D links. We then abstract the scheduling principles in the optimal algorithm, and propose a distributed scheduling algorithm for D2D communication with RF-EH, EHLinQ, which realizes the principles in a distributed manner. Moreover, we extend EHLinQ to a power beacon (PB) aided D2D communication system in which a PB transmits RF signals dedicated for RF-EH. The extended EHLinQ allows the PB to determine its own PB scheduling considering the QoS satisfaction of D2D links. Through simulation results, we show that EHLinQ outperforms conventional algorithms, while closely meeting the QoS requirements.

Transmission of RF Signal Through Energy Saving Glass Using Frequency Selective Surface

Energy saving glasses (ESG) are used in large building to provide less-load on the heating and cooling systems, saving a considerable amount of energy. But these glasses have a drawback of blocking the low frequencies(0 to 1.5GHz), creating problem in communication systems (GSM, 3G, GPS etc). In this paper, a novel FSS structure is proposed, to be used in ESG panels to solve the communication problem. The proposed FSS consists of two dimensional array of square patches, each patch containing circular ring slot. FSS is simulated using ANSOFT® Designer software. The simulated result, shows that, proposed FSS passes 0 to 1.5GHz, which can solve the communication problem.

Continuously tunable orthogonally polarized RF optical single sideband generator based on micro-ring resonators

We demonstrate a continuously RF tunable orthogonally polarized optical single sideband (OP-OSSB) generator based on dual cascaded micro-ring resonators (MRRs). By splitting the input double sideband signal into an orthogonally polarized carrier and lower sideband via TE- and TM-polarized MRRs, an OP-OSSB signal is generated. A large tuning range of the optical carrier to sideband ratio of up to 57.3 dB is achieved by adjusting the polarization angle of the input light. The operation RF frequency of the OP-OSSB generator can be continuously tuned with a 21.4 GHz range via independent thermal control of the two MRRs. Our device represents a competitive approach towards OP-OSSB generation with wideband tunable RF operation, and is promising for photonic RF signal transmission and processing in radar and communication systems.

Optimal Time Scheduling for Wireless-Powered Backscatter Communication Networks

This letter introduces a novel wireless-powered backscatter communication system which allows sensors to utilize RF signals transmitted from a dedicated RF energy source to transmit data. In the proposed system, when the RF energy source transmits RF signals, the sensors are able to backscatter the RF signals to transmit data to the gateway and/or harvest energy from the RF signals for their operations. By integrating backscattering and energy harvesting techniques, we can optimize the network throughput of the system. In particular, we first formulate the time scheduling problem for the system, and then propose an optimal solution using convex optimization to maximize the overall network throughput. Numerical results show a significant throughput gain achieved by our proposed design over two other baseline schemes.

High peak and high average radiofrequency power transmit/receive switch for thermal magnetic resonance.

To study the role of temperature in biological systems, diagnostic contrasts and thermal therapies, RF pulses for MR spin excitation can be deliberately used to apply a thermal stimulus. This application requires dedicated transmit/receive (Tx/Rx) switches that support high peak powers for MRI and high average powers for RF heating. To meet this goal, we propose a high-performance Tx/Rx switch based on positive-intrinsic-negative diodes and quarter-wavelength (λ/4) stubs. The λ/4 stubs in the proposed Tx/Rx switch design route the transmitted RF signal directly to the RF coil/antenna without passing through any electronic components (e.g., positive-intrinsic-negative diodes). Bench measurements, MRI, MR thermometry, and RF heating experiments were performed at f = 297 MHz (B0 = 7 T) to examine the characteristics and applicability of the switch. The proposed design provided an isolation of -35.7dB/-41.5dB during transmission/reception. The insertion loss was -0.41dB/-0.27dB during transmission/reception. The switch supports high peak (3.9 kW) and high average (120 W) RF powers for MRI and RF heating at f = 297 MHz. High-resolution MRI of the wrist yielded image quality competitive with that obtained with a conventional Tx/Rx switch. Radiofrequency heating in phantom monitored by MR thermometry demonstrated the switch applicability for thermal modulation. Upon these findings, thermally activated release of a model drug attached to thermoresponsive polymers was demonstrated. The high-power Tx/Rx switch enables thermal MR applications at 7 T, contributing to the study of the role of temperature in biological systems and diseases. All design files of the switch will be made available open source at www.opensourceimaging.org.

Photonics-Based Millimeter-Wave Band Remote Beamforming of Array-Antenna Integrated With Photodiode Using Variable Optical Delay Line and Attenuator

For simplification of mobile base station architecture, we present remote beamforming of an array antenna integrated with photodiode based on photonics. Variable optical delay lines (VDLs) and variable optical attenuators (VOAs) are utilized for tailoring the RF phases and amplitudes and radio-over-fiber (RoF) technique is adopted for RF signal transmission. First, we show a simple demonstration of 60-GHz antenna beamforming using VDLs and VOAs with the aim of simplification of RoF signal generation at a control site. Next, we present experimental results on 60-GHz band digital signal transmission at 7 and 14 Gbit/s with beamforming function, in which eight compact antenna modules are arrayed in a row. Finally, we investigate RoF signal generation at 40 GHz utilizing the 1.3- μ m band electroabsorption modulator-integrated laser diode, where an optical filter and an optical amplifier are used to boost the modulation component and the successful formation of various beam patterns by tuning VDL and VOA is shown.

Improved Model for Estimation of Spatial Averaging Path Length

In mobile communication systems, the transmitted RF signal is subject to mutually independent deterministic path loss and stochastic multipath and shadow fading. As at each spatial location mostly the composite signal samples are measured, their components are distinguished by averaging out the multipath‐caused signal level variations, while preserving just the ones due to shadowing. The prerequisite for this is the appropriateness of the local area averaging path length that enables obtaining the local mean (composed of mean path loss and shadow fading) and the multipath fading as difference between the composite signal sample and the local mean. However, the so far reported analytical approaches to estimation of the averaging path length are based on considering either the multipath or just the shadow fading, with applicability limited to only specific topologies and frequencies. Therefore, in this paper, the most widely used Lee analytical method is generalized and improved by considering multipath and shadowing concurrently, so providing the general closed‐form elementary‐function based estimation of the optimal averaging path length as a function of common multipath and shadow fading parameters characterizing particular propagation environment. The model enables recommendations for the optimal averaging length for all propagation conditions facing the mobile receiver.

Simultaneous Suppression of Even-Order and Third-Order Distortions in Directly Modulated Analog Photonic Links

A high-linearity directly-modulated analog photonic link (APL) with simultaneous suppression of the even-order intermodulation distortion, third-order intermodulation distortion (IMD3), and cross-modulation distortion (XMD) is proposed and experimentally demonstrated by the corporation of push–pull structure and an adaptive compensation algorithm. In the proposed directly-modulated APL system, the push–pull structure is introduced to effectively eliminate all the even-order nonlinear distortions, including the second-order intermodulation distortion and the second-order harmonic distortions. To further simultaneously suppress the IMD3 and XMD, an adaptive compensation algorithm is designed and adopted at the receiver. The experimental results show that the second-order spurious-free dynamic range and the third-order spurious-free dynamic range is improved by 19.8 and 12.4 dB, respectively, corresponding to 7.15% error vector magnitude performance improvement for a 120 Mb/s 64QAM-OFDM RF signal transmission when the input RF power is 13 dBm.

Design and characterization of a 3D encapsulation with silicon vias for radio frequency micro-electromechanical system resonator**Project supported by the National Natural Science Foundation of China (Grant Nos. 61234007, 61404136, and 61504130), the Fund from the Ministry of Science and Technology of China (Grant No. 2013YQ16055103), the Key Research & Development Program of Jiangsu Province, China (Grant No. BE2016007-2), and the

In this paper, we present a three-dimensional (3D) vacuum packaging technique at a wafer level for a radio frequency micro-electromechanical system (RF MEMS) resonator, in which low-loss silicon vias is used to transmit RF signals. Au–Sn solder bonding is adopted to provide a vacuum encapsulation as well as electrical conductions. A RF model of the encapsulation cap is established to evaluate the parasitic effect of the packaging, which provides an effective design solution of 3D RF MEMS encapsulation. With the proposed packaging structure, the signal-to-background ratio (SBR) of 24 dB is achieved, as well as the quality factor (Q-factor) of the resonator increases from 8000 to 10400 after packaging. The packaged resonator has a linear frequency–temperature (f–T) characteristic in a temperature range between 0 °C and 100 °C. And the package shows favorable long-term stability of the Q-factor over 200 days, which indicates that the package has excellent hermeticity. Furthermore, the average shear strength is measured to be 43.58 MPa among 10 samples.

Feasibility study of installation of solar panels on a high power HF antenna land

In HF broadcasting, the transmitters are typically very powerful. In the case of Turkish Radio and Television (TRT), total transmission average power may reach up to 5 MW. Therefore, it is natural to utilize solar panels as a means of alternative/backup energy for the continuous transmission of RF signal satisfying the requirement of broadcasting. In the TRT HF broadcasting array field, two areas are designated as the candidate areas for solar panel installation. In these areas, electric fields are simulated, measured, and compared. Simulations are done using the Numerical Electromagnetic Code (4nec2). The suitability of the regions for the solar panel installation are evaluated based on the ICNIRP human exposure limits. In addition, 4nec2 simulations are used to see the effect of metal frames of solar panels on the radiation patterns of the short-wave antenna arrays in the two solar panel candidate areas of TRT HF broadcasting station. Simulation results show that metal frames do not seem to have a significant effect on the radiation patterns of the short-wave antenna arrays. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2016.