Inherent Jitter Research Articles

A Multi-Regional Path-Planning Method for Rescue UAVs with Priority Constraints

This study focuses on the path-planning problem of rescue UAVs with regional detection priority. Initially, we propose a mixed-integer programming model that integrates coverage path planning (CPP) and the hierarchical traveling salesman problem (HTSP) to address multi-regional path planning under priority constraints. For intra-regional path planning, we present an enhanced method for acquiring reciprocating flight paths to ensure complete coverage of convex polygonal regions with shorter flight paths when a UAV is equipped with sensors featuring circular sampling ranges. An additional comparison was made for spiral flight paths, and second-order Bezier curves were employed to optimize both sets of paths. This optimization not only reduced the path length but also enhanced the ability to counteract inherent drone jitter. Additionally, we propose a variable neighborhood descent algorithm based on K-nearest neighbors to solve the inter-regional access order path-planning problem with priority. We establish parameters for measuring distance and evaluating the priority order of UAV flight paths. Simulation and experiment results demonstrate that the proposed algorithm can effectively assist UAVs in performing path-planning tasks with priority constraints, enabling faster information collection in important areas and facilitating quick exploration of three-dimensional characteristics in unknown disaster areas by rescue workers. This algorithm significantly enhances the safety of rescue workers and optimizes crucial rescue times in key areas.

An 18.24-Gb/s, 0.93-pJ/bit Receiver With an Input-Level-Sensing CDR Using Clock-Embedded C-PHY Signaling Over Trio Wires

This article presents a receiver (RX) with an input-level-sensing clock and data recovery (CDR) circuit for a C-PHY interface with trio wires. The proposed CDR circuit detects a “strong” signal from the clock-embedded three-phase-coded signals and recovers the 3-bit wire state and clock simultaneously based on the detected “strong” signal without the inherent switching jitter of conventional C-PHY RXs. Also, the proposed input-level-sensing circuit allows for low power consumption and small size by detecting a “strong” signal without reference voltage or static current consumption, and it automatically compensates for the gain of the analog front end to remain just high enough to detect a “strong” signal even with process, voltage, and temperature variation. This work is implemented using a 28-nm CMOS process with a 1-V supply and occupies an area of 0.022 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , achieving a total energy efficiency of 0.93 pJ/bit at 18.24 Gb/s.

Clocking Auger electrons

Intense X-ray free-electron lasers (XFELs) can rapidly excite matter, leaving it in inherently unstable states that decay on femtosecond timescales. As the relaxation occurs primarily via Auger emission, excited state observations are constrained by Auger decay. In situ measurement of this process is therefore crucial, yet it has thus far remained elusive at XFELs due to inherent timing and phase jitter, which can be orders of magnitude larger than the timescale of Auger decay. Here, we develop a new approach termed self-referenced attosecond streaking, based upon simultaneous measurements of streaked photo- and Auger electrons. Our technique enables sub-femtosecond resolution in spite of jitter. We exploit this method to make the first XFEL time-domain measurement of the Auger decay lifetime in atomic neon, and, by using a fully quantum-mechanical description, retrieve a lifetime of $2.2^{ + 0.2}_{ - 0.3}$ fs for the KLL decay channel. Importantly, our technique can be generalised to permit the extension of attosecond time-resolved experiments to all current and future FEL facilities.

High-precision nonlocal temporal correlation identification of entangled photon pairs for quantum clock synchronization.

High-precision nonlocal temporal correlation identification in entangled photon pairs is critical to measure the time offset between remote independent time scales for many quantum information applications. The first nonlocal correlation identification was reported in 2009, which extracts the time offset via the algorithm of iterative fast Fourier transformations and their inverse. The best identification resolution is restricted by the peak identification threshold of the algorithm, and thus the time offset calculation precision is limited. In this paper, an improvement for the identification is presented both in resolution and precision via a modified algorithm of direct cross correlation extraction. A flexible resolution down to 1 ps is realized, which is only dependent on the least significant bit resolution of the time-tagging device. The attainable precision is shown to be mainly determined by the inherent timing jitter of single photon detectors, the acquired pair rate, and acquisition time, and a sub-picosecond precision (0.72 ps) has been achieved at an acquisition time of 4.5 s. This high-precision nonlocal measurement realization provides a solid foundation for the field applications of entanglement-based quantum clock synchronization, ranging, and communications.

Beyond integration: modeling every pixel to obtain better structure factors from stills

Most crystallographic data processing methods use pixel integration. In serial femtosecond crystallography (SFX), the intricate interaction between the reciprocal lattice point and the Ewald sphere is integrated out by averaging symmetrically equivalent observations recorded across a large number (104-106) of exposures. Although sufficient for generating biological insights, this approach converges slowly, and using it to accurately measure anomalous differences has proved difficult. This report presents a novel approach for increasing the accuracy of structure factors obtained from SFX data. A physical model describing all observed pixels is defined to a degree of complexity such that it can decouple the various contributions to the pixel intensities. Model dependencies include lattice orientation, unit-cell dimensions, mosaic structure, incident photon spectra and structure factor amplitudes. Maximum likelihood estimation is used to optimize all model parameters. The application of prior knowledge that structure factor amplitudes are positive quantities is included in the form of a reparameterization. The method is tested using a synthesized SFX dataset of ytterbium(III) lysozyme, where each X-ray laser pulse energy is centered at 9034 eV. This energy is 100 eV above the Yb3+ L-III absorption edge, so the anomalous difference signal is stable at 10 electrons despite the inherent energy jitter of each femtosecond X-ray laser pulse. This work demonstrates that this approach allows the determination of anomalous structure factors with very high accuracy while requiring an order-of-magnitude fewer shots than conventional integration-based methods would require to achieve similar results.

Measurement Uncertainty of Precise Interpolating Time Counters

This paper presents a comprehensive analysis of measurement uncertainty of a wide class of precise time interval counters based on the most common two-stage time interpolation method. All nonnegligible sources of errors are discussed, including the quantization process, nonlinearity of time interpolators, timing jitter induced by elements of signal paths as well as inherent jitter of input pulses, and reference clock signal. A formula of the total measurement uncertainty and several design suggestions aiming at improving the time counter accuracy and precision is provided.

Synchronous multi-color laser network with daily sub-femtosecond timing drift

Filming atoms in motion with sub-atomic spatiotemporal resolution is one of the distinguished scientific endeavors of our time. Newly emerging X-ray laser facilities are the most likely candidates to enable such a detailed gazing of atoms due to their angstrom-level radiation wavelength. To provide the necessary temporal resolution, numerous mode-locked lasers must be synchronized with ultra-high precision across kilometer-distances. Here, we demonstrate a metronome synchronizing a network of pulsed-lasers operating at different center wavelengths and different repetition rates over 4.7-km distance. The network achieves a record-low timing drift of 0.6 fs RMS measured with 2-Hz sampling over 40 h. Short-term stability measurements show an out-of-loop timing jitter of only 1.3 fs RMS integrated from 1 Hz to 1 MHz. To validate the network performance, we present a comprehensive noise analysis based on the feedback flow between the setup elements. Our analysis identifies nine uncorrelated noise sources, out of which the slave laser’s inherent jitter dominates with 1.26 fs RMS. This suggests that the timing precision of the network is not limited by the synchronization technique, and so could be much further improved by developing lasers with lower inherent noise.

Quantification of turbulent mixing in colliding gravity currents

Collision between two identical counterflowing gravity currents was studied in the laboratory with the goal of understanding the fundamental turbulent mixing physics of flow collisions in nature, for example katabatic flows and thunderstorm outflows. The ensuing turbulent mixing is a subgrid process in mesoscale forecasting models, and needs to be parameterized using eddy diffusivity. Laboratory gravity currents were generated by simultaneously removing two identical locks, located at both ends of a long rectangular tank, which separated dense and lighter water columns with free surfaces of the same depth $H$. The frontal velocity $u_{f}$ and the velocity and density fields of the gravity currents were monitored using time-resolved particle image velocimetry and planar laser-induced fluorescence imaging. Ensemble averaging of identical experimental realizations was used to compute turbulence statistics, after removing inherent jitter via phase alignment of successive data realizations by iteratively maximizing the cross-correlation of each realization with the ensemble average. Four stages of flow evolution were identified: initial (independent) propagation of gravity currents, their approach while influencing one another, collision and resulting updraughts, and postcollision slumping of collided fluid. The collision stage, in turn, involved three phases, and produced the strongest turbulent mixing as quantified by the rate of change of density. Phase I spanned $-0.2\leqslant tu_{f}/H&lt;0.5$, where collision produced a rising density front (interface) with strong shear and intense turbulent kinetic energy production ($t$ is a suitably defined time coordinate such that gravity currents make the initial contact at $tu_{f}/H=-0.2$). In Phase II ($0.5\leqslant tu_{f}/H&lt;1.2$), the interface was flat and calm with negligible vertical velocity. Phase III ($1.2\leqslant tu_{f}/H&lt;2.8$) was characterized by slumping which led to hydraulic bores propagating away from the collision area. The measurements included root mean square turbulent velocities and their decay rates, interfacial velocity, rate of change of fluid-parcel density, and eddy diffusivity. These measures depended on the Reynolds number $Re$, but appeared to achieve Reynolds number similarity for $Re&gt;3000$. The eddy diffusivity $K_{T}$, space–time averaged over the spatial extent ($H\times H$) and the lifetime ($t\approx 3H/u_{f}$) of collision, was $K_{T}/u_{f}H=0.0036$ for $Re&gt;3000$, with the area $A$ of active mixing being $A/H^{2}=0.037$.

Modified Godard Timing Recovery for Non Integer Oversampling Receivers

A timing recovery algorithm is introduced that operates with less than two samples per symbol and provides an enormous complexity reduction. The complexity reduction is due to a synergy with the already existing Fourier transforms in a coherent receiver, an avoidance of terms that are dominated by noise, and a complete elimination of multiplications. A simulation and an experiment with a single carrier modulation format show that the inherent timing jitter is, despite of the significant complexity reduction, comparable with the state of the art, and in particular outperforms the Godard algorithm for low roll-off factors. In addition, it is one of the few algorithms that operates with less than two samples per symbol in the frequency domain, and thus enables the lowest complexity in a receiver.

Study on directional eye movements in non‐frontal face images for eye‐controlled interaction

AbstractDirectional eye movements based eye‐controlled interaction focuses on interpreting the horizontal, vertical, and diagonal eye movements or their combinations as inputs to design user interfaces for people who suffer with severe mobility disabilities. In this paper, we take into consideration the inherent eye jitter and evaluate the accuracy of dynamic tracking of horizontal, vertical, diagonal, and rectangular eye movements prior to using them. We observe that the rectangular eye gesture composed of short horizontal and vertical eye movements has the best tracking accuracy in the presence of jitter. Finally, we present methods for identifying horizontal and vertical eye movements based on the trajectory of eye pupil centers from non‐frontal face images. We find that the methods are robust and effective within ±20°deflective azimuths of non‐frontal faces. This effectiveness is demonstrated by using the rectangular eye gesture as an interface to perform a painting task.

Jitter analysis of timing-distribution and remote-laser synchronization systems.

We present a powerful jitter analysis method for timing-distribution and remote-laser synchronization systems based on feedback flow between setup elements. We synchronize two different mode-locked lasers in a master-slave configuration locally and remotely over a timing-stabilized fiber link network. Local synchronization reveals the inherent jitter of the slave laser as 2.1 fs RMS (>20 kHz), whereas remote synchronization exhibits an out-of-loop jitter of 8.55 fs RMS integrated for 1 Hz - 1 MHz. Our comprehensive feedback model yields excellent agreement with the experimental results and identifies seven uncorrelated noise sources, out of which the slave laser's jitter dominates with 8.19 fs RMS.

Jitter Amplifier for Oscillator-Based True Random Number Generator

We propose a jitter amplifier architecture for an oscillator-based true random number generator (TRNG). Two types of latency-controllable (LC) buffer, which are the key components of the proposed jitter amplifier, are presented. We derive an equation to estimate the gain of the jitter amplifier, and analyze sufficient conditions for the proposed circuit to work properly. The proposed jitter amplifier was fabricated with a 65nm CMOS process. The jitter amplifier with the two-voltage LC buffer occupied 3,300µm2 and attained 8.4x gain, and that with the single-voltage LC buffer achieved 2.2x gain with an 1,700µm2 area. The jitter amplification of the sampling clock increased the entropy of a bit stream and improved the results of the NIST test suite so that all the tests passed whereas TRNGs with simple correctors failed. The jitter amplifier attained higher throughput per area than a frequency divider when the required amount of jitter was more than two times larger than the inherent jitter in our test-chip implementations.

Photonic Analog-to-Digital Conversion with Femtosecond Lasers

Progress in developing high speedAnalog-to-Digital Converters (ADCs) occurs rather slowly due to the inherent jitter in electronic sampling and the difficulty in integrating low noise microwave sources. Currently, this electronic jitter is on the order of 100 femtoseconds in the most advanced CMOS circuitry. Advances in femtosecond lasers and laser stabilization have led to the development of sources of ultrafast optical pulse trains that show timing jitter on the level of a few femtoseconds over the time spans of typical sampling windows and can be made even smaller in the future. This paper reviews the progress made towards low noise femtosecond lasers, its jitter characterization, and its application in high-speed, high-resolution analog-to-digital conversion. Index Terms – Ultrafast optics, timing jitter in mode-locked lasers, photonic analog-to-digital conversion, femtosecond lasers

Improved Data Recovery from Patterned Media With Inherent Jitter Noise Using Low-Density Parity-Check Codes

Patterned magnetic media promises areal densities in excess of 1 Tbit/in2 for data storage. However, current imperfect patterning techniques result in a variation in the dimensions and distribution of the fabricated islands. As a result, this variation introduces jitter in the replay waveform that makes data recovery difficult. In this paper, we investigate the use of low-density parity-check (LDPC) codes and iterative decoding for mitigating the effects of lithography jitter and improving the read channel performance in patterned media storage systems. In addition, we show that the adoption of LDPC coding techniques permits an increase in the data storage capability of the medium to approximately 1.6 Tbit/in2 with acceptable bit-error-rate performance.

A bang-bang PLL employing dynamic gain control for low jitter and fast lock times

Bang-bang phase detector based PLLs are simple to design, suffer no systematic phase error, and can run at the highest speed a process can make a working flip-flop. For these reasons designers are employing them in the design of very high speed Clock Data Recovery (CDR) architectures. The major drawback of this class of PLL is the inherent jitter due to quantized phase and frequency corrections. Reducing loop gain can proportionally improve jitter performance, but also reduces locking time and pull-in range. This paper presents a novel PLL design that dynamically scales its gain in order to achieve fast lock times while improving jitter performance in lock. Under certain circumstances the design also demonstrates improved capture range. This paper also analyses the behaviour of a bang-bang type PLL when far from lock, and demonstrates that the pull-in range is proportional to the square root of the PLL loop gain.

CHAPS: a new precision laser-spectroscopic technique

We present a new technique for high-resolution pulsed spectroscopy that employs optical heterodyne detection to determine the instantaneous frequency of individual optical pulses, together with a frequency-binning method to generate high-precision spectra. We further demonstrate that active tuning of the light source is not necessary if the inherent frequency jitter of the source spans the spectral region of interest. This heterodyneassisted approach to coherent pulsed spectroscopy (CHAPS) is applied in real time by using output from a pulsed, injection-seeded optical parametric oscillator–amplifier (OPO–OPA) system, the optical bandwidth of which is characterized via two-photon excitation of the 6S–8S transition in cesium. The resulting sub-Doppler measurements demonstrate the utility of CHAPS as a high-resolution spectroscopic technique and confirm that the pulsed OPO–OPA system operates very close to the Fourier-transform limit. © 2006 Optical Society of America OCIS codes: 020.4180, 040.2840, 120.6200, 190.4970, 230.4320, 300.3700, 300.6320, 300.6410.

AN ALGORITHM TO COUNTERACT EYE JITTER IN GAZE-CONTROLLED INTERFACES

One of the major concerns in developing efficient gaze-controlled user interfaces is inherent eye jitter, which presents a key limitation on the pointing accuracy achievable with an eye tracker. To counteract eye jitter, we developed a grab-and-hold algorithm. The efficiency of the algorithm was tested experimentally in a target acquisition task. Results suggest that the grab-and-hold algorithm affords a dramatic 57% reduction in error rates overall. The reduction is as much as 68% for targets subtending 0.35 degrees of visual angle. However, there is a cost which surfaces as a slight increase in movement time (10%). These findings indicate that measures like the algorithm presented here have the potential of making eye gaze a more suitable input modality. 1. Indroduction

Circuit emulation services over Ethernet—Part 1: Clock synchronization using timestamps

AbstractDue to Ethernet's ubiquity, simplicity, scalability and cost effectiveness there is significant customer demand for Ethernet‐based access and transport in the metropolitan network. Many service providers have recognized this need and are currently establishing Ethernet‐based services to meet this demand. The migration to all‐Ethernet access will not be instantaneous since many customers currently have legacy TDM access interfaces on their routers and PBX equipment. Circuit Emulation Services (CES) over Ethernet provides TDM circuit emulation to support TDM traffic such as T1/E1, T3/E3, OC3/12, etc. This two‐part paper presents the application of CES over Ethernet as well as a new technology that addresses the issues associated with clock recovery and synchronization in an Ethernet network with its inherent network jitter. Part 1 describes a clock synchronization technique where a transmitter periodically sends explicit time indications or timestamps to a receiver to enable the receiver to synchronize its local clock to the transmitter's clock. Copyright © 2004 John Wiley &amp; Sons, Ltd.

A new frequency synthesis method based on "flying-adder" architecture

The "flying-adder" frequency and phase synthesis architecture was presented in papers published by Mair and Xiu in 2000 and Xiu and You in 2002. This architecture contains many excellent features and it can be implemented/integrated easily in a very large scale integration system. However, it has a drawback of inherent jitter on the output frequency, due to the frequency modulation of the output frequency. This brief presents a new frequency synthesis method that eliminates such jitter. The frequency accuracy of this new architecture is studied; subsequently, the frequency error upper bound is found. Furthermore, it leads to the development of a scheme that can be used to derive the frequency error distribution. The comparison to "integer-N" and "fractional-N" phase-locked loop (PLL) based frequency synthesis techniques is also presented.

An interpretation of the spectral measurement of optical pulse train noise

The validity of inferring statistical quantities, such as the variance of pulse jitter, from optical pulse train spectra is discussed in relation to a cyclostationary model. This cyclostationary model is derived from a low frequency, low noise approximation to a complete constant pulse shape model. It is shown that in order to gain information on the inherent timing jitter from the power spectrum, extra information on the optical signal is required. >