Digital Array Research Articles

Improving the Structure of a Signal Used for Real-Time Calibrating of the Receiving Channels of Digital Transceiver Modules in Digital Phased Antenna Arrays

Introduction. Modern digital phased array antenna (DPAA) systems incorporate a large number of identical transceiver modules (TMs). These modules require real-time calibration with a high level of accuracy. In a previous work, we proposed a real-time calibration method for all receiver channels, which is based on the use of a calibration signal (CalSig) of the same frequency spectrum as the reflected signal and modulated in phase and amplitude by BPSK and OOK codes, respectively. This method was found to have a number of advantages over conventional approaches. However, the use of the same CalSig sample for all receiving channels increases the noise power gain at the output of a digital beam-forming unit (DBU). To overcome this limitation, we set out to improve the structure of CalSigs by making them pseudo-orthogonal. As a result, the noise power gain at the DBU output can be significantly reduced compared to that obtained in our previous work.Aim. To propose an improved design of a controlled amplitude modulation code OOK generator, which allows creation of pseudo-orthogonal CalSigs. As a result, the noise power gain at the output will increase insignificantly, thus having no negative effect on the quality of digital beam forming, signal processing and calibration.Materials and methods. Theory of system engineering and technology; theory of digital signal processing; system analysis; mathematical modeling.Results. An improved CalSig for calibrating the receiving channels of TMs was obtained. A structural diagram allowing the formation of pseudo-orthogonal CalSigs was synthesized.Conclusions. We proposed a new approach to improving the structure of signals used for real-time calibrating the DPAA receiving channels. A structural diagram of an amplitude-modulated OOK code generator for pseudo-orthogonal CalSigs was developed.

Modeling and hardware-in-the-loop system realization of electric machine drives — A review

This paper presents a state-of-the-art review in modeling approach of hardware in the loop simulation (HILS) realization of electric machine drives using commercial real time machines. HILS implementation using digital signal processors (DSPs) and field programmable gate array (FPGA) for electric machine drives has been investigated but those methods have drawbacks such as complexity in development and verification. Among various HILS implementation approaches, more efficient development and verification for electric machine drives can be achieved through use of commercial real time machines. As well as implementation of the HILS, accurate modeling of a control target system plays an important role. Therefore, modeling trend in electric machine drives for HILS implementation is needed to be reviewed. This paper provides a background of HILS and commercially available real time machines and characteristics of each real time machine are introduced. Also, recent trends and progress of permanent magnet synchronous machines (PMSMs) modeling are presented for providing more accurate HILS implementation approaches in this paper.

Signals synthesis of artificial aperture in a digital antenna array by extrapolation of the opening function based on sequential processing of reflected radar signals

The problematic situation of increasing the detecting ability of over-the-horizon radars operating in the conditions of the formation of the background target environment is considered. The principle of synthesizing an artificial (virtual) aperture in a digital antenna array is proposed and substantiated, which makes it possible to significantly increase the resolution in angular coordinates without increasing the real geometric dimensions of the antenna system. Significant differences in the implementation of spatio-temporal processing in antenna arrays with synthesizing a virtual aperture from processing in conventional ARs are highlighted. The radiation pattern of an antenna array with synthesizing a virtual aperture is characterized by a significantly smaller width, which leads to the possibility of eliminating the influence of a significant part of the parasitic background radiation from the underlying surface. A functional diagram of a digital antenna array is presented, which makes it possible to implement the proposed principle. The main calculation ratios and the results of the modeling carried out on their basis are given.

A Wireless Electro-Optic Platform for Multimodal Electrophysiology and Optogenetics in Freely Moving Rodents.

This paper presents the design and the utilization of a wireless electro-optic platform to perform simultaneous multimodal electrophysiological recordings and optogenetic stimulation in freely moving rodents. The developed system can capture neural action potentials (AP), local field potentials (LFP) and electromyography (EMG) signals with up to 32 channels in parallel while providing four optical stimulation channels. The platform is using commercial off-the-shelf components (COTS) and a low-power digital field-programmable gate array (FPGA), to perform digital signal processing to digitally separate in real time the AP, LFP and EMG while performing signal detection and compression for mitigating wireless bandwidth and power consumption limitations. The different signal modalities collected on the 32 channels are time-multiplexed into a single data stream to decrease power consumption and optimize resource utilization. The data reduction strategy is based on signal processing and real-time data compression. Digital filtering, signal detection, and wavelet data compression are used inside the platform to separate the different electrophysiological signal modalities, namely the local field potentials (1–500 Hz), EMG (30–500 Hz), and the action potentials (300–5,000 Hz) and perform data reduction before transmitting the data. The platform achieves a measured data reduction ratio of 7.77 (for a firing rate of 50 AP/second) and weights 4.7 g with a 100-mAh battery, an on/off switch and a protective plastic enclosure. To validate the performance of the platform, we measured distinct electrophysiology signals and performed optogenetics stimulation in vivo in freely moving rondents. We recorded AP and LFP signals with the platform using a 16-microelectrode array implanted in the primary motor cortex of a Long Evans rat, both in anesthetized and freely moving conditions. EMG responses to optogenetic Channelrhodopsin-2 induced activation of motor cortex via optical fiber were also recorded in freely moving rodents.

An Investigation of NEXRAD-Based Quantitative Precipitation Estimates in Alaska

Precipitation estimation by weather radars in Alaska is challenging. In this study, we investigate National Weather Service (NWS) precipitation products that are produced from the seven NEXRAD radar sites in Alaska. The NWS precipitation processing subsystem generates stages of data at each NEXRAD site which are then input to the weather forecast office to generate a regionwide precipitation product. Data from the NEXRAD sites and the operational rain gauges in the weather forecast region are used to produce this regionwide product that is then sent to the National Centers for Environmental Prediction (NCEP) to be included in the NCEP Stage IV distribution. The NCEP Stage IV product for Alaska has been available since 2017. We use the United States Climate Reference Network (USCRN) data from Alaska to compare to the NCEP Stage IV data. Given that the USCRN can be used in the production of the NCEP Stage IV data for Alaska, we also used the NEXRAD Digital Precipitation Array (DPA) that is generated at the site for comparison of the radar-only products. Comparing the NEXRAD-based data from Alaska to the USCRN gauge estimates using the USCRN site information on air temperature, we are able to condition the analysis based on the hourly or 6-hourly average air temperature. The estimates in the frozen phase of precipitation largely underestimate as compared to the gauge, and the correlation is low with larger errors as compared to other phases of precipitation. In the mixed phase the underestimation of precipitation improves, but the correlation is still low with relatively large errors as compared to the rain phases of precipitation. The difficulties in precipitation estimation in cold temperatures are well known and we show the evaluation for the NCEP Stage IV regional data for Alaska and the NEXRAD site specific Digital Precipitation Array (DPA) data. Results show the challenges of estimating mixed-phase and frozen precipitation. However, the DPA data shows somewhat better performance in the mixed precipitation phase, which suggests that the NWS Precipitation Processing Subsystem (PPS) is tuned to the climatology as it relates to precipitation in Alaska.

Design, development and testing of digital MEMS pressure sensor array for full-scale vibroacoustic measurements

This manuscript addresses design, development, and application of micro-electro-mechanical systems (MEMS) based digital pressure sensor array for vibroacoustic measurements. These vibroacoustic measurements were conducted on a A320 type single aisle aircraft demonstrator subjected to broadband as well as tonal excitations. Cabin noise levels were measured with both condenser microphones as well as digital MEMS pressure sensor array. The measured cabin noise shows strong qualitative as well as quantitative agreement between both type of measurement devises for full scale cabin noise measurements inside an aircraft demonstrator. The observed strong agreement is valid for both single wall (fuselage with thermal insulation) and double wall (fuselage with thermal insulation and trim panel) cabin noise measurements. Such strong agreement within 1.0 dB tolerance is significantly motivating for further development of reliable but low-cost MEMS based measurement devises and corresponding efficient data post-processing algorithms for full scale vibroacoustic measurements in general. Additionally, it is also demonstrated that the large number of MEMS based digital pressure sensors can be used in areas where the physical space constraints are high. This demonstration shows strong potential to derive additional vibroacoustic indicator for the development and the testing of future noise control solutions in a non-traditional way.

Spacetime Frequency-Multiplexed Digital-RF Array Receivers With Reduced ADC Count

Wireless systems operating at mm-wave frequencies require dense antenna arrays to achieve directional gain for overcoming high path loss. Digital mm-wave arrays retain spatial degrees of freedom, but require a dedicated analog to data converter (ADC) per spatial channel, leading to undesirably high receiver complexity, large ADC count, and power consumption. This brief exploits directional sparsity to reduce the number of receivers and ADCs with minimal loss in performance. A multidimensional (MD) linear transformation using transmission lines and a K : 1 combiner is used to reduce the number of ADCs by a factor K. Simulations verify that the proposed method can lead to better than 50% ADC complexity reductions (for K ≥ 2) for linear arrays and more than 75% ADC complexity reduction (for K ≥ 4) for rectangular arrays when sparsity conditions are met. Unlike in analog-digital hybrid beamforming, where a phased-array combines K channels to a single ADC, the proposed method does not lead to loss of spatial degrees of freedom.

Проектування цифрових масивів траєкторій формоутворення – передумова моделювання контурного фрезерування

Представлена прикладна програма, яка здатна в автоматичному режимі створювати цифровий масив формоутворюючих рухів з текстового файлу управляючої програми контурного фрезерування, записаної в G-кодах. Представлений алгоритм з математичними залежностями формування цифрових масивів прямої та дуги кола. На прикладі управляючої програми, спроектованої в САМ-системі SolidCAM фрезерування контуру, утвореного двома прямими і спряженою дугою кола, була доведена адекватність функціонування програми.
 Presented an application program , which is able to automatically create a digital array of shape-forming movements from the text file of the control program of contour milling, written in G-codes. An algorithm with mathematical dependences of the formation of digital arrays of a straight line and an arc of a circle is presented. On the example of the control program designed in the SolidCAM system of milling of a contour formed by two direct and conjugate arc of a circle, adequacy of functioning of the program was proved.

A Simultaneous Wideband Calibration for Digital Beamforming Arrays at Short Distances [Measurements Corner

Massive multiple-input, multipleoutput (MIMO) is seen as an enabling technology for 5G communication systems [1]. Future base stations (BSs) featuring massive MIMO technology are expected to be equipped with a large number of antennas with digital beamforming structures, where the signals of all the channels are independently accessible. The array radiation pattern can be controlled via setting proper complex weights to the antenna elements to, e.g., form a beam in a desired direction to overcome the unfavorable propagation loss, or to form a null in an interference signal direction to suppress unwanted signals [2]. In addition, spatial multiplexing can also be utilized to serve multiple users simultaneously over the same time and frequency resource with various precoding schemes, which enlarges the network capacity.

Terahertz Ultra-Massive MIMO-Based Aeronautical Communications in Space-Air-Ground Integrated Networks

The emerging space-air-ground integrated network has attracted intensive research and necessitates reliable and efficient aeronautical communications. This paper investigates terahertz Ultra-Massive (UM)-MIMO-based aeronautical communications and proposes an effective channel estimation and tracking scheme, which can solve the performance degradation problem caused by the unique triple delay-beam-Doppler squint effects of aeronautical terahertz UM-MIMO channels. Specifically, based on the rough angle estimates acquired from navigation information, an initial aeronautical link is established, where the delay-beam squint at transceiver can be significantly mitigated by employing a Grouping True-Time Delay Unit (GTTDU) module (e.g., the designed Rotman lens -based GTTDU module). According to the proposed prior-aided iterative angle estimation algorithm, azimuth/elevation angles can be estimated, and these angles are adopted to achieve precise beam-alignment and refine GTTDU module for further eliminating delay-beam squint. Doppler shifts can be subsequently estimated using the proposed prior-aided iterative Doppler shift estimation algorithm. On this basis, path delays and channel gains can be estimated accurately, where the Doppler squint can be effectively attenuated via compensation process. For data transmission, a data-aided decision-directed based channel tracking algorithm is developed to track the beam-aligned effective channels. When the data-aided channel tracking is invalid, angles will be re-estimated at the pilot-aided channel tracking stage with an equivalent sparse digital array, where angle ambiguity can be resolved based on the previously estimated angles. The simulation results and the derived Cramer-Rao lower bounds verify the effectiveness of our solution.

Broadband linearity enhancement method for a 1.3 GHz–2.5 GHz digitally-assisted oscillator in a 55-nm CMOS technology

At the L/S band, the digital array radars with digital beam-forming characteristics require a compact RF module for a plane array. Such an RF module would require a small-sized local clock generation to synchronize with the central distributed clock signal. This paper proposes a 0.04 mm2, broadband local clock generation for the RF module in digital array radar. In such a multi-band digital array radar, the linearity of the clock generator is a bottleneck. A linearity enhanced algorithm for switched-capacitor digitally-assisted oscillators is proposed in this paper. In this linearity enhancement technique, a calibration resistor array is used to improve frequency-tuning characteristics. The digitally-assisted oscillator has a highly linearized frequency tuning curve without demanding much more power and silicon area. A prototype is fabricated using a 55-nm CMOS process. From measurement, it has a frequency tuning range from 1.3 GHz to 2.5 GHz while occupying 225 × 180 μm2. The measured coarse bank tuning maximum DNL is 0.39 LSB, and the maximum INL is 4.64 LSB, which has been reduced to 43% of the other state-of-art work. The maximum power consumption is 15.8 mW from a 1.2 V supply voltage.

Средняя диаграмма направленности и способ снижения среднего уровня боковых лепестков цифровой антенной решетки.

n the development of the existing statistical theory of antennas, new analytical relations are obtained for estimating the average radiation pattern of a digital antenna array. These ratios take into account the variance of rounding errors of the weight coefficients, errors in the amplitude and phase calibration of the antenna, jitter noise and rounding errors of the signal at the output of the analog-to-digital converter. It is shown that most of the factors affect the average level of the side lobes, as in analog antenna arrays. However, the variances of the phase calibration errors and the jitter noise determine the contribution of the new term, which has symmetry in the angular coordinate and has an extremums in the direction of the main beam of the antenna array and in the direction that is mirrored relative to the main beam. It is established that the variances of rounding errors depend on the signal-to-noise ratio and, when performing numerical studies, should be estimated based on the results of experimental studies. It is shown that digital processing in a sliding window reduces the average level of the side lobes by separating the spectral components of the signal and noise.

Factors for Sustainable Online Learning in Higher Education during the COVID-19 Pandemic

The coronavirus disease 2019 (COVID-19) pandemic has affected educational institutions and instructors in an unprecedented way. The majority of educational establishments were forced to take their courses online within a very short period of time, and both instructors and students had to learn to navigate the digital array of courses without much training. Our study examined factors that affect students’ attitude toward online teaching and learning during the COVID-19 pandemic. It is different from other online learning studies where online courses are mostly a method of choice, with suitable support from institutions and expectation from instructors and students, rather than a contingency. Under this specific environment, we utilized an online survey to collect students’ feedback from eleven universities across Hong Kong. Using partial least squares for analysis on the 400 valid samples we received, we found that peer interactions and course design have the most salient impact on students’ attitude, whereas interactions with instructors has no effect at all on students’ attitude. Furthermore, we also provide suggestions on using the existing technologies purchased during COVID-19 for a more sustainable learning environment going forward.

Model And Algorithm Super Resolution For Increase Effectively Digital Antenna Array

The focus of this research paper is to model super resolution algorithm based system for enhanced digital antenna array propagation. In most of these areas, a large effort has been made by researchers and system manufacturers to develop sensors and transmission components that enable super-resolution digital antenna array. However, resolution is inherently limited. The resolution of a digital signal transmission based system characterizes the level of spatial detail at which it captures signals and – besides the contrast resolution – it is considered as a major quality indicator. This is obvious in digital signal transmission, where the super resolution algorithm is directly related to the acquisition of fine textures in a scene. In remote sensing as another prominent example, one is interested in measuring information on a planet surface over long distances, which requires super-resolution algorithm. The focus of this research lies in computational techniques that consider the pixel pitch as the limiting property for digital antenna array. Super resolution method has the objective to reconstruct digital array at finer array sampling from one or an entire sequence of under-sampled array and have been widely investigated in signal processing. This improvement of the array sampling is due to redundancies or complementary information encoded in low-resolution arrays. As the primary goal in this area lies in an enhancement of the digital array sampling, we use the super resolution technique. The research introduces novel multi-channel super-resolution algorithms that are applicable to various digital antenna array setups. The multi-channel super resolution algorithm exploits the existence of a set of modalities in contrast to conventional methods that consider only a single one with an outstanding accuracy of 96.89% for classification of all digital antenna arrays at the clock speed of 100 MHz with the size of each processing element is 108 microns on python platform.

RF shielding materials for highly-integrated PET/MRI systems

Integration of magnetic resonance imaging (MRI) and positron emission tomography (PET) into a simultaneous device calls for adaptations of the radio frequency (RF) shielding concept. Conventional PET module housings fully encase the entire PET detector to reduce mutual interference. Excluding passive components, i.e. scintillators, from the housings, offers integration advantages, e.g. by reducing the overall housing volume or utilizing bigger scintillators. However, locating the scintillator outside of the RF shielding requires an optically transparent RF shielding interface between the scintillators and the photodetector to close the aperture. Therefore, a careful evaluation and selection of RF materials is essential to ensure an excellent PET/MRI system performance. To this end, we examined 10 materials (coated glasses, coated foils, meshes). The shielding effectiveness (SE) was evaluated at 100 and 300 MHz. PET performance was tested for single event registration and coincident events by integrating the material into the PET detector stack between the digital silicon photomultiplier photodetector array and one-to-one coupled scintillator. We determined photon attenuation (PA), energy resolution (dE/E), and coincidence resolving time (CRT) and compared to reference measurements for each material group. MRI compatibility was assessed by analyzing the material influence on the main magnetic field (B0) homogeneity. The coated glasses and foils exhibited SEs of up to 25 dB at 300 MHz. Both had a PA < 23% with dE/E and CRT comparable to the reference measurements, and no measurable impact on the B0 field was registered. The meshes exhibited higher SEs up to 56 dB, but also a PA > 58% with a higher impact on dE/E and CRT. Only one mesh affected B0 homogeneity. Overall, we recommend the coated foil HS 9400 for integration concepts as it exhibited a good performance with SE = 25 dB, PA = 22%, resulting in a PET performance of dE/E = 12% and CRT = 274 ps.

Digital Beamforming for Spaceborne Reflector-Based Synthetic Aperture Radar, Part 1: Basic imaging modes

Deployable reflector antennas illuminated by a digital feed array enable spaceborne synthetic aperture radar (SAR) systems to image an ultrawide, continuous swath at a fine azimuth resolution. This is facilitated by the use of dedicated imaging modes and by multidimensional digital beamforming (DBF) techniques. This article is part 1 of a tutorial trilogy, where a focus is put on the required onboard functionality, operational techniques, and DBF aspects, for which a rigorous mathematical description is included. To maintain general validity, the functional implementation for the various modes is detailed, thus avoiding restricting the description to a specific realization. The reader is assumed to be familiar with the general concept of SAR and, otherwise, referred to the literature on the topic. The approach followed in the trilogy is to start with a basic imaging concept and then move to more advanced modes, thus successively increasing the complexity; the mathematical description follows the same approach.

Influence of climatic factors on the amplitude-phase field distribution at the digital antenna array aperture

Problem statement. During operation, stationary large-aperture digital antenna arrays (DAA) are affected by climatic factors, including snow and ice cover. This influence inevitably leads to distortion of the amplitude-phase distribution (APD) of the field at the DAA aperture, which makes it necessary to consider and compensate for these factors on the APD of the antenna array field.Objective. Development of a more technically simple and precise method for compensating for APD field distortions at the aperture of a stationary large-aperture DAA caused by the influence of climatic factors of snow and ice cover.Results. The article analyzes the influence of climatic factors of snow and ice on the distortion of the APD field at the DAA aperture. The dependence of the power reduction of the probing signal on the thickness of the snow and ice layer at the aperture is obtained. The correction method of APD field distortions caused by climatic factors’ influence is developed, which is characterized by simplicity of technical implementation and higher accuracy of correction of distortions. A technical realization of the method of correction of distortions of the APD field is proposed.Practical implications. The developed method can be used at the stages of creation and operation of stationary large-aperture DAAs, taking into account the influence of climatic factors of snow and ice cover on the field APD.

Joint Channel and AoA Estimation in OFDM Systems: One Channel Tap With Multiple AoAs Problem

Recently, a joint channel and angle-of-arrival (AoA) estimation scheme for pilot-assisted multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with digital arrays has been proposed; in that scheme, compressive sensing-based time-domain channel estimation is applied. In the scheme, it is assumed that each channel tap has only one AoA. However, in reality, one channel tap may contain responses from multiple paths with different AoAs. In this letter, we propose an improved approach to solve the aforementioned problem. The underlying concept is to transmit multiple OFDM symbols with different beamforming vectors, rendering the time-invariant channel equivalently time-variant. Subsequently, the correlation matrix, imbedded with AoA information, can be estimated. Finally, subspace-based algorithms, such as multiple signal classification (MUSIC), can be used for AoA estimation. The advantage of the proposed method is that the number of detectable AoAs is much larger than that in conventional MUSIC. The performance of the proposed method was also theoretically analyzed. Simulation results demonstrated that with a small number of OFDM symbols, both channel gains and AoAs could be satisfactorily estimated and the theoretical analysis results were accurate.

A complete, parallel and autonomous photonic neural network in a semiconductor multimode laser

Neural networks are one of the disruptive computing concepts of our time. However, they fundamentally differ from classical, algorithmic computing. These differences result in equally fundamental, severe and relevant challenges for neural network computing using current computing substrates. Neural networks urge for parallelism across the entire processor and for a co-location of memory and arithmetic, i.e. beyond von Neumann architectures. Parallelism in particular made photonics a highly promising platform, yet until now scalable and integratable concepts are scarce. Here, we demonstrate for the first time how a fully parallel and fully implemented photonic neural network can be realized by spatially multiplexing neurons across the complex optical near-field of a semiconductor multimode laser. Discrete spatial sampling defines ∼90 nodes on the surface of a large-area vertical cavity surface emitting laser that is optically injected with the artificial neural networks input information. Importantly, all neural network connections are realized in hardware, and our processor produces results without pre- or post-processing. Input and output weights are realized via the complex transmission matrix of a multimode fiber and a digital micro-mirror array, respectively. We train the readout weights to perform 2-bit header recognition, a 2-bit XOR logical function and 2-bit digital to analog conversion, and obtain and 2.9 × 10−2 error rates for digit recognition and XOR, respectively. Finally, the digital to analog conversion can be realized with a standard deviation of only 5.4 × 10−2. Crucially, our proof-of-concept system is scalable to much larger sizes and to bandwidths in excess of 20 GHz.

Fast Beam Training With True-Time-Delay Arrays in Wideband Millimeter-Wave Systems

The best beam steering directions are estimated through beam training, which is one of the most important and challenging tasks in millimeter-wave and sub-terahertz communications. Novel array architectures and signal processing techniques are required to avoid prohibitive beam training overhead associated with large antenna arrays and narrow beams. In this work, we leverage recent developments in true-time-delay (TTD) arrays with large delay-bandwidth products to accelerate beam training using frequency-dependent probing beams. We propose and study two TTD architecture candidates, including analog and hybrid analog-digital arrays, that can facilitate beam training with only one wideband pilot. We also propose a suitable algorithm that requires a single pilot to achieve high-accuracy estimation of angle of arrival. The proposed array architectures are compared in terms of beam training requirements and performance, robustness to practical hardware impairments, and power consumption. The findings suggest that the analog and hybrid TTD arrays achieve a sub-degree beam alignment precision with 66% and 25% lower power consumption than a fully digital array, respectively. Our results yield important design trade-offs among the basic system parameters, power consumption, and accuracy of angle of arrival estimation in fast TTD beam training.