Sensor Network Synchronization Research Articles

Electro-Optical Diagnostics at KARA and FLUTE – Results and Prospects

Electro-optical (EO) methods are nowadays well-proven diagnostic tools, which are utilized to detect THz fields in countless experiments. The world’s first near-field EO sampling monitor at an electron storage ring was developed and installed at the KIT storage ring KARA (Karlsruhe Research Accelerator) and optimized to detect longitudinal bunch profiles. This experiment with other diagnostic techniques builds a distributed, synchronized sensor network to gain comprehensive data about the phase-space of electron bunches as well as the produced coherent synchrotron radiation (CSR). These measurements facilitate studies of physical conditions to provide, at the end, intense and stable CSR in the THz range. At KIT, we also operate FLUTE (Ferninfrarot Linac- und Test-Experiment), a new compact versatile linear accelerator as a test facility for novel techniques and diagnostics. There, EO diagnostics will be implemented to open up possibilities to evaluate and compare new techniques for longitudinal bunch diagnostics. In this contribution, we will give an overview of results achieved, the current status of the EO diagnostic setups at KARA and FLUTE and discuss future prospects.

Research on time synchronization of linear pulse-coupled oscillators model with delay in nearest neighbor wireless multi-hop networks

Time synchronicity works as a popular requirement in wireless sensor networks. Pulse-coupled oscillators similar to firefly flashing and synchronization via discrete pulse coupling are widely used in wireless sensor networks. In this article, we have studied the time synchronization with communication delay in the nearest neighbor network of distributed sensors, based on the pulse-coupled oscillators model of synchronicity achieved by biological systems. First, we present a linear pulse-coupled oscillators model with coupling delay and the model is used to analyze the wireless sensor networks synchronization with communication delay. Second, we mathematically analyze the firing behaviors in the linear pulse-coupled oscillators network using the delayed excitatory coupling and track the synchronization process of the two and multi-oscillators and obtain the synchronization conditions from the regression mapping. Finally, through the proposed model implementation in the wireless sensor networks simulation framework, we demonstrate that the multi-oscillators system can be synchronized from a random starting stage distribution under linear phase responding functions and the nearest neighbor communication. The results show that our approach can achieve clock synchronization in wireless sensor networks with delayed nearest neighbor communication.

Clock synchronization error compensation algorithm based on BP neural network model

Error compensation is an important guarantee method to ensure the accuracy of clock synchronization in underwater sensor networks. Existing research methods mainly use linear fitting and least square method to compensate for clock synchronization parameters. Underwater wireless sensor network nodes are mobile, which leads the network nodes to be always in a time-varying state. In the process of synchronous forwarding, the position where the node sends and receives data packets will change, resulting in a relative moving distance, leading the dynamic delay to an increase in. In this way, as the number of forwarding nodes increases, the error of the clock gradually increases, causing the synchronization accuracy of the underwater sensor wireless network to gradually decrease. The existing underwater wireless sensor network clock synchronization algorithm does not fully consider the dynamic time delay caused by the movement of the node with the ocean current. It only uses the time stamp mechanism to solve the clock synchronization parameters, and then uses the traditional linear fitting to refine the synchronization parameters. The accurate solution of dynamic time delay is a key factor of synchronization accuracy. The use of traditional optimization algorithms to refine the synchronization parameters can easily fall into a local optimum, which makes the synchronization accuracy not high. Therefore, the existing traditional research on clock synchronization algorithms cannot well solve the problem of clock synchronization accuracy caused by node mobility. However this type of method does not consider the clock synchronization accuracy of node movement affected by ocean currents. To solve this problem, this paper proposes a clock synchronization error compensation algorithm based on BP neural network model. First, the deep-sea Lagrangian ocean current model is used to describe the movement of underwater nodes and simulate the movement speed of underwater nodes, and then a clock synchronization parameter model is established, and finally a BP neural network clock synchronization error compensation model is build, which conforms to the underwater environment, and the excitation function is defined, and regular term factor and compensatory factor are introduced to avoid model over-fitting. The BP neural network model clock synchronization error compensation algorithm is established for error back propagation. Simulation experiments show that compared with the comparison algorithm TSHL, MM-sync, and MU-sync, the accuracy of clock synchronization, namely the error between clock synchronization time and standard time, increased by 37.42%, 17.29% and 21.86%, and the mean square error is significantly reduced.

Source localization in large-scale asynchronous sensor networks

The problem of uncooperative source localization and synchronization in asynchronous sensor networks has been considered previously in a centralized manner, where all the raw measurements are delivered to a processing center. However, for large-scale sensor networks the transmission of raw measurements over the networks requires considerable communication overhead, besides being vulnerable to transmission failure and interference, and the computational load at the processing center is rather heavy. A more suitable candidate to this problem is the distributed estimation considered in this paper, where each sensor node communicates with its neighboring nodes only, and the parameters are estimated at each sensor via information cooperation. In order to decouple the unknown source positions and sensor clock offsets, we propose to update them iteratively based on the belief propagation (BP) framework. To reduce the complexity of parameter update at each sensor, the sigma point based estimation method is adopted. Theoretical analyses concerning the computational complexity and communication overhead are carried out. Simulation results demonstrate that the proposed method could estimate the source positions distributively with much lower complexity and communication overhead compared with the centralized methods at the cost of acceptable performance degradation.

Exploring the effects of environmental conditions and design choices on IoT systems using formal methods

Wireless communication protocols are often used in critical applications, e.g., urban water supply networks or healthcare monitoring within the Internet of Things. It is essential that control software and protocols for such systems are verified to be both robust and reliable. The effects on the hardware caused by environmental conditions and the choice of parameters used by the protocol are among the largest obstacles to robustness and reliability in wireless systems. In this paper we use formal verification to verify that a wireless sensor network synchronization and dissemination protocol is not adversely affected by these factors.

SANSync: An Accurate Time Synchronization Protocol for Wireless Sensor and Actuator Networks

Wireless sensor and actuator networks (WSANs) consists of a large number of sensors and a relatively small number of actuators connected through wireless links. In the WSANs applications, sensors detect the events in their environment and inform actuators. The actuators cooperate together and respond quickly to events. To coordinate their operations, a common time reference to all nodes in the network is a critical need. In this paper, we propose an accurate time synchronization protocol for WSANs, namely Sensor and Actuator Networks Synchronization Protocol (SANSync), which allows the clocks of all sensors and actuators in the network to be synchronized with a reference clock. SANSync is based on clustering; it takes advantage of the large transmission capacity of actuators to increase the accuracy of time synchronization. The simulation results show that the proposed protocol increases significantly the accuracy of time synchronization compared to FTSP and FCSA protocols.

AUV-Aided Joint Localization and Time Synchronization for Underwater Acoustic Sensor Networks

For the purpose of localization and time synchronization of underwater sensor networks, buoys are generally distributed on the sea surface of the area of interest, serving as fixed anchors. However, this method is not economical and has poor scalability. An alternative is to employ an autonomous underwater vehicle (AUV) as a mobile anchor. By receiving the periodical broadcast signals from the AUV, any sensor in the communication range can measure time of arrival of received packets and obtain a series of nonlinear equations. In this letter, we proposed an efficient linear algorithm to solve the nonlinear equations, and gave closed-form positioning and synchronization error analysis. Besides, we show that the proposed method can approach the Cramér-Rao lower bound by both theoretical analysis and simulation.

Fast Unit-Modulus Least Squares With Applications in Beamforming

Unit-modulus least squares (ULS) problems arise in many applications, including phase-only beamforming, sensor network localization, synchronization, phase retrieval, and radar code design. ULS formulations can always be recast as unit-modulus quadratic programs, to which semidefinite relaxation (SDR) can be applied, and is often the state-of-the-art approach. However, SDR lifts the problem dimension (i.e., the number of variables) from $N$ to $N^2$ , which drastically increases the memory burden and computational cost when the problem size is already large—e.g., when designing phase-only beamformer weights for massive multiple-input-multiple-output systems. This paper focuses on scalable first-order algorithms for the ULS problem and some of its variants. It advocates using simple gradient projection (GP) as a starting point for solving the ULS problem, establishes global convergence of GP to a Karush–Kuhn–Tucker point for this NP-hard problem, and bounds its iteration complexity. Then it proposes ULS extensions tailored to reflect practical beamformer design objectives, bringing in and exploiting new degrees of freedom to improve the beampattern designs. Simple variants of GP are proposed to deal with these extended ULS problems. Simulations are used to showcase the effectiveness of the proposed algorithms in both the plain ULS problem and in the context of phase-only beamforming.

Travelling Wave Pulse Coupled Oscillator (TWPCO) Using a Self-Organizing Scheme for Energy-Efficient Wireless Sensor Networks.

Recently, Pulse Coupled Oscillator (PCO)-based travelling waves have attracted substantial attention by researchers in wireless sensor network (WSN) synchronization. Because WSNs are generally artificial occurrences that mimic natural phenomena, the PCO utilizes firefly synchronization of attracting mating partners for modelling the WSN. However, given that sensor nodes are unable to receive messages while transmitting data packets (due to deafness), the PCO model may not be efficient for sensor network modelling. To overcome this limitation, this paper proposed a new scheme called the Travelling Wave Pulse Coupled Oscillator (TWPCO). For this, the study used a self-organizing scheme for energy-efficient WSNs that adopted travelling wave biologically inspired network systems based on phase locking of the PCO model to counteract deafness. From the simulation, it was found that the proposed TWPCO scheme attained a steady state after a number of cycles. It also showed superior performance compared to other mechanisms, with a reduction in the total energy consumption of 25%. The results showed that the performance improved by 13% in terms of data gathering. Based on the results, the proposed scheme avoids the deafness that occurs in the transmit state in WSNs and increases the data collection throughout the transmission states in WSNs.

Time Synchronization Techniques in Wireless Network : A Survey

The time synchronization procedure is very important for power saving in wireless ad hoc network and method used by the synchronization that method chooses a particular node and gives priority for transmitting a signal to that node. All the Other nodes synchronize to the selected node according to Time Synchronization Function. Here increasing research focus on designing synchronization algorithms specifically for sensor networks. This paper look for reviews of time synchronization problem and the need for synchronization in sensor networks, then presents in detail time synchronization methods explicitly designed and proposed for sensor networks and AD-HOC networks.

Partial synchronization and controllability of asymmetric coupling wireless sensor networks

For a uniform complex dynamics networks, a synchronization criterion of this model is given by constructing a Lyapunov function. In this paper, we present a new asymmetric coupling wireless sensor networks (WSNs) synchronization control algorithm combining with clusters, it aimed at the application of a large scale, high-density WSNs. It is proved that this network can achieve synchronization dynamically under the control scheme. This model avoids the research under the specific network topology of network synchronization problems, instead of researching how to improve the synchronization performance of the network from the perspective of cybernetics. Particularly, this controller has strong robustness against the coupling strength and topological structure of the network. Numerical simulations show this model can significantly improve the performance of synchronization for WSNs. Our results offer important references on the performance issues depending on specific application scenarios of WSNs.

Underwater Acoustic Modems (S2CR Series) for Synchronization of Underwater Acoustic Network Clocks During Payload Data Exchange

Modern underwater acoustic modems, in addition to receiving and transmitting data, can measure signal propagation time and evaluate the distance between the transmitter and the receiver. These capabilities can be exploited to support the synchronization of underwater acoustic sensor networks, where sensing and actuation must be coordinated across multiple nodes. However, the problem of accurate propagation time measurement, especially in highly reverberant environments, and the evaluation of clock skew on acoustically interacting modems have been investigated rather poorly. In this paper, therefore, we conduct an experimental evaluation of stability/precision of propagation time measurements considering underwater acoustic modems communicating in reverberant environments. We also show how modem built-in tools can provide opportunities for precise estimation of the modems clock skews. Additionally, we demonstrate that payload data exchange can be used as a “comfortable” way for clock synchronization of underwater acoustic networks nodes. At-sea experiments have been carried out considering several modem pairs and node positions in conditions of reverberant underwater acoustic channels. These experiments have been conducted in collaboration with the NATO Centre for Maritime Research and Experimentation (CMRE, La Spezia, Italy) that we gratefully acknowledge.

A Joint Time Synchronization and Localization Design for Mobile Underwater Sensor Networks

Time synchronization and localization are basic services in a sensor network system. Although they often depend on each other, they are usually tackled independently. In this work, we investigate the time synchronization and localization problems in underwater sensor networks, where more challenges are introduced because of the unique characteristics of the water environment. These challenges include long propagation delay and transmission delay, low bandwidth, energy constraint, mobility, etc. We propose a joint solution for localization and time synchronization, in which the stratification effect of underwater medium is considered, so that the bias in the range estimates caused by assuming sound waves travel in straight lines in water environments is compensated. By combining time synchronization and localization, the accuracy of both are improved jointly. Additionally, an advanced tracking algorithm interactive multiple model (IMM) is adopted to improve the accuracy of localization in the mobile case. Furthermore, by combining both services, the number of required exchanged messages is significantly reduced, which saves on energy consumption. Simulation results show that both services are improved and benefit from this scheme.

Globally Exponential Synchronization of Complex Sensor Networks with Nonlinear Coupling by Adaptive Control

Globally Exponential Synchronization of Complex Sensor Networks with Nonlinear Coupling by Adaptive Control

Clock Synchronization in Wireless Sensor Network With Selective Convergence Rate for Event Driven Measurement Applications

In this paper, a novel wireless sensor network synchronization protocol for event-driven measurement applications is proposed. The objective is twofold: 1) to provide high accuracy in the area where an event is detected and 2) to ensure a long network lifetime. The complexity of the problem arises from the fact that these two properties are usually in conflict. To increase the synchronization accuracy, nodes are required to exchange synchronization packets at higher rate, thus impacting the network lifetime. Vice versa to ensure a long network life time, the number of packets to be exchanged should be minimized thus impacting the synchronization accuracy. A tradeoff can be achieved by observing that the packet rate should be increased only for the portion of the network surrounding the detected events as only these nodes require a higher accuracy to collect data. The proposed algorithm represents a formalization of this idea. Numerical and experimental results are provided to validate the effectiveness of the proposed algorithm. 0018-9456 © 2014 IEEE.

Time Synchronization Algorithms in Low-Cost Wireless Sensor Network Systems

Time synchronization is an essential building block of sensor network systems. In this paper, we present a comprehensive study of least squares algorithms for time synchronization in sensor networks, with a focus on continuous monitoring and data collection applications. We propose a set of algorithms to address a number of issues in practical implementation on typical low-cost sensor network platforms, including a scaled signal model to achieve numerical stability in an ill-conditioned problem, sequential estimators for the scaled signal model to reduce computational complexity, a fast initialization scheme to improve energy efficiency, and outlier detection algorithms to improve robustness in long-term autonomous operations. The proposed algorithms are implemented and a measurement-based simulation method is employed to study the performance.

A combined hardware–software approach for acoustic sensor network synchronization

In this paper we present an approach for synchronizing a wireless acoustic sensor network using a two-stage procedure. First the clock frequency and phase differences between pairs of nodes are estimated employing a two-way message exchange protocol. The estimates are further improved in a Kalman filter with a dedicated observation error model. In the second stage network-wide synchronization is achieved by means of a gossiping algorithm which estimates the average clock frequency and phase of the sensor nodes. These averages are viewed as frequency and phase of a virtual master clock, to which the clocks of the sensor nodes have to be adjusted. The amount of adjustment is computed in a specific control loop. While these steps are done in software, the actual sampling rate correction is carried out in hardware by using an adjustable frequency synthesizer. Experimental results obtained from hardware devices and software simulations of large scale networks are presented.

Passive Localization and Synchronization Using Arbitrary Signals

Time-of-arrival (TOA) localization is tightly coupled with sensor time synchronization. Synchronization can be obtained by GPS, atomic clocks, or message exchange protocols. All methods affect the energy sources and the synchronization protocols use valuable bandwidth. We present self-synchronized localization algorithms that rely exclusively on TOA measurements performed by the sensor network on passing sources rendering it completely passive. The same methods can be applied to time-difference-of- arrival (TDOA) measurements allowing the use of a larger family of signals. Localization performance is close to that provided by a perfectly synchronized network. Such algorithms can also be used for sensor network synchronization and communication networks in general.

Temporal synchronization in mobile sensor networks using image sequence analysis

This paper addresses the problem of estimating the temporal synchronization in mobile sensors' networks, by using image sequence analysis of their corresponding scene dynamics. Unlike existing methods, which are frequently based on adaptations of techniques originally designed for wired networks with static topologies, or even based on solutions specially designed for ad hoc wireless sensor networks, but that have a high energy consumption and a low scalability regarding the number of sensors, this work proposes a novel approach that reduces the problem of synchronizing a general number $$N$$ N of sensors to the robust estimation of a single line in $${\mathbb {R}}^{N+1}$$ R N + 1 . This line captures all temporal relations between the sensors and can be computed without any prior knowledge of these relations. It is assumed that (1) the network's mobile sensors cross the field of view of a stationary calibrated camera that operates with constant frame rate and (2) the sensors trajectories are estimated with a limited error at a constant sampling rate, both in the world coordinate system and in the camera's image plane. Experimental results with real-world and synthetic scenarios demonstrate that our method can be successfully used to determine the temporal alignment in mobile sensor networks.

Performance Evaluation of a Sensor Network Synchronization Scheme based on Noise Induced Phase Synchronization

Performance Evaluation of a Sensor Network Synchronization Scheme based on Noise Induced Phase Synchronization