Noise Tracking Research Articles

Properties of train load frequencies and their applications

A train in motion applies moving steady loads to the railway track as well as dynamic excitation; this causes track deflections, vibration and noise. At low frequency, the spectrum of measured track vibration has been found to have a distinct pattern; with spectral peaks occurring at multiples of the vehicle passing frequency. This pattern can be analysed to quantify aspects of train and track performance as well as to design sensors and systems for trackside condition monitoring. To this end, analytical methods are developed to determine frequency spectra based on known vehicle geometry and track properties. It is shown that the quasi-static wheel loads from a moving train, which are the most significant cause of the track deflections at low frequency, can be understood by considering a loading function representing the train geometry in combination with the response of the track to a single unit load. The Fourier transform of the loading function describes how the passage of repeating vehicles within a train leads to spectral peaks at various multiples of the vehicle passing frequency. When a train consists of a single type of repeating vehicle, these peaks depend on the geometry of that vehicle type as the separation of axles on a bogie and spacing of those bogies on a vehicle cause certain frequencies to be suppressed. Introduction of different vehicle types within a train or coupling of trainsets with a different inter-car length changes the spectrum, although local peaks still occur at multiples of the passing frequency of the primary vehicle. Using data from track-mounted geophones, it is shown that the properties of the train load spectrum, together with a model for track behaviour, allows calculation of the track system support modulus without knowledge of the axle loads, and enables rapid determination of the train speed. For continuous remote condition monitoring, track-mounted transducers are ideally powered using energy harvesting devices. These need to be tuned to optimise energy abstraction; the appropriate energy harvesting frequencies for given vehicle types and line speeds can also be predicted using the models developed.

Speech Enhancement Based on Full-Sentence Correlation and Clean Speech Recognition

Conventional speech enhancement methods, based on frame, multiframe, or segment estimation, require knowledge about the noise. This paper presents a new method that aims to reduce or effectively remove this requirement. It is shown that by using the zero-mean normalized correlation coefficient ZNCC as the comparison measure, and by extending the effective length of speech segment matching to sentence-long speech utterances, it is possible to obtain an accurate speech estimate from noise without requiring specific knowledge about the noise. The new method, thus, could be used to deal with unpredictable noise or noise without proper training data. This paper is focused on realizing and evaluating this potential. We propose a novel realization that integrates full-sentence speech correlation with clean speech recognition, formulated as a constrained maximization problem, to overcome the data sparsity problem. Then we propose an efficient implementation algorithm to solve this constrained maximization problem to produce speech sentence estimates. For evaluation, we build the new system on one training dataset and test it on two different test datasets across two databases, for a range of different noises including highly nonstationary ones. It is shown that the new approach, without any estimation of the noise, is able to significantly outperform conventional methods that use optimized noise tracking, in terms of various objective measures including automatic speech recognition.

Augmented virtual stiffness rendering of a cable-driven SEA for human-robot interaction

Human-robot interaction U+0028 HRI U+0029 is fundamental for human-centered robotics, and has been attracting intensive research for more than a decade. The series elastic actuator U+0028 SEA U+0029 provides inherent compliance, safety and further benefits for HRI, but the introduced elastic element also brings control difficulties. In this paper, we address the stiffness rendering problem for a cable-driven SEA system, to achieve either low stiffness for good transparency or high stiffness bigger than the physical spring constant, and to assess the rendering accuracy with quantified metrics. By taking a velocity-sourced model of the motor, a cascaded velocity-torque-impedance control structure is established. To achieve high fidelity torque control, the 2-DOF U+0028 degree of freedom U+0029 stabilizing control method together with a compensator has been used to handle the competing requirements on tracking performance, noise and disturbance rejection, and energy optimization in the cable-driven SEA system. The conventional passivity requirement for HRI usually leads to a conservative design of the impedance controller, and the rendered stiffness cannot go higher than the physical spring constant. By adding a phase-lead compensator into the impedance controller, the stiffness rendering capability was augmented with guaranteed relaxed passivity. Extensive simulations and experiments have been performed, and the virtual stiffness has been rendered in the extended range of 0.1 to 2.0 times of the physical spring constant with guaranteed relaxed passivity for physical humanrobot interaction below 5 Hz. Quantified metrics also verified good rendering accuracy.

Limitation of Gravitational Wave Detector Niobè Sensitivity by the Frequency Tracking Noise

The gravity wave detector at the University of Western Australia was based on a bending flap of [Formula: see text] tuned near the fundamental resonant frequency of a [Formula: see text] resonant-bar of [Formula: see text] at a temperature of [Formula: see text]. The displacement of the bending flap was monitored with a [Formula: see text] superconducting re-entrant cavity transducer. The performance of the transducer is related to the development of a low noise microwave pump oscillator to drive the transducer. This work studies the influence of the frequency tracking noise of Niobè. It had a burst sensitivity of [Formula: see text] with a long term operation from 1993 to early 1998. It had the lowest observed noise temperature. Using the characteristics of the detector, NIOBÈ should had reached a much better sensitivity that the one measure. It seems that the noise introduced in the system by the frequency tracking device was not taken into account at the time of operation, this noise gives a value of [Formula: see text], what is the value that limited the detector sensitivity to the one measured at the time of operation.

Estimation of Noise Magnitude for Speech Denoising Using Minima-Controlled-Recursive-Averaging Algorithm Adapted by Harmonic Properties

The accuracy of noise estimation is important for the performance of a speech denoising system. Most noise estimators suffer from either overestimation or underestimation on the noise level. An overestimate on noise magnitude will cause serious speech distortion for speech denoising. Conversely, a great quantity of residual noise will occur when the noise magnitude is underestimated. Accurately estimating noise magnitude is important for speech denoising. This study proposes employing variable segment length for noise tracking and variable thresholds for the determination of speech presence probability, resulting in the performance improvement for a minima-controlled-recursive-averaging (MCRA) algorithm in noise estimation. Initially, the fundamental frequency was estimated to determine whether a frame is a vowel. In the case of a vowel frame, the increment of segment lengths and the decrement of threshold for speech presence were performed which resulted in underestimating the level of noise magnitude. Accordingly, the speech distortion is reduced in denoised speech. On the contrary, the segment length decreases rapidly in noise-dominant regions. This enables the noise estimate to update quickly and the noise variation to track well, yielding interference noise being removed effectively through the process of speech denoising. Experimental results show that the proposed approach has been effective in improving the performance of the MCRA algorithm by preserving the weak vowels and consonants. The denoising performance is therefore improved.

Effect of linearized contact spring in track dynamic system

In recent years, a number of researches into dynamic characteristics of the noise and vibration in the railway have been performed. Since the high frequency vibration, which occurs in the irregularity(roughness) of the wheel and rail running surfaces, causes the track noise in railway system, analytic study with measurement of the vibration for the wheel and rail is needed. So, the algorithm and program for the vibration analysis in the track system were developed as a part of the analytic study. In this study, evaluation for the effect of the linearized contact spring in track dynamic system was studied with the developed program. In addition, analytical study for the comparison between hysteretic and viscous damping in this system was performed. The result shows that both the linearized contact spring stiffness and damping of track system are important factors in track dynamic analysis model.

High-Bandwidth Demodulation in MF-AFM: A Kalman Filtering Approach

Emerging multifrequency atomic force microscopy (MF-AFM) methods rely on coherent demodulation of the cantilever deflection signal at multiple frequencies. These measurements are needed in order to close the z -axis feedback loop and to acquire complementary information on the tip–sample interaction. While the common method is to use a lock-in amplifier capable of recovering low-level signals from noisy backgrounds, its performance is ultimately bounded by the bandwidth of low-pass filters. In light of the demand for constantly increasing imaging speeds while providing multifrequency flexibility, we propose to estimate the in-phase and quadrature components with a linear time-varying Kalman filter. The chosen representation allows for an efficient high-bandwidth implementation on a field programmable gate array. Tracking bandwidth and noise performance are verified experimentally, and trimodal AFM results on a two-component polymer sample highlight the applicability of the proposed method for MF-AFM.

Unscented Kalman filters for polarization state tracking and phase noise mitigation.

Simultaneous polarization and phase noise tracking and compensation is proposed based on an unscented Kalman filter (UKF). We experimentally demonstrate the tracking under noise-loading and after 800-km single-mode fiber transmission with 20-Gbaud QPSK and 16-QAM signals. These experiments show that the proposed UKF outperforms both conventional blind tracing algorithms and a previously proposed extended Kalman filter, at the cost of higher complexity. Additionally, we propose and test modified Kalman filter algorithms to reduce computational complexity.

The Effect of Rail Fastening System Modifications on Tram Traffic Noise and Vibration

Tram system is a backbone of public transportation in the City of Zagreb. In the last decade, its fleet has been renewed by 142 new low-floor trams. Shortly after their introduction, it was observed that they have a negative impact on the exploitation behavior of tram infrastructure, primarily on the durability of rail fastening systems. Because of that, it was decided to modify existing rail fastening systems to the new track exploitation conditions. When the (re)construction of tram infrastructure is carried out by applying new systems and technologies, it is necessary to take into account their impact on the future propagation of noise and vibration in the environment. This paper gives a short overview of the characteristics of the two newly developed rail fastening systems for Zagreb tram tracks, their application in construction of experimental track section, and performance and comparison of noise and vibration measurements results. Measured data on track vibrations and noise occurring during passage of the tram vehicles is analyzed in terms of track decay rates and equivalent noise levels of passing referent vehicle. Vibroacoustic performance of new fastening systems is evaluated and compared to referent fastening system, in order to investigate their ability to absorb vibration energy induced by tram operation and to reduce noise emission.

NEOBALLAST: New High-performance and Long-lasting Ballast for Sustainable Railway Infrastructures

With inherent advantages in environmental performance, land use, energy consumption and safety, railways are an essential component of a competitive and resource-efficient transport system. However, railways have still to face several important drawbacks in order to reinforce its competitiveness against the road mode. Reducing maintenance costs has been appointed as one key goal of Infrastructure Managers (IMs), as Western Europe spends annually between €15 and €25bn to maintain and renew a railway network of about 225,000 km (FP7 Mainline Project, 2011-2014). Future prospects of mobility growth (passenger-km is to be doubled in 40 years) will increase maintenance needs, evincing the need of innovative solutions that downsize maintenance costs.The increasing demand of higher axle loads and higher speeds has led to the improvement of track components (e.g. harder and heavier rails, pre-stressed sleepers, etc.). However, there has not been a significant change in ballast aggregates, even though it is the main cost-driver of maintenance costs.In this context, NEOBALLAST emerges as a high-performing, long-lasting and eco-friendly ballast aggregate solution designed to overcome two of the most important drawbacks of railway tracks: track degradation and noise and vibrations (N&V). Whilst the former is the main trigger of maintenance and eventually renewal works, thus representing one of the main cost drivers for IMs, the latter has become an issue of paramount importance not only to IMs but the whole EU, since according to the European Environment Agency rail noise affects around 12 million people during day time (55dBA) and 9 million at night (50dBA). NEOBALLAST is a research project funded by MINECO (Spanish Ministry of Economy and Competitiveness) carried out by COMSA, MAPEI, UPC and ADIF.NEOBALLAST benefits have been proven in an extensive laboratory campaign involving both reduced and large-scale testing. This paper will summarize the results obtained in terms of mechanical and vibration mitigation performance of NEOBALLAST aggregates itself and their behaviour as a whole.

Message Passing Algorithms for Phase Noise Tracking Using Tikhonov Mixtures

Phase noise poses a serious challenge for high-speed digital communications systems mainly when going to higher and higher carrier frequencies, such as in satellite communications. Traditionally, phase noise estimation was performed separately from the decoding task and it was shown, recently, that there is much to be gained from joint estimation and decoding, particularly when using LDPC (low-density parity check)/turbo codes. However, jointly estimating phase noise and decoding is a very complex and computationally demanding task. In this paper, we propose several algorithms based on the sum and product algorithm (SPA) for low complexity joint decoding and estimation of coded information in strong phase noise channels. These algorithms are based on a novel approximation of SPA messages as Tikhonov mixtures of a given order. Since mixture-based Bayesian inference such as SPA, creates an exponential increase in mixture order for consecutive messages, a mixture reduction scheme is a must. Therefore, in this paper, we propose a low complexity mixture reduction algorithm, which provably satisfies an upper bound on the Kullback Leibler (KL) divergence between the mixture and the reduced mixture. We then reduce the complexity even further, including limiting the model order and reducing the clustering effort to simple component selection. As an extreme case, it is even possible to reduce the number of modes to one. We show the relation between the simplified algorithm to the phase locked loop (PLL). Finally, we show simulation results and complexity analysis for the proposed algorithms, which show superior performance over other state of the art low complexity algorithms.

Machine Learning Techniques in Optical Communication

Machine learning techniques relevant for nonlinearity mitigation, carrier recovery, and nanoscale device characterization are reviewed and employed. Markov Chain Monte Carlo in combination with Bayesian filtering is employed within the nonlinear state-space framework and demonstrated for parameter estimation. It is shown that the time-varying effects of cross-phase modulation (XPM) induced polarization scattering and phase noise can be formulated within the nonlinear state-space model (SSM). This allows for tracking and compensation of the XPM induced impairments by employing approximate stochastic filtering methods such as extended Kalman or particle filtering. The achievable gains are dependent on the autocorrelation (AC) function properties of the impairments under consideration which is strongly dependent on the transmissions scenario. The gain of the compensation method are therefore investigated by varying the parameters of the AC function describing XPM-induced polarization scattering and phase noise. It is shown that an increase in the nonlinear tolerance of more than 2 dB is achievable for 32 Gbaud QPSK and 16-quadratic-amplitude modulation (QAM). It is also reviewed how laser rate equations can be formulated within the nonlinear state-space framework which allows for tracking of nonLorentzian laser phase noise lineshapes. It is experimentally demonstrated for 28 Gbaud 16-QAM signals that if the laser phase noise shape strongly deviates from the Lorentzian, phase noise tracking algorithms employing rate equation-based SSM result in a significant performance improvement ( $>$ 8 dB) compared to traditional approaches using digital phase-locked loop. Finally, Gaussian mixture model is reviewed and employed for nonlinear phase noise compensation and characterization of nanoscale devices structure variations.

Low-Complexity Tracking of Laser and Nonlinear Phase Noise in WDM Optical Fiber Systems

In this paper, the wavelength division multiplexed (WDM) fiber optic channel is considered. It is shown that for ideal distributed Raman amplification (IDRA), the Wiener process model is suitable for the non-linear phase noise due to cross phase modulation from neighboring channels. Based on this model, a phase noise tracking algorithm is presented. We approximate the distribution of the phase noise at each time instant by a mixture of Tikhonov distributions, and derive a closed form expression for the posterior probabilities of the input symbols. This reduces the complexity dramatically compared to previous trellis-based approaches, which require numerical integration. Further, the proposed method performs very well in low-to-moderate signal-to-noise ratio (SNR), where standard decision directed (DD) methods, especially for high-order modulation, fail. The proposed algorithm does not rely on averaging, and therefore does not experience high error floors at high SNR in severe phase noise scenarios. The laser linewidth (LLW) tolerance is thereby increased for the entire SNR region compared to previous DD methods. In IDRA WDM links, the algorithm is shown to effectively combat the combined effect of both laser phase noise and non-linear phase noise, which cannot be neglected in such scenarios. In a more practical lumped amplification scheme, we show near-optimal performance for 16 QAM, 64 QAM, and 256 QAM with LLW up to 100 kHz, and reasonable performance for LLW of 1 MHz for 16 QAM and 64 QAM, at the moderate received SNR region. The performance in these cases is close to the information rate achieved by the above mentioned trellis processing.

CSC Code Discriminator: Theoretical Analysis of Performance

This paper presents the theoretical development and analysis of a novel DLL discriminator robust to multipath errors, called the Combination of Squared Correlators (CSC). The CSC discriminator features a simple implementation based on four (complex) static correlators per channel, without falling into the wide family of patented architectures.In this paper, the theoretical analysis of the properties of the CSC architecture is developed in a well structured context: (i) definition of the discrimination rule; (ii) theoretical analysis in the absence of noise; (iii) theoretical noise tracking jitter analysis; and, (iv) multipath error envelope analysis. In all cases, the CSC results are compared to those of the Strobe discriminator, which is the natural benchmark.The promising performance of the CSC discriminator inserted in a complete software receiver is also proved in a heavy multipath scenario, expressly simulated to stress the code tracking loop robustness. Copyright © 2015 John Wiley & Sons, Ltd.

Yes, the CAPM is Absurd: OLS is Misunderstood and Incorrectly Modeled Mathematically

The Capital Asset Pricing Model (CAPM) purports to mathematically relate the expected return of an asset with its risk. Two types of risk are addressed: systematic risk, which is a function of the market; and unsystematic risk, which is independent of the market and is asset specific. The market risk is described as Beta (β), which linearly relates the asset return with the market return. The unsystematic risk is described in terms of errors which are deviations from the linear relationship between the market and asset. The β is estimated by ordinary least squares (OLS). In theory, OLS may be modeled as a linear signal processing with inputs and outputs (i.e., a black box with gosintas and gosoutas). Samples of signal and errors are treated as the input to the OLS system which transforms the samples into an output in the form of a prediction along with its expected value and variance. The purpose of OLS is to reduce the prediction variance by filtering out (a term from target tracking) error samples (described as noise in tracking) to improve future estimates. Unfortunately, the CAPM represents a devastating failure to understand, model, and use the OLS correctly while, as a detrimental myth, it continues to be perpetuated by the uninformed. Yes, the CAPM is patently absurd as Fernandez explains. In contrast, proven and long established engineering techniques are applied here to derive the empirical statistical OLS asset return prediction, expected value, and variance. This engineering model suggests that the CAPM should be completely scrapped. Instead, the well established and appropriately suited OLS should be correctly used in its place rather than be cannibalized by obsessively attempting to justify the preposterous delusion that α must be zero and then ridiculously force-fitting the mismatched β onto the fatally defunct CAPM.

Suspending effect on low-frequency charge noise in graphene quantum dot.

Charge noise is critical in the performance of gate-controlled quantum dots (QDs). Such information is not yet available for QDs made out of the new material graphene, where both substrate and edge states are known to have important effects. Here we show the 1/f noise for a microscopic graphene QD is substantially larger than that for a macroscopic graphene field-effect transistor (FET), increasing linearly with temperature. To understand its origin, we suspended the graphene QD above the substrate. In contrast to large area graphene FETs, we find that a suspended graphene QD has an almost-identical noise level as an unsuspended one. Tracking noise levels around the Coulomb blockade peak as a function of gate voltage yields potential fluctuations of order 1 μeV, almost one order larger than in GaAs/GaAlAs QDs. Edge states and surface impurities rather than substrate-induced disorders, appear to dominate the 1/f noise, thus affecting the coherency of graphene nano-devices.

Investigation of the Dynamic Properties of Railway Tracks using a Model for Calculation of Generation of Wheel/Rail Noise

For optimization of a low-noise track system, rail vibration and noise radiation needs to be investigated. The main influencing parameters for the noise radiation and the quantitative results of every track system can be obtained using a calculation model of generation and radiation of railway noise. This kind of model includes contact modeling and the calculation model of the dynamic properties of the wheel and the rail. This study used a nonlinear wheel/rail interaction model in the time domain to investigate the excitation of the rolling noise. Wheel/rail response is determined by time integrating Green's function of the rail together with force impulses from the wheel/rail contact. This model and the results of the study can be used for supporting calculation with the conventional model by an addition of the contributions due to nonlinearities to the roughness spectrum.

Improved pilot data aided feed forward based on maximum likelihood for carrier phase jitter recovery in coherent optical orthogonal frequency division multiplexing

Pilot data aided feed forward (PAFF) carrier recovery is essential for phase noise tracking in coherent optical receivers. This paper describes a new PAFF system based on new pilot arrangement and maximum likelihood (ML) to estimate the phase jitter in coherent receiver-induced by local oscillator’s lasers and sampling clock errors. Square M-ary quadrature amplitude modulation (M-QAM) (4, 16, 64, and 256) schemes were used. A detailed mathematical description of the method was presented. The system performance was evaluated through numerical simulations and compared to those with noise-free receiver (ideal receiver) and feed forward without ML. The simulation results show that PAFF performs near the expected ideal phase recovery. Results clearly suggest that ML significantly improves the tolerance of phase error variance. From bit error rate (BER) sensibility evaluation, it was clearly observed that the new estimation method performs better with a 4-QAM (or quadrature phase shift keying (QPSK)) format compared to three others square QAM schemes. Analog to digital converter (ADC) resolution effect on the system performance was analyzed in terms of Q-factor. Finite resolution effect on 4-QAM is negligible while it negatively affects the system performance when M increases.

A PDE-Based Regularization Algorithm Toward Reducing Speckle Tracking Noise: A Feasibility Study for Ultrasound Breast Elastography.

Obtaining accurate ultrasonically estimated displacements along both axial (parallel to the acoustic beam) and lateral (perpendicular to the beam) directions is an important task for various clinical elastography applications (e.g., modulus reconstruction and temperature imaging). In this study, a partial differential equation (PDE)-based regularization algorithm was proposed to enhance motion tracking accuracy. More specifically, the proposed PDE-based algorithm, utilizing two-dimensional (2D) displacement estimates from a conventional elastography system, attempted to iteratively reduce noise contained in the original displacement estimates by mathematical regularization. In this study, tissue incompressibility was the physical constraint used by the above-mentioned mathematical regularization. This proposed algorithm was tested using computer-simulated data, a tissue-mimicking phantom, and in vivo breast lesion data. Computer simulation results demonstrated that the method significantly improved the accuracy of lateral tracking (e.g., a factor of 17 at 0.5% compression). From in vivo breast lesion data investigated, we have found that, as compared with the conventional method, higher quality axial and lateral strain images (e.g., at least 78% improvements among the estimated contrast-to-noise ratios of lateral strain images) were obtained. Our initial results demonstrated that this conceptually and computationally simple method could be useful for improving the image quality of ultrasound elastography with current clinical equipment as a post-processing tool.

English

A compact, robust and high performance front-end of a radar receiver is designed and demonstrated in this paper. The important parameters like noise figure, sensitivity, selectivity, dynamic range and tracking range are superior to that of the existing systems and facilitate online monitoring of the above important parameters. The gain and phase matching facility are incorporated. The local oscillator is integrated within the module which in turn reduces the losses as compare with the existing local oscillator, placed in the instrumentation cabin. The frequency, amplitude, delay between skin and transponder frequency can be controlled remotely by computer program. Therefore, the mixed mode operation (skin and transponder) of radar receiver is possible. Moreover, the SPDT switch is integrated in the same module for RF simulation to facilitate the three channel mono-pulse receiver calibration, receiver health monitoring and range calibration of precision coherent mono-pulse C-band radar. The components used are monolithic microwave integrated circuit based technologies with superior specifications, makes the total module miniaturized and reduced the hardware complications. The total power consumption is much less and improves the overall performance than the existing front-end. Defence Science Journal, Vol. 64, No. 4, July 2014, pp. 358-365, DOI:http://dx.doi.org/10.14429/dsj.64.4245