Time Synchronization with Extended Clock Model for Wireless Sensor Networks

Experimental Characterization of Synchronization Protocols for Instrument Wireless Interface

Abstract: Nowadays, careful measurement applications are handed over to wireless sensor networks (WSNs). In most of these tasks, sensor nodes work together to recognize the data fusion process. Synchronization is a critical element in this scenario. Nodes have to be regulated to a common clock and regulated among them. Many synchronization algorithms can be found in literature, and some of them have been intentionally established for low-cost structural designing where efficient memory management and reduced computational burden are important constraints. The performance of these algorithms is usually evaluated either in simulation environments or by adopting ad hoc radio systems. Attention is rarely paid to the influence of factors, such as the following: clock stability, the dependence of the measurement application on the synchronization algorithm and vice versa, the effect of the limited bandwidth available on real radio systems, and the change of performance when common commercial wireless communication busses such as Wi-Fi, Bluetooth (BT), and ZigBee are adopted. This paper makes the first step toward this direction, proposing the experimental characterization of a small-scale WSN implementing some of these protocols versus common wireless busses such as BT, Wi-Fi, and ZigBee.

Experimental characterization of synchronization protocols for wireless networks

Abstract: Nowadays more and more measurement applications where sensor nodes cooperate to realize a data fusion process are entrusted to wireless sensor networks (WSN). Data fusion to be accurate requires that nodes be referred to a common clock and among themselves. In this scenario node synchronization got a crucial research topic and even sophisticated synchronization algorithms can be easily found in literature. Not a few others show to be especially designed for low cost, low memory and low power architectures. Their performance is usually evaluated either through analytical considerations or in simulation environments, but in some cases where ad hoc radio systems have been adopted. This paper makes a first step toward an experimental characterization of synchronization protocols that hold into account also influence factors which arise when commercial wireless communication busses as WiFi, BlueTooth (BT), ZigBee are adopted.

A step forward the on-line minimization of the synchronization events in TPSN

Abstract: The paper proposes an experimental approach to the optimization of synchronization protocols for wireless sensor networks. The authors' research is aimed in both minimizing the synchronization residual error and the wireless sensor node energy consumption. The approach has been thought to be applied to different synchronization protocols and to give the best results for small scale wireless sensor network. In particular, results concerning the well know Timing Synchronization Protocol for Sensor Networks (TPSN) are presented in the paper. The main idea is that the sensor node be synchronized with the master node on the basis of two suitable figures of merit: the former takes into account the past synchronizations, whilst the latter depends on the residual error after the last synchronization. On the basis of the on board and real time evaluation of these two indexes the number of synchronization events and the node energy consumption can be both reduced.

Time synchronization method among VANET devices

Abstract: Vehicular Ad hoc Network (VANET) is still a very attractive technology by which the construction of an Intelligent Transportation System (ITS) will be realized. The communication devices of VANET, i.e., OBUs and RSUs, are only allowed to transmit data in an assigned channel time and the channel switch will take place in about every 50 ms according to the standards of IEEE 802.11p and IEEE 1609.4. On the other hand, in the case of a large scale VANET, e.g., in the scenario of a traffic rush hour, available transmission time interval would be a few of milliseconds or even much less. Therefore, it is essential to achieve a precise time synchronization among the embedded devices. In this paper, we put forward a new specific time synchronization method among VANET devices. In our method, OBU can synchronize to other OBU or RSU initiatively. In the case that there is no center node in BSS (Basic Service Set), the proposed approach reduces synchronization error to that of less than 0.3 ms, which meets the accuracy requirement of VANET specification. In addition, we achieved time synchronization among RSUs. This can greatly reduce the frequency of handover performed by the high speed OBUs.

Fine-grained network time synchronization using reference broadcasts

Abstract: Recent advances in miniaturization and low-cost, low-power design have led to active research in large-scale networks of small, wireless, low-power sensors and actuators. Time synchronization is critical in sensor networks for diverse purposes including sensor data fusion, coordinated actuation, and power-efficient duty cycling. Though the clock accuracy and precision requirements are often stricter than in traditional distributed systems, strict energy constraints limit the resources available to meet these goals.We present Reference-Broadcast Synchronization, a scheme in which nodes send reference beacons to their neighbors using physical-layer broadcasts. A reference broadcast does not contain an explicit timestamp; instead, receivers use its arrival time as a point of reference for comparing their clocks. In this paper, we use measurements from two wireless implementations to show that removing the sender's nondeterminism from the critical path in this way produces high-precision clock agreement (1.85 ± 1.28μsec, using off-the-shelf 802.11 wireless Ethernet), while using minimal energy. We also describe a novel algorithm that uses this same broadcast property to federate clocks across broadcast domains with a slow decay in precision (3.68 ± 2.57μsec after 4 hops). RBS can be used without external references, forming a precise relative timescale, or can maintain microsecond-level synchronization to an external timescale such as UTC. We show a significant improvement over the Network Time Protocol (NTP) under similar conditions.

Timing-sync protocol for sensor networks

Abstract: Wireless ad-hoc sensor networks have emerged as an interesting and important research area in the last few years. The applications envisioned for such networks require collaborative execution of a distributed task amongst a large set of sensor nodes. This is realized by exchanging messages that are time-stamped using the local clocks on the nodes. Therefore, time synchronization becomes an indispensable piece of infrastructure in such systems. For years, protocols such as NTP have kept the clocks of networked systems in perfect synchrony. However, this new class of networks has a large density of nodes and very limited energy resource at every node; this leads to scalability requirements while limiting the resources that can be used to achieve them. A new approach to time synchronization is needed for sensor networks.In this paper, we present Timing-sync Protocol for Sensor Networks (TPSN) that aims at providing network-wide time synchronization in a sensor network. The algorithm works in two steps. In the first step, a hierarchical structure is established in the network and then a pair wise synchronization is performed along the edges of this structure to establish a global timescale throughout the network. Eventually all nodes in the network synchronize their clocks to a reference node. We implement our algorithm on Berkeley motes and show that it can synchronize a pair of neighboring motes to an average accuracy of less than 20ms. We argue that TPSN roughly gives a 2x better performance as compared to Reference Broadcast Synchronization (RBS) and verify this by implementing RBS on motes. We also show the performance of TPSN over small multihop networks of motes and use simulations to verify its accuracy over large-scale networks. We show that the synchronization accuracy does not degrade significantly with the increase in number of nodes being deployed, making TPSN completely scalable.

Internet time synchronization: the network time protocol

Abstract: The network time protocol (NTP), which is designed to distribute time information in a large, diverse system, is described. It uses a symmetric architecture in which a distributed subnet of time servers operating in a self-organizing, hierarchical configuration synchronizes local clocks within the subnet and to national time standards via wire, radio, or calibrated atomic clock. The servers can also redistribute time information within a network via local routing algorithms and time daemons. The NTP synchronization system, which has been in regular operation in the Internet for the last several years, is described, along with performance data which show that timekeeping accuracy throughout most portions of the Internet can be ordinarily maintained to within a few milliseconds, even in cases of failure or disruption of clocks, time servers, or networks. >

Clock synchronization for wireless sensor networks: a survey

Abstract: Recent advances in micro-electromechanical (MEMS) technology have led to the development of small, low-cost, and low-power sensors Wireless sensor networks (WSNs) are large-scale networks of such sensors, dedicated to observing and monitoring various aspects of the physical world In such networks, data from each sensor is agglomerated using data fusion to form a single meaningful result, which makes time synchronization between sensors highly desirable This paper surveys and evaluates existing clock synchronization protocols based on a palette of factors like precision, accuracy, cost, and complexity The design considerations presented here can help developers either in choosing an existing synchronization protocol or in defining a new protocol that is best suited to the specific needs of a sensor-network application Finally, the survey provides a valuable framework by which designers can compare new and existing synchronization protocols

Time synchronization in sensor networks: a survey

Abstract: Time synchronization is an important issue in multihop ad hoc wireless networks such as sensor networks. Many applications of sensor networks need local clocks of sensor nodes to be synchronized, requiring various degrees of precision. Some intrinsic properties of sensor networks, such as limited resources of energy, storage, computation, and bandwidth, combined with potentially high density of nodes make traditional synchronization methods unsuitable for these networks. Hence, there has been an increasing research focus on designing synchronization algorithms specifically for sensor networks. This article reviews the time synchronization problem and the need for synchronization in sensor networks, then presents in detail the basic synchronization methods explicitly designed and proposed for sensor networks.