Digital Signal Processing Methods Research Articles

INVESTIGATION ON CHARACTERISTICS OF TURBOCHARGER VIBRATION USING DIGITAL SIGNAL PROCESSING TECHNIQUE

High-speed rotating machinery such as a turbocharger is always subject to imperfection that causes strong vibrations. The problem is that there is no way of knowing the root causes of these vibrations by just using our five senses. This problem is significant since unattended heavy vibrations on a turbocharger may lead to permanent damage and a high cost to fix them. The purpose of this study is to investigate the vibration characteristics of a running turbocharger using the Digital Signal Processing (DSP) method, hence identifying the sources of such vibration profiles. In this context, DSP is the process of taking vibration signals that have been digitized and then mathematically manipulating them. Usually, it involves converting time domain data into frequency domain using Fast Fourier Transform (FFT). To identify the causes of turbocharger vibrations, a literature review was done by studying past research of the same methodology. An experiment was conducted by running the machine at different speeds and operating conditions across the choke, regular, and surge conditions. Vibrational data was obtained by mounting a piezoelectric accelerometer onto the compressor housing. The data was then later post-processed using MATLAB to execute FFT. The result shows high energy peaks at various frequencies associated with an unbalanced rotor, oil whirl, looseness, misalignment, and surging noise. On this basis, it is concluded that the vibrational data of a turbocharger can be identified using DSP.

A prince for the sleeping beauty - NFT for soliton signal processing

The soliton, the eigen-solution of nonlinear Schrodinger equation (NLSE), has been investigated in many branches of physics. The first prediction of a soliton in optical fiber could be dated back to 1973. Since then, numerous theoretical and experimental works on solitons have been carried out, including soliton communication and soliton generation in fiber lasers. However, due to the constraints of hardware and digital signal processing methods, research on solitons have been stalled for decades. Recently, the nonlinear Fourier transform (NFT) has attracted significant attention in the field of optical fiber communications and soliton-based signal processing, which provides a powerful mathematical framework for analyzing and understanding the behavior of solitons in optical fibers, enabling the development of novel signal processing techniques. The NFT technique has brought the soliton back to life. It has been widely recognized that in nonlinear frequency domain, the nonlinear crosstalk resulting from the Kerr effect is practically negligible, and fiber nonlinearity damage caused by the Kerr effect can be accounted for as a linear transform factor. Moreover, NFT has been demonstrated for the analysis of laser radiation, highlighting its potential in characterizing ultrafast pulses in the nonlinear frequency domain. In this submission, we review the advancements of NFT concerning both in soliton communication and characterization, focusing on practical implementation aspects. With many practical implementation aspects still being open, our mini review is aimed to assist researchers in evaluating the potential, identifying challenges, and envisioning future directions in NFT-based signal processing technologies. And wake up the sleeping beauty – the soliton!

Direction-of-arrival estimation for acoustic signals based on direction-dependent parameter tuning of a bioinspired binaural coupling system

Bioinspired methods for sound source localization offer opportunities for resource reduction as well as concurrent performance improvement in contrast to conventional techniques. Usually, sound source localization requires a large number of microphones arranged in irregular geometries, and thus has high resource requirements in terms of space and data processing. Motivated by biology and using digital signal processing methods, an approach that adapts the coupled hearing system of the fly Ormia ochracea with a minimally distant two-microphone array is presented. Despite its physiology, the fly is able to overcome physical limitations in localizing low-frequency sound sources. By exploiting the filtering effect of the coupling system, the direction-of-arrival of the sound is determined with two microphones at an intermediate distance of 0.06 m. For conventional beamforming algorithms, these physical limitations would result in degraded localization performance. In this work, the bioinspired coupling system is analyzed and subsequently parameterized direction-sensitive for different directions of incidence of the sound. For the parameterization, an optimization method is presented which can be adopted for excitation with plane as well as spherical sound wave propagation. Finally, the method was assessed using simulated and measured data. For 90% of the simulated scenarios, the correct direction of incidence could be determined with an accuracy of less than 1∘ despite the use of a minimal distant two-microphone array. The experiments with measured data also resulted in a correct determination of the direction of incidence, which qualifies the bioinspired method for practical use in digital hardware systems.

Restoration of a blurred photographic image of a moving object obtained at the resolution limit

Objectives. When processing images of the Earth’s surface obtained from satellites, the problem of restoring a blurry image of a moving object is of great practical importance. The aim of this work is to study the possibility of improving the quality of restoration of blurry images obtained at the limit of the resolution of the camera.Methods. Digital signal processing methods informed by the theory of incorrect and ill-conditioned problems were used.Results. The proposed method for restoring a blurred photographic image of a moving object differs from traditional approaches in that the discrete convolution equation, to which the problem of restoring a blurred image is reduced, is obtained by approximating the corresponding integral equation based on the Kotelnikov interpolation series rather than on the traditional basis of the quadrature formula. In the work, formulas are obtained for calculating the kernel of the convolution obtained using the Kotelnikov interpolation series. The discrete convolution inversion problem, which belongs to the class of ill-posed problems, requires regularization. Results of traditional approaches to restoring blurred images using the quadrature formula with Tikhonov regularization and the proposed method based on the Kotelnikov interpolation series are compared. Although the quality of the blurred image restoration is almost the same in both cases, in the quadrature formula the blur value is expressed as an integer number of pixels, while, when using the Kotelnikov series, this value can also be specified in fractions of a pixel.Conclusions. The expediency of discretizing the convolution describing the image distortion of the blur type on the basis of the Kotelnikov interpolation series when processing a blurred image obtained at the limit of the resolution of the camera is demonstrated. In this case, the amount of blur can be expressed in fractions of a pixel. This situation typically arises when processing satellite photography of the Earth’s surface.

Optical label-based cost-effective DWDM optical network performance monitoring using low-bandwidth PD with novel SRS mitigation DSP

Large-scale dense wavelength division multiplexing (DWDM) multi-channel performance monitoring is one of the indispensable technologies for the flexible optical networks. The existing Labelbased monitoring scheme requires expensive optical demultiplexing components/equipment to avoid the influence of stimulated Raman scattering (SRS), which is not only costly and bulky, but also could not monitor the wavelength channels simultaneously. In this paper, a low-cost, high-accuracy monitoring scheme based on Optical Label Method is proposed for DWDM networks, where the optical channel power and node identification (ID), as the main monitoring targets that both can indicate or evaluate the channel connection status, could be efficiently monitored. In the scheme, a novel digital signal processing (DSP) method of SRS mitigation is proposed and demonstrated, and an asynchronous code-division multiple access (A-CDMA) based digital label encoding and decoding method is adopted to distinguish the node ID so that channel initial added node can be accurately verified, thereby wavelength connection status can be reliably monitored by combining the channel power and node ID information. The simulation results show that each wavelength channel power and node ID can be accurately monitored only by low bandwidth photoelectric detector (PD) under the condition of 80 wavelengths and 10 spans at C-band.

Key Technologies for High-Speed Si-Substrate LED Based Visible Light Communication

Nowadays, the demand for high-speed information transmission is increasing rapidly. Visible light communication (VLC) based on light-emitting diodes (LEDs) is supposed as a potential candidate for future 6G communication networks. However, as an emerging field of optical communications, the data rate of VLC systems is restricted to the extremely limited modulation bandwidth and nonlinear characteristics of optoelectronic devices. In this paper, we outline the state of art and challenges of VLC, and introduce the key technologies for high-speed Silicon (Si) -substrate LED-based VLC systems. Based on an optimized integrated 4×4 8-wavelength LED array and advanced digital signal processing (DSP) methods, we demonstrate an ultrahigh-speed VLC system. Digital Zobel network (DZN) pre-equalization and transfer learning bidirectional gate recurrent unit (TL-Bi-GRU) based post-equalization are proposed to mitigate linear and nonlinear impairment. The yellow and green LEDs are especially enhanced in high-efficacy, and achieve the impressive data rates of 3.45Gbit/s, and 3.83Gbit/s respectively, which is a remarkable improvement. The achievable overall data rate of the device is 28.93 Gbit/s. As far as we know, it's the highest data rate achieved by a single-chip Si-substrate LED array.

Cooperative Multiband Spectrum Sensing Using Radio Environment Maps and Neural Networks.

Cogitive radio networks (CRNs) require high capacity and accuracy to detect the presence of licensed or primary users (PUs) in the sensed spectrum. In addition, they must correctly locate the spectral opportunities (holes) in order to be available to nonlicensed or secondary users (SUs). In this research, a centralized network of cognitive radios for monitoring a multiband spectrum in real time is proposed and implemented in a real wireless communication environment through generic communication devices such as software-defined radios (SDRs). Locally, each SU uses a monitoring technique based on sample entropy to determine spectrum occupancy. The determined features (power, bandwidth, and central frequency) of detected PUs are uploaded to a database. The uploaded data are then processed by a central entity. The objective of this work was to determine the number of PUs, their carrier frequency, bandwidth, and the spectral gaps in the sensed spectrum in a specific area through the construction of radioelectric environment maps (REMs). To this end, we compared the results of classical digital signal processing methods and neural networks performed by the central entity. Results show that both proposed cognitive networks (one working with a central entity using typical signal processing and one performing with neural networks) accurately locate PUs and give information to SUs to transmit, avoiding the hidden terminal problem. However, the best-performing cognitive radio network was the one working with neural networks to accurately detect PUs on both carrier frequency and bandwidth.

Experimental Demonstration of LLO Continuous-Variable Quantum Key Distribution With Polarization Loss Compensation

The compensation process for the state of polarization (SOP) from quantum signal plays an important role in the practical implementation of continuous-variable quantum key distribution (CV-QKD). In contrast to the previous scheme using an expensive digital dynamic polarization controller, we choose a cheaper manual polarization controller interfaced with a digital algorithm based on Kalman filter to achieve compensation of the polarization loss under the condition that the SOP of the fiber is relatively stable. This paper also enumerates the details of other digital signal processing method to achieve final secret key rate. And a pilot-sequential Gaussian modulated coherent state (GMCS) continuous-variable quantum key distribution system with a local local oscillator (LLO) is experimentally implemented based on the analysis of excess noise. Finally, the experimental results show that the method of polarization loss compensation takes advantages in maintaining the stability of the final secret key rate. And a secret key rate of 110 kbps is achieved within 20 km optical fiber (with 4 dB loss) under the finite-size block of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1 \times {10^{6}}$</tex-math></inline-formula> during a more extended time in the laboratory.

Optimal Adaptive Waveform Design Utilizing an End-to-End Learning-Based Pre-Equalization Neural Network in an UVLC System

Visible light communication (VLC) has emerged as a promising communication method in the special field of 6G, such as intersatellite communication (ISC) and underwater wireless optical communication (UWOC). Green light-emitting diode (LED)-based underwater visible light communication (VLC) is considered a potential candidate for UWOC of mobile autonomous underwater vehicle (AUV) and remotely operated underwater vehicle, particularly in coastal and harbor environments. However, due to bandwidth limitations and variable underwater channels, implementing high-speed underwater VLC remains a challenge. In this paper, a neural network-based auto equalization model (NNAEM) using end-to-end learning is proposed to achieve a high-speed underwater VLC link with a bandwidth-limited green LED. The entire NNAEM includes a neural network-based channel model, a pre-equalization neural network, and a post-equalization neural network. Based on the data-driven channel model, our auto equalization (AE) method can dynamically pre-equalize the discrete multitone (DMT) modulated signal in different bandwidth-limited cases and various nonlinearity cases. An underwater VLC link with a data rate of 3.451 Gbps and a transmission distance of 1.2 m is experimentally demonstrated by employing the proposed NNAEM under the hard decision-forward error correction (HD-FEC) threshold of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> . The data rate improvement is up to 30.4% compared to other advanced digital signal processing (DSP) methods. The scenario adaptation and robustness of the NNAEM are also verified in the experiments, which demonstrate that the NNAEM can serve an important role in underwater high-speed VLC transmission.

Direct Adaption Methods for Linear and Circular Antenna Arrays

Introduction. The mitigation of interferences that degrade the performance of navigation systems constitutes one of the most significant problems of contemporary satellite navigation. This problem is conventionally solved using digital adaptive space filters. Depending on a particular radio technical system, the mathematical description of digital signal processing methods may involve specific calculation structures implemented using specific calculation algorithms. For example, the use of centrosymmetric linear and circular antenna arrays in a radio navigation system allows the description of such systems in terms of Toeplitz and circulant sample covariance matrices, respectively, and the inversion of such matrices by means of special numerical methods in order to design a digital filter.Aim. A comparative analysis of the performance of space signal processing algorithms is carried out along with an estimation of Toeplitz and circulant sample covariance matrices and numerical methods of their inversion. The previously obtained results in this field are clarified.Materials and methods. An analysis of algorithm performance was carried out in the MATLAB environment using experimental recordings of satellite navigation signals and jammers obtained by an actual radio technical system.Results. A new expression was derived for estimating circulant sample covariance matrices. Formulae that describe a modification of the Bareiss numerical Toeplitz matrix inversion algorithm for the case of complex Hermitian matrix were introduced. An analysis of the results of computer simulation allowed the algorithms with the highest performance to be indicated. The amount of time taken by the algorithms based on Toeplitz and circulant matrices did not exceed 2.5 10⋅ −3 s and 0.04 s, respectively. The carrier-to-noise ratio in the processed signal was at least 46 dB. Conclusion. The formulae obtained and the algorithms analyzed can be used when implementing adaptive digital filtering of satellite navigation signals.

Development of a Digitising Data Acquisition Pipeline for Next Generation Pulsed Muon Spectrometers

The next generation of muon spin spectrometers at the ISIS pulsed source are being developed to make efficient use of the increased source intensity. They will provide a transformational improvement in counting rates: ‘Super-MuSR’ will be the first of these instruments, capable of counting at ≈1 G·event·hr−1. Key to delivering this capability is the development of highly pixelated, high density detector arrays that cover an appreciable solid angle, with each detector element optimised for counting at very high data rates. A series of ‘firsts’ are planned to optimise individual element count rate capability, where analogue waveforms recorded from SiPMs are fully digitised and processed using digital signal processing (DSP) methods at either software or firmware level. Full raw-signal digitisation will be achieved using the Xilinx Zynq® UltraScale+TM series of ‘system on a chip’ operating with ADCs capable of 1 GHz sampling, data handling using event streaming technology, and DSP to provide novel data correction techniques. We will discuss our concept and present preliminary results. Our prototype digitising data acquisition system, which is key to implementing a ‘digital data pipeline’ (DDP) is presented.

An Integrated Complete Ensemble Empirical Mode Decomposition with Adaptive Noise to Optimize LSTM for Significant Wave Height Forecasting

In recent years, wave energy has gained attention for its sustainability and cleanliness. As one of the most important parameters of wave energy, significant wave height (SWH) is difficult to accurately predict due to complex ocean conditions and the ubiquitous chaotic phenomena in nature. Therefore, this paper proposes an integrated CEEMDAN-LSTM joint model. Traditional computational fluid dynamics (CFD) has a long calculation period and high capital consumption, but artificial intelligence methods have the advantage of high accuracy and fast convergence. CEEMDAN is a commonly used method for digital signal processing in mechanical engineering, but has not yet been used for SWH prediction. It has better performance than the EMD and EEMD and is more suitable for LSTM prediction. In addition, this paper also proposes a novel filter formulation for SWH outliers based on the improved violin-box plot. The final empirical results show that CEEMDAN-LSTM significantly outperforms LSTM for each forecast duration, significantly improving the prediction accuracy. In particular, for a forecast duration of 1 h, CEEMDAN-LSTM has the most significant improvement over LSTM, with 71.91% of RMSE, 68.46% of MAE and 6.80% of NSE, respectively. In summary, our model can improve the real-time scheduling capability for marine engineering maintenance and operations.

Применение методов преобразования Фурье и вейвлет-преобразования для вибродиагностики технического состояния тоннельных эскалаторов

To consider the possibility of improving the detection of early signs of escalator defects. To develop and improve methods for testing and functional diagnostics of escalators. To propose methods for digital signal processing. To develop an approach for correcting interpretation of signal processing results. The methods of vibration diagnostics and digital signal processing were used: including Fourier and wavelet transform. A comparison of Fourier and wavelet transform methods is presented. The possibility of their successful application for signal processing is shown. It was shown that the parameters of vibration diagnostic techniques and the methods of digital signal processing – Fourier transform and wavelet transform-require improvement. The reliability of calculation results can be increased by considering highly variable operational conditions of tunnel escalators. The need for additional examination of the technical condition of tunnel escalators is revealed. Fourier transform and wavelet analysis reveal changes in the nature of oscillations along the leads (an increase or a decrease in the energy level in the leads in phase and diametrically change places depending on the operation mode of the machine). This circumstance indicates the presence of gaps that are «selected» in a characteristic manner every time the direction of movement is changed. When there are any inhomogeneities in the material, wavelet transform analysis may provide the necessary information to determine the design defects, along with their location and possible defect type. The above considerations make the proposed methods of Fourier and wavelet transform of signals to be practically feasible.

Исследование параметров окна частотно-временного преобразования при проведении декомпозиции сигнального радиопрофиля

Known methods of time-frequency transformation, such as the Gabor-Ville transform, wavelet transform, are complex and cumbersome in calculations, require the correct selection of basic expansion functions, may have interference points and negative values of the spectral density function. The presence of space-time uncertainty inherent in any frequency-time decomposition, as well as the lack of the possibility of correcting the found expansion coefficients, make modern methods of frequency-time transformation ineffective in the analysis of signal radio profiles (SRP). Decomposition of SRP with windowed correlation feedback eliminates the above disadvantages by multiple enumeration of parameters, however, this occurs at the expense of a significant increase in the transformation time. The transformation window here is understood as a rectangular function that moves along the time axis from the origin. In this work, the window width is understood as the number of sampling points falling into the rectangular window function, which is equivalent to the length of the function along the time axis. The window step is the number of sampling points to which the rectangular window function (transformation window) moves in the time-frequency decomposition. The purpose of this work is to increase the efficiency of the frequency-time decomposition of the SRP by analyzing the parameters of the transformation window in decomposition with windowed correlation feedback. In the study, experimental research methods are used to register the electrical component of the electromagnetic field radiated by the product - SRP. Correlation analysis methods for determining the best match between the reference and reconstructed SRP. Methods of digital signal processing with frequency-time decomposition. The paper presents the registered SRPs and their parameters, a correlation analysis of the SRP data is carried out. The dependences of the correlation functions on the width and step of the window are given for a different number of sampling points of the registered SRP. The results obtained for the first time showed the possibility of using certain parameters of the transformation window to improve the accuracy and significantly reduce the time of SRP decomposition, which makes the work novel. It has been established that with a window width equal to half the length of the SRP itself and a window step of not more than a tenth of the length of the SRP, it is possible to achieve an increase in the cross-correlation between the original and restored SRP up to 0.95. Recommendations are given on the speed of recording equipment when receiving PDS (sampling rate below 10 GS/s). The practical significance of the work lies in the reduction of iterations of the multi-parameter approximation when using correlation feedback in the course of SRP decomposition, which significantly reduces the conversion time and improves its accuracy.

ПОРІВНЯЛЬНИЙ АНАЛІЗ ЦИФРОВИХ ШУМІВ, ЗГЕНЕРОВАНИХ АДИТИВНИМИ ГЕНЕРАТОРАМИ ФІБОНАЧІ

Noise generators and pseudorandom number generators (PRNGs) are widely used in the field of information technology, including cybersecurity, for modeling, authorization key generation, and technical protection of information. It has been found that the characteristics of digital noise directly depend on the chosen PRNG algorithm. To determine the quality of the generated noise, special tests are performed, which are primarily applied to the sequence generated by the PRNG. The results of digital noise generated by an PRNG based on four different algorithms of additive Fibonacci generators (AFG) are investigated. The choice of generators of the same type allowed us to analyze the effect of different modifications on the final result of the generated sequences to determine their advantages and disadvantages. Digital signal processing techniques such as frequency, autocorrelation and visual analysis, signal-to-noise ratio, and statistical tests of the NIST package were used to test the noise and generated sequences. Functions for interpreting the obtained data were developed using the MATLAB (DSP System Toolbox) application package and the C programming language for automating NIST tests. It has been found that for effective testing, specific stages and their sequence should be determined: determination of the PRNG period, statistical tests of the NIST package, calculation of the autocorrelation function, and other methods of digital signal processing. It was found that modification of one AFG by using a carry bit (MAFG2) does not improve the results of the generated sequence, unlike the PIKE algorithm, which consists of three AFGs. The MAFG algorithm showed better results during the period testing and at the same time passed NIST tests, unlike the unmodified version. The dependence between the order of the generated sequences and the results of their autocorrelation function was revealed. It is proposed that, in addition to general statistical tests, applied tests should be carried out when choosing or developing a new generator, its effectiveness should be checked under the conditions required by existing standards and requirements. The compliance of the generated digital noise with the requirements for devices for technical protection of information, namely the protection of speech information, has been established.

РОЗРОБКА ЕЛЕКТРОННОГО БЛОКУ ПІДСИСТЕМИ ІДЕНТИФІКАЦІЇ МЕТАЛЕВИХ ВКЛЮЧЕНЬ У СИРОВИНІ НА КОНВЕЄРНІЙ СТРІЧЦІ З АВТОМАТИЧНИМ ВИЗНАЧЕННЯМ ЇХ КООРДИНАТ

Purpose. Ensuring reliability and efficiency manufacturing ceramic products technological process by integrating into it the subsystem for identifying metal inclusions in raw materials with automatic determination of their coordinates and dimensions for their further extraction. Methodology. Methods of circuit engineering, basics of system theory and automatic control, methods of electromagnetic circuits and digital signal processing are used, a comprehensive approach to the construction of a control system, mathematical methods of operations research are used as well. Results. The article provides a critical analysis of existing modern solutions for metal inclusions identification in loose raw materials for ceramic products manufacture during their movement on a conveyor belt. It was established that the presence of metal inclusions in raw materials inevitably leads to failures with subsequent breakdowns of technological equipment. The electronic unit for measuring and processing the signals from the receiving coils has been developed. The electronic unit for generating the excitation signal in the radiating coils has been carried out. Based on the proposed concept, the subsystem for detecting metal inclusions has been created, which is easily scaled to the width of the conveyor belt by selecting the number of measuring channels. The algorithm of signal processing for the receiving coils unit has been worked out, which allows implementing the synchronous signals forming, measurement, processing, and presentation of results. Scientific novelty. The identification subsystem structure of metal inclusions has been proposed, which is implemented on the parallax method of determining the position of the metal inclusion between the coils. Practical significance. The development and integration of the identification subsystem of metal inclusions into the structure of the automated control system of the raw material preparation process has been carried out, which includes the development of hardware and algorithmic support. As result of testing the identification subsystem of metal inclusions on a laboratory installation of conveyor line, it is possible to detect 89.8% ones of metal inclusions.

АВТОМАТИЗАЦІЯ ВИМІРЮВАНЬ НА ДЕРЖАВНОМУ ЕТАЛОНІ ОДИНИЦІ КУТА ЗСУВУ ФАЗ МІЖ ДВОМА НАПРУГАМИ

The phase is one of the main parameters of the oscillatory process in electric circuits and contains two components – constant and variable. More often, it is not the actual phase that is measured, but the phase shift angle (PSA) between two oscillating processes (voltages or currents) of the same frequency in the range from 0 to 360˚. Then the PSA is equal to the difference between the constant components of the phases of the two oscillations and does not depend on the start of the time count. Most of the modern methods of measuring the phase and PSA are based on the methods of discretization and digital signal processing – complex Fourier transform, least squares, etc. There are many varieties and improvements of these methods, which have different characteristics of measurement accuracy. The LabVIEW graphical programming environment has already become a general- purpose programming environment. Advantages of LabVIEW include simple networking, implementation of common communication protocols, powerful toolkits for process control and data fitting, fast and simple user interface design, and an efficient code execution environment. The article presents the results of the automation of measurements on the State Standard of the PSA between two voltages in the frequency range from 5 Hz to 10 MHz. Automation of precision measurements of PSA using the Lab- VIEW software environment provides advantages in comparison with manual measurements, in particular, reducing the time of measurement and processing of its results by at least three times. This ensures an increase in the productivity of metrological works; increasing their efficiency and quality, and the possibility of increasing the number of measurements (up to 1000), which allows for improve the root mean square deviation of not less than one and a half times, and reduce the overall standard measurement uncertainty, respectively.

Machine learning enabled digital compensation of phase-to-amplitude distor-tion in fibre-optical parametric amplifier based transmission links

We numerically demonstrate an advanced digital signal processing method for compensating the phase-to-amplitude distortion conversion caused by the interaction of the phase noise induced by pump dither-ing with the dispersive fibre channel in fibre-optical parametric amplifier based transmission systems.

Экспериментальная проверка способа выравнивания мощностей цилиндров многоцилиндрового дизеля

Purpose: The purpose of the present work is to test experimentally equalization method for the outputs of multi-cylinder diesel engine cylinders basing on energy minimization of amplitude spectrum low-frequency band for diesel crankshaft instantaneous angular speed signal. Methods: The work uses the methods of digital signal processing, spectral analysis, differential calculus, multidimensional undifferentiated function optimization, experimental results processing. Results: The fulfilled experimental studies at bench diesel generator device as a part of locomotive diesel D50 (6CHN31.8/33) and traction generator MPT 84/39 ensure the possibility to use proposed earlier method for power equalization for the cylinders of multi-cylinder diesel engine basing on energy control of amplitude spectrum low-frequency band of crankshaft instantaneous angular speed signal. Unrvenness index for cylinder power is proposed, its sensitivity to cyclic supply change and the advance angle of fuel supply to diesel engine individual cylinders is estimated. Practical significance: The possibility to apply being proposed equalization method for the powers of multi-cylinder diesel engine cylinders for to adjust fuel equipment after diesel engine repair as with the systems of electronic fuel supply control as well as with hydromechanical fuel equipment has been confirmed experimentally. The use of given method eliminates the need to measure the temperature of exhaust gases and flash pressure in cylinders for fuel equipment adjustment that’s especially important for high-speed diesel engines which cylinder cover construction doesn’t imply indicated valves.

Demonstration of 200 Gbps PAM-4 transmission in a limited-bandwidth system using a two-tap THP with nonlinearity compensator

In this paper, we have proposed a digital signal processing (DSP) method for a 200 Gbps pulse-amplitude modulation level-4 (PAM-4) transmission in a bandwidth-limited system. To mitigate inter-symbol interferences (ISI) in the system and reduce the propagation of errors in the receiver, the Tomlinson-Harashima precoding (THP) technique was applied to the transmitter. For simplicity, the number of THP taps was limited to two (i.e., one coefficient to be optimized); the residual ISI resulting from the short tap was compensated for with a decision feedback equalizer (DFE). The performance of the proposed DSP was analyzed via experiments and simulations. Compared to conventional DSP techniques (such as DFE and the maximum likelihood sequence estimation (MLSE) without THP), the proposed DSP performs better within the limited-bandwidth region. As a result, the soft-decision forward error correction (SD-FEC) threshold (of 2 × 10−2) was satisfied even when the bandwidth fell to below 35% of the baud rate. To enhance this performance, post-filter and MLSE were additionally applied, after which its performance was investigated. In addition, the nonlinear characteristics of the components were alleviated by applying a pre-distortion technique to the THP using look-up tables; this further enhanced performance, lowering the SD-FEC threshold’s bandwidth to 32% of the baud rate.