Synchronous Solutions Research Articles

Analysis on the Method of Enhanced Transient State of DLDO

As an important unit of power management system, traditional analog low-dropout regulator (ALDO) is widely used in System-on-Chip (SoC) design to provide stable and pure power for each sub-circuit block. However, in ultra-low-power design applications, low quiescent current greatly affects the loop gain of ALDO. Digital low-dropout regulator (DLDO) has good low-voltage working ability, process scalability and diversified control schemes, which is more suitable for low-power SoC design. However, a large number of digital circuits with fast switching devices will produce large load current changes, so DLDO needs fast transient response speed to adjust load changes. In recent years, DLDO can be divided into synchronous DLDO and asynchronous DLDO according to different control methods. Among them, the design structure of synchronous DLDO is relatively simple. It depends on an independent global clock, and there is a tradeoff between speed, accuracy and power consumption. When the clock frequency increases, the system needs fast transient response, but the power consumption will increase proportionally, and the current efficiency and loop stability will decrease. Using large output capacitor to deal with load transient is not conducive to improve chip integration. Although asynchronous DLDO can improve the response speed based on the advantages of asynchronous control scheme, the stability of DLDO will face greater risks. Therefore, this paper will introduce several transient response enhancement technologies that do not sacrifice system power consumption, accuracy or stability. It includes adaptive frequency technology and fast response algorithm to improve the transient response speed of synchronous DLDO, event-driven solution and coarse and fine adjustment technology to improve the transient response speed of asynchronous DLDO. On this basis, a typical DLDO structure with excellent performance in the recent 10 years is given.

DC offset rejection in a frequency-fixed second-order generalized integrator-based phase-locked loop for single-phase grid-connected applications

Fast and accurate monitoring of the phase, amplitude, and frequency of the grid voltage is essential for single-phase grid-connected converters. The presence of DC offset in the grid voltage is detrimental to not only grid synchronization but also the closed-loop stability of the grid-connected converters. In this paper, a new synchronization method to mitigate the effect of DC offset is presented using arbitrarily delayed signal cancelation (ADSC) in a second-order generalized integrator (SOGI) phase-locked loop (PLL). A frequency-fixed SOGI-based PLL (FFSOGI-PLL) is adopted to ensure better stability and to reduce the complexity compared with other SOGI-based PLLs. A small-signal model of the proposed PLL is derived for the systematic design of proportional-integral (PI) controller gains. The effects of frequency variation and ADSC on the proposed PLL are considered, and correction methods are adopted to accurately estimate grid information. The simulation results are presented, along with comparisons to other single-phase PLLs in terms of settling time, peak frequency, and phase error to validate the proposed PLL. The dynamic performance of the proposed PLL is also experimentally validated. Overall, the proposed PLL has the fastest transient response and better dynamic performance than the other PLLs for almost all performance indices, offering an improved solution for precise grid synchronization in single-phase applications.

STBC Identification for Multi-User Uplink SC-FDMA Asynchronous Transmissions Exploiting Iterative Soft Information Feedback of Error Correcting Codes

With the advancement and widespread implementation of multiple-input multiple-output (MIMO) wireless communication systems over the last decade, space-time block coding (STBC) identification has become a critical task for intelligent radios. Previous examinations of STBC identification were focused on single-user transmissions over single-carrier and multi-carrier systems in combination with uncoded broadcasts. Practical systems, on the other hand, contain many users and employ error-correcting codes. For the first time in literature, this work explores the problem of STBC identification for multi-user uplink transmissions in single-carrier frequency division multiple access (SC-FDMA) systems. We take another step closer to real systems by addressing asynchronous transmissions and by conducting multi-user channel estimation. We also exploit the outputs of the channel decoder, which is usually used in many practical systems, to improve the identification and estimation processes. The mathematical analysis demonstrates that the maximum-likelihood (ML) solution of STBC identification, channel estimation, and synchronization can be executed by an iterative approach. The space-alternating generalized expectation-maximization (SAGE) algorithm is used to separate the overlaid signals arriving at the base-station (BS). The parameters under consideration for each user are then updated using an expectation-maximization (EM) processor. Simulation results show that the proposed architecture outperforms other identification methods published in the literature while maintaining a reasonable level of processing time.

Joint Synchronization and Compressive Channel Estimation for Frequency-Selective Hybrid mmWave MIMO Systems

Synchronization is a fundamental procedure in cellular systems whereby user equipment (UE) acquires the time and frequency information required to decode the data transmitted by a base station (BS). Due to the small antenna aperture at millimeter wave (mmWave), large antenna arrays are used to compensate for the low signal-to-noise ratio (SNR) at the receiver. For this reason, synchronization is often performed jointly with beam training as in 5G New Radio (NR) to boost the receive SNR. However, if the mmWave multiple-input multiple-output (MIMO) channel is to be estimated, then synchronization must be performed in the low SNR regime owing to the lack of directional beamforming during compressive channel estimation. Current mmWave channel estimation algorithms implicitly take synchronization for granted, which is a not practical assumption in the low SNR regime. To solve this problem, this work proposes the first synchronization framework for hybrid mmWave MIMO that is robust to carrier frequency offset (CFO) and phase noise (PHN) synchronization errors. We propose two novel multi-stage algorithms to jointly estimate the various unknown parameters, based on the expectation-maximization (EM) algorithm. By using the QuaDRiGa 5G NR channel simulator, we show that compressive channel estimation without prior synchronization is possible, and the proposed approaches outperform current solutions for joint beam training and synchronization currently considered in 5G NR.

A robust auto-synchronizer for synchronverter

The increasing deployment of inertia-less power electronic converters poses serious concerns on power system frequency stability. Synchronverter has certain features like virtual inertia, damping and voltage regulation embedded in its controller. Therefore, it can support system frequency and voltage in power grids. Like synchronous generator, it has ability to remain synchronized with the grid. However, it requires a synchronizer to track grid phase and frequency as reference before grid connection. This paper proposes a robust PLL-less Auto-synchronizer for synchronverter that allows it to synchronize with grid without interrupting its output power. The proposed synchronizer ensures fast synchronization independent of adverse grid conditions. Moreover, it has less computational burden on controller. The robustness of proposed synchronizer is validated by simulations. Results have shown that the proposed synchronizer is a fast and promising solution of synchronization of synchronverter with grid independent of certain grid conditions.

Synchronization in Dynamically Coupled Fractional-Order Chaotic Systems: Studying the Effects of Fractional Derivatives

This study presents the effectiveness of dynamic coupling as a synchronization strategy for fractional chaotic systems. Using an auxiliary system as a link between the oscillators, we investigate the onset of synchronization in the coupled systems and we analytically determine the regions where both systems achieve complete synchronization. In the analysis, the integration order is considered as a key parameter affecting the onset of full synchronization, considering the stability conditions for fractional systems. The local stability of the synchronous solution is studied using the linearized error dynamics. Moreover, some statistical metrics such as the average synchronization error and Pearson’s correlation are used to numerically identify the synchronous behavior. Two particular examples are considered, namely, the fractional-order Rössler and Chua systems. By using bifurcation diagrams, it is also shown that the integration order has a strong influence not only on the onset of full synchronization but also on the individual dynamic behavior of the uncoupled systems.

A phase-locked loop with an improved dynamic response under abnormal grid conditions

The cascaded delayed signal cancelation (CDSC) method has attracted much attention recently as an efficient filtering technique to improve synchronous reference frame phase-locked loop (PLL) performance in grid synchronization under adverse grid conditions. The CDSC-based PLL suffers from slow transient response. Therefore, this study proposes a solution for grid synchronization under abnormal conditions utilizing an arbitrary time-delay operator to mitigate the DC offset and frequency adaptive CDSC operators for harmonic filtering. An accurate small-signal model was derived, opening the door to design the loop filter. The coefficient diagram method was adopted to systematically design the gains of the proportional–integral controller and a lead–lag compensator, yielding a faster dynamic response than the symmetrical optimum method-based design. The proposed PLL effectiveness was verified numerically under abnormal conditions, showing better dynamic and steady-state performance than other related PLLs. The proposed PLL requires less than two grid cycles to synchronize without ripples, meeting the grid code's requirement.

Boosting synchronization in chaotic systems: Combining past and present interactions

A classical interconnection for inducing synchronization in dynamical systems is static diffusive coupling, i.e., a coupling without dynamics that considers the output or state differences of neighboring systems. However, this type of coupling has some well-known limitations: 1) for some chaotic systems and certain input-output combinations, it is impossible to synchronize a pair or a network of identical systems, 2) the interval of coupling strength values for which synchronization is achieved is limited. Here, we show that these limitations may be removed, or at least considerably relaxed, by using a coupling with memory, i.e., a coupling composed by a standard diffusive-like term plus a delayed version of itself. As a particular example, we consider a pair of Rössler systems in a master-slave configuration, where we analyze the local stability of the synchronous solution using the linearized error dynamics in combination with the D-decomposition method. Also, analytic conditions for tuning the coupling strength values corresponding to the non-delayed and delayed terms of the overall coupling are provided. Furthermore, the applicability of the proposed coupling for boosting synchronization in other chaotic systems is also discussed. In particular, we show how the proposed coupling with memory is applicable for synchronizing a pair of uni-directionally coupled van der Pol oscillators with sinusoidal excitation and a pair of Hindmarsh-Rose neurons. Ultimately, the results presented in this paper suggest that the synchronizability of the coupled systems is enhanced when the present and past interactions are taken into account.

CoSiWiNeT: A Clock Synchronization Algorithm for Wide Area IIoT Network

Recent advances in the industrial internet of things (IIoT) and cyber–physical systems drive Industry 4.0 and have led to remote monitoring and control applications that require factories to be connected to remote sites over wide area networks (WAN). The adequate performance of remote applications depends on the use of a clock synchronization scheme. Packet delay variations adversely impact the clock synchronization performance. This impact is significant in WAN as it comprises wired and wireless segments belonging to public and private networks, and such heterogeneity results in inconsistent delays. Highly accurate, hardware–based time synchronization solutions, global positioning system (GPS), and precision time protocol (PTP) are not preferred in WAN due to cost, environmental effects, hardware failure modes, and reliability issues. As a software–based network time protocol (NTP) overcomes these challenges but lacks accuracy, the authors propose a software–based clock synchronization method, called CoSiWiNeT, based on the random sample consensus (RANSAC) algorithm that uses an iterative technique to estimate a correct offset from observed noisy data. To evaluate the algorithm’s performance, measurements captured in a WAN deployed within two cities were used in the simulation. The results show that the performance of the new algorithm matches well with NTP and state–of–the–art methods in good network conditions; however, it outperforms them in degrading network scenarios.

Spectral Asymptotics and Lamé Spectrum for Coupled Particles in Periodic Potentials

We make two observations on the motion of coupled particles in a periodic potential. Coupled pendula, or the space-discretized sine-Gordon equation is an example of this problem. Linearized spectrum of the synchronous motion turns out to have a hidden asymptotic periodicity in its dependence on the energy; this is the gist of the first observation. Our second observation is the discovery of a special property of the purely sinusoidal potentials: the linearization around the synchronous solution is equivalent to the classical Lamè equation. As a consequence, all but one instability zones of the linearized equation collapse to a point for the one-harmonic potentials. This provides a new example where Lamé’s finite zone potential arises in the simplest possible setting.

Intelligent Face Tracking for Collaborative Synchronous e-Learning using Pattern Recognition Model

Intelligent Face Tracking for Collaborative Synchronous e-Learning using Pattern Recognition Model can provide high levels of interaction for distance learning initiatives. With the rapid evolution of technology, face recognition login and tracking, continuous product evaluation is necessary to ensure optimal methods and resources for connecting students, instructors, and educational content in rich, online learning communities. This article presents the analysis of online, synchronous learning solutions. Focusing on their abilities to meet technical and pedagogical needs in higher education. To make a solid comparison, the systems were examined in online classrooms with instructors, guest speakers, and students. Relative to usability, instructional needs, technical aspects and compatibility are outlined for systems.

Dynamic characteristics of a simply supported elastic beam with three induction motors

In the paper, the dynamic characteristics of a three induction motor driven system on a simply supported elastic beam are studied. Firstly, a dynamic coupling model of the whole system is established according to the Hamilton principle and discretized by applying the assumed mode method. Next, the synchronization solutions containing the average rotation speeds and phase differences of three motors and their stability are calculated and analyzed by using the average perturbation method. As a result, the synchronization and stability conditions of self-synchronization of three motors are established. Finally, the feasibility of the average perturbation method is verified by comparing the theoretical results with the simulation results. The results indicate that the elastic support has a large influence on the motion states of three motors. There is the self-synchronization phenomenon of three motors on the elastic beam. There appear the Sommerfeld effect (rotational speed capture and jump phenomena) near the resonance of the beam and the synchronous states of three motors will rapidly change before and after the resonance of beam. The large changes of the motion states of three motors cause the impacts of the responses of the elastic beam structure. Additionally, the effects of the structure parameters such as unbalance mass, power frequency, beam size and vibration modes on the dynamic characteristics of the system are discussed. This paper can provide some references for the design of multi-motor systems on the elastic foundations.

Cluster synchronization of networks via a canonical transformation for simultaneous block diagonalization of matrices.

We study cluster synchronization of networks and propose a canonical transformation for simultaneous block diagonalization of matrices that we use to analyze the stability of the cluster synchronous solution. Our approach has several advantages as it allows us to: (1) decouple the stability problem into subproblems of minimal dimensionality while preserving physically meaningful information, (2) study stability of both orbital and equitable partitions of the network nodes, and (3) obtain a parameterization of the problem in a small number of parameters. For the last point, we show how the canonical transformation decouples the problem into blocks that preserve key physical properties of the original system. We also apply our proposed algorithm to analyze several real networks of interest, and we find that it runs faster than alternative algorithms from the literature.

Phase-Stabilized Side-Branch RoF Link for Extensible Frequency Dissemination in Distributed Systems

Synchronization is a long-standing challenge in modern large-scale distributed systems, and newly deployed systems such as 5G and modern netted radars require more extensive synchronization. As the number of distributed stations increasing, new synchronization solution with much effort on extensibility is highly expected. In this paper we first analyze the requirements on extensibility of fiber-based sync systems, and then propose a phase-stabilized side-branch radio-over-fiber (RoF) link, which fully satisfies the extensibility requirements. The extensible side-branch link can be constructed at any intermediate point along the main link, without any reconfiguration at the central station, which is especially feasible when adding extra stations in system capacity expansion. The main link phase shift is first stabilized by tuning the optical carrier wavelength, while another phase-locked-loop constructed at the starting point of the branch link stabilizes the phase shift from the central station to the end of branch link, by phase locking two phase-varying signals. Moreover, the phase-stable side branch is inherently extensible to multiple frequency signals, which can be used in receivers requiring multiple local oscillators (LOs). Two frequency signals are simultaneously disseminated to the end of branch link in the experiment, with frequency stability optimization of two orders of magnitude on both LOs achieved. The proposed stable side-branch RoF link shows the potential of constructing a highly-extensible frequency dissemination network for the synchronization in modern distributed systems.

GIẢM THIỂU ẢNH HƯỞNG ĐẾN BIẾN ĐỔI KHÍ HẬU ĐỐI VỚI GIÁO DỤC NGƯỜI KHUYẾT TẬT

Climate change has a negative effect on health and enrollment in activities, especially for education for people with disabilities. People with disabilities mostly come from impoverished families where public services are underdeveloped. Thus, they face disadvantages when participating in online and face-to-face education because the quality of infrastructure and learning materials is inadequate. The difficulties for education for people with disabilities are also exacerbated by climate change which also affects people without disabilities. In detail, the support for people with disabilities are significantly reduced in terms of special learning materials and facilities, which are consistently more expensive than the common ones. Since the life quality declines because of climate change, people without disabilities will contest for jobs and thus leading to difficulties in the output of education for people with disabilities and affecting their learning motivation adversely. To tackle these restrictions, a comprehensive and synchronous solution is required.

Synchronization using quantum photons for satellite-to-ground quantum key distribution.

Time synchronization is crucial for quantum key distribution (QKD) systems. In order to compensate for the time drift caused by the Doppler effect and adapt to the unstable optical link in satellite-to-ground QKD, previous demonstrations generally adopted synchronization methods requiring additional hardware. In this paper, we present a novel synchronization method based on the detected quantum photons, thus simplifying additional hardware and reducing the complexity and cost. This method adopts target frequency scanning to realize fast frequency recovery, utilizes polynomial fitting to compensate for the Doppler effect, and takes use of the vacuum state in the decoy-state BB84 protocol to recover the time offset. This method can avoid the influence of synchronization light jitter, thus improving the synchronization precision and the secure keys as well. Successful satellite-to-ground QKD based on this new synchronization scheme has been conducted to demonstrate its feasibility and performance. The presented scheme provides an effective synchronization solution for quantum communication applications.

Emergence of synchronous behavior in a network with chaotic multistable systems

In this work, we address the synchronization problem of complex dynamical networks with bidirectional, linear, and diffusive coupling, whose nodes have dynamics given by a particular class of piecewise linear (PWL) systems. The class of PWL systems are multistable unstable dissipative systems and exhibit chaotic behavior. The topologies that we consider are regular coupled network. Firstly, we consider that the complex network has a uniform coupling strength, and through the Lyapunov approach, we show that nodes can achieve complete or partial synchronization, where the synchronization solution depends on the inner coupling matrix and the initial conditions of each node. Secondly, we consider a weighted network, where the synchronization solution depends on the external coupling matrix, and even obtain a synchronous behavior type master-slave. Our theoretical results agree with the numerical simulations for a set of nodes in different topology networks.

Evaluation of Precise Microwave Ranging Technology for Low Earth Orbit Formation Missions with Beidou Time-Synchronize Receiver.

In this study, submillimeter level accuracy K-band microwave ranging (MWR) equipment is demonstrated, aiming to verify the detection of the Earth’s gravity field (EGF) and digital elevation models (DEM), through spacecraft formation flying (SFF) in low Earth orbit (LEO). In particular, this paper introduces in detail an integrated BeiDou III B1C/B2a dual frequency receiver we designed and developed, including signal processing scheme, gain allocation, and frequency planning. The receiver matched the 0.1 ns precise synchronize time-frequency benchmark for the MWR system, verified by a static and dynamic test, compared with a time interval counter synchronization solution. Moreover, MWR equipment ranging accuracy is explored in-depth by using different ranging techniques. The test results show that MWR achieved 40 m and 1.6 m/s accuracy for ranging and range rate during tests, using synchronous dual one-way ranging (DOWR) microwave phase accumulation frame, and 6 m/s range rate accuracy obtained through a one-way ranging experiment. The ranging error sources of the whole MWR system in-orbit are analyzed, while the relative orbit dynamic models, for formation scenes, and adaptive Kalman filter algorithms, for SFF relative navigation designs, are introduced. The performance of SFF relative navigation using MWR are tested in a hardware in loop (HIL) simulation system within a high precision six degree of freedom (6-DOF) moving platform. The final estimation error from adaptive relative navigation system using MWR are about 0.42 mm (range/RMS) and 0.87 m/s (range rate/RMS), which demonstrated the promising accuracy for future applications of EGF and DEM formation missions in space.

Wicsync: A wireless multi-node clock synchronization solution based on optimized UWB two-way clock synchronization protocol

The clock synchronization accuracy directly determines the performance of wireless distributed cooperative systems. However, the mature high accuracy wireless clock synchronization schemes are generally based on GNSS or other auxiliary sources to complete the synchronization process, which cannot be applied to GNSS degraded and denied environments. In this paper, a wireless high-accuracy clock synchronization solution for multi-node distributed cooperative systems – Wicsync – is proposed, which contains an optimized wireless two-way clock synchronization and mutual calibration protocol to support wireless multi-node clock synchronization. Based on the UWB synchronization hardware architecture with local clock phase adjustment we designed, Wicsync implements a non GNSS-aided, high-accuracy, multi-node, low cost wireless clock synchronization performance through the protocol. Experiments shows that the Wicsync can support the instantaneous clock synchronization accuracy of less than 3 ns (@75 m at least) for 10 nodes (more than 100 nodes theoretically).

Effect of Asynchronous Communications on Stationary Solutions for Discrete-Time Multiagent Systems

This paper investigates the effect of asynchronous communications on stationary solutions for discrete-time multiagent systems with a fixed topology. The asynchrony in this context implies that there is no global clock to synchronize the update time in each distributed agent and also each agent updates its own state asynchronously without waiting for values received from neighboring agents. It has been noted without much attention that asynchronous stationary solutions may not be unique and disagree with a synchronous stationary value. In some applications, this discrepancy may cause serious consequences, and thus it is critical to analyze the effect of asynchrony on stationary solutions. In this paper, we develop necessary and sufficient conditions for the uniqueness of stationary solutions for discrete-time multiagent systems. In the case of nonunique stationary solutions, the normalized expected error between synchronous and asynchronous stationary solutions is also analyzed. To validate the proposed methods, we provide three example problems: 1) containment control; 2) fixed-point iteration; and 3) distributed averaging formulated in a discrete-time setting.