Synchronization In Wireless Sensor Networks Research Articles

Time Delay Characterization in Wireless Sensor Networks for Distributed Measurement Applications

This paper investigates the critical aspect of synchronization in wireless sensor networks (WSNs) across diverse industrial applications. The low-cost sensor network topologies are analyzed. The communication delay measurements and quantitative jitter analysis are performed under different conditions, and dependencies of the propagation time delay on the data bitrate and modulation type for different hardware implementations of the WSNs are presented. The time delay distribution influence on the time synchronization error propagation over WSN layers was assessed from the experimental probability density functions. The network synchronization based on the controlled propagation delay jitter approach has been proposed. This research contributes quantitative insights into the complexities of synchronization in WSNs, offering a foundation for optimizing network configurations and parameters to extend the operational life of low-power sensor nodes.

Resilient Synchronization of Pulse-coupled Oscillators with Time Continuity

Clock synchronization of wireless sensor networks (WSNs) using pulse-coupled oscillators has been extensively studied. In this paper, we propose a resilient clock synchronization algorithm that can mitigate the influence of adversarial nodes that emit pulses at arbitrary time instants. Under the assumption that a bound on the number of nodes in the network is known, we provide distributed protocols that guarantee continuity of clocks by varying the phase speeds. We illustrate the usefulness of the proposed algorithms by comparing them with a conventional method in a numerical example.

Consensus-based time synchronization via sequential least squares for strongly rooted wireless sensor networks with random delays

Consensus-based time synchronization, which is built on multi-agent consensus technique, becomes an important synchronization strategy to achieve accurate time synchronization for wireless sensor networks in a fully distributed way. In practical network scenarios, random communication delays are inevitable and have a significant influence on the information exchange procedure. Without dealing with the delays, many synchronization algorithms based on consensus will diverge and the nodes in the network will fail to synchronize with each other. A feasible approach addressing this problem is to design powerful and effective relative skew estimator to suppress the influence caused by delays. In this paper, we propose a sequential least squares algorithm to estimate the skew under delays, which improves the estimation accuracy while reducing the memory requirement. Based on the estimation algorithm and considering the case of the varying skews, we also devise an improved estimation scheme by incorporating a forgetting factor so as to track the skew evolution. By applying the proposed estimation method to average consensus protocol, each node can achieve accurate synchronization in the presence of delays. We theoretically prove the convergence of the whole scheme by using Lyapunov theory and considering strongly rooted topology condition, and provide simulations to show that our scheme outperforms existing consensus-based synchronization schemes under random delays.

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.

Per-Hop Delay Compensation in Time Synchronization for Multi-Hop Wireless Sensor Networks Based on Packet-Relaying Gateways

Multi-hop time synchronization is essential to large-scale deployment of IoT and wireless sensor networks. Its performance, however, is affected by the processing delays at intermediate gateway nodes, which cause cumulative synchronization error. To address this, we propose a per-hop delay compensation scheme as a simple and effective multi-hop extension option based on packet-relaying gateway nodes for energy-efficient time synchronization in wireless sensor networks. Experimental results on a real testbed demonstrate that the per-hop delay compensation scheme significantly improves the multi-hop time synchronization performance when applied to the state-of-the-art beaconless asymmetric energy-efficient time synchronization scheme and the conventional flooding time synchronization protocol.

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.

Clock Synchronization in Wireless Sensor Networks Based on Bayesian Estimation

Clock synchronization is essential for the operation of upper layer applications in Wireless Sensor Networks. When the network hops needed for clock synchronization message transmission is large, synchronization error will accumulate and synchronization accuracy may be reduced significantly. Moreover, in the existing synchronization algorithms, large number of communication resources and node energy will be expended in sending and receiving time messages. To solve the problem, this paper proposes a Bayesian estimation-based time synchronization (BETS) algorithm which uses synchronization error compensation to reduce the amount of time message interaction in clock synchronization. The key idea of BETS is to calibrate the prior information of synchronization error with a small amount of field sampling time information, which will eliminate the impact of environment on clock synchronization accuracy. In addition, the gradient descent method is used to estimate the relative clock drift rate, which provides the reference for setting algorithm execution cycle and ensures clock synchronization during network operation time. In order to evaluate the theoretical lower bound of the performance of BETS, the Bayesian Cramer-Rao bound (BCRB) is derived. Both simulation and hardware experiments show that BETS algorithm makes full use of the prior information of synchronization error, hence fewer time messages are required in synchronization and the resource constraints of WSNs are satisfied.

Consensus-Based Clock Synchronization in Wireless Sensor Networks With Truncated Exponential Delays

Clock synchronization is a significant basis for many operations in wireless sensor networks. The distributed consensus-based clock synchronization has gained popularity for its robustness and scalability. However, most consensus-based clock synchronization protocols either ignore communication delay, or consider bounded delay without distribution model. In this article, based on the consensus theory, the clock synchronization problem with truncated exponential delay is investigated. We use the maximum likelihood method to estimate relative drift between nodes. A recursive method is presented to cope with the maximum likelihood estimation, which largely reduces the computational complexity and the storage overhead. Then, the estimated relative drift is adopted in the two main parts of consensus clock synchronization: drift compensation and offset compensation. We give the rigorous theoretical proof of the convergence of the network-wide synchronization. Simulations further verify the theoretical analysis and show that the synchronization performance of the proposed algorithm is better than existing similar schemes under truncated exponential delays.

Implementation of ITREE-MAC Protocol for Effective Power Management and Time Synchronization in Wireless Sensor Networks

The advent of wireless sensor networks (WSN) has led in recent revolutionary modifications in electronic and communication systems .Various applications in wireless network needs time synchronization as a basic requirement. Wireless sensor nodes are tiny in size and operated at low energy to record the required physical parameters for low-duty apps. Because nodes have a tiny battery with a lower life span, power management is crucial for long-term working with the sensors. Wireless Sensor Network is a set of sensor nodes used to send and receive data packets from one sensor node to another. This work aims to propose three protocols such as Receiver Centric MAC protocol (RC-MAC), Improved Receiver Centric MAC protocol (IRC-MAC) and Intelligent Traffic and Resource Elastic Energy MAC protocol (ITREE-MAC) for the WSN environment and based on the application. These protocols help in studying the parametric measures such as delay, energy consumption, packet delivery ratio and throughput. The comparative analysis is carried out to select the more efficient protocol for the application of wireless sensor networks. This research work is implemented and simulated by using NS 2.35 Simulator. Based on the simulation results obtained for proposed protocols using the NS2 simulator. The performance of ITREE-MAC protocol shows better results for parameters end to end delay, energy consumption, throughput, packet delivery ratio. So the overall performance of ITREE-MAC protocol is much better than other three IEEE802.11 MAC, RC-MAC and IRC-MAC protocols. As per results obtained, energy consumption is less in ITREE-MAC protocol and save the power in wireless sensor network applications

Security cooperation model based on topology control and time synchronization for wireless sensor networks

To address malicious attacks generated from wireless sensor networks (WSNs), in this paper, we study the difficulty of detecting uncoordinated behavior by using a model that is unreliable and has uncontrollable accuracy, trustless control, and an inextensible protocol. A security collaboration model involving coupled state vectors associated with topology control and time synchronization is proposed. The networks achieve synchronization using weights and by controlling the number of goals. The simple calculation of time synchronization values between neighboring nodes serves as the basis for judging the behavior of the node topology control. The coupling state vector calculation is the core of the model. The topology coupling strength rate, signal intensity reduction, clock drift, and clock delay are combined to form a comprehensive model. The network energy consumption is reduced by updating the coupling state vector regularly. The coupling cooperation threshold is set to make security decisions and effectively distinguish between attack nodes and dead nodes. Thus, to ensure the security and reliability of the network, we present a security cooperation collection tree protocol (SC-CTP) scheme that maintains a trusted environment and isolates misbehaving nodes. The simulation results show that the model can detect malicious nodes effectively, has a high detection rate, and greatly reduces the energy consumption of the whole network. In order to verify the effectiveness of the proposed model, a large-scale wireless sensor network with 200 nodes was deployed on a campus. The proposed model was applied to optimize the deployment of key nodes on the campus. Furthermore, a candidate set of these nodes were selected to achieve coupling cooperation of key goals. This test verified the reliability of the model, its customizable accuracy, and the reliability of the control.

Performance of clock sources and their influence on time synchronization in wireless sensor networks

Wireless sensor networks require time synchronization, which is the coordination of events or actions to make a system operate in unison. In this work, real experiments and a theoretical analysis of the behavior of the clock sources, most used in wireless sensor networks, have been carried out. The experiments have been performed on two real platforms from two different manufacturers in real environments with sudden changes in temperature. Complementary metal-oxide-semiconductor oscillators have a low accuracy, bigger than 500 ppm, and a high dependency with temperature. External crystal oscillators have good accuracy, around 20 ppm, and are stable with temperature. Temperature-compensated crystal oscillators are very accurate, around 5 ppm, and the temperature has no influence in their drift. The use of phase-locked loop circuits minimizes the impact of temperature and stabilizes oscillators. We highlight and demonstrate the importance of the early stages of design, especially the selection of the clock source, because that decision has a great impact on the performance of the time synchronization in wireless sensor networks.

Fast Convergence Time Synchronization in Wireless Sensor Networks Based on Average Consensus

Average consensus theory is intensely popular for building time synchronization in wireless sensor network (WSN). However, the average consensus-based time synchronization algorithm is based on iteration that pose challenges for efficiency, as they entail high communication cost and long convergence time in large-scale WSN. Based on the suggestion that the greater the algebraic connectivity leads to the faster the convergence, a novel multi-hop average consensus time synchronization (MACTS) is developed with innovative implementation in this paper. By employing multi-hop communication model, it shows that virtual communication links among multi-hop nodes are generated and algebraic connectivity of network increases. Meanwhile, a multihop controller is developed to balance the convergence time, accuracy and communication complexity. Moreover, the accurate relative clock offset estimation is yielded by delay compensation. Implementing the MACTS based on the popular one-way broadcast model and taking multi-hop over short distances, we achieve hundreds of times the MACTS convergence rate compared to ATS.

Integrated Cooperative Synchronization for Wireless Sensor Networks

A precise decentralized clock synchronization method, referred to as integrated cooperative synchronization (ICS) is proposed in this letter. ICS is a delay compensating method that relies on mean-field message passing, where the measurement phase is integrated into the message passing phase. By selecting an extended factorization of the underlying joint a-posteriori distribution of the clock parameters and an appropriate message scheduling for link initialization, ICS is conceptually much simpler than conventional message-passing methods while achieving similar accuracy and reduced computational complexity. Moreover, it has only slightly higher implementation requirements compared to less accurate consensus methods.

Secure Time Synchronization for Wireless Sensor Networks Based on Bilinear Pairing Functions

Time synchronization is crucial for wireless sensor networks (WSNs) and secure time synchronization is a key requirement for many sophisticated applications running on these networks. Most of the existing secure time synchronization protocols incur high communication and storage costs, and are subject to a few known security attacks. In this paper, we propose a novel secure time synchronization protocol for both homogeneous and heterogeneous WSN models; the protocol uses pairing-based cryptography to secure the time synchronization and to reduce the communication and storage requirements of each node. Security analysis of the protocol shows that it is highly robust against different attacks, namely selective forwarding attack, wormhole attack, masquerade attack, message manipulation attack, replay attack and delay attack.

Fault-Tolerant Clock Synchronization Over Unreliable Channels in Wireless Sensor Networks

In this paper, we study a distributed approach based on consensus algorithms for clock synchronization in wireless sensor networks. The sensor nodes face two types of uncertainties. One is that some of the nodes in the network can be faulty and transmit arbitrary signals by not following the given protocol; similar effects may be caused by false data injection by an external malicious attacker. The other is that the communication is unreliable and the packets exchanged may become lost. To deal with these uncertainties, we propose a resilient consensus-type algorithm based on the so-called mean subsequence reduced (MSR) technique, where each normal node ignores the outliers in the clock data collected from its neighbors and makes updates using data from the past if new data have not arrived yet. We establish network connectivity conditions in terms of graph robustness for the MSR algorithm to attain resilient properties.

Bi-iterative algorithm for joint localization and time synchronization in wireless sensor networks

Abstract This paper efficiently solves the problem of joint localization and synchronization in wireless sensor networks by using two-way message exchange mechanism. Employing an affine model of unsynchronized local clocks, we first establish the famous Maximum Likelihood (ML) estimator for joint localization and synchronization, which derives the best consistent solution. Unfortunately, achieving directly the ML estimator is usually difficult because the ML cost functions are highly non-linear and non-convex. In order to effectively obtain the ML estimator, a novel bi-iterative algorithm is proposed by alternately searching the sensor node location and clock parameters (clock skew and clock offset). We prove that the proposed algorithm is convergent, and analyze that its estimation accuracy for the sensor node locations and clock parameters can approximately reach the Cramer–Rao Lower Bound (CRLB) under the mild noise condition. Compared with some previous methods, the proposed bi-iterative algorithm is more computationally efficient, and takes fewer anchor nodes and less communication overhead. Simulation results verify theoretical analysis and show that the proposed algorithm has the better performance than the several existing algorithms.

Mobile beacon-based adaptive time synchronization for wireless sensor networks

Time synchronization of clocks in the sensor nodes for wireless sensor networks (WSNs) is a fundamental technology for most mission-critical applications. Most of past research in time synchronization for WSNs, however, has only focused on achieving some of the goals at a time, such as accuracy, energy consumption, completion time, etc., making these solutions less capable of adapting to different application requirements. In this paper, we propose a new time synchronization algorithm named MBATS (mobile beacon-based adaptive time synchronization) in which a mobile beacon is employed to move or fly over the sensor deployment area to complete time synchronization. Moreover, MBATS is designed so that the number of sensor nodes that are synchronized by one instance of time synchronization from the mobile beacon could vary dynamically to meet application requirements on accuracy, completion time and energy consumption, making the proposed MBATS algorithm highly adaptable to different application requirements. In addition to showing the advantage of the proposed MBATS algorithm on the adaptability of time synchronization as well as on some of the main metrics of synchronization over comparable schemes for WSNs, we also present the results of our study on comparing the performance of letting the mobile beacon traverse along a designing path versus follow a random path. Such a study is important since it would allow us to learn the performance gains that we can expect to achieve with extra control effort spent on designing the path over the effortless random path strategy. Such study could provide us with some clues on how to choose a suitable time synchronization strategy to better meet application requirements, which may not necessarily be the designed path strategy due to the tradeoff between cost and performance gains.

A Filter‐based Clock Synchronization Protocol for Wireless Sensor Networks

AbstractClock parameters in wireless sensors experience slow changes due to low‐cost construction and environmental conditions. In this paper, a filter‐based distributed protocol, called FBP, is proposed to dynamically achieve clock synchronization for wireless sensor networks. The idea of FBP is derived from a first‐order filter which is robust to environmental noises. The proposed protocol is fully distributed, meaning that each node relies only on its local clock readings and reading announcements from its neighbouring sensor nodes. This will allow the proposed protocol applicable to large sensor networks. By applying FBP, the compensated clock skews can be bounded into a small steady‐state error. Numerical simulations show that the proposed protocol yields better performances in both convergence property and synchronization accuracy.

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.

Simulation and evaluation of pulse-coupled oscillators in wireless sensor networks

ABSTRACTThe clock in embedded systems usually is driven by a crystal oscillator and implemented via a counter register, such a crystal clock is non-identical and drifting due to the manufacturing tolerance and variation of working conditions. Thus, a common time among distributed wireless sensor nodes, also referred to as Time Synchronization, is required for many time-sensitive wireless applications, such as collaborative condition monitoring, coordinated control and localization. Inspired by fireflies’ behaviour, the Pulse-Coupled Oscillators (PCO) has been proposed for synchronization in complex networks. Since the concurrent transmission of PCO’s Pulses is impossible in Wireless Sensor Networks (WSNs), the desynchronization mechanism is adopted to ensure the implementation of PCO in WSNs. Moreover, due to the uncertainties in radio channels and the complexities of communication protocols and packet-exchange behaviours in wireless networks, it is challenging to have a closed-form solution to the performance of PCO synchronization in WSNs. The realistic software simulation, in particular, the discrete event simulator has been a powerful tool to exam the performance of communication protocols in various scenarios, since an order sequence of well-defined event in time is to represent the behaviour of a complex system. This paper presents the development of a pulse-coupled oscillators time synchronization simulator on the OMNeT++ platform for simulating and studying its behaviour and performance in sensor networks. A clock module with configurable phase and frequency noises, and adjustable and higher resolution is developed to mimic various crystal oscillators in embedded systems, for example, the real-time clock. The developed simulator also supports the full functions devices defined by ZigBee protocol, which allows realistic simulation of multi-hop IEEE 802.15.4 wireless networks. Finally, the intensive simulations of classical PCO with the refractory period in IEEE 802.15.4-based WSNs have been carried out to demonstrate the features and benefits of the developed simulator. It is shown that for the non-identical and time-varying PCO clocks in the WSNs, the achieved synchronization will lose gradually, and the time that maintained synchronization depends on the length of refractory period.