Sampling Jitter Research Articles

Analysis and Design of Timing Recovery Schemes for DMT Systems over Indoor Power-Line Channels

Discrete multitone (DMT) modulation is a suitable technique to cope with main impairments of broadband indoor power-line channels: spectral selectivity and cyclic time variations. Due to the high-density constellations employed to achieve the required bit-rates, synchronization issues became an important concern in these scenarios. This paper analyzes the performance of a conventional DMT timing recovery scheme designed for linear time-invariant (LTI) channels when employed over indoor power lines. The influence of the channel cyclic short-term variations and the sampling jitter on the system performance is assessed. Bit-rate degradation due to timing errors is evaluated in a set of measured channels. It is shown that this synchronization mechanism limits the system performance in many residential channels. Two improvements are proposed to avoid this end: a new phase error estimator that takes into account the short-term changes in the channel response, and the introduction of notch filters in the timing recovery loop. Simulations confirm that the new scheme eliminates the bit-rate loss in most situations.

Block-Based Methods for the Reconstruction of Finite-Length Signals From Nonuniform Samples

Two novel block-based algorithms are presented for the reconstruction of uniform samples given the nonuniform samples. The first algorithm uses a sinc interpolator whereas the second one uses a DFT-based interpolator. It is shown that the proposed algorithms are stable and the error due to noise and sampling jitter is bounded by the corresponding error norms of noise and jitter, respectively. We show that both of the block-based algorithms provide nearly perfect reconstruction for a class of practically time and bandlimited signals. Boundary effects are considered and single and multiblock processing is discussed. A modified block-based algorithm is developed by using the windowing technique in order to improve the mean-squared error (MSE) performance for nonbandlimited signals. It is shown that this algorithm performs better than a group of alternative algorithms, including Yen's third algorithm, for a variety of signal, noise, and sampling grids

Parasitic diffuse reflection in a Fourier transform spectrometer yielding subharmonic ghosts and line-shape distortion

When using a high-resolution Fourier transform spectrometer (FTS) in a cube-corner configuration, subharmonic ghosts are observed in the spectrum. These ghosts are attributable to parasitic diffuse reflections on the mirrors of the FTS arm. The reflected beams skip a part of the interferometer and travel a different path from the main beam thus experiencing a smaller optomechanical gain. These reflections are present in the reference laser channel as well as on the measurement channel, and each affect the estimated spectrum differently. The sampling grid generated by the reference laser has periodic errors that are synchronized with the fringe signal. The measured spectrum can therefore exhibit sampling jitter ghosts at submultiples of the reference laser wavenumber in addition to its own additive subharmonics. The diffuse reflection experiencing the nominal optomechanical gain, such as in a plane-mirror configuration, will impact directly on the instrument line shape and on the radiometric accuracy of the spectrometer since some radiation is not propagating at the expected angles in the instrument.

Effects of Reference Laser Intensity Noise in a Fourier Transform Spectrometer

Many noise sources deteriorate the performance of a Fourier-transform spectrometer. When such an instrument utilizes a reference source such as an HeNe laser to sample the measurement data, it is desirable to determine how the intensity fluctuations of the reference source will affect the final spectrum. This text shows how the intensity noise of the reference laser is transformed at the output of the interferometer, how it translates into a sampling jitter by a simple linear relation under a small bandwidth approximation, and how it is manifested in the final spectrum as a noise floor. Analytical and simulation results show that for an instrument designed for optical communication applications, the intensity noise of the reference laser may be one of the dominant noise source limiting the overall performance of the instrument.

BIAS COMPENSATED LEAST SQUARES ESTIMATION OF CONTINUOUS TIME OUTPUT ERROR MODELS IN THE CASE OF STOCHASTIC SAMPLING TIME JITTER

This work investigates how stochastic unmeasureable sampling jitter noise affects the result of system identification, and proposes a modification of known approaches to mitigate the effects of sampling jitter. By just assuming conventional additive measurement noise, the analysis shows that the identified model will get a bias in the transfer function amplitude that increases for higher frequencies. A frequency domain approach with a continuous time system model allows an analysis framework for sampling jitter noise. This leads to a bias compensated (weighted) least squares algorithm. A continuous time output error model is used for numerical illustration.

Approximate models for continuous-time linear systems with sampling jitter

The behaviour of single input, single output, continuous time systems sampled with various types of jitter in both measurement and control action is investigated. It is shown that the effects of jitter can be modelled by approximations for the plant dynamics, and additive noise constructed by the modulation of plant signals with the jitter. These approximations give useful insights for digital controller design.

CDMA System Sensitivity to<tex>$SigmaDelta$</tex>A/D Conversion

In this paper, the performance of a code-division multiple-access (CDMA) system using digital frequency conversion is analyzed and modeled. The joint effect of channel noise, sampling jitter, and analog-digital converter (ADC) errors is discussed and modeled assuming uniform converters. Variable resolution memoryless and /spl Sigma//spl Delta/ ADCs are considered, and the sensitivities of the resulting systems to channel noise, sampling jitter, and overloading errors are compared.

Experimental Study of Jitter Effect on Digital Downconversion Receiver with Undersampling Scheme

Undersampling (or bandpass sampling) phase modulated signals directly at high frequency band, the harmful effects of the aperture jitter characteristics of ADCs (Analog-to-Digital converters) and sampling clock instability of the system can not be ignored. In communication systems the sampling jitter brings additional phase noise to the constellation pattern besides thermal noise, thus the BER (bit error rate) performance will be degraded. This paper examines the relationship between the input frequency to ADC and the sampling jitter in digital IF (Intermediate Frequency) downconversion receivers with undersampling scheme. This paper presents the measurement results with a real hardware prototype system as well as the computer simulation results with a theoretically modeled IF sampling receiver. We evaluated EVM (Error Vector Magnitude) in various clock jitter configurations with commonly used and reasonable cost ADCs of which sampling rates was 40 MHz. According to the results, the IF input frequencies of QPSK (16 QAM) signals were limited below around 290 (210) MHz for wireless LAN standard, and 730 (450) MHz for W-CDMA standard, respectively, in our best configuration.

Fault-Tolerant Vibration Control in a Networked and Embedded Rocket Fairing System

Active vibration control using piezoelectric actuators in a networked and embedded environment has been widely applied to solve the rocket fairing vibration problem. However, actuator failures may lead to performance deterioration or system dysfunction. To guarantee the desired system performance, the remaining actuators should be able to coordinate with each other to compensate for the damaging effects caused by the failed actuator in a timely manner. Further, in the networked control environment, timing issues such as sampling jitter and network-induced delay should be considered in the controller design. In this study, a timing compensation approach is implemented in an adaptive actuator failure compensation controller to maintain the fairing system performance by also considering the detrimental effects from real-time constraints. In addition, time-delay compensation in the networked control system is discussed, which is able to reduce damaging effects of network-induced delays.

Timing Uncertainties of A/D Converters: Theoretical Study and Experiments

For high-speed analog-to-digital converters, sampling jitter is a relevant parameter, limiting over-all performances of mixed-signal systems. Among the several contributions usually encountered in such systems, this paper focuses on the one generated by the clock interface and sampling circuits of the converter. To have an accurate description of this internal sampling jitter, a theoretical model is first introduced and then experimentally validated.

Improved high-T/sub c/ superconductor sampler circuits using Josephson transmission line buffers

We report on an increase of the measurement bandwidth of a high-T/sub c/ superconductor sampler circuit. The circuit composes a waveform measurement system, in which it is cooled by a compact single-stage cryocooler and operates at a temperature of 35-40 K. In the sampler circuit, there exists a sampling jitter due to thermal fluctuation in the critical current of the pulse generator trigger junction. To reduce the jitter, one can overdrive the trigger junction. However, leakage current into the adjacent sampler element due to parasitic inductance is an obstacle to the use of a larger trigger current. We attempted to suppress the leakage current by inserting a Josephson transmission line (JTL) buffer into the sampler circuit. It was found that a trigger current two-times larger than that of the conventional circuit became possible with the addition of a four-stage JTL and that the frequency at which the measured amplitude decreases by 3 dB increased from 7 GHz to 14 GHz. This result suggests that the jitter was suppressed in the sampler circuit with the JTL buffer.

Behavioral modeling of switched-capacitor sigma-delta modulators

This paper presents a complete set of blocks implemented in the popular MATLAB SIMULINK environment, which allows designers to perform time-domain behavioral simulations of switched-capacitor (SC) sigma-delta (/spl Sigma//spl Delta/) modulators. The proposed set of blocks takes into account most of the SC /spl Sigma//spl Delta/ modulator nonidealities, such as sampling jitter, kT/C noise, and operational amplifier parameters (white noise, finite DC gain, finite bandwidth, slew rate and saturation voltages). For each block, a description of the considered effect as well as all of the implementative details are provided. The proposed simulation environment is validated by comparing the simulated behavior with the experimental results obtained from two actual circuits, namely a second-order low-pass and a sixth-order bandpass SC /spl Sigma//spl Delta/ modulator.

Sampling clock jitter effects in digital-to-analog converters

This paper describes sampling clock jitter effects in digital-to-analog converters. A formula for the output error power due to sampling clock jitter for a sinusoidal input is derived and verified by numerical simulations, and its spectrum characteristics is shown. Also its effects on DAC SNR is clarified by numerical simulation as follows: (i) When the total noise power outside as well as inside the signal band is taken into account, the DAC SNR remains almost constant regardless of the sampling jitter. (ii) However, when an analog lowpass filter follows the DAC and only the noise power inside the signal band is considered, the DAC SNR degrades as the jitter increases and the input signal frequency becomes higher. Thus the sampling clock jitter is serious for the high speed DAC.

Stability of On-line Compensated Real-time Scheduled Control Tasks

Real-time scheduling methods introduce various types of jitter in task instance execution. For real-time computer-controlled systems, the introduced sampling jitter and sampling-actuation delays may degrade the system performance and even lead to instability in the system. The degradation of the system performance can be compensated on-line by updating the controller parameters at each controller task instance execution, in what we call the compensation approach. In this paper we present stability analysis for controller tasks that perform the compensation approach.

Bit-rate sensitivity of filter-bank-based VDSL transmission to timing errors

The performance degradation of filter-bank-based multicarrier transmission due to timing errors is investigated. The receiver is made of a fractionally spaced linear or decision-feedback equalizer designed for some sampling phase. The actual sampling phase is different and the impact of the difference on the performance is investigated. Sampling phase offset and jitter are considered. Besides, assuming the sampling phase error can be estimated the efficiency of various types of interpolation is investigated.

A NRZ-output amplifier for RSFQ circuits

Interfaces between RSFQ circuits in the Return-to-Zero (RZ) and semiconductor circuits in the Non-Return-to-Zero (NRZ) mode are developed for data transmission at about 10 GHz clock frequencies reducing the errors owing to a finite sampling jitter of conventional room temperature equipment. A prototype of a NRZ output interface with the Nb-Al/sub 2/O/sub 3/-Nb technology has been simulated, implemented and successfully tested at 100 MHz. The interface can easily be combined with a superconducting pulse amplifier for NRZ output signals in the range of several mV. Corresponding simulations and a layout of the amplifier are presented.

Sensitivity of a 1.4 GHz direct-sampling digital radiometer

This paper presents a novel direct RF sampling receiver architecture that will greatly facilitate the implementation of higher spatial resolution satellite radiometers for improved near-term climate forecasting. Direct-sampling is especially suitable for integration onto the distributed, multiple element platform used in L-band synthetic thinned array radiometry (STAR). To evaluate the direct-sampling concept, the authors have developed a statistical model that predicts the worst case radiometric sensitivity for a 1.4 GHz digital receiver. Theoretical results show that only 2-3 bits of converter resolution are needed to approach the performance of an ideal analog radiometer and that sampling jitter will not significantly degrade the performance of STAR.

アニーリングによるパラメータ推定を伴う最大エントロピー法に基づく画像復元

A method for spatial resolution enhancement based on Maximum Entropy Method (MEM) with simulated annieling is proposed. Using overlap sampling with a low resolution of sensor, high spatial resolution (corresponding to the sampling interval) can be achieved through ground data processing with image restoration methods. Through the experiments with simulation imagery data derived from AVHRR data, it was found that spatial resolution enhancement can be achieved, MEM is superior to the others when S/N is poor (less than 33) while Conjugate Gradient method is superior when the S/N is higher than 33. It was also found that the Conjugate Gradient method is superior to the proposed method for the existing sampling jitter.

Intersymbol interference due to mismatched roll-offfactors and sampling jitter over a Gaussian channel

Two new results are presented for intersymbol interference in raised-cosine filtered communication over an additive white Gaussian noise channel: the interference due to roll-off factor mismatch is negligibly small, and a reasonably accurate approximation formula for the bit error probability is derived for matched roll-off factors.

Stationary clock changes on stationary processes

Properties of clock changes on stationary (wide sense) continuous processes are studied. We show that such a model fits several physical phenomena and can be used for coding and as a modulation scheme. Lastly, unobserved jitter sampling study can be performed with such probability tools.