Radio Frequency Subsystem Research Articles

RF technology in wireless communications:From transceiver architecture to subsystem specifications

Radiofrequency (RF) technology is essential to wireless communication.The demand for RF technology research is growing as mobile, satellite, radar, and other fields advance. In recent years, the development of 5G and 6G technologies has raised the bar for in-depth RF technology research, requiring greater frequency and data transmission efficiency, among other things. In addition to providing a brief overview of the transceiver's components, the signal chain, and an introduction to the major RF technologies, this paper will concentrate on the architecture of RF transceivers in RF systems and the specification of sub-systems. It will also include references for the RF sub-system specifications and integration techniques. The comprehensive study of communication technology will benefit greatly from an in-depth grasp of the transceiver's capabilities. Lastly, an overview of the layout and features of RF transceivers is provided, along with a prediction of the future application-focused path of RF technology.

Demonstration of Intelligent Hybrid FSO/RF System Based on Enhanced GRU Prediction and Real-World Meteorological Dataset

Hybrid free space optical (FSO)/radio frequency (RF) system has emerged as a high-data-rate solution for the last mile access network. In this paper, we establish a hybrid FSO/RF testbed including an intensity modulation/direct detection (IM/DD) FSO subsystem with space diversity and a high-order quadrature amplitude modulation (QAM) RF subsystem with polarization diversity, respectively. Based on the testbed, we propose and experimentally validate an intelligent transmission system where the link selection and switching technology is implemented. In particular, we propose a gated recurrent unit (GRU) neural network enhanced by time attention mechanism for the hybrid system. The experimental results demonstrate that the proposed system can achieve the prediction of FSO channel fading with a high precision where absolute percentage error (APE) values lower than 3% account for up to 90% of the prediction results. The implemented intelligent hybrid system can significantly reduce the link switching frequency and link interruption duration. Then the BER is further verified on the testbed, and results show that the intelligent hybrid system can improve the BER from the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> to the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> during the time periods when link switching occurs.

MIMO Hybrid FSO/RF System Over Generalized Fading Channels

Free-space optics (FSO) communication is often unreliable, especially for long distances, as it suffers from attenuation due to foggy weather, atmospheric turbulence, and pointing errors. To avoid communication link failure, radio frequency (RF) communication, which is unaffected from these effects, is utilized when FSO communication is in outage. Diversity is known to counteract the adverse fading effects, therefore, this paper presents a transmit aperture/antenna selection (TAS) and selection combining (SC)-based multiple-input-multiple-output (MIMO) hybrid FSO/RF system. The proposed system consists of a MIMO FSO and RF sub-systems. The MIMO FSO sub-system is given higher priority to transmit and receive using the selected best link. The best link of the MIMO RF sub-system is used when the FSO sub-system is in outage. The probability density function (PDF) and cumulative distribution function (CDF) expressions for TAS/SC-based MIMO FSO and RF sub-systems are derived. The derived PDF and CDF expressions are used further to derive the exact and asymptotic expressions for outage probability, average symbol error rate (SER), and capacity of the hybrid system. From the asymptotic SER expressions, the diversity order of the proposed system is determined. The optimum values for the threshold SNR and transmit beam waist, which minimize the average SER, are obtained. Further, the obtained optimal values using analytical expressions are verified using numerical optimization technique. The effect of multiple apertures/antennas, pointing errors, and atmospheric attenuation over the system performance is analyzed extensively by varying the FSO and RF channel parameters. The results show that the proposed hybrid FSO/RF system is more reliable compared to the individual MIMO FSO and RF systems and achieves higher capacity compared to the MIMO RF system.

Full-Duplex DF Relaying With Parallel Hybrid FSO/RF Transmissions

The ever-increasing demands for higher data rates in telecommunications networks, along with the significant benefits offered by wireless communications, have pushed the technological developments to new frontiers. Free-space optical (FSO) communications are among the technologies that can address these emerging demands, offering large and unregulated bandwidth. In addition, recent advances in radio frequency (RF) systems have enabled the development of in-band full-duplex (FD) radios with the employment of advanced self-interference cancellation techniques. Therefore, in this paper we study a robust FD relaying system comprised of parallel hybrid FSO/RF communication links, where the coordination of transmissions between the FSO/RF subsystems is carried out by the hard-switching protocol. The operation of the RF links is impaired by Nakagami-m fading, the residual self-interference due to the FD relaying operation, and the in-phase and quadrature-phase imbalance effect due to imperfect RF front-ends. As far as the FSO links are concerned, we consider the influence of the joint effects of atmospheric turbulence, beam wander and pointing errors. We first derive analytical closed-form expressions for the outage probability of both subsystems as well as for the overall FD relaying hybrid system. Then, asymptotic expressions are extracted for the outage performance in the high signal-to-noise ratio regime. The achievable outage diversity orders of both FSO and RF subsystems are determined, which provide significant insight into the design of such hybrid systems in a wide variety of operating conditions. Finally, the numerical results are presented using the derived outcomes, and significant conclusions are drawn about FD relaying hybrid systems.

Performance optimisation for dual‐hop hybrid FSO/RF system with selection combining

This study investigates the performance of a decode-and-forward-relay-based hybrid free space optical (FSO)/radio frequency (RF) system with selection combining. The proposed hybrid system considers an FSO sub-system as a default transmission option and RF sub-system is utilised when FSO is in outage. For the proposed system, the outage threshold signal-to-noise ratio (SNR) is an important parameter and the optimum value for the same has been calculated to achieve the target average symbol error rate (SER) and high capacity. The presented model considers the effect of transmit beam waist, detector size, and jitter variance explicitly for the FSO link. Transmit beam waist and detector size are optimised to minimise the average SER considering various weather conditions and link distances. A unified performance analysis is addressed and exact expressions for outage probability and average SER are obtained. Simple asymptotic expressions are also derived for high SNR to obtain the diversity order. Large coding gains are observed for optimum beam waist compared to any arbitrary beam waist for same average SER. Significant performance improvement is also observed for the proposed system compared to the individual FSO and RF systems. The theoretical and asymptotic analyses are verified by Monte-Carlo simulations.

Non-Orthogonal Multiple Access for Hybrid VLC-RF Networks With Imperfect Channel State Information

This paper proposes a general framework for the energy efficiency analysis of a hybrid visible light communication (VLC) and Radio Frequency (RF) wireless system, in which both VLC and RF subsystems utilize non-orthogonal multiple access (NOMA) technology. The proposed framework is based on realistic communication scenarios as it takes into account the mobility of users and assumes imperfect channel-state information (CSI). In this context, tractable closed-form expressions are derived for the corresponding average sum-rate of NOMA-VLC and orthogonal frequency division multiple access (OFDMA)-VLC. It is shown extensively that incurred CSI errors have a considerable impact on the average energy efficiency of both NOMA-VLC and OFDMA-VLC systems. Hence, they should be taken into detailed account in the design of practical systems. We further demonstrate that the average energy efficiency of the hybrid NOMA-VLC-RF system outperforms the NOMA-VLC system under imperfect CSI. Respective computer simulations corroborate the derived analytic results, and interesting theoretical and practical insights are provided, which will be useful in the effective design and deployment of conventional VLC and hybrid VLC-RF systems.

On the Use of Glint-Doppler-Azimuth Correlation for Speed Estimation of Nearby Tangential Targets

This article introduces a new radar architecture, which implements a new signal processing scheme, with applications to the Intelligent Transportation Systems. The proposed solution exploits a well-known problem regarding low range radar systems, the Glint Effect, in order to improve previous results. For that purpose, the presented system is required to measure azimuth and Doppler of targets, for which it opts for a 2-channel Digital Array Receiver scheme working with a frequency-modulated continuous wave. This involves more complex hardware and signal processing software, comparing to the common mono-channel non coherent systems, nevertheless latest devices (radio frequency subsystems, field-programmable gate arrays, digitizers, etc) make it simple and affordable. The proposed system, with an easy-and-fast side-looking installation, exploits several advantages of its 2-channel synchronous architecture (e.g. clutter cancellation, Doppler history availability, etc) to achieve a better estimation of two key measurements: traffic flow (instantaneous and average) and vehicles speed.

Developing a High-Power Multilayer Ceramic Capacitor Qualification Test Setup for RF Subsystems

Radio frequency (RF) power-matching circuits are used in many applications that require controllable and efficient power transfer for a variable load. They are commonly found in plasma chambers in the semiconductor manufacturing industries which deal with highly dynamic loading conditions. State-of-the-art technologies for the power-matching circuits in plasma generation utilize multilayer ceramic capacitors (MLCCs) as one of the main passive components in the tuning circuitry. Such matching circuits must have the capability of withstanding high RF currents without thermal breakdown. A thermal breakdown is caused by the dissipated heat in the MLCC units at high RF currents. Therefore, a qualifying process is required for testing the MLCC functionality. This paper develops a repeatable test-bench setup for the qualification of MLCC units for power matching in a plasma generating circuits. The setup described in this paper enables the industry to develop performance criteria for the MLCC units. The test bench was built using a conventional tunable matching network to deliver the RF power to the MLCC unit under test. The functionality of the test bench is verified using Keysight’s Advanced Design System simulation tool. Finally, instrumentation software of the National Instruments’ LabVIEW is utilized as a graphical user interface to automate the inspection process.

Performance evaluation of 2 × 2 MIMO–OFDM‐based radio‐over‐fibre system using Alamouti coding and Hammerstein equaliser

Radio-over-fibre (RoF) systems consist of two subsystems including optical subsystem and wireless radio frequency subsystem. It is shown that by using multiple-input multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) systems, the RoF transmission can be improved in frequency-selective channels. In this study, two different configurations of MIMO–OFDM-based RoF systems are compared for the long-term evolution standard under different non-linearity levels, bandwidths, and fading channel conditions. Using the total degradations (TD) criterion, an appropriate quiescent point is determined to decrease the impact of non-linearity level, and hence the performances of different MIMO detection methods are compared. Bit error rate results demonstrate that by using Hammerstein type equaliser, the system performance is improved under different conditions including different fading channels, Doppler frequencies, bandwidths, and output back off levels. Results demonstrate that with an appropriate structure for MIMO–OFDM–RoF systems, a suitable quiescent point can be found for all scenarios by employing Alamouti coding and Hammerstein equaliser.

Parallel-Plate Luneburg Lens Antenna for Broadband Multibeam Radiation at Millimeter-Wave Frequencies With Design Optimization

This paper presents the implementation of Luneburg lens antenna based on a 2-D parallel-plate structure for broadband multibeam radiation at millimeter-wave frequencies. In particular, each beam pattern of this 2-D Luneburg lens antenna has a narrow beamwidth along the multibeam dimension, and exhibits a broad beamwidth along the other cross section, analogous to the radiation from a 1-D array of antennas embedded inside the parallel-plate structure. Furthermore, the isolation to external structures by the top and bottom metal parallel plates may reduce the beam distortion from external interferences, and therefore enhance its compatibility to integrate with other radio frequency (RF) components to form an RF subsystem module. In addition, a theoretic model to realize the dielectric variation of Luneburg lens is developed by using stacked multiple planar layered dielectric materials for a cheap manufacture. In this paper, numerical simulation to validate the developed model of 2-D Luneburg lens design is first presented. Afterward, simulation and experimental measurement results of a practical design are both presented to validate the design concept.

Iterative Learning Control for the Radio Frequency Subsystems of a Free-Electron Laser

In linear particle accelerators used for free-electron lasers, it is often required that the electron bunches experience the same electric field as they pass through the accelerating structures. For radio frequency (RF) pulsed mode machines, like the SwissFEL, this means that the amplitude and phase of the RF pulses feeding the structures through the waveguides should be kept constant over the pulselength. This raises an interesting problem that can be addressed by an iterative learning control (ILC) technique. This method manipulates the input waveforms iteratively, in order to generate flat amplitude and phase pulses at the output of the system. In this paper, we introduce two ILC algorithms, one with a model and one without, which have been tested on three different high-power RF subsystems, namely, the klystron, pulse compressor, and RF Gun.

Evaluation of Radio Resource Management Impact on RoF Signal Transmission for Downlink LTE

Analog radio-over-fiber (RoF) is a suitable technology for efficiently developing the cloud-RAN concept in fifth generation deployments based on long-term evolution advanced (LTE-A). Distortion and radiofrequency (RF) power amplifier gain should be taken into account in order to achieve the desired transmission power at the base station. Both mainly depend on several parameters that characterize the optical link, such as the RF input power and bias current. This paper analyzes the link performance due to variations on the traffic load as expected under real operation. In this paper, we show that it is possible in this scenario to adaptively choose the optimum RF input power to minimize the measured error vector magnitude and reduce the RF subsystem gain. Results show that this adaptation allows to relax the RF amplifier gain requirements up to 3-4 dB for medium load conditions.

System Scaling With Nanostructured Power and RF Components

The emergence of smartphones and other smart systems is driving new trends in electronics scaling that goes beyond transistors or active devices, to include all the system components such as packaging substrates, passive components, thermal structures, power sources, and the system interconnections. Current system components are at milliscale, creating a $10^{3}$ to $10^{6}$ scaling gap with the packaging interfaces at microscale, and transistors at nanodimensions. With current microstructured materials, component miniaturization also degrades performance metrics such as efficiency, tolerance or precision, thermal and frequency stability. Nanostructured materials and processes can potentially miniaturize these system components, while simultaneously enhancing the performance. These nanostructured components are assembled close to the active devices, resulting in ultraminiaturized and ultrathin systems with 3-D integration of passives with actives. This paper shows the impact of nanostructured materials toward enhancing the performance and miniaturization of power and radio-frequency (RF) passive components in emerging smart systems. Opportunities for nanostructured materials in improving the power density and efficiency of capacitors and inductors in power-supply modules are reviewed in the first part of the paper. The impact of nanostructured magnetic, dielectric and magneto-dielectric films on emerging RF subsystems is illustrated in the last part of the paper.

Optimal Relay Selection for the Parallel Hybrid RF/FSO Relay Channel: Non-Buffer-Aided and Buffer-Aided Designs

Hybrid radio frequency (RF)/free space optical (FSO) systems are among the candidate enabling technologies for the next generation of wireless networks, since they benefit from both the high data rates of the FSO subsystem and the high reliability of the RF subsystem. In this paper, we focus on the problem of throughput maximization in the parallel hybrid RF/FSO relay channel. In the parallel hybrid RF/FSO relay channel, a source node sends its data to a destination node with the help of multiple relay nodes. Thereby, for a given relay, the source-relay and the relay-destination FSO links are orthogonal with respect to each other due to the narrow beam employed for FSO transmission, whereas due to the broadcast nature of the RF channel, half-duplex operation is required for the RF links if self-interference is to be avoided. Moreover, we consider the two cases where the relays are and are not equipped with buffers. For both cases, we derive the optimal relay selection policies for the RF and FSO links and the optimal time allocation policy for transmission and reception for the RF links. The proposed optimal protocols provide important insights for an optimal system design. Since the optimal buffer-aided policy introduces an unbounded delay, we also propose a suboptimal buffer-aided policy, which ensures certain target average delays. Moreover, we present distributed implementations for both the proposed optimal protocols. Simulation results demonstrate that a considerable gain can be achieved by the proposed adaptive protocols in comparison with benchmark schemes from the literature.

Progress for Behavioral Challenges: A Summary of Time-domain Behavioral Modeling of RF and Microwave Subsystems

The quest for the best compromise between the requirements for battery preservation and system operation linearity in the radio frequency (RF) and microwave front end has been a constant push for research on behavioral modeling of active devices since the early days of satellite communications [1] and has accelerated with the growth of modern mobile communication infrastructures. This focus has resulted today in a vast amount of behavioral model options, especially for the RF power amplifier (PA), in which it is not always simple for a designer to find his or her way as discussed in [2]-[5]. Using the term "behavioral model," we define these models as those derived from the observation of the electrical variables at the block ports (with very little insight on the internal composition of the block) and dedicated to the modeling of baseband/bandpass subsystems. Unlike transistor-level compact modeling, where there are well-established initiatives for model standardization driven by foundries and computer-aided design vendor companies [6], [7], there is, unfortunately, no such comparable effort yet at the subsystem level [8]. This article offers a concise summary of the recent progress on time-domain behavioral modeling with a particular focus on the continuous-time (CT) modeling theory [9].

Formation Flying Radio-Frequency metrology validation and performance: The PRISMA case

The Radio-Frequency (RF) metrology sub-system developed by Thales Alenia Space© under contract from French (CNES) and Spanish (CDTI) space agencies provides autonomous relative positioning for high-altitude formation flying missions, where Global Navigation Satellite System (GNSS) services are not available. The RF sub-system basically provides navigation products such as relative distance, Line-of-Sight (LoS) and velocity estimates over a wide relative distance range starting from three meters and up to 30km. It allows full-space coverage thanks to multiple antennae and offers an Inter-Satellite communication Link (ISL) featuring a 12kbps throughput.The first two Flight Model (FM) units have been delivered at the end of 2009 in the framework of PRISMA flight demonstration mission. Thales Alenia Space© performed the integration and validation of the units in the conductive mode, covering functional and performance aspects. A complementary validation phase was achieved by CNES in radiated conditions, including multi-path and antennae phase center characterization in anechoic chamber.

Drain Current and Noise Model of Cylindrical Surrounding Double-Gate MOSFET for RF Switch

In this paper, we have explored the drain current model and subthreshold model of Cylindrical Surrounding Double-Gate (CSDG) MOSFETs, for the wireless telecommunication systems to operate at the microwave frequency regime of the spectrum. This CSDG MOSFET can be used as the RF switch for selecting the data streams from antennas for both the transmitting and receiving processes. We emphasize on the basics of the drain current with DIBL and SCE, for the integrated circuit of the radio frequency sub-system. Using this device we analyzed that the drain current is higher, output conductance is lower which shows that the isolation is better in CSDG MOSFET as compared to double-gate MOSFET and single-gate MOSFET.

Design and performance analysis of cylindrical surrounding double-gate MOSFET for RF switch

In this paper, we have analyzed the design parameters of Cylindrical Surrounding Double-Gate (CSDG) MOSFETs as an RF switch for the advanced wireless telecommunication systems. The proposed CSDG RF MOSFET is operated at the microwave regime of the spectrum. We emphasize on the basics of the circuit elements such as drain current, threshold voltage, resonant frequency, resistances at switch ON condition, capacitances, energy stored, cross talk and switching speed required for the integrated circuit of the radio frequency sub-system of the CSDG RF CMOS device and the physical significance of these basic circuit elements is also discussed. We observed that the total capacitance between the source to drain for the proposed CSDG MOSFET is more compared to the Cylindrical Surrounding Single-Gate (CSSG) MOSFET due to the greater drain current passing area of the CSDG MOSFET, which reveals that the isolation is better in the CSDG MOSFET compared to that of the simple double-gate MOSFET and single-gate MOSFET. We analyzed that the CSDG MOSFET stores more energy (1.4 times) as compared to the CSSG MOSFET. Therefore, the CSDG MOSFET has more stored energy. The ON-resistance of CSDG MOSFET is half than that of the double-gate MOSFET and single-gate MOSFET, which reveals that the current flow from source to drain in CSDG MOSFET is better than the double-gate MOSFET and single-gate MOSFET.

Design of RF subsystem for dynamic spectrum sharing system in UHF band

A radio frequency (RF) subsystem used in ultra-high frequency (UHF) band dynamic spectrum sharing wireless communication system is presented.It is composed of three data RF transceivers and one cognitive RF receiver. Every RF transceiver consists of transmitting chain and receiving chain, and the receiving chain is designed the same as cognitive RF receiver. The measured error vector magnitude (EVM) of transmitting chain is less than 1.5%, when the output signal power is 30 dBm. The measured IMD3 of transmitting chain is less than −50 dBc, when the input signal is two tones with 10 kHz space, and the output signal power is 30 dBm. The measured EVM of cognitive RF receiver and receiving chain is less than 1.0% when the input signal power is −50 dBm. The measured lowest noise figure of cognitive RF receiver and receiving chain is 3.41 dB, and it shows agreement with the analysis result. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26181

Design and performance analysis of double-gate MOSFET over single-gate MOSFET for RF switch

In this paper, we have designed a double-gate MOSFET and compared its performance parameters with the single-gate MOSFET as RF CMOS switch, particularly the double-pole four-throw (DP4T) switch, for the wireless telecommunication systems. A double-gate radio-frequency complementary metal-oxide-semiconductor (DG RF CMOS) switch operating at the frequency of microwave range is investigated. This RF switch is capable to select the data streams from antennas for both the transmitting and receiving processes. We emphasize on the basics of the circuit elements (such as drain current, threshold voltage, resonant frequency, resistances at switch ON condition, capacitances, and switching speed) required for the integrated circuit of the radio frequency sub-system of the DG RF CMOS switch and the role of these basic circuit elements are also discussed. These properties presented in the switches due to the double-gate MOSFET and single-gate MOSFET have been discussed.