Jitter Noise Research Articles

Squeezed quadrature fluctuations in a gravitational wave detector using squeezed light

Squeezed states of light are an important tool for optical measurements below the shot noise limit and for optical realizations of quantum information systems. Recently, squeezed vacuum states were deployed to enhance the shot noise limited performance of gravitational wave detectors. In most practical implementations of squeezing enhancement, relative fluctuations between the squeezed quadrature angle and the measured quadrature (sometimes called squeezing angle jitter or phase noise) are one limit to the noise reduction that can be achieved. We present calculations of several effects that lead to quadrature fluctuations, and use these estimates to account for the observed quadrature fluctuations in a LIGO gravitational wave detector. We discuss the implications of this work for quantum enhanced advanced detectors and even more sensitive third generation detectors.

Transition Parameter “a” Variation of Individual Writing Process

The jitter noise is the dominant media noise in perpendicular recording. It is proportional to cross track correlation and the square of transition parameter “a” [1]. Besides the efforts of minimizing the value of “a,” it is also very important to control the variation of “a” in each individual writing process. In this work, from the time domain head media spacing measurement, there is a significant signal amplitude variation arising from individual writing process at the same writing conditions. After removing the change related to disk morphology, the amplitude difference of individual writing reflects the variation of “a.” Reducing such “a” variation is helpful to control the transition noise.

Bidirectional Pattern-Dependent Noise Prediction With LDPC Codes for HAMR

As areal densities increase, substantial jitter noise is expected in heat-assisted magnetic recording (HAMR). To mitigate the effects of jitter noise, in an earlier work we proposed the bidirectional pattern-dependent noise prediction (BiPDNP) detector, which employs backward linear prediction as well as the conventional forward linear prediction. However, no error correction codes were used in this earlier work. In this paper, we implement BiPDNP in the Bahl-Cocke-Jelinek-Raviv (BCJR) detector, and investigate its performance with low-density parity check (LDPC) codes. For the LDPC coded channel, by combining the BCJR detector with BiPDNP, we observe that a SNR gain of 1 dB (at bit error rate 10 $^{-4}$ with 30% microtrack jitter) is achieved over the conventional BCJR detector. Further, in HAMR channel modeling we employ the thermal Williams-Comstock (TWC) model. Conventionally, a linear relationship for coercivity with temperature is used. In this paper, we update the TWC model by using a nonlinear relationship for coercivity with temperature.

The role of across-frequency envelope processing for speech intelligibility

Speech intelligibility models consist of a preprocessing part that transforms the stimuli into some internal (auditory) representation, and a decision metric that quantifies effects of transmission channel, speech interferers, and auditory processing on the speech intelligibility. Here, two recent speech intelligibility models, the spectro-temporal modulation index [STMI; Elhilali et al. (2003)] and the speech-based envelope power spectrum model [sEPSM; Jo/rgensen and Dau (2011)] were evaluated in conditions of noisy speech subjected to reverberation, and to nonlinear distortions through either a phase jitter process or noise reduction via spectral subtraction. The contributions of the individual preprocessing stages in the models and the role of the decision metrics were analyzed in the different experimental conditions. It is demonstrated that an explicit across-frequency envelope processing stage, as assumed in the STMI, together with the metric based on the envelope power signal-to-noise ratio, as assumed in the sEPSM, are required to account for all three conditions. However, a simple weighting of the across-frequency variance of the modulation power at the output of the (purely temporal) modulation filterbank is assumed to be sufficient to describe the data, i.e., a joint two-dimensional modulation filterbank might not be required.

Unique Measurement and Modeling of Total Phase Noise in RF Receiver

Radio frequency (RF) receivers are common in many modern communications and radar systems, and they suffer from many performance degradation factors due to hardware limitations. Among all performance degradation contributors, phase noise and time jitter are particularly troublesome since they cause random errors which are difficult to compensate. The local oscillator in the receiver front end is a major contributor of phase noise, while the analog-to-digital converter (ADC) introduces time jitter. It is desired to know the accumulated effect of individual phase noise sources and time jitter. The total effect of all phase noise and jitter can be represented by an accumulated phase noise term at the ADC's output, called total phase noise (TPN) in this brief. The focus of this work is on measuring and modeling TPN in the RF receiver by applying optimization techniques. In contrast to traditional phase noise measurement that typically requires a high-quality tunable downconverter, a digital approach using the data captured directly by the RF receiver is proposed. In addition, iterative optimization-based TPN spectral model fitting and statistic modeling are introduced. The model is examined using the measured TPN. It is confirmed that the RF receiver TPN can be viewed as a wide-sense stationary zero-mean Gaussian process with certain spectral profile.

A Time-Domain High-Order MASH $\Delta\Sigma$ ADC Using Voltage-Controlled Gated-Ring Oscillator

In this paper, a time-domain high-order ΔΣ analog-to-digital converter (ADC) using voltage-controlled gated-ring oscillator (VC-GRO) and time-domain multi-stage-noise-shaping (MASH) is introduced. To implement the high-order noise transfer function (NTF), a voltage-controlled oscillator (VCO) and VC-GRO quantizers are cascaded. Unlike conventional high-order ΔΣ ADC using feedback loop, the proposed ADC has advantages that the architecture is open-loop and the quantizer resolution depends on the time resolution, thus making it attractive for deep submicron CMOS process. The performance of the proposed ADC is theoretically analyzed and simulated, including non-ideal conditions such as nonlinearity, mismatch, propagation delay of logic gates, phase noise, and sampling clock jitter.

Influence of monolayer contamination on electric-field-noise heating in ion traps

Electric field noise is a hinderance to the assembly of large scale quantum computers based on entangled trapped ions. Apart from ubiquitous technical noise sources, experimental studies of trapped ion heating have revealed additional limiting contributions to this noise, originating from atomic processes on the electrode surfaces. In a recent work [A. Safavi-Naini et al., Phys. Rev. A 84, 023412 (2011)] we described a microscopic model for this excess electric field noise, which points a way towards a more systematic understanding of surface adsorbates as progenitors of electric field jitter noise. Here, we address the impact of surface monolayer contamination on adsorbate induced noise processes. By using exact numerical calculations for H and N atomic monolayers on an Au(111) surface representing opposite extremes of physisorption and chemisorption, we show that an additional monolayer can significantly affect the noise power spectrum and either enhance or suppress the resulting heating rates.

Improved Decoding Algorithm of Serial Belief Propagation With a Stop Updating Criterion for LDPC Codes and Applications in Patterned Media Storage

In high density patterned media storage system, the “multiple islands per read head” model is taken into account for inter-track interference (ITI) in bit-patterned media (BPM). It has been proposed that low-density parity-check (LDPC) codes could improve the symbol error rate (SER) performance significantly when only considering AWGN noise alone over the storage channel. LDPC decoding algorithm could be applied in LDPC joint decoder of patterned media storage system. In this paper, we proposed a decoding algorithm of serial belief propagation (SBP) with a stop updating criterion for LDPC decoder. Simulation results show that the proposed decoding algorithm could reduce the times of generating and propagating the message in decoding with negligible error rate performance loss over AWGN channels when appropriately choosing the parameter that determines which variable node has been converged. By taking advantage of extrinsic information transfer (EXIT) charts, it is demonstrated that the proposed decoding algorithm could maintain superior SER performance and convergence rate compared with the traditional SBP decoding algorithm. To further explore the performance of the proposed decoding algorithm in “multiple islands per read head” model, we performed a large number of simulations over this channel model with different distribution percentages between the AWGN and the island position jitter noise. Simulation results show that the LDPC codes could improve the SER performance when considering jitter noise while the proposed decoding algorithm behaves excellently over the patterned media storage channel and over the AWGN channel.

Jitter noise dependence on grain structure in recording layer of hard disk drive

Jitter noise dependence on grain structure in recording layer of hard disk drive

A Recorded-Bit Patterning Scheme with Accumulated Weight Decision for Bit-Patterned Media Recording

To achieve high recording density in a bit-patterned media recording system, the spacing between data bit islands in both the along-track and the across-track directions must be decreased, thus leading to the increase of two-dimensional (2D) interference. One way to reduce the 2D interference is to apply a 2D coding scheme on a data sequence before recording; however, this method usually requires many redundant bits, thus lowering a code rate. Therefore, we propose a novel 2D coding scheme referred to as a recorded-bit patterning (RBP) scheme to mitigate the 2D interference, which requires no redundant bits at the expense of using more buffer memory. Specifically, an input data sequence is first split into three tracks in which will then be rotated to find the best 3-track data pattern based on a look-up table before recording, such that the shifted data tracks yield the least effect of 2D interference in the readback signal. Numerical results indicate that the proposed RBP scheme provides a significant performance improvement if compared to a conventional system (without 2D coding), especially when the recording density is high and/or the position jitter noise is large.

Low timing jitter and intensity noise from a soliton Er-fiber laser mode-locked by a fiber taper carbon nanotube saturable absorber

We characterize the timing jitter and intensity noise of an 80-MHz soliton Er-fiber laser mode-locked by a fiber taper carbon nanotube saturable absorber (ft-CNT-SA) up to the Nyquist frequency. The measured rms timing jitter is 3.0 fs (11.0 fs) integrated from 10 kHz (1 kHz) to 40 MHz offset frequency. The measured rms relative intensity noise (RIN) is 0.069% (0.021%) integrated from 10 Hz to 40 MHz (1 MHz) offset frequency. We identify that the resulting timing jitter is dominated by the Gordon-Haus jitter originated from the negative dispersion necessary for soliton mode-locking with a slow saturable absorber.

Seismic attenuation system for the external injection bench of the Advanced Virgo gravitational wave detector

In November 2011 a major upgrade of the Virgo gravitational wave detector was started. After these improvements the detector's sensitivity will have increased by an order of magnitude, increasing the expected event rate by 103 compared to its predecessor. Extensive noise studies showed that this improvement can only be accomplished if a number of optical benches, hosting ancillary optics and optical sensors for the alignment of the interferometer, are isolated from seismic ground motion to reduce the amount of beam jitter and control noise they introduce. Here we present the first of these systems: the External Injection Bench Seismic Attenuation System, or EIB-SAS, which is able to reduce seismically induced motion of the external injection bench (last bench before laser beam enters the vacuum system) by more than 40dB above 10Hz in 6 degrees of freedom.

Effect of interpolation filter in digital quadrature amplitude modulation signal resampling

In this study, a closed-form equation is derived which relates the mean-squared error (MSE) to the frequency response of the interpolation filter. Effects of additive white Gaussian noise and timing jitter on the MSE are accounted for in the equation. By using properties of the Nyquist signalling pulse, a simple approximation to the MSE equation is obtained, which is found to be accurate over the range of excess bandwidths commonly used in quadrature amplitude modulation receivers.

Determination of Bit Patterned Media Noise Based on Island Perimeter Fluctuations

We measured the fluctuation in shape of magnetic islands in bit patterned media fabricated by laser interference lithography. This fluctuation can be accurately described by a model based on a Fourier series expansion of the perimeter of the islands. The model can be easily linked to amplitude and jitter noise. We show that the amplitude and jitter noise are in principle correlated, and the jitter noise increases with increasing island area. The correlation is small for media prepared by laser interference lithography, but expected to gain importance for high density bit patterned media.

Analytical Expressions for the Readback Signal of Timing-Based Servo Schemes

Timing-based servo (TBS) is a powerful technology widely used in state-of-the-art tape systems for track following. To optimize TBS systems for future operating points with aggressive track-density scaling, an accurate model is needed to characterize how the servo read head geometry, servo format parameters, and magnetic media properties affect the readback signal. In this paper, we derive new analytical closed-form expressions for the readback signal of shielded magneto-resistive (MR) heads scanning over the magnetic transitions of TBS patterns. The expressions, derived via the reciprocity principle, are applicable to arctan-shaped transitions between arbitrarily magnetized areas of a thin-film magnetic medium and are given in the displacement and wavevector domain. We apply these new expressions to analyze isolated transitions as well as multi-transition TBS patterns on longitudinal, non-oriented or perpendicular media. Comparison between experimentally captured servo readback signals and the analytical expressions show an excellent match. By adding electronics and transition jitter noise, the readback signal expressions can be extended to a servo channel model suitable for TBS performance prediction by means of Monte Carlo simulations and/or bounds on the variance of the position-error signal.

Establishment of a Normative Pediatric Acoustic Database

OBJECTIVES To establish a normative pediatric acoustic database and to analyze the acoustic characteristics of the age groups studied. DESIGN Prospective gathering of acoustic parameters on healthy children aged 4 to 18 years. SETTING An outpatient pediatric otolaryngology clinic. PATIENTS A total of 335 children (165 girls and 170 boys) were evaluated. MAIN OUTCOME MEASURES Normative values were obtained for the acoustic parameters studied. RESULTS Discrete fundamental frequency changes occurred at ages 11 and 14 years in girls and ages 12 and 16 years in boys. Values for jitter percentage, shimmer percentage, and noise to harmonic ratio fell within the normative thresholds of adult values. CONCLUSIONS This is the largest pediatric computerized voice analysis database in the English language. This database has been designed to develop an age- and sex-based growth chart to track the developing pediatric voice as it changes with maturation. A distinct vocal profile of girls and boys is evident, with key changes noted at critical periods of development and with significant differences among fundamental frequency between and within sexes. A comprehensive database can be used to help aid future voice therapy and phonosurgical strategies and provide the foundation for future studies into the development of the pediatric voice as it matures into adulthood.

Extended Kalman Filter Based Frequency Estimation for High Dynamic Environment

Suppressing jitter noises and keep precise track is of great importance in coherent communication systems. This paper proposes and analyzes a new extended kalman filter (EKF) based carrier recovery loop for high dynamic and low carrier-to-noise ratio environment. In this algorithm, EKF filter take the phase error between input signal and local oscillator and has a simple measurement equation. Simulations show that the method is feasible and has good performance.

수신 성능 분석을 이용한 위성항법 신호 설계 방안

GNSS의 중요성이 점점 증가하면서, 독자적인 위성항법시스템의 구축에 대한 필요성이 제기되고 있다. 위성항법 시스템 구축 시 위성 신호 설계는 반드시 필요한 과정이며, 이를 위한 요구조건 규정이 필수적이다. 본 논문에서는 위성 항법 설계 요소에 대한 수신 성능 분석을 수행하며, 이를 이용한 신호 설계 방안에 대해 제시한다. 먼저 설계 요소에 따른 후보군 정의 후, 성능 평가 지표에 따라 신호 후보의 수신 성능을 분석한다. 이때 다양한 적용 분야에서의 신호 성능을 판단하기 위하여 성능 평가 지표가 갖는 가중치를 정의하였으며, 정규화된 성능 평가 지표와 가중치간의 연산을 통해 최종적으로 성능 비교값을 도출하였다. 위성 항법 신호 설계 요소로 코드, 변조 기법, 반송파를 고려하였으며, 성능을 평가하기 위한 평가 지표로는 상관폭, DLL 및 PLL 열잡음 지터, 주파수 대역폭, 사이드로브 피크율을 정의하였다. 또한 적용 분야로는 측위 성능, 잡음에 대한 강인성, 대역 효율성을 고려하였다. 제안한 설계 방안 적용 시 소프트웨어 기반의 시뮬레이터를 이용하여 성능 분석을 수행하였으며, 최종적으로 성능 분석 결과로부터 신호 후보의 성능을 객관적으로 판단하고 비교하였다. As the importance of GNSS system increases, the necessity of independent system is increased also. When the independent GNSS system is required, GNSS signal design is necessary with requirement definition. This paper suggests the design method of GNSS signal using the analysis result of receiver performance. First, the candidates are defined based on the design elements. Then the receiver performance of the candidates is analyzed based on the performance evaluation parameters. The weights of performance evaluation parameter are defined in order to consider the receiver performance in a various aspects. Finally, the calculation of normalized performance evaluation parameters and weights are derived to obtain the compared value for signal selection. Spreading code, modulation method and carrier frequency are considered as design parameters. Also, correlation width, DLL PLL thermal noise jitter, frequency bandwidth and side lobe peak ratio are considered as performance evaluation parameters. And positioning performance, robustness to noise, bandwidth efficiency are considered as the performance aspects. This paper analyzes the performance of each candidate using software based simulator and suggest the method to compare objectively the performance of each candidates.

Multilayer Architectures for Facial Action Unit Recognition.

In expression recognition and many other computer vision applications, the recognition performance is greatly improved by adding a layer of nonlinear texture filters between the raw input pixels and the classifier. The function of this layer is typically known as feature extraction. Popular filter types for this layer are Gabor energy filters (GEFs) and local binary patterns (LBPs). Recent work [1] suggests that adding a second layer of nonlinear filters on top of the first layer may be beneficial. However, it is unclear what is the best architecture of layers and selection of filters. In this paper, we present a thorough empirical analysis of the performance of single-layer and dual-layer texture-based approaches for action unit recognition. For the single hidden layer case, GEFs perform consistently better than LBPs, which may be due to their robustness to jitter and illumination noise as well as to their ability to encode texture at multiple resolutions. For dual-layer case, we confirm that, while small, the benefit of adding this second layer is reliable and consistent across data sets. Interestingly for this second layer, LBPs appear to perform better than GEFs.

Bi-Directional Pattern-Dependent Noise Prediction for Heat-Assisted Magnetic Recording With High Jitter Noise

In this paper, we first report the results of an investigation of perpendicular heat-assisted magnetic recording (HAMR) channels containing high jitter noise that is likely to be the case at very high areal densities (e.g., 4 Tb/in2). To model the HAMR channel, we use the thermal Williams-Comstock model and the microtrack model to derive the transition response, without large thermal spot approximation. Further, we propose a novel bi-directional pattern-dependent noise prediction (biPDNP) detector to improve the performance of the HAMR channel under high jitter noise conditions. The biPDNP detector utilizes backward linear prediction in the noise prediction process, as well as the conventional forward linear prediction. At bit error rate of 10-3, biPDNP detector offers 0.6-1.4 dB performance gain over the conventional PDNP detector.