Noise Compensation Research Articles

Digital Compensation of Relative Phase Noise for DSCM Based Coherent Transmission System Using Forward Pumped Distributed Raman Amplification

Digital Compensation of Relative Phase Noise for DSCM Based Coherent Transmission System Using Forward Pumped Distributed Raman Amplification

Parameter estimation via weak measurement with machine learning

Weak measurement technique can provide high sensitivity for parameter estimation tasks. However in practice, time-varying errors induced by noises significantly compromise its advantages. While prolonging the measurement time can reduce the effect of short-term correlated noises (e.g. white noise), it will on the other hand increase the estimation errors in the presence of long-term correlated noises(e.g. 1/f and 1/f2 noises). The main obstacle of compensating these kind of errors is to precisely predict the time-varying trend of error, where the disturbances that causing error are highly unpredictable. In this work, we propose a weak measurement scheme with assistance of machine learning algorithm, which can ‘learn’ the time-varying trend of errors from data without an explicit model. In order to verify the feasibility of this scheme, we carry out a time-delay measurement experiment and achieve the noise compensation via machine learning algorithm. Experimental results demonstrate a 6 dB reduction of mean-square error comparing to the setup without machine learning, which suggest that our scheme can effectively improve the performance of weak measurement in the presence of long-time correlated noises.

Output Feedback Algorithm for Nonlinear Systems with Compensation of Bounded Disturbances and Measurement Noises

The output feedback algorithm for dynamic plants with compensation of parametric uncertainty, external disturbances and measurement noises is synthesized. The plants are described by a nonlinear system of differential equations with vector input and output signals. Unlike most existing control schemes in this paper the dimensions of the measurement interference and the output signal are equal, the sources of the signals of disturbances and disturbances are different, parametric and external disturbances can be present in any equation of the plant model. For simultaneous compensation of disturbances and measurement noises it is proposed to consider two channels. On the first channel a part of the measurement noises will be estimated which will allow partial recovery the information about the plant noisy output. On the second channel the disturbances will be compensated. Thus, at least two independent measurement channels are required for simultaneous compensation of disturbances and measurement noises. Sufficient conditions for calculating the parameters of the algorithm in the form of solvability of the linear matrix inequality are obtained. It is shown that the equation of a closed-loop system obtained on the basis of the proposed algorithm depends on the disturbances and the smallest component of the measurement noise. However, if the smallest component cannot be identified a priory, the results of the transients depend on the component of the noise that will be selected in the synthesis of the control system. Thus, unlike most existing control schemes, where the equation of a closed-loop system depends on disturbance and noise, the resulting algorithm provides better transients, because they do not depend on the entire noise vector, but only on its smallest (one) component. The simulations for a third-order nonlinear plant and the synchronization of an electrical generator connected to the power grid are presented. Numerical examples illustrate the effectiveness of the proposed scheme and the robustness with respect to random components in the noises and disturbances.

A new optical frequency transfer method via fibre based on active phase noise compensation with single acousto-optic modulator

A new optical frequency transfer method via fibre based on active phase noise compensation with single acousto-optic modulator

Model Based Control for Automatic Compensation of Combustion Noise and Smoke

Model Based Control for Automatic Compensation of Combustion Noise and Smoke

Компенсация шума движения электродного датчика напряжённости электрического поля в морской воде

Компенсация шума движения электродного датчика напряжённости электрического поля в морской воде

Exploration of Multiscale Geometric Analysis for Enhancement and Structure Detection in MRCP Images

Magnetic Resonance Cholangiopancreatography (MRCP) images are used in the diagnosis and treatment planning of the bile ducts and the liver. The ability to diagnose and treat such diseases in recent times has increased with greater importance placed on the effective use of non-invasive medical imaging. However, MRCP images are often noisy (low signal-to-noise ratio) and suffer from the influence of artifacts, partial volume and large inter-image variations. This paper evaluates the suitability of several Multiscale Geometric Analysis (MGA) techniques, to improve the quality of the 2D MRCP images and enhance the detection of the biliary structures within them. Tests results, evaluated subjectively to correspond with the human visual perception, achieved promising results for contourlets, curvelets as well as a non-orthogonal wavelet noise compensation implementation. The findings may contribute to assist in the development of automatic computer-aided diagnosis systems for liver diseases affecting the bile ducts as well as in clinical diagnosis.

Autonomous relative navigation for noncooperative target using stereo vision measurements

An autonomous relative navigation method based on stereo vision measurements is proposed for noncooperative targets without any prior information. Firstly, a target identification model using only stereo vision measurements is established. Based on the relative position vector computed from the stereo image sequence, the initial state vector of the noncooperative target and navigation filter covariance matrix are initialized by taken spacecraft attitude and camera installation information into account. Then, an extended Kalman filter considering state noise compensation as well as observation variance matrix and state noise matrix adaptive correction is formulated to solve the noncooperative relative navigation problem. Finally, a low Earth orbit, noncooperative target approaching navigation scenario is considered. The simulation results demonstrate the effectiveness of the proposed method for noncooperative autonomous relative navigation.

Quantifying choriocapillaris flow deficits using global and localized thresholding methods: a correlation study.

To investigate the correlation and agreement of two previously published choriocapillaris (CC) quantification methods using a normal database with swept-source optical coherence tomography angiography (SS-OCTA). Normal adult subjects from all age groups imaged by SS-OCTA were used in this study. Each subject was imaged with 3 mm × 3 mm and 6 mm × 6 mm scan patterns centered on fovea, upon which en face CC images were generated by segmenting volumetric OCTA data. After signal compensation and removal of projection artifacts and noise, CC images were analyzed to identify flow deficits (FD) using two published methods. The first method utilized standard deviation from a young normal database (SD method) as the global thresholding while the second method utilized fuzzy C-means algorithm (FCM method) with local thresholding. Both methods segmented FDs from CC images and quantified FD density (FDD) and mean FD size (MFDS). In each 3 mm × 3 mm scan, three regions were quantified: a 1 mm circle (C1), a 1.5 mm rim (R1.5) and a 2.5 mm circle (C2.5). In each 6 mm × 6 mm scan, five regions were quantified: C1, R1.5, C2.5, a 2.5 mm rim (R2.5) and a 5 mm circle (C5). Spearman correlation and Bland-Altman plot analyses were conducted to compare the two methods. Data obtained from 164 normal subjects (age: 56±19, 59% females) were used in this study. Strong correlations were observed between the two methods in all comparisons (r: 0.78-0.94, all P<0.0001). Overall MFDS provided higher or comparable correlation coefficients (r) compared to FDD. We have also observed stronger correlations in the central macula compared to parafoveal and perifoveal regions for both FDD and MFDS. In regions of C1, R1.5 and C2.5, 6 mm × 6 mm scans resulted in better agreement (smaller mean bias, similar or tighter limit of agreement) between the two methods for both FDD and MFDS compared to 3 mm × 3 mm scans. There are strong correlations and satisfactory agreement between SD method and FCM method. SD method requires the reference to a normal database for CC quantification while FCM does not. Both methods could be used for the analysis of CC FDs in clinical settings depending on specific study designs such as the availability of a normal database.

Fiber Propagation-Induced Mode Partition Noise in Millimeter-Wave Radio-Over-Fiber Systems

In this letter, we study and demonstrate, for the first time, how chromatic dispersion causes laser mode partition noise at millimeter-wave (mm-wave) frequencies. A 60-GHz radio-over-fiber (RoF) transmission system employing an optical frequency comb is theoretically and experimentally investigated. Chromatic dispersion is a limiting factor in RoF systems, which induces power fading and phase noise on the resultant mm-wave beating carriers. Furthermore, experimental measurements in this letter show that when transmitting optical comb spectrum across kilometers of optical fiber, chromatic dispersion destroys partition noise compensation between modes. Therefore, the beat note carrier suffers from intensity noise impairments that degrade the system performance.

A Carry Chain-Based ADMFC Design on an FPGA for EMI Reduction and Noise Compensation

An all-digital multi-frequency clocking (ADMFC) circuit is proposed to reduce electromagnetic interference (EMI) on a field-programmable gate array (FPGA) architecture, while supporting dynamic adaptation to voltage noises. The proposed ADMFC uses dedicated high-speed carry chain paths in an FPGA to finely adjust the clock frequency by controlling the number of carry propagations on the carry chain logics (CARRY4 cells) in the delay line of a ring oscillator. Moreover, supply voltage variation and noise caused by circuit switchings can be compensated by dynamically adjusting the length of ripple carry propagations on the cascaded CARRY4 cells in response to the detected voltage variation. Finally, a selectable modulation profile is devised to provide a much suitable profile between two different profiles at run-time for the given noise constraints and working environment of a chip. Measurement results show that at the frequency of 44.6[Formula: see text]MHz, the ADMFC can obtain 17[Formula: see text]dB and 19.4[Formula: see text]dB EMI attenuations with a 7.5% spreading ratio when using triangular and sawtooth profiles, respectively. The proposed ADMFC is suitable for applications such as biological sensor nodes or IoT related systems which typically operate at a low-frequency band.

Passive compensation of intensity and polarization-induced noise by a quadrature demodulation technique in a resonator optic gyroscope.

Polarization-induced noise is a dominant noise that seriously hinders the progress of resonator optic gyroscopes. Many countermeasures have been developed but showed insufficient performance. In this paper, we propose a quadrature demodulation technique (QDT) that adopts references of both sine and cosine to demodulate the signal. Theoretical analyses of the polarization effect and QDT are shown, and experimental results are listed and compared. Experimental results are consistent with theoretical analyses. QDT shows great performance in suppressing environment- and polarization-induced phase fluctuation of signal. We also demodulate the intensity-dependent coefficient of 2Ωt term, which is demonstrated effective for compensating polarization-induced intensity noise together with QDT. The scheme shows significant progress in improving long-term stability.

Transfer of Highly Stable Frequency Signals on a 150 km Fiber-Optic Communications Line

The results are presented for the study of an installation for transmission of a highly stable frequency signal with relative instability no greater than 4·10–17 on a fiber-optic communications line over a distance of 150 km. The installation uses external modulation of laser radiation and active electronic compensation of phase noise. The installation makes it possible to provide synchronization or time scale comparison of mutually separated time and frequency standards that are a component of the highest-category time and frequency standards.

A Universal Microwave Photonic Receiving Channel

Main characteristics of a model of the microwave photonic receiving channel with optical heterodyning have been numerically simulated and experimentally investigated. The transducer is based on a twoarm (signal and reference) balanced circuit with a continuous wave laser, amplitude modulators, narrow-band optical filters, and a photodetector. The possibility of implementation of the receiving channel with a signal-to-noise ratio of up to 60–70 dB, a carrier frequency of up to 40 GHz and more, and a detection bandwidth of up to 1 GHz is demonstrated. It is shown that semiconductor lasers without outer stabilizing cavities can be used in an optical pumping source by means of compensation of the laser frequency noise. It has been found, that if the modulator working point corresponds to the optical carrier frequency suppression mode, the noise characteristics of the detector can be maintained without application of narrow-band optical filters.

Experimental demonstration of 72% reach enhancement of 36Tbps optical transmission system using mid-link optical phase conjugation

We experimentally demonstrate nonlinear noise compensation in an optical phase conjugation assisted 1st order Raman amplified 30x30Gbaud DP-QPSK transmission system with a spectral efficiency of 3.6b/s/Hz. We show that by optimizing the link symmetry, even with only 1st order Raman amplification a single, mid-link, optical phase conjugation compensates for 90% of the signal-signal nonlinear interference resulting in a 2.3dB performance enhancement. We show that increasing the number of optical phase conjugations in the presence of 10% residual nonlinearity results in a reduction in the performance enhancement owing to an enhancement in the nonlinear noise generation efficiency of the system. We achieve a record 72% optical phase conjugation enabled reach enhancement of the 30x30Gbaud DP-QPSK signals.

Experimental Demonstration of a Low-Complexity Phase Noise Compensation for CO-OFDM Systems

In this letter, a low-complexity phase noise compensation scheme based on Kalman filtering theory is experimentally demonstrated for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) transmissions. The proposed scheme can operate in two modes, pilot-aided mode and blind mode, resulting in a variety of phase noise tracking configurations upon particular transmission scenario. At a bit error rate of $3.8\times 10^{-3}$ and for 40 GBaud 16-QAM 64 subcarriers CO-OFDM systems, the proposed method operating in the pilot-aided mode reduces the pilot overhead by a factor of 2 in comparison with the conventional pilot-aided scheme, while in the blind mode, our scheme’s complexity is far superior to one of the state-of-the-art computational efficient decision-direct-free blind approach by a factor of 20.

Delay Effect on Coherent Transfer of Optical Frequency Based on a Triple-Pass Scheme**Supported by the National Natural Science Foundation of China under Grant No 61378037, and the Fundamental Research Funds for the Central Universities under Grant No JUSRP51628B.

We demonstrate a triple-pass scheme for coherent transfer of optical frequency and the delay effect on the fiber phase noise compensation. It is theoretically proved that the delay effect consists of both fiber delay and servo delay. The delay effect confines the servo bandwidth within 1/8τ and induces a residual fiber phase noise after noise compensation. For a 25-km-long fiber, the servo bandwidth is found to be around 1 kHz, and the fiber phase noise is suppressed approaching to the theoretical limitation. The triple-pass scheme enables the simultaneous transfer of optical frequency to multiple remote users. The performance of noise compensator in the triple-pass scheme can achieve a similar level result compared with that in the double-pass scheme.

Digital Phase Noise Compensation for DSCM-Based Superchannel Transmission System With Quantum Dot Passive Mode-Locked Laser

We propose a simplified digital phase noise compensation technique for a Nyquist pulse-shaped digital subcarrier multiplexed (DSCM) coherent optical transmission system, employing an optical frequency comb based on Quantum dot passive mode-locked laser (QD-PMLL). Our results show that the impact of dominant common mode phase noise can be efficiently compensated at the receiver by digitally mixing the data sideband with the complex conjugate of the residual carrier component. This digital mixing technique resulted in better bit error rate performance compared to the conventional mth power Viterbi-Viterbi algorithm for QPSK and blind phase noise compensation for 16-quadratic-amplitude modulation formats, especially in the presence of large phase noise. To this end, exploiting the mutual coherence between the mode-locked comb lines of QD-PMLL, we numerically demonstrate its potential applicability as a transmission source for coherent optical superchannel transmission.

2.8 km fiber link with phase noise compensation for transportable Yb+ optical clock characterization

The operation of a 2.8 km fiber link at 1.14 µm for ultrastable optical frequency dissemination, which will allow for the characterization of transportable Yb+ based optical clock instability via a comparison to another frequency standard, was demonstrated. Active fiber noise compensation allows for the obtaining of a fractional frequency instability of at a 1100 s averaging time. The performance of the link under the influence of mechanical perturbations was also tested.

Realistic Lower Bound on Elevation Estimation for Tomographic SAR

The noise in a tomographic synthetic aperture radar (Tomo-SAR) model is normally assumed to be independent and identically distributed (i.i.d.) Gaussian. In this paper, the correlated Tomo-SAR model is introduced by studying the effect of random residual phase and correlated additive Gaussian noise, and a realistic and general hybrid Cramer–Rao bound (HCRB) on elevation estimation is derived for such a model. Then, a simplified calculation of the HCRB is proposed when the bound of elevation is the main focus. Computer simulations are performed to analyze the proposed HCRB for elevation estimation. The results obtained from estimators based on compressive sensing and distributed compressive sensing show that the proposed HCRB can provide a more realistic bound than the CRB derived with the white additive noise and perfect phase compensation assumption. This is also validated through processing results on real data acquired by TerraSAR-X/Tandem-X sensors.