Digital Receiver Research Articles

The NASA GSFC 94-GHz Airborne Solid-State Cloud Radar System (CRS)

AbstractThe NASA Goddard Space Flight Center’s (GSFC’s) W-band (94 GHz) Cloud Radar System (CRS) has been comprehensively updated to modern solid-state and digital technology. This W-band (94 GHz) radar flies in nadir-pointing mode on the NASA ER-2 high-altitude aircraft, providing polarimetric reflectivity and Doppler measurements of clouds and precipitation. This paper describes the design and signal processing of the upgraded CRS. It includes details on the hardware upgrades [solid-state power amplifier (SSPA) transmitter, antenna, and digital receiver] including a new reflectarray antenna and solid-state transmitter. It also includes algorithms, including internal loop-back calibration, external calibration using a direct relationship between volume reflectivity and the range-integrated backscatter of the ocean, and a modified staggered–pulse repetition frequency (PRF) Doppler algorithm that is highly resistant to unfolding errors. Data samples obtained by upgraded CRS through recent NASA airborne science missions are provided.

An agile very low frequency radio spectrum explorer

The very low frequency (VLF) regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources, transients, and so on. However, the nontransparency of the Earth’s ionosphere, ionospheric distortion and artificial radio frequency interference (RFI) have made it difficult to detect the VLF celestial radio emission with ground-based instruments. A straightforward solution to overcome these problems is a space-based VLF radio telescope, just like the VLF radio instruments onboard the Chang’E-4 spacecraft. But building such a space telescope would be inevitably costly and technically challenging. The alternative approach would be then a ground-based VLF radio telescope. Particularly, in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a ‘calm’ state, it will provide us a good chance to perform VLF ground-based radio observations. Anticipating such an opportunity, we built an agile VLF radio spectrum explorer co-located with the currently operationalMingantu Spectra Radio Heliograph (MUSER). The instrument includes four antennas operating in the VLF frequency range 1–70 MHz. Along with them, we employ an eight-channel analog and digital receivers to amplify, digitize and process the radio signals received by the antennas. We present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions.

Enhanced Noise Tolerance Levels for Digital Receiver using Non-Linear Frequency Modulation

One of the critical issues concerning the industries of aerospace and Defence is the accuracy and precision levels of the possible range resolution. And equally important is the detection of the signal in the presence of noisy environments. Signal-to-Noise ratio is one such measure that ensures enhancement of target detection in tough environments. Besides this, high range resolution is also essential for the digital receiver to identify closely spaced multiple targets. The projected digital receiver design primarily highlights the possibility of pulse compression techniques combined with linear frequency modulation and non-linear frequency modulation waveforms for refining the range resolution of targets compared to their counterpsrts, the traditional waveforms. The range resolution and detection enhancement using the advanced signal processing techniques in the presence of noisy environments have been presented with evidence from the simulations accomplished in MATLAB. The ability of the pulse compression waveform to perform in the presence of noise has been tested. Further, this paper presents the minimum signal to noise ratio of the received echo signal for achieving the required range resolution with MATLAB simulations. The paper also includes further plan of work to make this design more robust as an adaptable receiver for industrial applications.

Array Manifold Measurement and Verification for UCA Calibration in Multistatic PCL System based on FM Broadcasting

This study describes a method of measurement and verification of array manifold of uniform circular array antenna applicable to multistatic Passive Coherent Location(PCL) system using FM broadcasting. In an environment of outdoor test where FM broadcast signals are scattered, array manifold measurement methods using network analyzer and multi-channel digital receiver are introduced. Also, the descriptions and solutions for the test limits of each measurement method and the considerations affecting the measurement accuracy are presented. In addition, to verify the validity of the measured array manifold, the gain and phase difference were compared with the array manifold data obtained by EM simulation, and the effectiveness and accuracy of the measured array manifolds were compared and analyzed by estimating the direction of arrival of the FM broadcast signal received from the multistatic PCL system. Keywords: Multistatic PCL, Uniform Circular Array, Array Manifold, DOA Estimation Keywords: 멀티스태틱 PCL, 원형 배열 ì•ˆí Œë‚˜, ì–´ë ˆì´ 매니폴드, 도래각 ì¶”ì •

Review of the radiographic modalities used during dental implant therapy - A narrative

The introduction of digital x-ray receivers which replaced conventional films was a significant radiographic development that is commonly used in daily dental practice. Dental implant therapy (DIT) is a sought after dental therapeutic intervention and dental radiography is an essential component contributing to the success of treatment. Dental radiographs taken in daily practice are generally conventional two-dimensional images and/or three-dimensional images. Ideally, the choice of radiographic technique should be determined after a thorough clinical examination and comprehensive consideration of the advantages, indications, and drawbacks. Digital three-dimensional modalities that have emerged over the last decade have been incorporated into DIT with the assumption that treatment outcomes will be improved. These modalities are constantly being reassessed and improved but there is a paucity of published information regarding the assessment of variables such as dosages and dimensional accuracy, suggesting that further research in these matters is necessary. This is crucial in order to obtain evidence-based information that may influence future radiographic practices. In this narrative, the authors present the most commonly used dental radiographic modalities currently used in DIT.

Mingantu Spectral Radioheliograph for Solar and Space Weather Studies

The Chinese Spectral Radioheliograph (CSRH) covering 400 MHz-15 GHz frequency range was constructed during 2009–2016 in Mingantu Observing Station, National Astronomical Observatories, Chinese Academy of Sciences at Zhengxiangbaiqi, Inner Mongolia of China. The CSRH is renamed as MingantU SpEctral Radioheliograph (MUSER) after its accomplishment. Currently, MUSER consists of two arrays spreading over three spiral-shaped arms. The maximum baseline length is ∼3 km in both east-west and north-south directions. The MUSER array configuration is optimized to meet the needs of observing the full-disk Sun over ultrawide wavebands with images of high temporal, spatial and spectral resolutions and high dynamic range. The low frequency array, called MUSER-I, covers 400 MHz-2.0 GHz with 40 antennas of 4.5-m-diameter each and the high frequency array, called MUSER-II, covers 2–15 GHz with 60 antennas of 2-m-diameter each. The MUSER-I can obtain full-disk solar radio images in 64 frequency channels with a time cadence of 25 ms and a spatial resolution of 51.6″ to 10.3″ (corresponding to the frequency range 400 MHz to 2 GHz), whereas the MUSER-II can obtain full-disk solar images in 520 channels with a time cadence of 206.25 ms and a spatial resolution of 10.3″ to 1.3 (corresponding to the frequency range 2 to 15 GHz). A dynamic range of 25 dB can be obtained with snapshot images produced with the MUSER. An extension of MUSER in the further lower frequency range covering 30–400 MHz with an array of 224 logarithm-periodic dipole antennas (LPDAs) has been approved and will be completed during the next 4 years. The MUSER, as a dedicated solar instrument, has the following advantages providing simultaneous images over a wide frequency range with a unique high temporal-spatial-spectral resolutions; high-performing ultrawide-band dual-polarization feeds for wide-band signal collection; advanced high data-rate, large-scale digital correlation receiver for multiple-frequency and faster snapshot observations; and applications of new technologies such as using optical fiber to obtain remote antenna and wide-band analog signal transmission. The MUSER thus provides a unique opportunity to measure solar magnetic fields and trace dynamic evolution of energetic electrons in several radio frequencies, which, in turn, will help to have better understandings of the origin of various solar activities and the basic drivers of space weather.

Bunch-by-bunch three-dimensional position and charge measurement in a storage ring

Bunch-by-bunch beam parameters monitor is a very useful tool for accelerator operation and optimization. An in situ bunch-by-bunch three-dimensional position and charge measurement system has been developed at the Shanghai Synchrotron Radiation Facility. Signals from beam position monitors carry almost full beam information, a broadband digital receiver can retain most information. Therefore, a four-channel wideband oscilloscope is employed to capture the signals from all electrodes of the beam position monitor. Correlation coefficient-based methods are used to extract these bunch-by-bunch parameters synchronously. We evaluated the performance of this bunch-by-bunch information extraction method, the measurement uncertainty of longitudinal phase is less than 0.2 ps, the uncertainty of transverse position is less than $10\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ and the charge uncertainty is 0.3% under the condition that the bunch charge is 600 pC. Thanks to the great performance of the new system, it is accurate enough to study the transient state during injection. In addition, an in situ wakefield measurement system is planned to be established based on this system.

A wideband mono-bit digital receiver circuit using InP/CMOS 3D heterogeneous integration

A mono-bit digital receiver circuit for instantaneous frequency measurement is presented. The circuit is co-designed with Indium Phosphide Double Heterojunction Bipolar Transistor and complementary metal oxide semiconductor (CMOS) devices. The chip is fabricated by InP/CMOS three-dimensional (3D) heterogeneous integration using the wafer-level bonding technique. The measurable signal frequency within + 15 to − 25 dBm power is up to 7.5 GHz with a 14-GHz clock. Compared to an integrated circuit (IC) with a traditional InP or CMOS technologies, the proposed chip could benefit from both InP and CMOS technology. In the heterogeneous integration, InP devices provide high operating frequency, broad signal bandwidth, and large input signal dynamic range, while CMOS devices achieve complex function with low power consumption. In this way, the system FoM is improved for a mono-bit digital receiver while the system power consumption is kept the same. This work also shows the great potential of the 3D heterogeneous integration for the high-performance mixed-signal and multifunction radio-frequency ICs.

Study of the truncation strategy in the FPGA of a solar radio digital receiver

Abstract Computation resource is the limiting factor in higher operational accuracy of field-programmable gate arrays (FPGAs) in solar radio digital receivers. The data truncation strategy which determines the accuracy of data is then the essential technology in the design of a receiving system. Based on the solar radio spectrometer (dual channel, 14 bit, 1.25 gigasamples per second) at the Chashan Solar Radio Observatory (CSO), this paper presents a data truncation strategy which can realize real-time solar radio observation (35–40 GHz) with high time and frequency resolution as well as a large dynamic range, and at the same time saves the computation resource to a large extent. Simulations of truncations during signal processing are carried out in MATLAB, and the best truncation mechanisms are deduced for windowing and fast Fourier transform (FFT). Using the simulation results, the best truncation strategies have been implemented in the solar radio receiver at CSO with the result that the best truncation bits for the windowing operation are [27 : 14], with an error of 2.5 × 10−4, and the best truncation bits for the FFT output are [20 : 5] with an error of 1.5 × 10−3. Compared with the processing of full-precision data, occupation of the computation resources in the FPGA can be reduced significantly. For instance, the lookup table, lookup table RAM, flip flop, and digital signal processing slices are reduced by 7.36%, 14.65%, 8.38%, and 24.94%, respectively, which guarantees broad-band real-time solar radio observations (35–40 GHz).

ADC-DSP-Based 10-to-112-Gb/s Multi-Standard Receiver in 7-nm FinFET

This article describes a 4 × 112 Gb/s digital receiver targeting long-reach (LR) channels. An SNR optimized approach is presented, which relaxes the ADC resolution requirement and the number of FFE taps without sacrificing BER. The discrete-time front end overcomes gain-BW limitations to provide 10+ dB gain at 28 GHz. A 56-GS/s ADC then converts the signal to 6-b digital consuming only 195 mW. The following DFE-FFE-based digital equalizer is capable of compensating 36-dB loss achieving a BER of 2e-5. Furthermore, TDC and ISI filter-based low-latency timing recovery meet jitter tolerance specs over a wide range of data rates from 10 to 112 Gb/s, including 28-Gb/s NRZ. The overall receiver consumes 338 mW with 3.18-pJ/bit energy efficiency.

No-instruction-set-computer design experience of flexible and efficient architectures for digital communication applications: two case studies on MIMO turbo detection and universal turbo demapping

The emerging flexibility need in designing application-specific processors dedicated for modules of digital receiver imposes a new design metric, which is added to the requirements of efficiency and productivity. In order to cope with the emerging flexibility requirement combined with the best performance efficiency, many application-specific processor design approaches have been proposed and investigated. In general, available design approaches that adopt dynamic scheduling of instructions add an overhead due to the instruction decoding. To minimize this overhead, several approaches have been introduced, which opt static scheduling. In this context, No-Instruction-Set-Computer (NISC) concept has been introduced to design application-specific processors without an instruction set. NISC concept proposes that there is no need to first design and then use an instruction set when the hardware is programmed by its designers rather than its users. NISC designing approach offers a good compromise between flexibility, productivity, and quality for the design of a digital system. In our work, NISC approach is explored through the design of flexible and efficient architectures dedicated for digital communication applications which fulfill the requirements imposed by multiple emergent communication standards. This paper introduces briefly the NISC concept and the corresponding design methodology. Also, it provides an overview of the related design approach. In addition, the relevance of NISC in realizing flexible and efficient implementation in the domain of digital communication is demonstrated through two case studies on MIMO turbo detection and universal turbo demapping. Both designed NISC-based architectures have been compared to state-of-the-art ASIP-based architectures using similar computational resources and supporting same flexibility parameters. The obtained results show that the proposed NISC-based architectures provide a significant improvement in execution performance while having reduced implementation costs. The results also illustrates how the control memory requirements depend on the application and the devised architecture choices. In the detector module, the adopted re-usability of allocated resources imposes separate controlling of each component; hence, additional control signals are implied. Whereas for the demapper module, implemented hardware components are considered to perform specific operations and to deal with the same type of data; hence, the number of control signals can be reduced significantly.

Low-Power Wireless Data Transfer System for Stimulation in an Intracortical Visual Prosthesis.

There is a growing interest to improve the quality of life of blind people. An implanted intracortical prosthesis could be the last resort in many cases of visual impairment. Technology at this moment is at a stage that implementation is at sight. Making the data communication to and from the implanted electrodes wireless is beneficial to avoid infection and to ease mobility. Here, we focus on the stimulation side, or downlink, for which we propose a low-power non-coherent digital demodulator on the implanted receiver. The experimentally demonstrated downlink is on a scaled-down version at a 1 MHz carrier frequency showing a data rate of 125 kbps. This provides proof of principle for the system with a 12 MHz carrier frequency and a data rate of 4 Mbps, which consumes under 1 mW at the receiver side in integrated circuit (IC) simulation. Due to its digital architecture, the system is easily adjustable to an ISM frequency band with its power consumption scaling linearly with the carrier frequency. The tested system uses off-the-shelf coils, which gave sufficient bandwidth, while staying within safe SAR limits. The digital receiver achieved a reduction in power consumption by skipping clock cycles of redundant bits. The system shows a promising pathway to a low-power wireless-enabled visual prosthesis.

Evaluation of Adaptive Loop-Bandwidth Tracking Techniques in GNSS Receivers.

Global navigation satellite system (GNSS) receivers use tracking loops to lock onto GNSS signals. Fixed loop settings limit the tracking performance against noise, receiver dynamics, and the current scenario. Adaptive tracking loops adjust these settings to achieve optimal performance for a given scenario. This paper evaluates the performance and complexity of state-of-the-art adaptive scalar tracking techniques used in modern digital GNSS receivers. Ideally, a tracking channel should be adjusted to both noisy and dynamic environments for optimal performance, defined by tracking precision and loop robustness. The difference between the average tracking jitter of the discriminator’s output and the square-root Cramér-Rao bound (CRB) indicates the loops’ tracking capability. The ability to maintain lock characterizes the robustness in highly dynamic scenarios. From a system perspective, the average lock indicator is chosen as a metric to measure the performance in terms of precision, whereas the average number of visible satellites being tracked indicates the system’s robustness against dynamics. The average of these metrics’ product at different noise levels leads to a reliable system performance metric. Adaptive tracking techniques, such as the fast adaptive bandwidth (FAB), the fuzzy logic (FL), and the loop-bandwidth control algorithm (LBCA), facilitate a trade-off for optimal performance. These adaptive tracking techniques are implemented in an open software interface GNSS hardware receiver. All three methods steer a third-order adaptive phase locked loop (PLL) and are tested in simulated scenarios emulating static and high-dynamic vehicular conditions. The measured tracking performance, system performance, and time complexity of each algorithm present a detailed analysis of the adaptive techniques. The results show that the LBCA with a piece-wise linear approximation is above the other adaptive loop-bandwidth tracking techniques while preserving the best performance and lowest time complexity. This technique achieves superior static and dynamic system performance being 1.5 times more complex than the traditional tracking loop.

Performance optimization of OADM based DP-QPSK DWDM optical network with 37.5 GHz channel spacing

Advanced modulation formats like dual-polarization quadrature phase-shift keying (DP-QPSK) along with the digital coherent receiver are enabling optical networks to provide high spectral efficiency (SE) over long-haul transmission reach. The DP-QPSK based dense wavelength division multiplexing (DWDM) system with 37.5 GHz channel spacing can provide extra throughput of 33% compared to 50 GHz channel spacing. However, at 37.5 GHz channel spacing, optical add-drop multiplexers (OADMs) at intermediate nodes, impact the performance of WDM based optical networks in terms of increased BER, thereby reducing transmission reach drastically. In this paper, we have analyzed with the help of numerical simulations, the performance of a differentially encoded eight-channel 112 Gb/s, OADM based DWDM optical network with a channel spacing of 37.5 GHz. We propose that the selection of optimum values of system parameters can result in reducing the impact of crosstalk propagation and narrowband optical filtering introduced by a chain of OADMs at 37.5 GHz channel spacing. The paper exhibited that the selection of optimum values of parameters like filter order of multiplexer and demultiplexer, launch power per channel and filter taps of adaptive equalizer (AE) result in achieving minimum BER on all the channels over a long transmission reach up to 3600 km.

Clock conversion for burst-mode digital coherent QPSK receivers in a PON upstream transmission with a 100-ppm clock mismatch.

This paper presents a clock conversion scheme for burst-mode digital coherent QPSK receivers in an asynchronous PON upstream and confirms its validity. The scheme converts the number of samplings of transmitted signal based on the clock at Rx. We demonstrate the proposed scheme in a realistic environment that emulates a fixed clock difference by two independent synthesizers at Tx and Rx mixed together with clock jitter induced by 20-km fiber transmission. In the real-time demonstration, a digital coherent receiver employing the proposed clock conversion successfully receives 330-µs burst QPSK frames over 20-km transmission in the presence of a 100-ppm clock mismatch.

Joint Fiber Nonlinear Noise Estimation, OSNR Estimation and Modulation Format Identification Based on Asynchronous Complex Histograms and Deep Learning for Digital Coherent Receivers.

In this paper, asynchronous complex histogram (ACH)-based multi-task artificial neural networks (MT-ANNs), are proposed to realize modulation format identification (MFI), optical signal-to-noise ratio (OSNR) estimation and fiber nonlinear (NL) noise power estimation simultaneously for coherent optical communication. Optical performance monitoring (OPM) is demonstrated with polarization mode multiplexing (PDM), 16 quadrature amplitude modulation (QAM), PDM-32QAM, as well as PDM-star 16QAM (S-16QAM) for the first time. The range of launched power is −3 to −2 dBm with a fiber link of 160–1600 km. Then, the accuracy of MFI reaches 100%. The average root mean square error (RMSE) of OSNR estimation can reach 0.37 dB. The average RMSE of NL noise power estimation can reach 0.25 dB. The results show that the monitoring scheme is robust to the increase of fiber length, and the solution can monitor more optical network parameters with better performance and fewer training data, simultaneously. The proposed ACH MT-ANN has certain reference significance for the future long-haul coherent OPM system.

Detection performance characteristics of the digital undersampling receiver

Multichannel digital receivers based on the signal processing technology involving undersampling are used for the instantaneous wideband analysis of the electronic environment. One of the most common algorithms for measuring input signal’s carrier frequency in such receivers includes unfolding of the signal’s spectrums from the first Nyquist zone of all receiver’s channels to the single frequency axis and searching for the frequency where the spectrum components from all of the receiver’s channels coincided. Performance of the signal detector, which uses this algorithm in its operation, was not studied. In the absence of a mathematical description of such a detector, evaluating the digital undersampling receiver’s sensitivity becomes possible only in the late stages of prototyping when it can be done through experimental study. Additionally, it is impossible to set a detection threshold in the receiver according to the Neyman-Pearson criterion, which hardens building constant false alarm rate (CFAR) systems based on this type's receivers. This paper aims to develop the mathematical description of the digital undersampling receiver's detector and then, using this model, to get expressions and computer models to evaluate the characteristics of such receiver even in early stages of its development. This paper's main result is the developed mathematical tools necessary to evaluate the multichannel digital undersampling receiver’s signal detector performance. It is shown that the false alarm probability in such a detector does not exceed some value no matter how small the detection threshold is. The expression for evaluating the maximum false alarm probability by the receiver’s parameters is also presented in the paper alongside the true positive rate plots as a function of signal-to-noise ratio for the three-channel receiver. These results can be used in evaluating the digital undersampling receiver’s characteristics in the early stages of its development. It allows one to choose optimal values of the receiver’s parameters which are hard and expensive to change after prototyping is done, and there is an opportunity to evaluate the receiver’s characteristics experimentally. Moreover, the obtained mathematical expressions make it possible to set the receiver's detection threshold according to the Neyman-Pearson criterion and build on its base a CFAR-systems widely used for wideband signal analysis.

Design and Implementation of a Digital Front-End With Digital Compensation for Low-Complexity 4G Radio Transceivers

A digital front-end with digital compensation is designed and implemented for low-complexity 4G radio transceivers targeted for wearable devices such as smart watches. The proposed digital front-end in the radio receiver consists of an anti-drooping filter, a decimation chain, a DC offset cancellation circuit, and an in-phase and quadrature estimation and compensation circuit whereas the digital front-end in the radio transmitter includes an anti-drooping filter, a root raised cosine filter, and an interpolation chain. The proposed DC offset cancellation circuit is based on both infinite-duration impulse response filter and moving average. The proposed in-phase and quadrature estimation and compensation circuit attains lower complexity with negligible performance loss, compared with an existing circuit. A systematic top-down strategy is taken to design and implement the proposed digital front-end from the algorithm level to the application-specific integrated circuit or ASIC hardware level. The inter-symbol interference in the transmitter and the receiver is analyzed and the unwanted emission in the transmitter is simulated as well. For all the seven bandwidths or modes in 3G and 4G, the digital front end receiver ASIC satisfies all the interference requirements, namely, in-band blocker, narrowband blocker, and adjacent channel selectivity requirements whereas the digital front end transmitter ASIC meets all the unwanted emission requirements, namely, spectrum emission mask, spurious emission, and adjacent channel leakage ratio requirements. The proposed multimode 4G digital front end receiver and transmitter ASICs exhibit a >40dB mean signal-to-noise ratio for all the seven modes and are implemented in a 180nm CMOS process technology.

Расширение динамического диапазона устройства выборки и хранения весовым интегрированием узкополосного колебания

The most bottleneck of high-frequency digital radio receivers in terms of dynamic characteristics is the process of analog-to-digital conversion. Most often, to meet the requirements for the speed and dynamic range of the analog-to-digital conversion, a sampling and storage device (UHF) is included in front of the analog-to-digital converter (ADC), which is significantly simpler in structure than the ADC structure, but reduces the requirements for its speed and dynamic range [1, 2]. A method for expanding the dynamic range of the integrating sampling and storage device for digital radio receivers using the weight integration of the input narrow-band oscillation is proposed

Experimental study of the accuracy of determining the time-frequency parameters of a pulse in a digital receiver with undersampling under a single-signal impact

Experimental study of the accuracy of determining the time-frequency parameters of a pulse in a digital receiver with undersampling under a single-signal impact