Clock Data Research Articles

On the capabilities of the inaction method for extracting the periodic components from GPS clock data

Almost all GPS signal clocks show a periodic fluctuation. Harmonics in GPS satellites are a well-known feature, such as 3-, 4-, 6- and 12-h terms, accurate extraction of these harmonics are helpful to improve the clock modeling. The inaction method (IM) originating from the concept of normal time–frequency transform (NTFT) can precisely extract the periodic signals which significantly present the NTFT spectrum. This method is essentially line-pass filtering, so it can avoid being polluted by noises to the maximum extent and then have the ability to extract the time-varying periodic signals with robustness. The simulation test demonstrates that IM is the best method for extracting the harmonics and time-varying harmonics from a time signal, compared to singular spectrum analysis and zero-phase digital filter. We focus on GPS satellite clock data, after removing 6- and 12-h terms extracted by IM, the oscillation phenomenon in Hadamard deviation virtually disappears; this demonstrates that these periodic signals have been extracted effectively by the IM.

Regulations and Technology Behind HFT Latency, Batch Auctions and Payments for Order Flow in the US and EU

Abstract Since the appearance of high-frequency trading in the 1990s, speed has become one of the key issues in trading and with it, the controversy around High-Frequency Trading. In recent years, there have been many discussions and analyses of how high-frequency trading may affect the financial market – but still without any clear conclusions. Leaving these opinions behind, many adjustments have already been made in the US and Europe - both to regulations and market rules, impacting not only High-Frequency Trading but general electronic trading as well. These rules and regulations are the result of technological developments in electronic trading and more specifically, High-Frequency Trading and the practice of Payments for Order Flow. The question remains as to how deep regulations should go, especially in the case of HFT which can be severely affected by harsh regulatory requirements or procedures. Because two of the most important issues in HFT are time and information, some of the rules and regulations affect aspects such as not only what type of information and how it should be gathered, but also clock synchronisation and time-stamp granularity. Another issue that may be considered controversial in the field of HFT (although it is not a practice limited to HFT) is Payment For Order Flows. Under this mechanism, wholesale market makers pay brokers for their client’s order flow – a practice that performed in great amounts and at high speeds may give a considerable level of “inside” information. Regulations, especially from ESMA (MiFID II). try in great part to thus mitigate the practice of Payments For Order Flows. The aim of this paper is to present technological advancements in the field of trading communications used, not only by HFT firms, but also by exchanges. Additionally, the objective is to underline some challenges regarding regulatory changes that try to adapt to the current level of technology – for example, those related to clock synchronisation and data processing. One last issue brought forward is the possibility of converting markets from continuous-time auctions to discrete-time auctions - a concept that is aimed at liquidating the speed advantage and competition only to price level and hence, eliminating HFT advantages.

Bordetella pertussis population dynamics and phylogeny in Japan after adoption of acellular pertussis vaccines.

Bordetella pertussis, the causative agent of whooping cough, has experienced a resurgence in the past 15 years, despite the existence of both whole-cell and acellular vaccines. Here, we performed whole genome sequencing analysis of 149 clinical strains, provided by the National Institute of Infectious Diseases (NIID), Japan, isolated in 1982–2014, after Japan became the first country to adopt acellular vaccines against B. pertussis. Additionally, we sequenced 39 strains provided by the Konan Kosei Hospital in Aichi prefecture, Japan, isolated in 2008–2013. The genome sequences afforded insight into B. pertussis genome variability and population dynamics in Japan, and revealed that the B. pertussis population in Japan was characterized by two major clades that divided more than 40 years ago. The pertactin gene was disrupted in about 20 % of the 149 NIID isolates, by either a deletion within the signal sequence (ΔSS) or the insertion of IS element IS481 (prn :: IS481). Phylogeny suggests that the parent clones for these isolates originated in Japan. Divergence dating traced the first generation of the pertactin-deficient mutants in Japan to around 1990, and indicated that strains containing the alternative pertactin allele prn2 may have appeared in Japan around 1974. Molecular clock data suggested that observed fluctuations in B. pertussis population size may have coincided with changes in vaccine usage in the country. The continuing failure to eradicate the disease warrants an exploration of novel vaccine compositions.

Search for transient ultralight dark matter signatures with networks of precision measurement devices using a Bayesian statistics method

We analyze the prospects of employing a distributed global network of precision measurement devices as a dark matter and exotic physics observatory. In particular, we consider the atomic clocks of the Global Positioning System (GPS), consisting of a constellation of 32 medium-Earth orbit satellites equipped with either Cs or Rb microwave clocks and a number of Earth-based receiver stations, some of which employ highly-stable H-maser atomic clocks. High-accuracy timing data is available for almost two decades. By analyzing the satellite and terrestrial atomic clock data, it is possible to search for transient signatures of exotic physics, such as "clumpy" dark matter and dark energy, effectively transforming the GPS constellation into a 50,000km aperture sensor array. Here we characterize the noise of the GPS satellite atomic clocks, describe the search method based on Bayesian statistics, and test the method using simulated clock data. We present the projected discovery reach using our method, and demonstrate that it can surpass the existing constrains by several order of magnitude for certain models. Our method is not limited in scope to GPS or atomic clock networks, and can also be applied to other networks of precision measurement devices.

Power Efficient Clock Distribuition for Switched Capacitor DC-DC Converters

<p>In various VLSI based digital systems, on-chip interconnects have become the system bottleneck in state-of-the-art chips, limiting the performance of high-speed clock distributions and data communication devices in terms of propagation delay and power consumption. Increasing power requirements and power distribution to multi-core architectures is also posing a challenge to power distribution networks in the integrated circuits. Clock distribution networks for the switched capacitor converters becomes a non-trivial task and the increased interconnect lengths cause clock degradation and power dissipation. Therefore, this paper introduce low swing signaling schemes to decrease delay and power consumption. A comparative study presented of low voltage signaling schemes in terms of delay, power consumption and power delay product. Here, we have presented a power efficient signaling topology for driving the clocks to higher interconnect lengths.</p>

Kinematic-PPP using Single/Dual Frequency Observations from (GPS, GLONASS and GPS/GLONASS) Constellations for Hydrography

Abstract Global Positioning System (GPS) technology is ideally suited for inshore and offshore positioning because of its high accuracy and the short observation time required for a position fix. Precise point positioning (PPP) is a technique used for position computation with a high accuracy using a single GNSS receiver. It relies on highly accurate satellite position and clock data that can be acquired from different sources such as the International GNSS Service (IGS). PPP precision varies based on positioning technique (static or kinematic), observations type (single or dual frequency) and the duration of observations among other factors. PPP offers comparable accuracy to differential GPS with safe in cost and time. For many years, PPP users depended on GPS (American system) which considered the solely reliable system. GLONASS's contribution in PPP techniques was limited due to fail in maintaining full constellation. Yet, GLONASS limited observations could be integrated into GPS-based PPP to improve availability and precision. As GLONASS reached its full constellation early 2013, there is a wide interest in PPP systems based on GLONASS only and independent of GPS. This paper investigates the performance of kinematic PPP solution for the hydrographic applications in the Nile river (Aswan, Egypt) based on GPS, GLONASS and GPS/GLONASS constellations. The study investigates also the effect of using two different observation types; single-frequency and dual frequency observations from the tested constellations.

Predicting Long-Term Stability of Precise Oscillators under Influence of Frequency Drift.

High-performance oscillators, atomic clocks for instance, are important in modern industries, finance and scientific research. In this paper, the authors study the estimation and prediction of long-term stability based on convex optimization techniques and compressive sensing. To take frequency drift into account, its influence on Allan and modified Allan variances is formulated. Meanwhile, expressions for the expectation and variance of discrete-time Hadamard variance are derived. Methods that reduce the computational complexity of these expressions are also introduced. Tests against GPS precise clock data show that the method can correctly predict one-week frequency stability from 14-day measured data.

Fault‐tolerant delay cell for ring oscillator application in 65 nm CMOS technology

A novel fault tolerant delay cell for ring oscillator (RO) is proposed. As RO is one of the crucial blocks in phased locked loop, delayed locked loo and clock data recovery, it should be tolerated against single event transient (SET) and stuck at faults for harsh environment. Their proposed hybrid fault tolerant topology is combination of triple and quad transistors redundancy, which is applied to the delay cell structure based on the sensitivity role of each transistor. The simulation results with Cadence software show that the proposed fault-tolerant delay cell dissipates 34.34 μW power, while it occupies 127.2 μm 2 chip area. The proposed topology not only has lower power dissipation in comparison with existing fault tolerant delay cells but also is more reliable against stuck at single and multiple faults and also SETs. By using the proposed reliable delay cell in the RO, the achieved power dissipation and phase noise are about 249 μW and -96 dBc/Hz, respectively, while higher reliability is achieved in comparison with non-redundant RO s.

입력 지터에 강한 순수 디지털 클럭 데이터 복원 및 복호 회로

직렬 데이터 수신기는 입력되는 데이터를 복원하기 위해 일반적으로 클록 데이터 복원 회로(CDR)가 필요하다. 대부분의 클록 정보 복원 회로들은 위상 고정 루프(PLL)를 기반으로 한 방식의 설계가 주를 이루고 있다. 본 논문에서는 PLL을 사용하지 않는 합성 가능한 디지털 방식의 클록 데이터 및 전송로 부호(Line code)를 복원하는 회로를 제안한다. 제안하는 회로는 PLL을 사용하지 않고, 시스템에서 사용되는 클록을 이용하여 동작시킬 수 있으며 순수한 HDL만을 이용하여 설계가 가능하고 공정에 관계없이 합성 가능한 소프트 코드로 설계할 수 있다. 제안된 회로 구조는 높은 입력 지터(jitter)를 견딜 수 있으며, PLL을 사용하지 않아 매우 작은 면적을 가지게 되고 다양한 샘플링 주파수를 갖는 경우에도 동작 가능하다. 제안한 회로 구조를 S/PDIF(Sony/Philips Digital Interface Format)를 위한 CDR 회로에 적용하여 Verilog-HDL을 이용하여 설계하고 FPGA를 통해 검증하고 구현하였다.

High Performance Clocks and Gravity Field Determination

Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in manufacturing high-precision atomic clocks have rapidly improved their accuracy and stability over the last decade that approached the level of 10$^{-18}$. Based on a fully relativistic description of the background gravitational physics, we discuss the impact of those highly-precise clocks on the realization of reference frames and time scales used in geodesy. We discuss the current definitions of basic geodetic concepts and come to the conclusion that the advances in clocks and other metrological technologies will soon require the re-definition of time scales or, at least, clarification to ensure their continuity and consistent use in practice. The relative frequency shift between two clocks is directly related to the difference in the values of the gravity potential at the points of clock's localization. According to general relativity the relative accuracy of clocks in 10$^{-18}$ is equivalent to measuring the gravitational red shift effect between two clocks with the height difference amounting to 1 cm. We show how clock measurements can provide geopotential numbers for the realization of gravity-field-related height systems and can resolve discrepancies in classically-determined height systems as well as between national height systems. Another application of clocks is the direct use of observed potential differences for the improved recovery of regional gravity field solutions. Finally, clock measurements for space-borne gravimetry are analyzed along with closely-related deficiencies of this method like an extra-ordinary knowledge of the spacecraft velocity, etc. For all these applications besides the near-future prospects, we also discuss the challenges that are related to using those novel clock data in geodesy.

An approach to GPS clock prediction for real-time PPP during outages of RTS stream

The international GNSS service (IGS) has been providing an open-access real-time service (RTS) since 2013, which allows users to carry out real-time precise point positioning (RT-PPP). As the availability of RTS products is vital for RT-PPP, a disruption in receiving RTS products will be a concern. Currently, the IGS Ultra-rapid (IGU) orbit is accurate enough to be used as an alternative orbit for RTS during RTS outages, while the precision of the IGU predicted clock offsets is far below that of the RTS clock product. The existing clock prediction methods based on received RTS clock data will not work well if the discontinuity arises shortly after the start of the RT-PPP processing due to the lack of RTS clock data to fit the prediction model or to predict clock offsets at a high precision. Even if there is a sufficient amount of RTS clock data available, saving large amounts of RTS clock data would also use processor memory. An alternate approach for GPS clock prediction is proposed. The prediction model, composed of linear polynomial and sinusoidal terms, is similar to those used by the precious methods. The main innovation is the determination of the model coefficients: coefficients of linear and sinusoidal terms are estimated with the epoch-differenced clock offsets from the IGU observed part, while the constant coefficient is computed with the latest RTS clock corrections. There is no need to save the received RTS clock corrections, and clock prediction can be carried out even with only one epoch of RTS data. Evaluation of the proposed method shows that the predicted clock offsets within a short period of prediction time, e.g., 5 min, are slightly worse than RTS clock data. Even when the predicted time reaches up to 1 h, the precision of the predicted clock offsets is still higher than that of IGU predicted clock offsets by about 50%.

Backreaction and FRW consistency conditions

If the FRW metric is a good approximation on large scales, then the distance and the expansion rate, as well different notions of distance, satisfy certain consistency conditions. We fit the JLA SNIa distance data to determine the expected amplitude of the violation of these conditions if accelerated expansion is due to backreaction. Adding cosmic clock and BAO expansion rate data, we also model-independently determine the current observational limits on such violation. We find that the predicted maximum backreaction amplitude |kH| ≲ 1 (95% C.I.) is of the same order as the current observational constraints |kH| ≲ 1, the precise numbers depending on the adopted fitting method (polynomials or splines) and stellar population evolution model. We also find that constraints on the value of H0 determined from expansion rate data are sensitive to the stellar evolution model. We forecast constraints from projected LSST+Euclid-like SNIa plus Euclid galaxy differential age data. We find improvement by factor of 6 for the backreaction case and 3 for the model-independent case, probing an interesting region of possible signatures.

A 40-Gb/s Quarter-Rate SerDes Transmitter and Receiver Chipset in 65-nm CMOS

This paper presents a 40-Gb/s transmitter (TX) and receiver (RX) chipset for chip-to-chip communications in a 65-nm CMOS process. The TX implements a quarter-rate multi-multiplexer (MUX)-based four-tap feed-forward equalizer (FFE), where a charge-sharing-effect elimination technique is introduced into the 4:1 MUX to optimize its jitter performance and power efficiency. The RX employs a two-stage continuous-time linear equalizer as the analog front end and integrates a low-cost sign-based zero-forcing engine relying on edge-data correlation to automatically adjust the tap weights of the TX-FFE. By embedding low-pass filters with an adaptively adjusting bandwidth into the data-sampling path and adopting high-linearity compensating phase interpolators, the clock data recovery achieves both high jitter tolerance and low jitter generation. The fabricated TX and RX chipset delivers 40-Gb/s PRBS data at BER 16-dB loss at half-baud frequency, while consuming a total power of 370 mW.

Ultra-compact structure in radio quasars as a cosmological probe: a revised study of the interaction between cosmic dark sectors

A new compilation of 012 angular-size/redshift data for compact radio quasars from very-long-baseline interferometry (VLBI) surveys motivates us to revisit the interaction between dark energy and dark matter with these probes reaching high redshifts z∼ 3.0. In this paper, we investigate observational constraints on different phenomenological interacting dark energy (IDE) models with the intermediate-luminosity radio quasars acting as individual standard rulers, combined with the newest BAO and CMB observation from Planck results acting as statistical rulers. The results obtained from the MCMC method and other statistical methods including figure of Merit and Information Criteria show that: (1) Compared with the current standard candle data and standard clock data, the intermediate-luminosity radio quasar standard rulers , probing much higher redshifts, could provide comparable constraints on different IDE scenarios. (2) The strong degeneracies between the interaction term and Hubble constant may contribute to alleviate the tension of H0 between the recent Planck and HST measurements. (3) Concerning the ranking of competing dark energy models, IDE with more free parameters are substantially penalized by the BIC criterion, which agrees very well with the previous results derived from other cosmological probes.

Satellite-to-ground quantum-limited communication using a 50-kg-class microsatellite

Recent rapid growth in the number of satellite-constellation programs for remote sensing and communications, thanks to the availability of small-size and low-cost satellites, provides impetus for high capacity laser communication (lasercom) in space. Quantum communication can enhance the overall performance of lasercom, and also enables intrinsically hack-proof secure communication known as Quantum Key Distribution (QKD). Here, we report a quantum communication experiment between a micro-satellite (48 kg and 50 cm cube) in a low earth orbit and a ground station with single-photon counters. Non-orthogonal polarization states were transmitted from the satellite at a 10-MHz repetition rate. On the ground, by post-processing the received quantum states at an average of 0.14 photons/pulse, clock data recovery and polarization reference-frame synchronization were successfully done even under remarkable Doppler shifts. A quantum bit error rate below 5% was measured, demonstrating the feasibility of quantum communication in a real scenario from space.

Variation of Static-PPP Positioning Accuracy Using GPS-Single Frequency Observations (Aswan, Egypt)

Abstract Precise Point Positioning (PPP) is a technique used for position computation with a high accuracy using only one GNSS receiver. It depends on highly accurate satellite position and clock data rather than broadcast ephemeries. PPP precision varies based on positioning technique (static or kinematic), observations type (single or dual frequency) and the duration of collected observations. PPP-(dual frequency receivers) offers comparable accuracy to differential GPS. PPP-single frequency receivers has many applications such as infrastructure, hydrography and precision agriculture. PPP using low cost GPS single-frequency receivers is an area of great interest for millions of users in developing countries such as Egypt. This research presents a study for the variability of single frequency static GPS-PPP precision based on different observation durations.

Kinematic precise point positioning using GPS and GLONASS measurements in marine environments

The Precise Point Positioning (PPP) technique has received increased attention in recent years. When employing PPP, users need only a single GNSS receiver data to obtain a cm to dm accuracy level on a global datum, both in static and kinematic modes. This technique has become more popular due to its easy use, simple field operations, no base station(s) requirement, and provides cost effective high accuracy positioning. In satellite-based positioning, the accuracy and reliability of the positioning results are strongly dependent on the number and geometry of visible satellites, and quality of the observations. This issue is more important when the measurements are conducted in environments where satellite signals are blocked or degraded in some places like narrow channels, ravines, congested harbors, coastal areas with intense urbanization, inland waterways, in waters having severe terrain obstructions or surrounded by high mountains. To overcome this limitation, a combination of GPS and GLONASS measurements are proposed, especially to achieve more reliable and accurate solutions by increasing the number of visible satellites. The additional satellite system’s observations like GLONASS, are expected to enhance the positioning accuracy and solution availability where especially not enough numbers of GPS satellites are visible. As of today, precise orbits and clock data are available not only for GPS but also for GLONASS. This provides an opportunity to apply the PPP technique to GPS and GLONASS observations. In this study, performance of the PPP method is assessed in a dynamic environment using GPS-only and GPS+GLONASS observations. Accordingly, a kinematic test is carried out at the Obruk Lake Dam in the Çorum province, of Turkey. The collected data is processed using a globally popular on-line processing service: the Canadian Spatial Reference System-Precise Point Positioning Service (CSRS-PPP) operated by the Geodetic Survey Division of Natural Resources Canada (NRCan). The results show that the combined GPS+GLONASS data produced almost the same level of accuracy with the GPS-only data if there is a sufficient number of GPS satellites with good geometry. In the extreme cases, such as the elevation of satellites above 40 degrees, the GPS cannot provide a solution. However, when data and both satellites systems are combined, it is then possible to provide the solution. The results also reveal that a dm-level of accuracy can be achieved with the PPP technique in a dynamic environment. This accuracy level largely meets the requirements of many marine applications, including precise hydrographic surveying, marine geodesy, navigation and oceanography.

Determination of a high spatial resolution geopotential model using atomic clock comparisons

Recent technological advances in optical atomic clocks are opening new perspectives for the direct determination of geopotential differences between any two points at a centimeter-level accuracy in geoid height. However, so far detailed quantitative estimates of the possible improvement in geoid determination when adding such clock measurements to existing data are lacking. We present a first step in that direction with the aim and hope of triggering further work and efforts in this emerging field of chronometric geodesy and geophysics. We specifically focus on evaluating the contribution of this new kind of direct measurements in determining the geopotential at high spatial resolution (approx 10 km). We studied two test areas, both located in France and corresponding to a middle (Massif Central) and high (Alps) mountainous terrain. These regions are interesting because the gravitational field strength varies greatly from place to place at high spatial resolution due to the complex topography. Our method consists in first generating a synthetic high-resolution geopotential map, then drawing synthetic measurement data (gravimetry and clock data) from it, and finally reconstructing the geopotential map from that data using least squares collocation. The quality of the reconstructed map is then assessed by comparing it to the original one used to generate the data. We show that adding only a few clock data points (less than 1% of the gravimetry data) reduces the bias significantly and improves the standard deviation by a factor 3. The effect of the data coverage and data quality on the results is investigated, and the trade-off between the measurement noise level and the number of data points is discussed.

基于北斗/GPS秒脉冲的高稳时钟源设计

基于UM220IIIN双系统接收机和FPGA，设计一种北斗/GPS秒脉冲高稳同步时钟源。利用两块UM220IIIN分别接收北斗和GPS秒脉冲[1]，将秒脉冲输入到FPGA的cyclone IV芯片，先分别对两路秒脉冲信号进行有效性判断。若两路秒脉冲都有效，则在10秒内对它们分别进行的高频计数，计数基准是利用FPGA内部自带的高频时钟；若只有一路有效，就只对有效支路进行高频计数。然后求取10秒内计数值的均值和方差，通过比较两路秒脉冲的方差，输出最优一路的秒脉冲；或输出其中有效支路的秒脉冲均值。当北斗和GPS秒脉冲都失效时，利用FPGA内部自带的高频时钟以及历史数据，预测下一时刻的秒脉冲输出周期，系统可以继续输出高精度的秒脉冲作为时钟源。 Based on the UM220IIIN double system receiver and FPGA, a clock source of the Beidou or GPS second pulse high stability is designed in this paper. Two UM220IIIN receive the second pulse of Beidou satellite and GPS, inputting to the cyclone IV chip of FPGA, and then it is first to judge the validity of the second pulse signal of Beidou and GPS. If the two second pulses are valid, they were carried out by the high frequency count in 10 seconds, and counting is based on the use of FPGA internal own high-frequency clock; if only one way is valid, only the effective second pulse is counted. Then calculating the mean and variance of the count in 10 seconds, the best second pulse or the effective branch of the second pulse is output by comparing the variance of the second pulse. If the second pulse of Beidou satellite and GPS are invalid and the use of FPGA internal clock and historical data predict next output cycle of the second pulse, the system can continue to output high precision of the second pulse as a clock source.

Pengiriman Citra pada Komunikasi Cahaya Tampak IEEE 802.15.7 Lapisan Fisik II.f-n

Visible light communication (VLC) is a communication technology using visible light as a transmission medium that can have larger bandwidth than other wireless communications. VLC has a standard of IEEE 802.15.7 which has two layers. One of the layers is Physical Layer (PHY) II which has characterictic for indoor and line of sight communication. In this layer, the standard for data rate and optical clock rate is higher than the other types of layers using on off keying (OOK) modulation. This research investigated variation effect of clock rate, data rate, and Reed Solomon (RS) coding to bit error rate (BER) of the received signal. Nowadays, mostly data are pictures and videos. So, this research also test the VLC PHY II to transmit a picture under the varied conditions using peak signal to noise ratio (PSNR). All investigations are built in simulation. The results show that the lower RS coding rates, the lower BER values, and the higher optical clock rate, the higher data rate obtained. Good quality of picture is obtained with BER 10-4 and PSNR 39 dB.