Radio Frequency Receiver Research Articles

Modeling and evaluation of enhanced reception techniques for ADS-B signals in high interference environments

The RTCA (Radio Technical Commission for Aeronautics) DO-260B document has stimulated in latest years the adoption of novel algorithms to improve the ability of receivers to detect and decode ADS-B (Automatic Dependent Surveillance-Broadcast) signals, with particular emphasis on preamble detection, declaration of bit state and confidence level, detection and correction of errors. Motivated by an industry-driven research project, this paper reports on performance analysis of a set of enhanced techniques that we have implemented for detection and decoding of ADS-B signals transmitted at 1090 MHz carrier frequency also in high interference conditions. An extensive set of results has been derived through a specifically developed simulation environment, able to closely model a wide range of operational scenarios by generating ADS-B frames and Mode A/C interfering signals. The simulation environment also includes an implementation of two RF (Radio Frequency) receiver chains that refer to a linear amplifier and a logarithmic amplifier, respectively. The investigations are mainly focused on evaluating the impact of the interference generated by Mode A/C replies on preamble detection and data decoding for ADS-B signals. In this regard, the ability of enhanced reception techniques to improve detection performance is assessed. Numerical results obtained from extensive simulation runs are reported and commented. They actually demonstrate that enhanced techniques are essential to guarantee adequate detection performance in the harsh environments envisaged by increased intensity of air traffic and the extensive use of ADS-B for traffic control.

All-Optical and Broadband Microwave Image-Reject Receiver Based on Phase Modulation and I/Q Balanced Detection

Image-reject radio frequency (RF) receiver is the backbone of modern RF systems, but often suffers from limited bandwidth, local oscillator (LO) leakage, even-order distortion, and I/Q imbalance. A wideband photonic image-reject RF receiver based on two phase-modulators (PMs) in a Sagnac loop and an I/Q balanced detector is proposed. In the experiment, excellent I/Q amplitude balance (<0.8 dB) and phase balance (<0.7 degrees) over a wide operating frequency from 8 to 40 GHz are achieved. Due to balanced detection, the even-order distortion and dc-offset are significantly suppressed. Combined with an analog intermediate frequency (IF) quadrature coupler, the image-reject RF receiver is implemented with a spurious free dynamic range (SFDR) of 99.4 dB·Hz2/3 and an image rejection of 50.3 dB. An antenna remoting RF vector signal with image interference is down-converted to the IF domain. Benefiting from the significant image rejection and Sagnac loop architecture, a good constellation diagram and a low error vector magnitude (EVM) of the desired signal are obtained.

Iterative Nonlinear Self-Interference Cancellation for In-Band Full-Duplex Wireless Communications Under Mixer Imbalance and Amplifier Nonlinearity

This paper presents an iterative estimation and cancellation technique for nonlinear in-band full-duplex transceivers with IQ imbalances and amplifier nonlinearities. The estimation process of the proposed scheme consists of three stages, namely, the channel response estimation, IQ imbalance estimation, and power amplifier and low-noise amplifier (LNA) nonlinearities estimation. For the estimation of the parameters and improvement of the accuracy, distortions are compensated by cancellation or inversion with the latest estimated parameters. On the one hand, the channel response is estimated on the time domain; on the other hand, the IQ imbalance and nonlinearities are estimated on the frequency domain for a more straightforward estimation and superior accuracy. In the cancellation process of the proposed scheme, the received signal is compensated with the estimated parameters of the LNA and receiver IQ imbalance before cancellation because the desired signal is received with a high-power self-interference and is distorted by the radio-frequency receiver impairments. Simulation results show that the proposed technique can achieve higher cancellation performance compared with the Hammerstein canceller when the LNA is saturated by the self-interference. Additionally, the performance of the proposed canceller converges much faster than that of the Hammerstein canceller.

Design and Implementation of a Wireless Fluid Level Display System Using Ultrasonic Sensing Technique

The wireless fluid level indicator comprises a sensing and transmitting circuit for detecting and transmitting the levels of fluids from a container to the receiving circuit which receives and displays the amount of the measured volume. This has been achieved using an ultrasonic sensor (HC-SR04), a firmware (PIC16F648A/PIC16F876A microcontroller programmed in C/assembly languages), an encoder (HT12E) and a radio frequency (RF) transmitter transmitting at a bandwidth of 433MHz to an RF receiver interfaced with a decoder (HT12D), liquid crystal display (LCD) and a Buzzer. The device when tested measured water levels and transmitted same over a distance of up to 98.5 meters in open areas and up to 50 meters in highly obstructed areas. The average response time was also estimated to be 0.1 second. As a contact-less depth detection system, the device finds useful applications in measurement of fluid levels in homes and industries where concentrates, table water, transmission oils are produced, without affecting the chemical or physical properties of such substances-an advantage over the contact methods used in fluid level detection.&#x0D; Aims: To design and implement a wireless microcontroller based fluid level display system using ultrasonic sensing method.&#x0D; Study Design: By encoding the Transmitter module to sense and detect the amount of water level, while the decoder module decodes the received data and display the result.&#x0D; Place and Duration of Study: Department of Physics, University of Agriculture Makurdi, Benue State, Nigeria, between November 2018 and April 2019.&#x0D; Methodology: An RF transceiver, encoder/decoder (HT12E/HT12D), a 2x16 Liquid display module, 4MHz crystal oscillator, a buzzer and other peripherals were interfaced to two 8-bit controllers; PIC16F648A and PIC16F876A. The controllers were programmed in C/Assembly languages to enable effective communication of the system. The system was then calibrated to read and transmit water level values from a 30-centimeter deep tank over a distance of 1.0 - 98.5 meters.&#x0D; Results: The system was tested to have maximum sensitivity over a distance of 98.5 meters in non-obstructed areas and 50 meters in obstructed areas. The average response time was also estimated to be 0.5 seconds.&#x0D; Conclusion: The design and implementation of a wireless fluid level display system using ultrasonic sensing technique has been successfully done. The system workability is suitable for deployment and usage in domestic and industrial purposes.

A Zero-Power Ubiquitous Wireless Liquid-Level Sensor Based on Microfluidic-Integrated Microstrip Antenna

Harmonic transponder sensors, receiving radio-frequency (RF) signal and converting it to a modulated second harmonic, have been demonstrated to be effective for signal interrogation in environments with strong clutters. Here, we propose a compact dual-resonance microstrip antenna consisting of an elliptical patch loaded with shorting pins. Such an antenna utilizes the TM e 110 resonant mode to intercept the perpendicularly-polarized fundamental tone (2.86 GHz) and uses the TM o 110 resonant mode to retransmits the parallelly-polarized second harmonic (5.72 GHz). Moreover, we have developed a harmonic-based wireless liquid sensor comprising the proposed antenna and a micromachined liquid channel. Our measurement results show that even in the noisy environment, the second harmonic strength can precisely indicate the dielectric property of liquid filled in the microfluidic tank (e.g., acetone-water mixtures with various concentrations). However, a similar setup without frequency and polarization modulations (i.e., linear and passive backscatter tag) fails to provide a sensitive and quantitative measurement of liquid property. The proposed low-profile dual-resonance antenna with sensing capability will pave the way for the development of harmonic sensors and nonlinear radio-frequency identification (RFID) tags.

Broadband Photonic RF Channelizer With 92 Channels Based on a Soliton Crystal Microcomb

We report a broadband radio frequency (RF) channelizer with up to 92 channels using a coherent microcomb source. A soliton crystal microcomb, generated by a 49 GHz micro-ring resonator (MRR), is used as a multi-wavelength source. Due to its ultra-low comb spacing, up to 92 wavelengths are available in the C band, yielding a broad operation bandwidth. Another high-Q MRR is employed as a passive optical periodic filter to slice the RF spectrum with a high resolution of 121.4 MHz. We experimentally achieve an instantaneous RF operation bandwidth of 8.08 GHz and verify RF channelization up to 17.55 GHz via thermal tuning. Our approach is a significant step towards the monolithically integrated photonic RF receivers with reduced complexity, size, and unprecedented performance, which is important for wide RF applications ranging from broadband analog signal processing to digital-compatible signal detection.

A Portable NMR Spectrometer With a Probe Head Combining RF and DC Capabilities to Generate Pulsed-Field Gradients

Portable nuclear magnetic resonance (NMR) spectrometers are used in various scientific fields. A vast number of applications are suitable for low-field permanent magnets. However, most of these systems lack the ability of pulsed-field gradients as these require cumbersome additional hardware. We herein report an NMR probe head that incorporates a radio frequency (RF)-coil equipped with pulsed-field gradient capabilities in a single center-tapped solenoid. We developed a circuitry allowing for the application of direct currents without disturbing the RF reception capabilities. Furthermore, we present a System-on-Chip-based NMR spectrometer. Combined with the NMR probe head, it represents a versatile low-cost system capable of field gradient generation. The probe head is characterized in terms of scatter parameters, quality factor, and transversal field homogeneity. We exhibit simulation data of the field gradient and present the required external circuitry. Experimental results show further the dephasing capabilities of the gradient and give insights into the spatial shape. Finally, the system is applied for the mapping of J-couplings in 1-butanol via zero-quantum coherences. A theoretical analysis of the pulse sequence is given for a homonuclear two-spin system. The experimental results demonstrate the potential use of this setup.

The Methods toward Improving Communication Performance in Transparent Radio Frequency Signals

In wireless digital communications, amplitude-shift keying (ASK) and frequency-shift keying (FSK) modules are often used and radio frequency (RF), communication synchronization, and noise problems affect the performance very much. In particular, the sending of byte-type data called synchronous and preamble before sending data in intermodule communication increases the sent data and decreases the speed. Also, the microcontroller at the output of the RF receiver module continuously listens to the RF noise and analyzes incoming data, but this increases the processing load of the microcontroller. Moreover, it reduces the speed of performing other operations. In this study, a transparent RF transmitter and receiver have been investigated, and methods for increasing the communication performance of the modules have been proposed and performed. Two of the proposed methods prevented the continuous listening of the microprocessor in the RF receiver structure so that the microprocessor can be used with other processes. In other methods, the compression of the data size was achieved because the transmission of a series of data in RF communication systems was limited to a certain extent. In the last section of the study, since the RF modules have failed to transmit the data due to corruption in the extended data dimensions, the bit carrier control security code has been created for the data series and more healthy communication has been performed.

Tunable Ultrahigh Dielectric Constant (tuHDC) Ceramic Technique to Largely Improve RF Coil Efficiency and MR Imaging Performance.

This work introduces an innovative magnetic resonance (MR) imaging technology that incorporates radiofrequency (RF) coil(s) with permittivity-tunable ultrahigh dielectric constant (tuHDC) ceramics to significantly improve RF coil transmission and reception efficiencies, MR imaging sensitivity and signal-to-noise ratio (SNR). The tuHDC ceramics made of composite barium strontium titanate (BST) compounds (Ba0.6 Sr0.4 TiO3) have low dielectric loss and very high permittivity tunability from 2,000 to 15000 by varying the ceramic temperature between 0°C and 40°C to achieve an optimal permittivity for MR imaging application. We demonstrated for the first time the proof of concept using the BST-based tuHDC-RF-coil technology to improve MR spectroscopic imaging performance of 17O nuclide at 10.5 Tesla (T) at a low ceramic temperature and 23Na nuclide at 7T at room temperature. We discovered a large and spatially independent noise reduction under an optimal ceramic temperature, which synergistically resulted in an unprecedented SNR improvement. Large improvements were also demonstrated for 1H MRI on a 1.5T clinical scanner using the same ceramics. The tuHDC-RF-coil technology is robust, flexible and cost-effective; it presents a technical breakthrough to significantly improve imaging sensitivity and resolution for broad MR imaging applications; which is critical for advancing biomedical and neuroscience research, and improving diagnostic imaging.

Detection of Atmospheric Lightning Activity with Ground-Based Radiofrequency Receivers – Establishment and Initial Results

Understanding atmospheric lightning flashes and their occurrences is one of the most important aspects of the Earth’s climate science. Real-time lightning data have profound importance in climate science, air-quality research and atmospheric nitrogen budget, apart from lightning being one of the major natural disasters. Keeping these in view, a lightning detection sensor (LDS) network has been established at six locations in India, viz. Kolkata, Ranchi, Raipur, Bhubaneswar, Nagpur and Visakhapatnam. Preliminary analysis of the data suggests that it is possible to detect the phenomenon and identify vulnerable zones of lightning activity. We analysed the Kolkata, Ranchi and Visakhapatnam data during June–July 2017 to identify the areas with major impact by cloud-to-ground lightning events and also see if a warning can be provided based on single-sensor data. Status of the ongoing development in LDS network is discussed here based on the current understanding of existing lightning detection networks.

Damage accumulation mechanism in PIN diode limiters induced via multiple microwave pulses

Positive-intrinsic-negative (PIN) diodes are widely used as limiters to protect sensitive components from damage in radio frequency (RF) receiver systems and communication front-ends. However, PIN diode limiters can be burnt out due to the microwave pulses coupling through the front-end of RF receiver systems. The damage processes and mechanisms in PIN limiters are undoubtedly important topics. Here, the damage accumulation process in PIN limiters induced by external microwave pulses is studied via the injection experiments. The relationship between the degree of damage (i.e., insertion loss) in the limiters and number of the injected pulses is reported. The maximum temperature criterion for burnout in PIN limiters is theoretically predicted and experimentally verified not accurate, and it is further observed that the insertion loss of the PIN diode limiter changes significantly only if more energy is injected into the limiter via microwave pulses.

Characterization of a COTS-Based RF Receiver for Cubesat Applications.

This paper reports the experimental results of a test campaign performed on the radio-frequency (RF) receiver prototype operating at a 2025–2110 MHz frequency range, designed and fabricated for CubeSat applications. The prototype has been tested through a board-level test approach for the verification of the functional requirements and a component-level one for specific characterization measures. The tests have shown the following results: a −115–−70 dBm sensitivity range, 390 MHz intermediate frequency, a 0 dBm output power level with ±1 dB error, a 2.34 dB noise figure, and a 4.86 W power absorption. Such results have been largely achieved implementing an automatic gain control system by cascading two Commercial Off-The-Shelf (COTS) amplifiers. Moreover, an innovative technique based on RF test points has been successfully experimented and validated to measure the S-parameters of a custom low-pass filter integrated on the receiver, showing the possibility of even characterizing the single COTS components exposed to radiation through a unique board-level test setup. The technique may have a great impact on the cost reduction of electronic boards for space applications, since it would avoid using expensive evaluation boards for each COTS component that needs a radiation test.

RF Receiver Front-End Employing IIP2-Enhanced 25% Duty-Cycle Quadrature Passive Mixer for Advanced Cellular Applications

This paper proposes a second-order input-referred intercept point (IIP2)-enhanced 25% duty-cycle local oscillator (LO) quadrature passive mixer configuration with developing a wideband radio frequency (RF) receiver front-end, suitable for 4G and 5G new radio (NR) sub-6 GHz applications. By combining mixer switches operated by several combinations of quadrature-phase RF and LO signals, the inherent second-order nonlinear characteristics produced by the asymmetric factors of the mixer are greatly improved without any additional calibration process. This second-order linearity improvement is theoretically analyzed in terms of the 25% duty-cycle mixing operations, and is compared to the linearity characteristic observed in the conventional mixer design. To validate the IIP2 performance improvement, a wideband RF receiver front-end with the proposed mixer design is fabricated in a 65-nm CMOS technology. The implemented receiver front-end incorporates a wideband low noise amplifier with a polyphase filter, the proposed quadrature passive mixers, wideband transimpedance amplifiers, and 25% duty-cycle LO circuitry. The performance is characterized mainly in the long-term evolution and 5G NR frequency bands, which range from 1800 MHz to 2700 MHz. The demonstrated design achieves approximately 16 dB higher mean values of the out-of-band (OB) IIP2s compared to a conventional design approach without calibration. The design also attains conversion gains greater than 43 dB, double-sideband noise figures less than 4.4 dB, OB IIP3s greater than −1.52 dBm, and OB input P1dB greater than −23.1 dBm, for all measured frequency bands even in the presence of transmitter blockers. The proposed configuration, excluding the LO circuitry, consumes a bias current of 17.4 mA with a nominal supply of 1.2 V. The active area of the proposed implemented design is 0.6 mm2.

Differences in Reliability and Predictability of Harvested Energy from Battery-less Intermittently Powered Systems

Solar and radio frequency harvesters serve as a viable alternative energy source to batteries in many cases where the battery cannot be easily replaced. However, energy harvesters do not consistently produce enough energy to sustain an energy consumer; thus, both the energy availability and execution of the energy-consuming process are intermittent. By simulating intermittent systems with large-scale energy demands using specifically-designed circuit models, the harvested voltage and other parameters such as the voltages across the capacitor and the load were determined. We plotted these data, for both harvested solar and harvested radio frequency energy, to make probability plots depicting the likelihood that energy will be available now given that N number of energy events have occurred. Additionally, we designated a metric as the η-factor, which was calculated from these probability plots for the solar and radio frequency data to quantify the reliability of the power source. The η-factor for harvested solar energy was statistically significantly higher than the η-factor for harvested radio frequency energy, meaning harvested solar energy was more consistently available than harvested radio frequency energy. Finally, we collected data to determine the effects on the output voltage of various obstacles between the radio frequency transmitter and receiver. We found that obstacles like metal and people caused a more pronounced drop in the amount of energy harvested when compared to other obstacles like foam or wood. Quantifying the reliability of different harvested sources would help in identifying the most practical and efficient forms of renewable energy; determining which obstacles cause the most obstruction to a signal can aid in the strategic placement of harvesters for maximum energy efficiency.

How Much do Hardware Imperfections Affect the Performance of Reconfigurable Intelligent Surface-Assisted Systems?

In the present work, we investigate the impact of transceiver hardware imperfection on reconfigurable intelligent surface (RIS)-assisted wireless systems. In this direction, first, we present a general model that accommodates the impact of the transmitter (TX) and receiver (RX) radio frequency impairments. Next, we derive novel closed-form expressions for the instantaneous end-to-end signal-to-noise-plus-distortion-ratio (SNDR). Building upon these expressions, we extract an exact closed-form expression for the system's outage probability, which allows us not only to quantify RIS-assisted systems' outage performance but also reveals that the maximum allowed spectral efficiency of the transmission scheme is limited by the levels of the transceiver hardware imperfection. Likewise, a diversity analysis is provided. Moreover, in order to characterize the capacity of RIS-assisted systems, we report a new upper-bound for the ergodic capacity, which takes into account the number of the RIS's reflective units (RUs), the level of TX and RX hardware imperfection, as well as the transmission signal-to-noise-ratio (SNR). Finally, two insightful ergodic capacity ceilings are extracted for the high-SNR and high-RUs regimes. Our results highlight the importance of accurately modeling the transceiver hardware imperfection and reveals that they significantly limit the RIS-assisted wireless system performance.

A CMOS RF BeiDou-1 Transceiver for Regional Positioning and Short Message Service Applications

This paper presents a fully integrated CMOS radio-frequency (RF) transceiver for BeiDou-1, a radio determination satellite service system which can provide regional positioning and short message service. The proposed transceiver incorporates a low-IF receiver and a BPSK transmitter to realize a dual-way communication between users and the central control station via satellites. The receiver (RX) RF front-end down-converts the 2491.75 MHz RF signals to a 12.24 MHz IF band with a bandwidth of 8.16 MHz. The complex band-pass filter utilizes passive compensation technique to compensate the phase lag and achieve in-band flatness. The 4.08 Mchip/s baseband signal alternatively selects one of the differential 1615.68 MHz local signals to achieve BPSK modulation for the transmitter (TX). Besides, on-chip low dropout regulators adopt improved power supply rejection ratio techniques by integrating active filtering to obtain stable 1.5 V supply voltages. The transceiver is fabricated in a 130 nm CMOS technology and occupies an area of 5.88 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with electrostatic discharge circuitry and pads included. The RX channel achieves a 106 dB maximum voltage gain with a 65 dB dynamic range, a 4.95 dB noise figure and a 46 dB image rejection ratio. The output power for the TX ranges from -10 dBm to 5 dBm, with a phase error less than 1.5 degree.

Respiratory Motion Detection and Correction for MR Using the Pilot Tone

The aim of this study was to develop a method for tracking respiratory motion throughout full MR or PET/MR studies that requires only minimal additional hardware and no modifications to the sequences. Patient motion that is caused by respiration affects the quality of the signal of the individual radiofrequency receive coil elements. This effect can be detected as a modulation of a monofrequent signal that is emitted by a small portable transmitter placed inside the bore (Pilot Tone). The frequency is selected such that it is located outside of the frequency band of the actual MR readout experiment but well within the bandwidth of the radiofrequency receiver, that is, the oversampling area. Temporal variations of the detected signal indicate motion. After extraction of the signal from the raw data, principal component analysis was used to identify respiratory motion. The approach and potential applications during MR and PET/MR examinations that rely on a continuous respiratory signal were validated with an anthropomorphic, PET/MR-compatible motion phantom as well as in a volunteer study. Respiratory motion detection and correction were presented for MR and PET data in phantom and volunteer studies. The Pilot Tone successfully recovered the ground-truth respiratory signal provided by the phantom. The presented method provides reliable respiratory motion tracking during arbitrary imaging sequences throughout a full PET/MR study. All results can directly be transferred to MR-only applications as well.

Optimal Resource Allocation in Wireless Powered Relay Networks With Nonlinear Energy Harvesters

This letter investigates a multiple-relay decode-and-forward (DF) network with simultaneous wireless information and power transfer (SWIPT). The relays use the power splitting (PS) technique to receive radio frequency (RF) energy and information simultaneously from the source. To characterize nonlinearity of energy harvesters at the relays, two existing models are adopted, which are the logistic function model and the constant-linear-constant (CLC) model. We target end-to-end throughput maximization by optimizing the power and bandwidth assignment for every source-relay-destination link and the PS ratio at every relay node. The formulated problems are demonstrated to be nonconvex. Through a series of analysis and transformations, we find global optimal solutions for the formulated problems. Numerical results verify the effectiveness of our proposed methods.

Performance analysis of NOMA with generalised selection combining receivers

In this Letter, the authors present a comprehensive performance analysis of a non-orthogonal multiple access (NOMA) system with generalised selection combining (GSC), which bridges the gap between the performance of NOMA with selection combining (SC) and NOMA with maximal-ratio combining (MRC). In particular, the authors derive a closed-form expression for an upper bound on the average achievable sum rate and an exact closed-form expression for the outage probability. The analysis reveals a tradeoff between the number of implemented receiver radio-frequency (RF) chains and the achieved performance and can be used to determine the appropriate number of paths to combine into a practical receiver design. A demonstrated agreement between the analytical and simulation results confirms the correctness of the analysis.

Microstrip Transmission Line RF Coil for a PET/MRI Insert

Purpose:We proposed and developed a new microstrip transmission line radiofrequency (RF) coil for a positron emission tomography (PET) insert for MRI, which has low electrical interactions with PET shield boxes. We performed imaging experiments using a single-channel and a four-channel proposed RF coils for proof-of-concept.Methods:A conventional microstrip coil consists of a microstrip conductor, a ground conductor, and a dielectric between the two conductors. We proposed a microstrip coil for the PET insert that replaced the conventional single-layer ground conductor with the RF shield of the PET insert. A dielectric material, which could otherwise attenuate gamma photons radiated from the PET imaging tracer, was not used. As proof-of-concept, we compared conventional and the proposed single-channel coils. To study multichannel performance, we further developed a four-channel proposed RF coil. Since the MRI system had a single-channel transmission port, an interfacing four-way RF power division circuit was designed. The coils were implemented as both RF transmitters and receivers in a cylindrical frame of diameter 150 mm. Coil bench performances were tested with a network analyzer (Rohde & Schwarz, Germany), and a homogeneous phantom study was conducted for gradient echo imaging and RF field (B1) mapping in a 3T clinical MRI system (Verio, Siemens, Erlangen, Germany).Results:For all coils, the power reflection coefficient was below −30 dB, and the transmission coefficients in the four-channel configuration were near or below −20 dB. The comparative single-channel coil study showed good similarity between the conventional and proposed coils. The gradient echo image of the four-channel coil showed expected flashing image intensity near the coils and no phase distortion was visible. Transmit B1 field map resembled the image performance.Conclusion:The proposed PET-microstrip coil performed similarly to the conventional microstrip transmission line coil and is promising for the development of a compact coil-PET system capable of simultaneous PET/MRI analysis with an existing MRI system.