Radio Frequency Transceiver Research Articles

Quasi-Distributed Antenna Selection for Spectral Efficiency Maximization in Subarray Switching XL-MIMO Systems

In this paper, we consider the downlink (DL) of a zero-forcing (ZF) precoded extra-large scale massive MIMO (XL-MIMO) system. The base-station (BS) operates with limited number of radio-frequency (RF) transceivers due to high cost, power consumption and interconnection bandwidth associated to the fully digital implementation. The BS, which is implemented with a subarray switching architecture, selects groups of active antennas inside each subarray to transmit the DL signal. This work proposes efficient resource allocation (RA) procedures to perform joint antenna selection (AS) and power allocation (PA) to maximize the DL spectral efficiency (SE) of an XL-MIMO system operating under different loading settings. Two metaheuristic RA procedures based on the genetic algorithm (GA) are assessed and compared in terms of performance, coordination data size and computational complexity. One algorithm is based on a quasi-distributed methodology while the other is based on the conventional centralized processing. Numerical results demonstrate that the quasi-distributed GA-based procedure results in a suitable trade-off between performance, complexity and exchanged coordination data. At the same time, it outperforms the centralized procedures with appropriate system operation settings.

6G Wireless Systems: Vision, Requirements, Challenges, Insights, and Opportunities

Mobile communications have been undergoing a generational change every ten years or so. However, the time difference between the so-called “G's” is also decreasing. While fifth-generation (5G) systems are becoming a commercial reality, there is already significant interest in systems beyond 5G, which we refer to as the sixth generation (6G) of wireless systems. In contrast to the already published papers on the topic, we take a top-down approach to 6G. More precisely, we present a holistic discussion of 6G systems beginning with lifestyle and societal changes driving the need for next-generation networks. This is followed by a discussion into the technical requirements needed to enable 6G applications, based on which we dissect key challenges and possibilities for practically realizable system solutions across all layers of the Open Systems Interconnection stack (i.e., from applications to the physical layer). Since many of the 6G applications will need access to an order-of-magnitude more spectrum, utilization of frequencies between 100 GHz and 1 THz becomes of paramount importance. As such, the 6G ecosystem will feature a diverse range of frequency bands, ranging from below 6 GHz up to 1 THz. We comprehensively characterize the limitations that must be overcome to realize working systems in these bands and provide a unique perspective on the physical and higher layer challenges relating to the design of next-generation core networks, new modulation and coding methods, novel multiple-access techniques, antenna arrays, wave propagation, radio frequency transceiver design, and real-time signal processing. We rigorously discuss the fundamental changes required in the core networks of the future, such as the redesign or significant reduction of the transport architecture that serves as a major source of latency for time-sensitive applications. This is in sharp contrast to the present hierarchical network architectures that are not suitable to realize many of the anticipated 6G services. While evaluating the strengths and weaknesses of key candidate 6G technologies, we differentiate what may be practically achievable over the next decade, relative to what is possible in theory. Keeping this in mind, we present concrete research challenges for each of the discussed system aspects, providing inspiration for what follows.

Bearing estimation of low probability of intercept sources via polynomial matrices and sparse linear arrays

Recent years have seen a steady convergence of Radar and Communications band Radio Frequency (RF) transceiver systems. Not only have Communications systems colonised large swathes of previously allocated Radar bands but there is also a convergence of technologies driven by the relatively low cost of software-defined transceivers and solid-sate RF sources. Thus, where conventional radar transmissions are characterised by short narrowband pulses with high peak power, new classes of ‘pulse-compression’ radar are being developed to exploit this new technology. The resulting Low Probability of Intercept waveforms are designed to spread energy in both time and frequency, yielding a very low instantaneous power spectral density. Methods to detect, analyse and distinguish such sources require longer acquisition periods to collect more energy from the sources. Here, a novel solution is provided for detection and separation based on direction-finding utilising polynomial matrix methods in conjunction with sparse array geometries. This approach provides enhanced detection, separation and direction finding while using relatively few antenna elements.

A Fast Self-Jamming Cancellation Architecture and Algorithm for Passive RFID Sensor System

In this letter, we propose a fast self-jamming cancellation (SJC) architecture for Ultra High Frequency (UHF) radio-frequency identification (RFID) interrogators. The core SJC architecture includes a Field Programmable Gate Array (FPGA) as the RFID baseband processor, a radio frequency (RF) agile transceiver which has two transmitting ports as the RF front-end, and a combiner. By detecting the amplitude and phase of the interference carrier, the SJC algorithm transmits a suppression carrier through the second transmitting port of the agile RF transceiver. The suppression carrier could effectively suppress the self-jamming carrier without designing complex circuits. Our test results showed the isolation between the transmitting and receiving port achieves 100dB at UHF band, and the cancellation processes can be finished within 0.4ms.

Deep unfolding based hyper‐parameter optimisation for self‐interference cancellation in LTE‐A/5G‐transceivers

Deep unfolding is a very promising concept that allows to combine the advantages of traditional estimation techniques, such as adaptive filters, and machine learning approaches, like artificial neural networks. Focusing on a challenging self-interference problem occurring in frequency-division duplex radio frequency transceivers, namely modulated spurs, it is shown that deep unfolding enables remarkable performance gains. Based on the hyper-parameter optimisation of several least-mean squares (LMS) variants and the recursive-least squares algorithm, the importance of a well-chosen loss function are highlighted. Especially the variable step-size LMS and the transform-domain LMS vastly benefit without increased runtime complexity.

Spline-Based Adaptive Cancellation of Even-Order Intermodulation Distortions in LTE-A/5G RF Transceivers

Radio frequency transceivers operating in in-band full-duplex or frequency-division duplex mode experience strong transmitter leakage. Combined with receiver nonlinearities, this causes intermodulation products in the baseband, possibly with higher power than the desired receive signal. In order to restore the receiver signal-to-noise ratio in such scenarios, we propose two novel digital self-interference cancellation approaches based on spline interpolation. Both employ a Wiener structure, thereby matching the baseband model of the intermodulation effect. Unlike most state-of-the-art spline-based adaptive learning schemes, the proposed concept allows for complex-valued in- and out-put signals. The optimization of the model parameters is based on the stochastic gradient descent concept, where the convergence is supported by an appropriate step-size normalization. Additionally, we provide a gain control scheme and enable pipelining in order to facilitate a hardware implementation. An optional input transform improves the performance consistency for correlated sequences. In a realistic interference scenario, the proposed algorithms clearly outperform a state-of-the-art least mean squares variant with comparable complexity, which is specifically tailored to second-order intermodulation distortions. The high flexibility of the spline interpolation allows the spline-based Wiener models to match the performance of the kernel recursive least squares algorithm at less than 0.6% of the arithmetic operations.

Dithering Concepts for Spur-Free Nonlinear DTC-Based Frequency Synthesizers

Digital-to-time converters (DTCs) are a promising technology for radio frequency (RF) transceivers but are prone to spur generation. A common approach to change the spurious emissions to a spur-free shape is a method called dithering. The power added due to dithering is an important aspect of this approach and gives raise to investigations on additive dither as well as methods for subtractive dithering. This work presents a mathematical model for dithering DTC-based local oscillator (LO) generators. It proposes concepts for the application of subtractive dither and it introduces a novel generalization of quantization-dither to allow for optimal dithering of nonlinear quantizers.

Circuit-on-Display: A Flexible, Invisible Hybrid Electromagnetic Sensor Concept

There have been scarce interactions between microwave circuits and display technologies over the past few decades. However, the two share many similarities leaving room for integration and co-development. Hence, we present a Circuit-on-Display (CoD) concept that dually functions as a radio-frequency transceiver and a high-resolution touch screen display. The approach is realized through a flexible, invisible hybrid electromagnetic sensor (HEMS) which is situated inside a high-resolution display panel. The CoD is integrated within a real-life millimeter-wave 5G NR Android-based cellular handset prototype to demonstrate a foreside beamforming coverage and a touch operation with high-resolution and optimal image quality. The devised HEMS prototype independently features flexibility, optically invisibility (transmittance >88%), and multi-functionality (system gain of 20.72 dB, beam scanning range of ±40°, and mutual capacitance change ratio >4.42%). The devised approach provides a new class of approach to enable microwave integrated circuits for new generation wireless electronics.

Review of FET Ring mixer topologies for wireless communication

This paper presents an important component of the radio frequency transceiver called as mixer. It is a critical component and plays an important role as it has the ability for frequency conversion in RF systems. This paper focuses on double balanced ring topology of passive mixers. Ring mixer is one of the best example of passive mixers because of double balanced in nature. Double balanced is one of the most widely used topology as it suppresses both LO and RF at the output the of mixer. Various techniques have been used to improve the performance of standard topology of the ring mixer such as noise figure, linearity, conversion gain and port isolation, so these techniques have been re-viewed and compared with the previous studies. This paper also have brief discussion about a useful passive circuitry say balun and its designing with mixer as this is generally used to convert single ended signal to differential signal.

RF-Based Moisture Content Determination in Rice Using Machine Learning Techniques.

Seasonal crops require reliable storage conditions to protect the yield once harvested. For long term storage, controlling the moisture content level in grains is challenging because existing moisture measuring techniques are time-consuming and laborious as measurements are carried out manually. The measurements are carried out using a sample and moisture may be unevenly distributed inside the silo/bin. Numerous studies have been conducted to measure the moisture content in grains utilising dielectric properties. To the best of authors’ knowledge, the utilisation of low-cost wireless technology operating in the 2.4 GHz and 915 MHz ISM bands such as Wireless Sensor Network (WSN) and Radio Frequency Identification (RFID) have not been widely investigated. This study focuses on the characterisation of 2.4 GHz Radio Frequency (RF) transceivers using ZigBee Standard and 868 to 915 MHz UHF RFID transceiver for moisture content classification and prediction using Artificial Neural Network (ANN) models. The Received Signal Strength Indicator (RSSI) from the wireless transceivers is used for moisture content prediction in rice. Four samples (2 kg of rice each) were conditioned to 10%, 15%, 20%, and 25% moisture contents. The RSSI from both systems were obtained and processed. The processed data is used as input to different ANNs models such as Support Vector Machine (SVM), K-Nearest Neighbour (KNN), Random Forest, and Multi-layer Perceptron (MLP). The results show that the Random Forest method with one input feature (RSSI_WSN) provides the highest accuracy of 87% compared to the other four models. All models show more than 98% accuracy when two input features (RSSI_WSN and RSSI_TAG2) are used. Hence, Random Forest is a reliable model that can be used to predict the moisture content level in rice as it gives a high accuracy even when only one input feature is used.

Adjustable RF Transmitter Head Coil: Improving Transmit Efficiency With SAR Management for 7-T Magnetic Resonance Imaging

In ultrahigh field magnetic resonance imaging (MRI) using a static magnetic field over 7 T, the inhomogeneity in the time-varying magnetic field ( $B_{1}$ ), which is caused by its short wavelength, is mitigated by using a multichannel radio frequency (RF) coil as an antenna. However, the conventional multichannel RF coil has a fixed configuration; consequently, its transmit efficiency (TE) changes according to the head shape of the patient. In this study, a geometrically adjustable eight-channel RF transmitter head coil for 7-T MRI was proposed. All resonators and supporting structures (called bridges) in the coil have interlocking teeth at their sides, allowing each channel to adjust its geometric location according to the head shape of the patient. Scenarios for conventional and proposed coils in three different configurations were simulated and compared in terms of the transmitted component of the $B_{1}$ field ( $B_{1}^{+}$ field) and specific absorption rate (SAR) maps. The simulation results indicate that, for a given configuration and head shape, the TE of the proposed coil was higher than that of the conventional coil, while the SAR efficiency remained unchanged. Furthermore, the S-parameter matrix of the proposed coil and the measured $B_{1}$ field produced by the two channels facing each other show that the proposed coil resonates at 298 MHz with acceptable mutual coupling and effectively improves the $B_{1}$ field intensity. Moreover, the obtained signal-to-noise ratio (SNR) maps and magnetic resonance (MR) images prove that the proposed coil is an efficient candidate for an RF transmitter or transceiver head coil used in 7-T MRI.

Power efficiency enhancement analysis of an inverse class D power amplifier for NB-IoT applications

The power amplifiers (PAs) are generally the most power-consuming building blocks in Radio Frequency (RF) transceivers. This paper presents a high efficiency fully integrated inverse class D power amplifier for the narrowband Internet of Things (NB-IoT) applications. In this design, the PA's power added efficiency (PAE) is improved by inserting two auxiliary PMOS transistors into the conventional topology of class D−1 PA, and the chip area is reduced by proper selection of the RF choke. An on-chip balun is designed to combine the output power of the two transistors, while its primary equivalent inductor resonates with a capacitor at the fundamental frequency. Based on simulation results, the proposed PA achieves 16.5 dBm output power with a peak power added efficiency (PAE) of 51.3%, while operating from a 1-V supply. Moreover, the proposed PA demonstrates the power gain of 21.6 dB and drain efficiency of 57% at the frequency band of 1.85–1.91 GHz. By using 180 nm TSMC technology, the proposed PA occupies a total chip area of 1.19 mm2 (0.85 mm × 1.4 mm), including pads.

Integrated multi-band RF transceiver design for multi-standard applications using 130 ​nm CMOS technology

This paper presents high efficiency, high integration, and wideband low-IF radio frequency transceiver for multi-standard applications using 130 ​nm CMOS technology. The proposed low-IF transceiver includes receiver, transmitter, and quadrature voltage-controlled power oscillator (QVCO). The proposed receiver consists of a low-noise driver stage designed using Capacitive Cross-Coupling (CCC) common-gate configuration, and I/Q demodulator. While, the proposed transmitter composes of an I/Q modulator and an RF power amplifier, where the I/Q modulator consists of two up-conversion mixers, a five ports transformer along with switched capacitors bank for reconfigurable RF output matching. The proposed receiver has a frequency band of 0–10 ​GHz, while the operating frequency of the proposed transmitter equals 1.5–4 ​GHz. The proposed RF transceiver design is suitable for multi-band LTE, IOT, WSN, and multi-standard applications. The proposed receiver achieves a power gain of 15.4 ​dB, noise figure (NF) equals 3.8 ​dB, sensitivity equals −100.2 dBm and a dynamic range of 92.2 dBm. On the other hand, the proposed transmitter has a saturated output power of 23 dBm, power added efficiency (PAE) equals 41%, the power gain of 25 ​dB, and adjacent channel power ratio (ACPR) of equals −31.8dBc. The proposed receiver and transmitter consume 10.85 ​mW, and 180.95 ​mW, respectively, including the QVCO. The receiver and transmitter Figures of Merit (FoM) equal 191.5 ​dB and 2.45 ​dB respectively. The active areas of the proposed receiver and transmitter equal 0.56mm2 and 1.6mm2, respectively while the chip areas are1.6mm2 and 2.4mm2, respectively.

A Survey on Self-Interference Cancellation in Mobile LTE-A/5G FDD Transceivers

This brief deals with self-interference (SI) effects in mobile communication radio frequency (RF) transceivers. The basics of current communication standards, namely Long-Term Evolution (LTE) and 5G, are outlined with a focus on carrier aggregation (CA). RF transceivers that support frequency-division duplex (FDD) and CA variants operate multiple receivers and transmitters simultaneously. We illustrate the resulting SI problems, present suitable models for different SI categories and discuss the associated interference estimation tasks. Moreover, we explain the basic architecture of two common countermeasures: digital and mixed-signal SI cancellation.

A zero intermediate frequencyRFtransceiver with tunable operating frequency band

A zero intermediate frequency (zero-IF) radio frequency (RF) transceiver with tunable operating frequency band is proposed in this article, which consists of a transmitter (Tx), a receiver (Rx). Both the Tx and the Rx can achieve broadband operation. By tuning the carrier signal frequency (fc), the Tx and Rx can work in variable frequency band which is determined by fc. Therefore, a transceiver with tunable operating frequency band was realized. A prototype of the designed transceiver was designed, simulated, manufactured, and measured. In the end, a zero-IF RF transceiver with tunable frequency band during 2.3 to 3.5 GHz was implemented. The gain range of the Tx is −35 to 28 dB. The gain range of the Rx is 28 to 78 dB. For 16-QAM signal with a symbol rate of 15 MHz, the error vector magnitude of proposed Tx and Rx are less than 7.8% and 5.0%, respectively.

A CMOS implementation of controller based all digital phase locked loop (ADPLL)

PurposeBiomedical radio frequency (RF) transceivers require miniaturized forms with long battery life and low power consumption. The medical implant communication service (MICS) band in the frequency range of 402–405 MHz is widely used for medical RF transceivers because the MICS band signals have reasonable propagation characteristics and are suited to achieve good results. The implementation of the RF front-end for medical devices has many challenges as these dictate low power consumption. In particular, phase-locked loop is one of the most critical blocks of the RF front-end. The purpose of this paper is to the design of controller-based all-digital phase-locked loop (ADPLL) in a 45 nm CMOS process.Design/methodology/approachInitially, an open-loop architecture phase frequency detector (PFD) is designed. Then based on the concept of differential buffer, a differential ring oscillator (RO) is built using capacitive boosting technique. After that, the frequency controller block is built by proper mathematical modeling that does the job of loop filter, which behaves like a phase interpolator. Frequency controller block has tuning register block, tuning word register. The tuning block is built using the Metal Oxide Semiconductor (MOS) caps. Finally, the integration of all the blocks is done and the ADPLL architecture that locks at 402 MHz is achieved.FindingsThe designed PFD is dead zone free that operates at 1 GHz. The differential RO oscillates at 495 MHz. The proposed ADPLL operates at 402 MHz with measured phase noise of −98.36 at 1-MHz offset. This ADPLL exhibits rms jitter of 4.626 ps with a total power consumption of 216.5 µW.Research limitations/implicationsA time to digital converter (TDC)-less controller-based low power ADPLL covering the MICS frequency band for biomedical applications has been designed in 45 nm/0.68 V CMOS technology. The ADPLL proposed in this draft uses differential oscillator with capacitively boosted technique which reduced the operating voltage to as low as 0.68 V. This ADPLL has a bandwidth of 20 kHz and works at reference frequency of 20 MHz consumed power of 216.5 µW, while generating an output frequency of 402 MHz. The tuning range is from 375 to 428 MHz. With the phase noise of −98.36 dbc/Hz at 1 MHz, a frequency controller block replaces the usage of TDC.Social implicationsThe designed ADPLL will definitely pave way to greater research arena in the field of biomedical field. This ADPLL is a unique combination that combines electronics and biomedical field. The designed ADPLL is itself a broader application to biomedical field that will have a positive impact on the society.Originality/valueThe implementation of open-loop PFD and RO using the capacitive boosting technique is a unique combination. This is comprehended well with frequency controller block that eliminates the usage of TDC and behaves as phase interpolator. The entire design of ADPLL which suits the application of MICS band of frequency has been designed carefully to work at low power.

Sample-Efficient Spatio-Spectral Whitespace Detection Using Least Matching Pursuit

Multi-antenna wireless communication improves spectral efficiency by reusing frequencies at different locations in space using beamforming and spatial multiplexing. In the past, research has extensively focused on dynamically reusing unused frequency bands to optimize spectrum usage, but methods that identify unused resources in space appear to be unexplored. In this paper, we propose a sample-efficient whitespace detection pipeline for multi-antenna radio-frequency (RF) transceivers that detects unused resources in both frequency and space. Our spatio-spectral whitespace detection pipeline relies on multi-antenna nonuniform wavelet sampling, which identifies unused frequencies in space at sub-Nyquist sampling rates. We demonstrate the efficacy of our approach via system simulations and show that reliable spatio-spectral whitespace detection is possible with 16× lower sampling rates than methods relying on Nyquist sampling.

A Spatial-Diversity MIMO Dataset for RF Signal Processing Research

The procedure of classifying a detected signal’s modulation scheme with no a priori information is known as automatic modulation classification (AMC). AMC has presented numerous contributions toward civilian and military applications. However, in the scientific literature, designing automatic modulation classifiers has been limited to a single particular simulated environment in most cases of study. Hence, the performance of such classifiers lacks: 1) reliability in real-world environments and 2) multivariate environment analysis for AMC operation in dissimilar surroundings. These two reasons represent a significant obstacle to the real-world implementation of such classifiers. Therefore, in this research, we present our contribution to remove these obstacles by generating an emulated signal reference dataset named MIMOSigRef-SD. It includes a wide variety of signal streams modulated by different digital modulation schemes, such as M-QAM, MIL-STD-188-110 B/C standard-specific QAM, M-PSK, M-APSK, DVB-S2/S2X/SH standard-specific APSK, and M-PAM with different modulation orders, each with different multiple-input multiple-output (MIMO) system configurations in order to provide an extensive signal reference. Each signal is also exposed to the realistic impact of different channel models at 2450 MHz, specifically Vehicular-A/B, Pedestrian-A/B, and the Butler, through a channel emulator. This signal reference includes the randomly generated transmit signals, characteristics of the emulated environments, and the recorded received symbols. This enables the dataset to be highly applicable to applications beyond AMC as well. In general, this signal reference can help analyze, evaluate, and design any other radio frequency transceiver tasks under realistic environmental effects. We also validate the elements of the signal reference by comparing the emulation and simulation bit error rate of the designed communication system.

Low-Complex Digital Cancellation of Transmitter Harmonics in LTE-A/5G Transceivers

Nowadays, mobile communication radio frequency transceivers for LTE-A/5G usually operate in frequency-division duplex mode and support carrier aggregation. The resulting complexity requires compromises in the analog front-end. One consequence is a limited stop-band attenuation of the duplex filters that separate the transmit and the receive paths. The resulting transmit leakage signal combined with other non-idealities, like power amplifier (PA) harmonics, can create self-interference problems that desensitize the receivers. In this work, we propose an optimized digital self-interference cancellation scheme to mitigate the unacceptable performance degradation caused by PA induced harmonics. We derive an appropriate interference model and quantify the interference power levels for a specific PA. Based on these results, our low-complex cancellation approach solely targets the dominating components. Our algorithm relies on the auto-covariance matrix for the second and third power of LTE signals, which we derive for the first time in an analytic form. This statistical information can be combined with the transform-domain concept to noticeably improve the performance of a least-mean squares based cancellation algorithm. The capabilities of the approach are demonstrated by means of simulations and are validated on measurement data.

Continuous-Phase Modulation for DFT-Spread Localized OFDM

Massive machine-type communications to support a large number of low-cost, low-power, and/or low-rate radio-frequency transceivers such as Internet-of-Things (IoT) devices is a major usage scenario of the 5G mobile communication system. To save cost and power, highly nonlinear power amplifiers (PAs) are expected to be used in the devices. However, the envelope fluctuation of the input of a PA may make the output suffer from severe nonlinear distortion. In this paper, a continuous-phase modulation is proposed for discrete-Fourier transform (DFT)-spread localized orthogonal frequency-division multiplexing (OFDM) of π/2-BPSK symbols. In particular, the combination of a spectrum shaping vector and an extra rotation angle is proposed, which enables the use of a receiver that is fully compatible with the current standard. It is shown that the proposed design significantly outperforms the conventional designs in terms of effective signal-to-distortion ratio and error vector magnitude at the cost of a negligible increase in out-of-band emission.