Time Synchronization Error Research Articles

다중경로 채널 환경에서 시간 동기 오차에 따른 FBMC 시스템 분석

본 논문에서는 다중경로 채널 환경에서 filter bank multicarrier (FBMC) 시스템을 기반으로 데이터를 전송할 때, 시간 동기화 과정과 채널 등화 과정을 포함한 전반적인 송수신 과정을 정리하여 유효채널 행렬을 정의하고, 이를 기반으로 시간 동기오차에 따라 발생하는 간섭을 살펴본다. 또한, 모의실험을 통하여 시간 동기 오차에 따른 FBMC 시스템의 성능 결과에 대하여 논의한다.

Decentralized Robust Dynamic State Estimation in Power Systems Using Instrument Transformers

This paper proposes a decentralized method for estimation of dynamic states of a power system. The method remains robust to time-synchronization errors and high noise levels in measurements. Robustness of the method has been achieved by incorporating internal angle in the dynamic model used for estimation and by decoupling the estimation process into two stages with continuous updation of measurement-noise variances. Additionally, the proposed estimation method does not need measurements obtained from phasor measurement units; instead, it just requires analog measurements of voltages and currents directly acquired from instrument transformers. This is achieved through statistical signal processing of analog voltages and currents to obtain their magnitudes and frequencies, followed by application of unscented Kalman filtering for nonlinear estimation. The robustness and feasibility of the method have been demonstrated on a benchmark power system model.

Synchronised/unsynchronised measurements based novel fault location algorithm for transmission line

The authors propose a novel algorithm to compute distance to fault on the transmission line. The loss of time synchronisation due to failure of global positioning system leads to synchronisation error. Time synchronisation error is computed non-iteratively in phase domain using measurements available from two ends of the transmission line. The proposed algorithm computes distance to fault accurately even under current transformer saturation. Algorithm compensates the synchronisation error and estimates accurate fault location in a step. The proposed algorithm also works accurately for synchronised measurements. Simulations are carried on ATP/EMTP on IEEE 14-bus system, and algorithm is implemented in MATLAB. Extensive simulation studies demonstrate the merits of proposed algorithm.

A hierarchical time synchronization algorithm for WSN

Wireless sensor networks generally require large-scale deployment. Each node in the network is solely responsible for data sensing in a certain area. In order to determine the sequence in which sensing data is generated, time synchronization between nodes is necessary. Due to the delay of multi-hop transmission and the influence of the frequency shift of the node crystal frequencies, the error of time synchronization between the nodes is larger. In order to reduce the error of time synchronization, it is common practice to increase the number of synchronizations. But this method will cause the node energy consumption to increase, affecting the network survival time. In order to solve this problem, a layered wireless sensor network time synchronization algorithm is proposed with reference to the unidirectional broadcast mechanism and bidirectional pairing mechanism. The algorithm uses a hierarchical strategy for time synchronization, while introducing a synchronization error compensation mechanism and clock compensation mechanism. Under the premise of ensuring the accuracy of time synchronization, the algorithm reduces the energy consumption of nodes and prolongs the network lifetime.

Improved-Precision Time Synchronization Protocol for WSNs Based on Averaging Consensus Control

Accurate and simple time synchronization is a crucial requirement for decentralized wireless sensor networks (WSNs) to function well specially in harsh environments. The averaging consensus control protocol (ACCP), that uses single hop communication, performs well in such environments. This paper provides rigorous analysis of its time synchronization error which is by basic definition the difference between the gateway node time and the average virtual times of the other nodes in the network. Also, the paper presents a modified synchronizer protocol of the ACCP that further improves the precision of the time synchronization in WSNs. The improved time precision protocol is achieved reducing the forced response part of the time synchronization error. The proposed protocol is compared by simulations and by experiments and shown to achieve a synchronization error that is orders of magnitude less than these resulted from other known protocols which are. Finally, the proposed protocol was found to utilize the least memory and consume the least energy relative to some existing protocols.

Depth resolution improvement of streak tube imaging lidar system using three laser beams

The work proposes a three-laser-beam streak tube imaging lidar system. Besides the main measuring laser beam, the second beam is used to decrease the error of time synchronization. The third beam has n+0.5 pixels’ difference compared to the main measuring beam on a CCD, and it is used to correct the error caused by CCD discrete sampling. A three-dimensional (3D) imaging experiment using this scheme is carried out with time bin size of 0.066 ns (i.e., corresponding to a distance of 9.9 mm). An image of a 3D model is obtained with the depth resolution of <2 mm, which corresponds to ∼0.2 pixel.

A New Method of D-TDOA Time Measurement Based on RTT

In this paper, a novel difference-time difference of arrival (D-TDOA) time measurement method based on round-trip transmission (RTT) is proposed. The accuracy of time measurement is critical for high accuracy positioning, yet the traditional time difference of arrival (TDOA) time measurement method cannot deal well with the problem of time synchronization error, such as the initial time offset and transmission cumulate time error caused by clock frequency offset and drift. We formulate a D-TDOA time measurement mechanism to overcome the shortcoming of the traditional TDOA method in eliminating the influence of clock error. It is proved that the D-TDOA method can effectively eliminate the influence of initial time offset by analyzing the simulation data, which can also reduce the cumulate time error remarkably. The simulation results demonstrate that the D-TDOA method can significantly enhance the accuracy of time measurement in the circumstance that the AP clock synchronization is not required seriously.

Impact and mitigation of XT-induced time-synchronization errors in MDM transmission systems through a minimized residual inter-block-interference (MRI) algorithm

Multiple-input-multiple-output (MIMO) mode-division-multiplexed (MDM) transmission in few-mode fiber (FMF) has been widely investigated to further enhance the capacity of optical systems and networks. In this paper, for the first time, we discuss the impact and mitigation method of random mode crosstalk induced by perturbations in FMF on timing synchronization in MIMO-MDM transmission. We show by simulation that traditional maximum correlation-based synchronization algorithms are vulnerable to random mode crosstalk and consequently cause performance degradation. To solve this problem, a novel synchronization algorithm based on minimum residual inter-block-interference (MRI) criterion is developed for frequency domain equalization (FDE) MDM systems. Theoretical analysis proves that the MRI algorithm can effectively compensate the crosstalk-induced synchronization error. Then Monte Carlo simulations are carried out under different crosstalk conditions. For 100-km 12 × 12 MDM transmission, Q2-factor improvement up to 8.7-dB has been observed and the system outage probability has been substantially reduced from 0.3 to 5e−4. The proposed MRI timing synchronization will be beneficial for the design of practical MIMO-MDM systems.

Time Synchronization in WSNs With Random Bounded Communication Delays

Recently, it was pointed out that many popular consensus-based time synchronization algorithms, such as Average TimeSynch (ATS), are all divergent in a network with arbitrarily small random communication delays under any interconnection topology. This note proposes a least-squares estimation-based time synchronization (LSTS for short) algorithm. This algorithm modifies the ATS algorithm in relative drift estimator, low-pass filter, and consensus protocol. By analyzing the mathematic model of the algorithm, it is proved that LSTS ensures asymptotic convergence of the drift estimation and boundedness of the global time synchronization error under random bounded communication delays if the network topology satisfies some connectedness conditions.

Distributed travelling‐wave‐based fault location without time synchronisation and wave velocity error

Existing single- and double-terminal travelling-wave fault-location approaches have some disadvantages including difficulty in distinguishing the sources of reflect and refract waves, system error in time synchronisation and wave propagation velocity. In this study, a distributed travelling-wave-based fault-location system, which eliminates the time synchronisation and wave propagation velocity error, is introduced. This novel system is consisted of three measurement points, which are located at both ends and the mid-point of the line. At first, the measurement points, installed at both line ends, record the post-fault current data for a time interval. The measurement point, located at the mid-point, records the time tags of the three sequential wavefronts as t 1 , t 2 and t 3 separately including the initial wave and following waves reflected at both the ends. Second, by comparing fault current recorded by the three measurement points, the fault interval can be determined based on current deviation theorem. Finally, travelling-wave propagation velocity is calculated according to mathematic equation in terms of t 1 , 2 , 3 . Then, the fault point is located without the need of time synchronisation. The simulation and hardware tests match the theoretical analysis well, showing that the proposed location method provides not only high accuracy, but also good reliability.

The research on system error of Inter-Satellite-Link (ISL) measurements for autonomous navigation of Beidou system

In this paper, the system error of inter-satellite-link measurements for autonomous navigation is studied, which is an important parameter for autonomous navigation technology based on inter-satellite-link of Beidou system. The physical meaning of system error of inter-satellite-link measurements and the influence of its error on autonomous navigation are clarified. On this basis, to solve the problem that it is difficult to calibrate the system error of inter-satellite-link measurements precisely on the ground before the satellite launches, a calibration method based on onboard measurement data for this parameter is put forward. Onboard test results show that the mean of the user range error of autonomous orbit determination is less than 6m in 9days using the system error of inter-satellite-link measurements calibrated according to the proposed method. Specially, the user range error is less than 3m when the system error calibrated based on the latest measurement data is used. And in post-process, using the latest system error, the mean of user range error is less than 2.5m and the error of autonomous time synchronization is within ±10ns. All the results above prove the effectiveness of the calibration method for the system error of inter-satellite-link measurements and the effectiveness of the autonomous navigation algorithm.

Impact of time synchronization error on the mode-shape identification and damage detection/localization in WSNs for structural health monitoring

Time synchronization in wireless sensor networks (WSNs) is a critical challenge for any distributed system such as WSNs for structural health monitoring (SHM). In SHM, mode shape identification, damage detection and damage localization are sensitive to time synchronization errors (TSEs). Indeed, the errors, due to the time shift between the incoming raw data from each sensor node, may hugely affect the data integrity and then the mode shape identification of the structure under analysis. In this paper, we characterize the impact of TSE on the modal analysis, damage detection and damage localization using frequency domain decomposition (FDD) implemented in a semi-local manner. In order to decrease the size of the transmitted data by the sensor nodes and reduce the processing load and the needed storage capacity on the central unit, we adopt a semi-local processing approach where each sensor node partially processed data and transmit it to a central unit for further processing such as mode shape identification, damage detection and damage localization. We adopt the model where each sensor node performs the Fast Fourier Transform (FFT) of the measured vibration signal and the transmission of the FFT values to a central unit or to a cluster head for further processing. The results show that TSE has a strong impact on the mode shape identification, damage detection and damage localization. Furthermore, results show that semi-local processing is more sensitive to TSE compared to centralized processing.

Vulnerability of Synchrophasor-Based WAMPAC Applications’ to Time Synchronization Spoofing

This paper experimentally assesses the impact of time synchronization spoofing attacks (TSSA) on synchrophasor-based wide-area monitoring, protection and control (WAMPAC) applications. Phase angle monitoring, anti-islanding protection, and power oscillation damping applications are investigated. TSSA are created using a real-time (RT) IRIG-B signal generator and power system models are executed using an RT simulator with commercial phasor measurement units (PMUs) coupled to them as hardware-in-the-loop. Because PMUs utilize time synchronization signals to compute synchrophasors, an error in the PMUs’ time input introduces a proportional phase error in the voltage or current phase measurements provided by the PMU. The experiments conclude that a phase angle monitoring application will show erroneous power transfers, whereas the anti-islanding protection mal-operates and the damping controller introduces negative damping in the system as a result of the time synchronization error incurred in the PMUs due to TSSA. The proposed test-bench and TSSA approach can be used to investigate the impact of TSSA on any WAMPAC application and to determine the time synchronization error threshold that can be tolerated by these WAMPAC applications.

Misalignment Angle Calculation Accuracy Analysis of Three-Axis Stabilized Geostationary Satellite

The most challenging problem of navigation in three-axis stabilized geostationary satellite is accurate calculation of misalignment angles, deduced by orbit measurement error, attitude measurement error, thermal elastic deformation, time synchronization error, and so on. Before the satellite is launched, the misalignment model must be established and validated. But there were no observation data, which is a non-negligible risk of yielding the greatest returns on investment. On the basis of misalignment modeling using landmarks and stars, which is not available between different organizations and is developed by ourselves, experimental data are constructed to validate the navigation processing flow as well as misalignment calculation accuracy. In the condition of using landmarks, the maximum misalignment calculation errors of roll, pitch, and yaw axis are 2, 2, and 104 micro radians, respectively, without considering the accuracy of image edge detection. While in the condition of using stars, the maximum errors of roll, pitch, and yaw axis are 1, 1, and 3 micro radians, respectively, without considering the accuracy of star center extraction. Results are rather encouraging, which pave the way for high-accuracy image navigation of three-axis stabilized geostationary satellite. The misalignment modeling as well as calculation method has been used in the new generation of geostationary meteorological satellite in China, FY-4 series, the first satellite of which was launched at the end of 2016.

On the Road to 5G: Comparative Study of Physical Layer in MTC Context

During the past few years, we are witnessing the emergence of 5G and its high-level performance targets. Waveform (WF) design is one of the important aspects for 5G that received considerable attention from the research community in recent years. To find an alternative to the classical orthogonal frequency division multiplexing (OFDM), several multicarrier approaches addressing different 5G technical challenges, have been proposed. In this paper, we focus on critical machine-type communications (C-MTC), which is one of the key features of the foreseen 5G system. We provide a comparative performance study of the most promising multicarrier WFs. We consider several C-MTC key performance indicators: out-of-band radiations, spectral efficiency, end-to-end physical layer latency, robustness to time and frequency synchronization errors, power fluctuation, and transceiver complexity. The investigated multicarrier WFs are classified into three groups based on their ability to keep the orthogonality: in the complex domain, e.g., most of the OFDM-inspired WFs, in the real domain like offset-quadrature amplitude modulation (QAM)-based techniques, and non-orthogonal WFs like generalized frequency division multiplexing and filter bank-based multicarrier-QAM. Finally, the performances of these WFs are thoroughly discussed in order to highlight their pros and cons and permit a better understanding of their capabilities in the context of C-MTC.

Understanding STDMA via computer simulation: feasibility to vehicular safety applications, configurations, and time synchronization errors

Recently, several researchers have proposed to employ self-organized time division multiple access (STDMA) as an alternative Medium Access Control (MAC) protocol of vehicular communications and have studied STDMA to verify its feasibility to vehicular safety applications. However, most of studies have mainly focused on comparing STDMA with enhanced distributed channel access (EDCA) and have several limitations to reveal the feasibility: (1) they have not considered time synchronization error and (2) they have evaluated STDMA with only a single set of configurable parameters. Thus, the feasibility of STDMA to vehicular safety applications still remains unexplored and is an open issue. In this paper, we examine the performances of STDMA to confirm two points: (1) whether or not STDMA is feasible to safety applications even with time synchronization error and (2) whether or not proper configuration really helps to improve the performances. Our simulation results corroborate that current form of STDMA is not feasible to vehicular safety applications and we can improve STDMA via proper parameter configurations.

An Algorithm for Inter-Satellite Autonomous Time Synchronization and Ranging in the Beidou Navigation Satellite System

Aiming at the requirement of the autonomous time synchronization in BeiDou Navigation Satellite System (BDS), an algorithm for inter-satellite autonomous time synchronization and ranging is proposed. Based on the establishment of the inter-satellite link length model of the BDS, a series of simulation has been carried out through the use of STK (Satellite Tool Kit), which includes the simulation of the length changing rules, the length variation scale and its variation ratio. Based on these simulations, an analysis of the impact of satellite motion on the inter-satellite two-way time synchronization and range has been presented. In this algorithm, the inter-satellite clock-offset and range with minimal error are acquired by utilizing the combination of clock-offset fitting polynomial and range fitting polynomial based on the least square fitting of data generated from the inter-satellite two-way time synchronization. Empirical evaluation of the BDS simulation shows that our time synchronization error is 2ns, and ranging error is 2m under the condition of acceptable simulation error. With the application of the algorithm to the inter-satellite autonomous time synchronization and ranging, the high-accuracy measurement of inter-satellite clock-offset and range of BDS can be reached.

A New Cyclic-Prefix Based Algorithm for Blind CFO Estimation in OFDM Systems

In this paper, a new algorithm based on cyclic prefix (CP) is proposed for blind carrier frequency offset (CFO) estimation in orthogonal frequency division multiplexing (OFDM) transmission over multipath channels. Like other CP-based methods, the proposed method enjoys low complexity. The proposed method is very robust to the symbol timing synchronization error. Closed-form formulas for CFO estimates are derived. In addition, we also carry out the theoretical mean-square-error analysis and derive the Cramer-Rao bound. Simulation results show that the proposed method performs very well.

Wideband distributed coherent aperture radar based on stepped frequency signal: theory and experimental results

As the next generation radar, although the distributed coherent aperture radar (DCAR) has been proposed and some basic works have been developed in recent years, this new radar technology has not been researched systematically. In this study, the concept and closed-loop workflow of DCAR are described in detail first. Then, the coherent parameters (CPs), which play an important role to realise full coherence in DCAR, are estimated based on orthogonal signal and coherent signal. To investigate the limits of estimation accuracy of CPs, the Cramer–Rao lower bounds are derived. The estimation values of CPs are filtered using Kalman filter to improve the estimation accuracy. In the following, the wideband full coherence technology based on stepped frequency signal is proposed to improve system robustness to time synchronisation error, which makes the DCAR technology more realisable in engineering. Furthermore, a grating lobe suppression method based on modified genetic algorithm in synthetic array pattern of DCAR is presented. Ultimately, the experiments are carried out using test system to verify the theory of wideband DCAR.

On the Capacity of Channels With Timing Synchronization Errors

We consider a new formulation of a class of synchronization error channels and derive analytical bounds and numerical estimates for the capacity of these channels. For the binary channel with only deletions, we obtain an expression for the symmetric information rate in terms of subsequence weights which reduces to a tight lower bound for small deletion probabilities. We are also able to exactly characterize the Markov-1 rate for the binary channel with only replications. For a channel that introduces deletions as well as replications of input symbols, we design approximating channels that parameterize the state space and show that the information rates of these approximate channels approach that of the deletion-replication channel as the state space grows. For the case of the channel where deletions and replications occur with the same probabilities, a stronger result in the convergence of mutual information rates is shown. The numerous advantages this new formulation presents are explored.