Flooding Time Synchronization Protocol Research Articles

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

Based on the reverse asymmetric time synchronization framework, we have proposed several schemes with a major focus on the energy efficiency and computational complexity of a large number of battery-powered, low-cost sensor nodes in wireless sensor networks (WSNs). To address the cumulative end-to-end synchronization error, we have also introduced an idea of compensating for the processing delays at packet-relaying gateways as an energy-efficient way of multi-hop extension of WSN time synchronization schemes. In this paper, we present a comprehensive analysis of the multi-hop extension of WSN time synchronization schemes based on packet-relaying gateways with the per-hop delay compensation and the results of extensive experiments for the energy-efficient time synchronization schemes based on the reverse asymmetric time synchronization framework together with the flooding time synchronization protocol as a representative of existing schemes. Experimental results based on a real testbed demonstrate that the multi-hop extension based on packet-relaying gateways with the per-hop delay compensation greatly improves the performance of time synchronization of all the schemes considered compared to the multi-hop extension based on the conventional time-translating gateways.

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.

A Beaconless Asymmetric Energy-Efficient Time Synchronization Scheme for Resource-Constrained Multi-Hop Wireless Sensor Networks

The ever-increasing number of WSN deployments based on a large number of battery-powered, low-cost sensor nodes, which are limited in their computing and power resources, puts the focus of WSN time synchronization research on three major aspects, i.e., accuracy, energy consumption and computational complexity. In the literature, the latter two aspects have not received much attention compared to the accuracy of WSN time synchronization. Especially in multi-hop WSNs, intermediate gateway nodes are overloaded with tasks for not only relaying messages but also a variety of computations for their offspring nodes as well as themselves. Therefore, not only minimizing the energy consumption but also lowering the computational complexity while maintaining the synchronization accuracy is crucial to the design of time synchronization schemes for resource-constrained sensor nodes. In this paper, focusing on the three aspects of WSN time synchronization, we introduce a framework of reverse asymmetric time synchronization for resource-constrained multi-hop WSNs and propose a beaconless energy-efficient time synchronization scheme based on reverse one-way message dissemination. Experimental results with a WSN testbed based on TelosB motes running TinyOS demonstrate that the proposed scheme conserves up to 95% energy consumption compared to the flooding time synchronization protocol while achieving microsecond-level synchronization accuracy.

An improvement mechanism for heartbeat‐driven MAC synchronization in wireless body sensor network

SummaryThis paper aims to improve the TDMA‐based Heartbeat‐Driven MAC (H‐MAC) protocol for WBAN. H‐MAC is designed to be used in star‐topology WBAN for time synchronization realization by using heartbeat rhythm information, instead of periodic synchronization beacons. H‐MAC therefore saves power of WBAN sensor nodes and reduces the negative effects of electromagnetic radiation on human health during the packet delivery process. To embed heartbeat rhythm information into different bio‐signals and check the peak values of wave forms can contribute to time synchronization for BSN. As the heart contracts via systole and relaxes via diastole, pulse is the number of times one's heart beats every minute and the number of pulses measured at different body parts is the same. However, blood vessels run over the whole human body and their distances away from the heart greatly vary in the same systole, leading to an imperceptible time difference and the synchronization problem. We propose to include the presently most mature method for time synchronization, Flooding Time Synchronization Protocol (FTSP), to deal with time differences.

Performance Analysis of Time Synchronization Protocols in Wireless Sensor Networks

The time synchronization protocol is indispensable in various applications of wireless sensor networks, such as scheduling, monitoring, and tracking. Numerous protocols and algorithms have been proposed in recent decades, and many of them provide micro-scale resolutions. However, designing and implementing a time synchronization protocol in a practical wireless network is very challenging compared to implementation in a wired network; this is because its performance can be deteriorated significantly by many factors, including hardware quality, message delay jitter, ambient environment, and network topology. In this study, we measure the performance of the Flooding Time Synchronization Protocol (FTSP) and Gradient Time Synchronization Protocol (GTSP) in terms of practical network conditions, such as message delay jitter, synchronization period, network topology, and packet loss. This study provides insights into the operation and optimization of time synchronization protocols. In addition, the performance evaluation identifies that FTSP is highly affected by message delay jitter due to error accumulation over multi-hops. We demonstrate that the proposed extended version of the FTSP (E-FTSP) alleviates the effect of message delay jitter and enhances the overall performance of FTSP in terms of error, time, and other factors.

An effective data fusion-based routing algorithm with time synchronization support for vehicular wireless sensor networks

In the field of vehicular wireless sensor networks-based structural health monitoring, the structural damage identification is achieved by two structural features, namely natural frequencies and mode shapes. The kind of data fusion-based routing algorithm in specific applications needs to meet time synchronization requirements and meet certain constraints, such as the single-hop communication between cluster head node and each node in cluster, the overlap between different clusters and so on. To meet the special constraints for data fusion-based routing algorithm in structural health monitoring, this paper proposed a new method based on an improved flooding time synchronization protocol, which is called time synchronization and enhanced greedy algorithm based on D(v) (TSDEGA) routing algorithm. The TSDEGA method can achieve the minimum connected cover by node’s own degree D(v), and it can also meet the structural health monitoring routing constraints. The simulation experiments show that TSDEGA has better energy resistance and longer network lifetime, and it is superior to the traditional greedy algorithms. The proposed algorithm can effectively eliminate interference of outliers and improve the accuracy in order to meet time synchronization requirements in structural health monitoring applications.

에너지 제한적인 무선 네트워크에서 동작하는 시각 동기화 프로토콜

사물인터넷에서 전력이나 컴퓨팅 등 자원이 한정된 무선 노드 사이에 데이터를 효율적으로 전송하는 무선 네트워크 기술이 중요하며, 의미 있는 데이터 생성과 전송을 위해서 모든 노드 사이에 시각 동기화가 필요하다. 무선 센서 네트워크에서 여러 방식의 시각 동기화 프로토콜이 제안되었는데, 플러딩에 의한 방안도 그중의 하나이다. 이 방식은 다른 방식에 비하여 알고리즘이 간단하고, 토폴로지 변화에 영향을 받지 않는 장점을 가지고 있음에도 불구하고 지나치게 많은 데이터 전송이 요구되어 결과적으로 전력 소모가 많다. 전력이 한정적인 무선 노드에서는 가능한 성능을 저하시키지 않으면서 전력 소모를 줄이는 것이 중요하므로, 이 논문에서는 플러딩에 기반한 에너지 효율적인 시각 동기화 프로토콜을 제안한다. 시뮬레이션을 통하여 가장 대표적인 프로토콜인 FTSP(Flooding Time Synchronization Protocol)와 성능을 비교하고, 에너지 효율 면에서 우수한 프로토콜임을 보인다. In IoT(Internet of Things), it is important for wireless networks to communicate data created among resource-constrained wireless nodes, where time synchronization is needed for meaningful data creation and transmission. Time Synchronization by flooding is one of the mostly used protocols for WSN(Wireless Sensor Networks). Even though this type of scheme has some advantages over other types (i.e. a simple algorithm and independency of topology and so on), too many data transmission is required, leading to large power consumption. So, reducing transmission data is an important issue for energy efficiency in this kind of networks. In this paper, a new Flooding-based time synchronization protocol is proposed to use energy efficiently by reducing a transmitted traffic. The proposed scheme's performance has been evaluated and compared with an representative scheme, FTSP(Flooding Time Synchronization Protocol) by simulation. The results are shown that the proposed scheme is better than FTSP.

Proposing a novel method for clock synchronization by Reducing the Number of Synchronization Messages and Eliminating Non-Deterministic Errors in Wireless Sensor Network

Wireless sensor networks (WSNs) of spatially distributed autonomous sensors are used to monitor physical or environmental conditions such as temperature, sound, pressure, etc. They are also used to cooperatively pass the collected data through the network to a main location. Due to the application of wireless sensor networks as a monitoring device in the real world, the physical time of the occurrence of events is important. Since WSNs have particular constraints and limitations, synchronizing the physical times for these networks is considered to be a complex task. Although many algorithms have been proposed for synchronizing time in the network, there are two main error factors in all the proposed algorithms. The first factor is the clock drift which might be caused by the influence of different environmental factors such as temperature, ambient temperature, humidity, it might be generated on crystal oscillator which is inevitable The second error factor is indeterminacy which is attributed to the existence of non-deterministic delays in sending and receiving messages between sensor nodes. These two factors together reduce the precision of synchronization algorithms. In this paper, the researchers proposed a new approach for dealing with the above-mentioned two problems and achieving better synchronization. The proposed approach is a combination of flooding time synchronization protocol (FTSP) and reference broadcast synchronization (RBS).This approach is intended to increase synchronization accuracy and network lifetime by reducing the number of synchronization messages sent between nodes and eliminating the most of non-deterministic errors in sending messages. The results of simulations conducted in the study indicated that the proposed approach is significantly more efficient than the FTSP and RBS methods in terms of parameters such as accurate synchronization, amount of sent packets and power consumption.

Energy-balanced Time Synchronization Algorithm Based on Flooding for Multi-hop Wireless Sensor Networks

To achieve network-wide time synchronization in multi-hop wireless sensor networks (WSN), this paper proposes an accurate and energy-balanced time synchronization algorithm based on flooding. Flooding Time-Synchronization Protocol (FTSP) has advanced features, such as implicitly dynamic topology and high time accuracy, which can't be affected by some node's losing. FTSP propagates its time information of the reference node without concern about the network topology. However, in large-scale WSN applications, the efficiency of FTSP will be reduced drastically because of serious network storm. Meanwhile, the energy consumption of the network breaks the energy balance. In this paper, our aim is to solve the problems of synchronization error accumulation and unbalanced energy consumption. Our theoretical findings and experimental results show that forbidding possibly invalid forwarding among the sensor nodes drastically improves the synchronization accuracy and performance of energy-balanced.

Real-Time Performance Evaluation for Flooding and Recursive Time Synchronization Protocols over Arduino and XBee

Time synchronization is a crucial part of distributed systems. It is often required for data reliability and coordination in wireless sensor networks (WSNs). Wireless sensor networks have three major goals: time synchronization, low bandwidth operation, and energy efficiency. Different time synchronization algorithms are aimed at achieving these objectives using various methods. This paper presents performance evaluation of two state-of-the-art time synchronization protocols, namely, Flooding Time Synchronization Protocol and Recursive Time Synchronization Protocol. To achieve time synchronization in wireless sensor networks, these two protocols make use of broadcast and peer-to-peer mechanisms. Flooding Time Synchronization Protocol uses the former mechanism, while Recursive Time Synchronization Protocol uses the latter mechanism. To perform the performance evaluation, three performance metrics are used including synchronization message count per cycle, bandwidth, and convergence time. Arduino is used as a micro-controller and XBee as transceiver to verify these metrics by utilizing different topologies.

Time Synchronization Based on Slow-Flooding in Wireless Sensor Networks

The accurate and efficient operation of many applications and protocols in wireless sensor networks require synchronized notion of time. To achieve network-wide time synchronization, a common strategy is to flood current time information of a reference node into the network, which is utilized by the de facto time-synchronization protocol Flooding Time-Synchronization Protocol (FTSP). In FTSP, the propagation speed of the flood is slow because each node waits for a given period of time to propagate its time information about the reference node. It has been shown that slow-flooding decreases the synchronization accuracy and scalability of FTSP drastically. Alternatively, rapid-flooding approach is proposed in the literature, which allows nodes to propagate time information as quickly as possible. However, rapid flooding is difficult and has several drawbacks in wireless sensor networks. In this paper, our aim is to reduce the undesired effect of slow-flooding on the synchronization accuracy without changing the propagation speed of the flood. Within this context, we realize that the smaller the difference between the speeds of the clocks, the smaller the undesired effect of waiting times on the synchronization accuracy. In the light of this realization, our main contribution is to show that the synchronization accuracy and scalability of slow-flooding can drastically be improved by employing a clock speed agreement algorithm among the sensor nodes. We present an evaluation of this strategy on a testbed setup including 20 MICAz sensor nodes. Our theoretical findings and experimental results show that employing a clock speed agreement algorithm among the sensor nodes drastically improves the synchronization accuracy and scalability of slow-flooding.

Temperature-Compensated Clock Skew Adjustment

This work analyzes several drift compensation mechanisms in wireless sensor networks (WSN). Temperature is an environmental factor that greatly affects oscillators shipped in every WSN mote. This behavior creates the need of improving drift compensation mechanisms in synchronization protocols. Using the Flooding Time Synchronization Protocol (FTSP), this work demonstrates that crystal oscillators are affected by temperature variations. Thus, the influence of temperature provokes a low performance of FTSP in changing conditions of temperature. This article proposes an innovative correction factor that minimizes the impact of temperature in the clock skew. By means of this factor, two new mechanisms are proposed in this paper: the Adjusted Temperature (AT) and the Advanced Adjusted Temperature (A2T). These mechanisms have been combined with FTSP to produce AT-FTSP and A2T-FTSP Both have been tested in a network of TelosB motes running TinyOS. Results show that both AT-FTSP and A2T-FTSP improve the average synchronization errors compared to FTSP and other temperature-compensated protocols (Environment-Aware Clock Skew Estimation and Synchronization for WSN (EACS) and Temperature Compensated Time Synchronization (TCTS)).

Secured flooding time synchronization protocol with moderator

SUMMARYThis work aims to address the security vulnerability of the Flooding Time Synchronization Protocol (FTSP), which is currently one of the most popular approaches for time synchronization in wireless sensor networks. FTSP has advanced features, such as implicitly dynamic topology and high time accuracy, but still has unresolved security issues. In order to defend against attacks from malicious nodes, we propose several technologies to reinforce the structure of FTSP. First, a reference node selecting mechanism is proposed to reduce the effect of multiple reference nodes, and four filters are proposed to defend againstseqNumattack, global time attack and node replication attack. Experiment results show that the proposed sequence number blacklist filter and the global time blacklist filter are effective in defending against the aforementioned attacks. Second, a new root selection mechanism is proposed to secure the process of updating the root node. Combining the root selection mechanism with the global time black list filter, the proposed mechanisms successfully defend against traitor attacks on FTSP in our experiment. Copyright © 2013 John Wiley & Sons, Ltd.

基于随机时间自动机和统计模型检验技术的无线传感网络协议建模与分析

Recently, sensor technology has seen significant achievement. Meanwhile, Wireless Sensor Network (WSN) technique has attracted lots of attention because of its open and dynamic behaviors, and has become a very important component of the Internet-based computing. The behavior of WSN system is very complex and may encounter lots of stochastic uncertainties and disturbances like message loss and node dynamics. Furthermore, WSN system is difficult to change and maintain once it is deployed. Thus, it is critical to ensure the quality of the low level protocols of WSN system in design phase. Designers should ensure the logical correctness of a protocol, as well as evaluate the performance of the protocol under certain target environments. To handle these issues, in this paper, we propose a framework to analyze and evaluate WSN protocols based on stochastic timed automata and statistical model checking. We propose to address the modeling of the uncertainties in the realistic behaviors by weighted stochastic transitions in the timed automata model of the protocol. Furthermore, we propose that the performance of the protocol under realistic environments should be evaluated by statistical model checking which is much cheaper and more scalable. To illustrate the feasibility and detail of the modeling and verification approach presented in this paper, two well-known WSN protocols, Timing-sync Protocol for Sensor Networks (TPSN) and Flooding Time Synchronization Protocol (FTSP), are studied thoroughly throughout the paper.

基于动态路径列表的无线传感器网络时间同步协议

To reduce the error accumulation of time synchronization in multihops for large-scale wireless sensor networks,a Dynamic Route List based Time Synchronization Protocol(DRL-TSP)is proposed.The protocol uses an available synchronization route list in each node,and allows the node to choose an optimal synchronization route to reduce the error accumulation.An identification called TTA(Time to Available)is used to deal with the synchronization failure and to ensure the reliability of the synchronization process.Experimental results indicate that the synchronization error in single hop is 5.29μs when the optional upper links are 12for each node,and the synchronization error is controlled under 11.10μs within 10hops.Moreover,the nodes of synchronization failure caused by time scale node invalidation are more low than that of Timing-sync Protocol for Sensor Network(TPSN)and close to that of Flooding Time Synchronization Protocol(FTSP).Experimental results show that the proposed protocol has a better performance than the current protocols in precision and reliability.

Clock Drift Management Using Nature Inspired Algorithms

Time Synchronization is common requirement for most network applications. It is particularly essential in a Wireless Sensor Networks (WSNs) to allow collective signal processing, proper correlation of diverse measurements taken from a set of distributed sensor elements and for an efficient sharing of the communication channel. The Flooding Time Synchronization Protocol (FTSP) was developed explicitly for time synchronization of wireless sensor networks. In this paper, we optimized FTSP for clock drift management using Particle Swarm Optimization (PSO), Variant of PSO and Differential Evolution (DE). The paper estimates the clock offset, clock skew, generates linear line and optimizes the value of average time synchronization error using PSO, Variant of PSO and DE. In this paper we present implementation and experimental results that produces reduced average time synchronization error using PSO, Variant of PSO and DE, compared to that of linear regression used in FTSP.

Drift estimation using pairwise slope with minimum variance in wireless sensor networks

Time synchronization is mandatory for applications and services in wireless sensor networks which demand common notion of time. If synchronization to stable time sources such as Coordinated Universal Time (UTC) is required, employing the method of flooding in order to provide time synchronization becomes crucial. In flooding based time synchronization protocols, current time information of a reference node is periodically flooded into the network. Sensor nodes collect the time information of the reference node and perform least-squares regression in order to estimate the reference time. However, least-squares regression exhibits a poor performance since sensor nodes far away from the reference node collect the time information with large deviations. Due to this fact, the slopes of their least-squares line exhibit large errors and instabilities. As a consequence, the reference time estimates of these nodes also exhibit large errors.This paper proposes a new slope estimation strategy for linear regression to be used by flooding based time synchronization protocols. The proposed method, namely Pairwise Slope With Minimum Variance (PSMV), calculates the slope of the estimated regression line by considering the pairwise slope between the earliest and the most recently collected data points. The PSMV slope is less affected by the large errors on the received data, i.e. it is more stable, and it is more computationally efficient when compared to the slope of the least-squares line. We incorporated PSMV into two flooding based time synchronization protocols, namely Flooding Time Synchronization Protocol (FTSP) and PulseSync. Experimental results collected from a testbed setup including 20 sensor nodes show that PSMV strategy improves the performance of FTSP by a factor of 4 and preserves the performance of PulseSync in terms of synchronization error with 40% less CPU overhead for linear regression. Our simulations show that these results also hold for networks with larger diameters and densities.

Clapping and Broadcasting Synchronization in Wireless Sensor Networks

The Clapping and Broadcasting Synchronization (CBS) algorithm, which is specifically designed for large-scale sensor networks with low communication overhead and high synchronization accuracy, is introduced. The CBS protocol uses broadcasting rather than pairwise communication to accomplish synchronization. In the CBS scheme, the initial offset of local clocks can be successfully eliminated by the operation of clapping nodes, which leads to significant improvement in synchronization accuracy. The CBS protocol was implemented on the TelosB platform and its performance was evaluated in a variety of experiments. The results demonstrate that the CBS protocol outperforms the current state-of-the-art approach, the Flooding Time Synchronization Protocol (FTSP), in both single-hop and multi-hop scenarios in terms of synchronous precision and energy consumption. In multi-hop scenarios, the CBS algorithm keeps about 50% of its synchronization errors within 1 ms. In comparison, the FTSP keeps less than 7% of its synchronization errors within this range. In both single-hop and multi-hop scenarios, the CBS protocol is over 3.2 times more energy-efficient than the FTSP.

Feedback-Based Clock Synchronization in Wireless Sensor Networks: A Control Theoretic Approach

Most wireless sensor networks (WSNs) employ a sleep clock to enable sensor on-off mode to save energy. Since the sleep clock usually works at a relatively low frequency, it is important to correct the long-term synchronization error caused by instability and nonlinearity. In this paper, the time synchronization issue in a WSN is formulated as a closed-loop control problem. Using the proportional-integral (PI) control principle, we propose a feedback-based synchronization (FBS) scheme to compensate the clock drift caused by both internal perturbation and external disturbance. Synchronization accuracy and FBS dynamics are analyzed in terms of response time and overshoot. We also derive a formula to determine the controller parameters for different synchronization accuracy and response-time requirements. Extensive experiments have been conducted to evaluate this synchronization scheme. The results indicate that FBS is much more robust than the delay measurement time-synchronization (DMTS) protocol in different synchronization durations and sensor node configurations. It is shown that FBS achieves almost the same accuracy as the flooding time-synchronization protocol (FTSP) when synchronization period P is less than 60 s, and it outperforms FTSP when P is longer than 60 s. Furthermore, the experimental results reveal that FBS's response to an external disturbance is faster than that of FTSP in one- or two-hop WSN scenarios. In addition, FBS consumes fewer resources than FTSP.

Temperature Compensated Time Synchronization

Time synchronization in embedded sensor networks is an important service for correlating data between nodes and communication scheduling. While many different approaches to the problem are possible, one major effect of clock frequency difference between nodes, environmental temperature changes, has often been left out of the solution. The common assumption that the temperature is static over a certain period of time is often used as an excuse to assume constant frequency errors in a clock. This assumption forces synchronization protocols to resynchronize too often. While there exists hardware solutions to this problem, their prohibitive high cost and power consumption make them unsuitable for some applications, such as wireless sensor networks. Temperature compensated time synchronization (TCTS) exploits the on-board temperature sensor existing in many sensor network platforms. It uses this temperature sensor to autonomously calibrate the local oscillator and removes effects of environmental temperature changes. This allows a time synchronization protocol to increase its resynchronization period, without loosing synchronization accuracy, and thus saves energy and communication overhead. In addition, TCTS provides a stable clock source when radio communication is impaired. We present the theory behind TCTS, and provide initial results of a simulated comparison of TCTS and the flooding time synchronization protocol.