Choice and properties of adaptive and tunable digital boxcar (moving average) filters for power systems and other signal processing applications

The humble boxcar (or moving average) filter has many uses, perhaps the most well-known being the Dirichlet kernel inside a short-time discrete Fourier transform. A particularly useful feature of the boxcar filter is the ease of placement of (and tuning of) regular filter zeros, simply by defining (and varying) the time length of the boxcar window. This is of particular use within power system measurements to eliminate harmonics, inter-harmonics and image components from Fourier, Park and Clarke transforms, and other measurements related to power flow, power quality, protection, and converter control. However, implementation of the filter in real-time requires care, to minimise the execution time, provide the best frequency-domain response, know (exactly) the group delay, and avoid cumulative numerical precision errors over long periods. This paper reviews the basic properties of the boxcar filter, and explores different digital implementations, which have subtle differences in performance and computational intensity. It is shown that generally, an algorithm using trapezoidal integration and interpolation has the most desirable characteristics

Dealing with front-end white noise on differentiated measurements such as frequency and ROCOF in power systems

This paper describes the way that white noise (including quantised input section sampling) imparts errors onto frequency and rate-of-change-of-frequency (ROCOF) measurements. The main paper focus concerns the use of filtered heterodyned (i.e. Fourier) analyses for single-phase and 3-phase systems, and the filtered Clarke transform for 3-phase systems. The rules and equations governing the effect of white noise on frequency and ROCOF are formulated for these techniques, explaining the subtle effects of aliasing, splitting signals and noise into their positive and negative frequency components, and the correlation or de-correlation of noise. It is shown that - as expected - for 3-phase AC measurements, averaging 3 single-phase Fourier measurements produces the same performance against noise as using a method based on Clarke’s transform, if identical filtering is used. Furthermore, by understanding the theory behind the frequency and ROCOF measurement processes, it is shown that to achieve the lowest RMS errors, in the presence of front-end white noise (alone, ignoring other dynamic signal and power quality aspects), a filter which provides ~40 dB/decade attenuation (i.e. a 2-boxcar cascade) is recommended for a frequency measurement, but a filter which rolls off at ~60 dB/decade (i.e. a 3-boxcar cascade) is recommended for a ROCOF measurement

Image Restoration Methods for Retinal Images: Denoising and Interpolation

Retinal imaging provides an opportunity to detect pathological and natural age-related physiological changes in the interior of the eye. Diagnosis of retinal abnormality requires an image that is sharp, clear and free of noise and artifacts. However, to prevent tissue damage, retinal imaging instruments use low illumination radiation, hence, the signal-to-noise ratio (SNR) is reduced which means the total noise power is increased. Furthermore, noise is inherent in some imaging techniques. For example, in Optical Coherence Tomography (OCT) speckle noise is produced due to the coherence between the unwanted backscattered light. Improving OCT image quality by reducing speckle noise increases the accuracy of analyses and hence the diagnostic sensitivity. However, the challenge is to preserve image features while reducing speckle noise. There is a clear trade-off between image feature preservation and speckle noise reduction in OCT. Averaging multiple OCT images taken from a unique position provides a high SNR image, but it drastically increases the scanning time. In this thesis, we develop a multi-frame image denoising method for Spectral Domain OCT (SD-OCT) images extracted from a very close locations of a SD-OCT volume. The proposed denoising method was tested using two dictionaries: nonlinear (NL) and KSVD-based adaptive dictionary. The NL dictionary was constructed by adding phases, polynomial, exponential and boxcar functions to the conventional Discrete Cosine Transform (DCT) dictionary. The proposed denoising method denoises nearby frames of SD-OCT volume using a sparse representation method and combines them by selecting median intensity pixels from the denoised nearby frames. The result showed that both dictionaries reduced the speckle noise from the OCT images; however, the adaptive dictionary showed slightly better results at the cost of a higher computational complexity. The NL dictionary was also used for fundus and OCT image reconstruction. The performance of the NL dictionary was always better than that of other analytical-based dictionaries, such as DCT and Haar. The adaptive dictionary involves a lengthy dictionary learning process, and therefore cannot be used in real situations. We dealt this problem by utilizing a low-rank approximation. In this approach SD-OCT frames were divided into a group of noisy matrices that consist of non-local similar patches. A noise-free patch matrix was obtained from a noisy patch matrix utilizing a low-rank approximation. The noise-free patches from nearby frames were averaged to enhance the denoising. The denoised image obtained from the proposed approach was better than those obtained by several state-of-the-art methods. The proposed approach was extended to jointly denoise and interpolate SD-OCT image. The results show that joint denoising and interpolation method outperforms several existing state-of-the-art denoising methods plus bicubic interpolation.4 month

Object detection and recognition with event driven cameras

This thesis presents study, analysis and implementation of algorithms to perform object detection and recognition using an event-based cam era. This sensor represents a novel paradigm which opens a wide range of possibilities for future developments of computer vision. In partic ular it allows to produce a fast, compressed, illumination invariant output, which can be exploited for robotic tasks, where fast dynamics and signi\ufb01cant illumination changes are frequent. The experiments are carried out on the neuromorphic version of the iCub humanoid platform. The robot is equipped with a novel dual camera setup mounted directly in the robot\u2019s eyes, used to generate data with a moving camera. The motion causes the presence of background clut ter in the event stream. In such scenario the detection problem has been addressed with an at tention mechanism, speci\ufb01cally designed to respond to the presence of objects, while discarding clutter. The proposed implementation takes advantage of the nature of the data to simplify the original proto object saliency model which inspired this work. Successively, the recognition task was \ufb01rst tackled with a feasibility study to demonstrate that the event stream carries su\ufb03cient informa tion to classify objects and then with the implementation of a spiking neural network. The feasibility study provides the proof-of-concept that events are informative enough in the context of object classi\ufb01 cation, whereas the spiking implementation improves the results by employing an architecture speci\ufb01cally designed to process event data. The spiking network was trained with a three-factor local learning rule which overcomes weight transport, update locking and non-locality problem. The presented results prove that both detection and classi\ufb01cation can be carried-out in the target application using the event data

LASER Tech Briefs, September 1993

This edition of LASER Tech briefs contains a feature on photonics. The other topics include: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Computer Programs, Mechanics, Machinery, Fabrication Technology, Mathematics and Information Sciences, Life Sciences and books and reports

Dual-comb spectroscopy of fundamental vibrational transitions

Spectroscopy of fundamental vibrational transitions offers a label-free alternative for high-chemical contrast measurements. These transitions can be interrogated either directly by using mid-infrared light or indirectly through Raman scattering. This thesis aims to advance dual-comb spectroscopy to improve the acquisition speed, resolution and spectral coverage of vibrational spectroscopy. Dual-comb spectroscopy is a time domain technique, which combines optical frequency combs -coherent light sources with a spectrum constituted of discrete evenly spaced lines - and Fourier transform spectroscopy. For linear spectroscopy, a mid-infrared optical parametric oscillator was developed and characterized. Its idler-pulse duration can be as short as a few cycles (~3 to 6 cycles), with a central wavelength tunable from 2180nm to 3732nm (2679cm-1 - 4587cm-1), allowing more than 2500nm (2861 cm-1) of total coverage while maintaining an average power of tens of milliwatts. The high peak power of this system was exploited for spectral broadening; generation of phase-coherent supercontinua was achieved in waveguides, made from either silicon or chalcogenide glass, producing octave spanning spectra ~1500nm to 3300nm (3030cm-1 - 6666cm-1) for silicon and from ~1600nm beyond 3860nm (2590 cm-1 - 6250 cm-1) for chalcogenide glass). Two optical parametric oscillator were constructed, advancing toward a dual-comb mid-infrared spectrometer. Since the optical parametric oscillators are not stabilized, an additional correction scheme was set up and characterized. Coherent Raman scattering was also investigated, as a means to access optically active and inactive fundamental vibrational transitions. Several spectroscopy setups were developed to measure the Raman blue or red shifted light in forward and backward scattered direction as well as a differential detection between blue and red shifted light. There is a dead time between consecutive interferograms existent, up to a factor of 1000 larger than the measurement time. This dead time could be reduced by an order of magnitude using a laser with ~1GHz and a laser with 100MHz repetition rate instead of two lasers with ~100MHz repetition rate. All implementations achieved excellent acquisition times (in the microsecond range), signal-to-noise ratios up to 1000 and spectral coverage of about ~1200 cm-1). These advantages enabled measuring spectrally resolved images, in a first rudimentary microscopy-setup.Spektroskopie fundamentaler Schwingungsübergänge erlaubt einen markierungsfreien Zugang zu Messungen mit hohem chemischen Kontrast. Diese Übergänge sind entweder direkt über lineare mittlere Infrarot Spektroskopie oder indirekt durch Raman Streuung zugänglich. Der dieser Arbeit zugrundeliegende Gedanke war Zwei- Kamm-Spektroskopie weiter zu entwickeln um Schwingungsspektroskopie in Hinsicht auf Messzeit, spektraler Bandbreite und Auflösung von zu verbessern. Zwei-Kamm- Spektroskopie ist eine Technik die optische Frequenzkämme - kohärente Lichtquellen mit einem Spektrum aus Linien exakt gleichen Abstands - und Fourier Transformations Spektroskopie vereint. Zur linearen Spektroskopie fundamentaler Schwingungsübergänge wurde ein optisch parametrischer Oszillator entwickelt und charakterisiert. Idealerweise beträgt die Idler- Pulsdauer nur einige Feld Zyklen (~3 - 6 Zyklen). Die Zentralwellenlänge ist von 2180nm bis 3732nm (2679 cm-1 - 4587 cm-1) durchstimmbar , sodass sich eine Gesamtabdeckung von etwa 2500nm (2861cm-1) bei einer Durchschnittsleistung im zweistelligen Milliwatt Bereich ergibt. Die hohe Spitzenintensität dieses Systems wurde zur spektralen Verbreiterung genutzt. Mit Hilfe zweier verschiedener Wellenleitern konnte ein jeweils oktavenumspannendes, phasen-kohärentes Superkontinuum erzeugt werden, das im Falle des Siliziumwellenleiters einen Bereich von ~1500nm bis 3300nm (3030cm-1 - 6666 cm-1) abdeckt und von etwa 1600nm bis 3860nm (2590 cm-1 - 6250 cm-1) für den Chalkogenidglaswellenleiter. Es wurden zwei identische Oszillatoren aufgebaut und ein erster Versuch unternommen, sie in einem Zwei-Kamm-Experiment zu nutzen. Diese Oszillatoren wurden nicht stabilisiert, was die Entwicklung und Charakterisierung eines zusätzlichen Korrektursystems erforderlich machte. Kohärente Raman-Streuung wurde als weiterer Zugang zu fundamentalen Schwingungsübergängen untersucht. Mehrere Spektroskopie Aufbauten wurden entwickelt, um blau oder rot verschobenes Raman-Licht in vorwärts- und rückwärtsgestreuter Richtung zu messen, sowie eine differentielle Messung zwischen blau und rot verschoben Licht. Zwischen aufeinanderfolgenden Interferogrammen ist eine Totzeit vorhanden, die bis zu einem Faktor 1000 größer sein kann als die Messzeit. In einen Aufbau der einem Laser mit ~1GHz und 100MHz Repetitionsrate anstatt der üblichen zwei Laser mit ~100MHz Repetitionsrate verwendet, konnte diese Totzeit um eine Größenordung verringert werden. All diese Implementierungen konnten ausgezeichnete Messzeiten (im Mikrosekundenbereich), ein Signal-Rausch Verhältnis von bis zu 1000 und eine spektrale Abdeckung von etwa 1200 cm-1 erzielen. Damit waren die Voraussetzung erfüllt, spektral aufgelöste Bilder in einem rudiemnären Mikroskopieaufbau zu messen

Digital Compensation of Transmission Impairments in Multi-Subcarrier Fiber Optic Transmission Systems

Time and again, fiber optic medium has proved to be the best means for transporting global data traffic which is following an exponential growth trajectory. Rapid development of high bandwidth applications since the past decade based on cloud, virtual reality, 5G and big data to name a few have resulted in a sudden surge of research activities across the globe to maximize effective utilization of available fiber bandwidth which until then was supporting low speed (< 10Gbps) services. To this end, higher order modulation formats together with multicarrier super channel based fiber optic transmission systems have proved to enhance spectral efficiency and achieve multi tera-bit per second bit rates. However, spectrally efficient systems are extremely sensitive to transmission impairments stemming from both optical devices and fiber itself. Therefore, such systems mandate the use of robust digital signal processing (DSP) to compensate and/or mitigate the undesired artifacts. The central theme of this research is to propose and validate few efficient DSP techniques to compensate specific impairments as delineated in the next three paragraphs. For short reach data center and passive optical network related applications which adopt direct detection, a single optical amplifier is generally used to meet the power budget requirements in order to achieve the desired receiver sensitivity or bit error ratio (BER). Semiconductor Optical Amplifier (SOA) with its small form factor is a low-cost power booster that can be designed to operate in any desired wavelength and more importantly can be integrated with other electro-optic components. However, saturated SOAs exhibit nonlinear amplification that introduce distortions on the amplified signal. Alongside SOA, the photodiode also introduces nonlinear mixing among the signal subcarriers in the form of Signal-Signal Beat Interference (SSBI). In this research, we study the impact of SOA nonlinearity on the effectiveness of SSBI compensation in a direct detection OFDM based transmission system. We experimentally demonstrate a digital compensation technique to undo the SOA nonlinearity effect by digitally backpropagating the received signal through a virtual SOA with inverse gain characteristics, thereby effectively eliminating the SSBI. With respect to transmission sources, laser technology has made some significant strides especially in the domain of multiwavelength sources such as quantum dot passive mode-locked laser (QD-PMLL) based optical frequency combs. In the present research work, we characterize the phase dynamics of comb lines from a QD-PMLL based on a novel multiheterodyne coherent detection technique. The inherently broad linewidth of comb lines which is on the order of tens of MHz make it difficult for conventional digital phase noise compensation algorithms to track the large phase noise especially for low baud rate subcarriers using higher cardinality modulation formats. In the context of multi-subcarrier, Nyquist pulse shaped, superchannel transmission system with coherent detection, we demonstrate through measurements and numerical simulations an efficient phase noise compensation technique called “Digital Mixing” that operates using a shared pilot tone exploiting mutual phase coherence among the comb lines. For QPSK and 16 QAM modulation formats, digital mixing provided significant improvement in BER performance in comparison to conventional phase tracking algorithms. Coherent solutions for regional and long haul systems make use of in-line optical amplifiers to compensate fiber loss. Ideally, distributed amplification based on stimulated Raman effect offers enhanced optical signal to noise ratios (OSNR) compared to lumped amplification using erbium doped fiber amplifiers and semiconductor optical amplifiers. However, this benefit of enhanced OSNRs in distributed Raman amplification is offset by the transfer of intensity noise of pump laser on to both signal’s phase and intensity, resulting in performance degradation. In this work, we propose and experimentally validate a practical pilot aided relative phase noise compensation technique for forward pumped distributed Raman amplified, digital subcarrier multiplexed coherent transmission systems

NASA Tech Briefs, December 1988

This month's technical section includes forecasts for 1989 and beyond by NASA experts in the following fields: Integrated Circuits; Communications; Computational Fluid Dynamics; Ceramics; Image Processing; Sensors; Dynamic Power; Superconductivity; Artificial Intelligence; and Flow Cytometry. The quotes provide a brief overview of emerging trends, and describe inventions and innovations being developed by NASA, other government agencies, and private industry that could make a significant impact in coming years. A second bonus feature in this month's issue is the expanded subject index that begins on page 98. The index contains cross-referenced listings for all technical briefs appearing in NASA Tech Briefs during 1988

Adaptive-Filter PMU Hardware Validation to IEEE C37.118.1a Requirements : Strathclyde ENG52 REG D6 Report

This report documents the implementation and testing of a hardware Phasor Measurement Unit (PMU) prototype, using a Beckhoff-based hardware platform. This platform offers several convenient features for PMU development, such as hardware modularity, support for integrating C++ and Simulink models, IEEE 1588 support, and scalability to multiple measurement locations. The Strathclyde M-class PMU algorithm can be deployed on this platform requiring less than 8% of the CPU time of a single CPU core, with 10 kHz analogue sampling. A closed-loop testing procedure, using RTDS hardware and software, has been used to quantify the performance of the Strathclyde PMU algorithm. With proper calibration of the analogue system, as would be the case for a PMU to be deployed in the field, the PMU can achieve relatively low error metrics according to the Synchrophasor standard requirements. For example, for the “static” PMU tests, Total Vector Error (TVE) values as low as 0.01% can be achieved (where the Synchrophasor standard requires a maximum TVE of 1%). Additional tests with multiple disturbances and with emulation of a power system fault have been conducted to demonstrate that PMU algorithms require resilience under realistic worst-case scenarios – and to make a case for testing all PMUs in this way. A new method has been devised for accurately and conveniently characterising the reporting latency of PMUs. This method can also be used to measure the end-to-end performance of transmitting PMU data over wide-area communications networks, thereby providing more accurate knowledge of the actual latency of the measurement systems used to implement novel power system control and protection schemes. The algorithm will be integrated within Synaptec’s passive and distributed optical sensing platform for wide area synchrophasor-based monitoring, protection, and control