Noise Compensation Research Articles

Amar Gopal Bose

Amar Gopal Bose

Experimental Demonstration of Nonlinearity and Phase Noise Tolerant 16-QAM OFDM W-Band (75–110 GHz) Signal Over Fiber System

We propose a nonlinearity and phase noise tolerant orthogonal frequency division multiplexing (OFDM) W-band signal over fiber system based on phase modulation and photonic heterodyne up-conversion techniques. By heterodyne mixing the phase-modulated optical OFDM signal with a free-running laser in the photodiode, the constant envelope OFDM W-band wireless signal is obtained to suppress the nonlinear impairments. Moreover, the phase noises of the beating lasers appear as additive terms to the desired signal, and could be easily filtered out without complex phase noise estimation and compensation algorithms. In our experiment, 4 Gb/s QPSK and 8 Gb/s 16-QAM constant envelope OFDM W-band signals are transmitted over 22.8 km single mode fiber and 2.3 m air distance with achieved bit-error-rate performance below the forward error correction limit.

In-line extraction of an ultrastable frequency signal over an optical fiber link

We demonstrate in-line extraction of an ultra-stable frequency signal over an optical link of 92-km of installed telecommunication fibers, following the proposition of G. Grosche in 2010. We show that the residual frequency noise at the extraction end is noticeably below that at the main link output when the extraction is near the input end, as expected from a simple model of the noise compensation. We obtain relative frequency instabilities, expressed as overlapping Allan deviation, of 8x10-16 at 1 s averaging time and a few 10-19 at 1 day. These results are at the state-of-the-art for a link using urban telecommunication fibers. We also propose an improved scheme which delivers an ultra-stable signal of higher power, in order to feed a secondary link. In-line extraction opens the way to a broad distribution of an ultra-stable frequency reference, enabling a wide range of applications beyond metrology.

Quasi-Pilot Aided Phase Noise Estimation for Coherent Optical OFDM Systems

In this letter, a novel phase noise estimation scheme has been proposed for coherent optical orthogonal frequency division multiplexing systems, the quasi-pilot-aided method. In this method, the phases of transmitted pilot subcarriers are deliberately correlated to the phases of data subcarriers. Accounting for this correlation in the receiver allows the required number of pilots needed for a sufficient estimation and compensation of phase noise to be reduced by a factor of 2 in comparison with the traditional pilot-aided phase noise estimation method. We carried out numerical simulation of a 40 Gb/s single polarization transmission system, and the outcome of the investigation indicates that by applying quasi-pilot-aided phase estimation, only four pilot subcarriers are needed for effective phase noise compensation.

Comparison of Noise Compensation Methods for Room Acoustic Impulse Response Evaluations

Comparison of Noise Compensation Methods for Room Acoustic Impulse Response Evaluations

Stochastic feature compensation methods for speaker verification in noisy environments

This paper explores the significance of stereo-based stochastic feature compensation (SFC) methods for robust speaker verification (SV) in mismatched training and test environments. Gaussian Mixture Model (GMM)-based SFC methods developed in past has been solely restricted for speech recognition tasks. Application of these algorithms in a SV framework for background noise compensation is proposed in this paper. A priori knowledge about the test environment and availability of stereo training data is assumed. During the training phase, Mel frequency cepstral coefficient (MFCC) features extracted from a speaker's noisy and clean speech utterance (stereo data) are used to build front end GMMs. During the evaluation phase, noisy test utterances are transformed on the basis of a minimum mean squared error (MMSE) or maximum likelihood (MLE) estimate, using the target speaker GMMs. Experiments conducted on the NIST-2003-SRE database with clean speech utterances artificially degraded with different types of additive noises reveal that the proposed SV systems strictly outperform baseline SV systems in mismatched conditions across all noisy background environments.

Basic characteristics of tissue-equivalent phantom thermoluminescence slab dosimeter using new TL phosphor Li3B7012:Cu

Here we investigate the basic characteristics of the tissue-equivalent phantom thermoluminescence slab dosimeter with synthetic resin type 1 (TEP-TLSD/SR1), a two-dimensional TLD based on TL phosphor Li3B7012:Cu developed by the Urushiyama Research Group. Li3B7O12:Cu has a single glow peak at 120 °C at a heating rate of 0.317 °C s−1. The dose response is linear between 0.1 and 10 Gy. The phosphor, when combined with a synthetic resin, can be molded into 200 mm × 200 mm × 2.5 mm slabs. The system has a Charge Coupled Device (CCD) dependent spatial resolution (pixel pitch) of 640 μm and a pixel response standard deviation of 1.33%. Using simple pixel-based noise compensation, we were able to improve the signal-to-noise ratio (SNR) in the final image. In tests as a TEP, this system gives off axis ratio and percentage dose depth results highly correlated with those of an ion chamber suspended in a water phantom. The TEP-TLSD/SR1 produces similar images to Gafchromic film for X-ray imaging. This TEP-TLSD/SR1 is not only larger than the prototype, but also has a better SNR and improved usability. With further improvements in tissue equivalence, we foresee a system where a TEP and dosimeter are combined into a three-dimensional dosimeter.

A vehicle magnetic noise compensation method for the tetrahedron magnetic gradiometer

The magnetic noise of a vehicle has a strong impact on the magnetic gradiometer, so a vehicle magnetic noise compensation method is proposed. Based on the production mechanism of the vehicle magnetic noise, a mathematic model for vehicle magnetic noise on the tetrahedron magnetic gradiometer is proposed, in which the difference algorithm of the magnetic gradiometer is used to fuse the magnetic noise of each vector magnetometer. In terms of this mathematic model, we propose the noise compensation algorithm and the compensation coefficients recognition method by using the mathematic relations of the 9 components of the magnetic gradient tensor. Simulation results show that the proposed method can efficiently compensate 95.9% vehicle magnetic noise on the magnetic gradiometer. This method can compensate vehicle magnetic noise on the magnetic gradiometer output directly by the compensation coefficients, and realize the holistic noise compensation of the magnetic gradiometer theoretically.

Nonlinear Phase Noise Estimate Based on Electronic Orthogonal Coherent for 112 Gb/s PDM-4QAM System

In this paper, we proposed a novel method of joint phase noise estimate (JPNE) for PDM-M-QAM (M = 4, 16, 32, 64, …) transmission systems, and established the theoretical model to illustrate the operation mechanism. The simulation of laser phase noise and fiber nonlinearity compensation based on the proposed JPNE method had also been demonstrated. For 112 Gb/s PDM-4QAM transmission system, the simulation results had showed that the optimum launch power increased from -4 dBm to at least 0 dBm compared with the condition of no phase noise compensation in reach of all simulation distances.

Electroplated Multi-ring Core Planar Fluxgate

Abstract In this paper we studied multi-ring planar fluxgate with different number of rings. In particular we investigated the effect of the number of rings on the sensitivity and noise of the sensors. Multi-ring cores were expected to return lower noise due to mutual compensation of uncorrelated noise of every ring. Nevertheless, we observed an increase of noise for cores with higher number of rings. We believe this is due to non-uniform composition of the electroplated film, which make the inner rings magnetostrictive and therefore source of larger noise.

Novel iteration-free blind phase noise estimation for coherent optical OFDM

We propose a novel iteration-free blind phase noise estimation scheme for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. In the new algorithm, the cost function is selected as the similar expression with real and imaginary parts as that in the modified constant modulus algorithm, and the new cost function is derived under some assumptions, where it is infinitely approximated by the sine and cosine functions. By means of the analytical formula of the cost function, the initial coarse common phase error can be obtained with only some samples, where the algorithm avoids computational complexity of conventional blind phase noise compensation scheme. In CO-OFDM systems with high-order modulation format (32 quadrature amplitude modulation) and narrow linewidth lasers, it is proved by the simulation results that the phase noise can be effectively compensated with the proposed blind estimation method.

Simple 60-GHz Radio-over-Fiber System with Transmission Distance Improvement Employing Signal-to-Signal Beat Noise Compensation

We propose a simple 60-GHz RoF system using one single-electrode Mach-Zehnder modulator (MZM). By choosing proper carrier frequencies of two MZM driving signals, fiber transmission distance can be extended up to 12 km. Compared with conventional intensity modulation with direct detection using 60-GHz MZM or electro-absorption modulator (EAM), the proposed RoF system can support longer fiber transmission distance (up to 12 km) and has less bandwidth requirement of optical orthogonal frequency-division multiplexing (OFDM) transmitter (34 GHz vs. 64 GHz). However, the generated 60-GHz OFDM signal will have beat noise after square-law photo-detection. In this paper, the beat noise is analytically analyzed. Hence, the beat noise mitigation algorithm with the beat noise re-construction technique is proposed and utilized to reduce beat-noise-induced interference and improve signal-to-noise ratio (SNR). 60-GHz 13.75-Gbps quadrature phase shift keying (QPSK) and 20.625-Gbps 8-quadrature-amplitude-modulation (QAM) OFDM signals with 3-m wireless transmission are experimentally demonstrated and transmitted over 12-km and 6-km single-mode fiber, respectively.

A behavioural modelling of nonlinear RF power amplifiers using noise compensation technique

A nonlinear behavioural model of power amplifiers is proposed with an improved modelling method to fit up to the alternate channels where the noise contributions are dominant. From a memory polynomial model incorporating memory effects (Ku and Kenney 2003), noise contributions are considered for a better modelling. The proposed modelling method is utilised to model power amplifiers for Wideband Code Division Multiple Access (WCDMA) 1700 and 2100 bands. The power amplifier behaviour is modelled within 1 dB accuracy up to the alternate channels.

The effects of site and instrument variability on recognizing odontocete species by their echolocation clicks

This work conducts a systematic study of the impact of variable site and instrument conditions on the performance of a species recognition task. Echolocation clicks were collected from six different sites in the Southern California Bight from multiple deployments of instruments with nine different preamplifiers. The classification performance of a Gaussian mixture model using cepstral features is examined on Risso’s and Pacific White-Sided dolphins. One hundred three-fold Monte Carlo experiments are conducted. When grouped so that each acoustic encounter is either in the training or test set, a mean error rate of 1.9%±4.4σ is obtained. In spite of correction for preamplifier response curves, grouping by preamplifier and site increases error dramatically to 20.9%±18.1σ and 25.9%±28.1σ, respectively. We introduce noise compensation techniques that reduce error rates as follows: by encounter, 0.5%±0.3σ, by preamplifier, 1.7%±2.3σ, and by site, 9.4%±16.7σ.

Efficient MAP-based estimation and compensation of phase noise in MIMO-OFDM receivers

This article proposes an iterative orthogonal frequency division multiplexing receiver employing low-complexity phase noise mitigation to alleviate degradation in the channel estimation and the data detection stages of a spatially multiplexed multiple-input multiple-output communication system. Severe oscillator phase noise gives rise to inter-carrier interference that becomes a limiting factor in sustaining reliable communication link. To mitigate phase distortion in a multi-path Rayleigh fading channel, we built an iterative Bayesian algorithm based on the statistical modeling of the phase noise process. However, the resultant informed estimators require computationally intensive inversion of large dimensional matrices. Taking advantage of the approximate sparsity pattern inherent to the phase noise spectral composition and exploiting decoupled compensators, the proposed sub-optimal scheme suppresses phase noise induced perturbation with a modest complexity increment. Our claims are supported by the numerical analysis, which demonstrate the estimator efficacy considering a generalized oscillator signal distribution network based on the spatial correlation of the phase noise processes.

Joint Uncertainty Decoding for Noise Robust Subspace Gaussian Mixture Models

Joint uncertainty decoding (JUD) is a model-based noise compensation technique for conventional Gaussian Mixture Model (GMM) based speech recognition systems. Unlike vector Taylor series (VTS) compensation which operates on the individual Gaussian components in an acoustic model, JUD clusters the Gaussian components into a smaller number of classes, sharing the compensation parameters for the set of Gaussians in a given class. This significantly reduces the computational cost. In this paper, we investigate noise compensation for subspace Gaussian mixture model (SGMM) based speech recognition systems using JUD. The total number of Gaussian components in an SGMM is typically very large. Therefore direct compensation of the individual Gaussian components, as performed by VTS, is computationally expensive. In this paper we show that JUD-based noise compensation can be successfully applied to SGMMs in a computationally efficient way. We evaluate the JUD/SGMM technique on the standard Aurora 4 corpus. Our experimental results indicate that the JUD/SGMM system results in lower word error rates compared with a conventional GMM system with either VTS-based or JUD-based noise compensation.

A CO-OFDM System With Almost Blind Phase Noise Suppression

We propose a high spectral efficiency coherent optical orthogonal frequency division multiplexing system utilizing a novel and almost blind phase noise compensation method. With the aid of pseudo pilots instead of pilots, laser phase noise can be suppressed effectively while the overhead of system is reduced successfully. Numerical results show that the performance of the proposed pseudo pilot-aided phase noise compensation scheme can approach that of the pilot-aided counterpart, yet achieve higher spectral efficiency even when the phase noise is severe.

Distributed Raman Optical Amplification in Phase Coherent Transfer of Optical Frequencies

We describe the application of Raman Optical-fiber Amplification (ROA) for the phase coherent transfer of optical frequencies in an optical fiber link. ROA uses the transmission fiber itself as a gain medium for bi-directional coherent amplification. In a test setup we evaluated the ROA in terms of on-off gain, signal-to-noise ratio, and phase noise added to the carrier. We transferred a laser frequency in a 200 km optical fiber link with an additional 16 dB fixed attenuator (equivalent to 275 km of fiber on a single span), and evaluated both co-propagating and counter-propagating amplification pump schemes, demonstrating nonlinear effects limiting the co-propagating pump configuration. The frequency at the remote end has a fractional frequency instability of 3e-19 over 1000 s with the optical fiber link noise compensation.

Non-Data-Aided Phase Noise Suppression Scheme for CO-OFDM Systems

We propose a non-data-aided phase noise compensation technique that overcomes the limitation of the zero-overhead decision-directed (DD) phase noise suppression method in high-order constellations for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. The proposed technique consists of two equalization stages. First, a blind adaptive phase offset recovery scheme based on high-order statics, called the dispersion minimization de-rotator, is applied to subcarrier symbols to achieve rough correction of the common phase error because of phase noise. Second, the conventional DD phase noise correction scheme is used to remove the residual common phase error. The proposed method effectively compensates phase noise without the help of pilot signals, especially for high-order constellation CO-OFDM systems, as confirmed by our simulation results.

Stochastic speckle noise compensation in optical coherence tomography using non-stationary spline-based speckle noise modelling.

Optical coherence tomography (OCT) allows for non-invasive 3D visualization of biological tissue at cellular level resolution. Often hindered by speckle noise, the visualization of important biological tissue details in OCT that can aid disease diagnosis can be improved by speckle noise compensation. A challenge with handling speckle noise is its inherent non-stationary nature, where the underlying noise characteristics vary with the spatial location. In this study, an innovative speckle noise compensation method is presented for handling the non-stationary traits of speckle noise in OCT imagery. The proposed approach centers on a non-stationary spline-based speckle noise modeling strategy to characterize the speckle noise. The novel method was applied to ultra high-resolution OCT (UHROCT) images of the human retina and corneo-scleral limbus acquired in-vivo that vary in tissue structure and optical properties. Test results showed improved performance of the proposed novel algorithm compared to a number of previously published speckle noise compensation approaches in terms of higher signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and better overall visual assessment.