Clock synchronization is a critical component in the operation of wireless sensor networks (WSNs), as it provides a common time frame to different nodes. It supports functions such as fusing voice and video data from different sensor nodes, time-based channel sharing, and coordinated sleep wake-up node scheduling mechanisms. Early studies on clock synchronization for WSNs mainly focused on protocol design. However, the clock synchronization problem is inherently related to parameter estimation, and, recently, studies on clock synchronization began to emerge by adopting a statistical signal processing framework. In this article, a survey on the latest advances in the field of clock synchronization of WSNs is provided by following a signal processing viewpoint. This article illustrates that many of the proposed clock synchronization protocols can be interpreted and their performance assessed using common statistical signal processing methods. It is also shown that advanced signal processing techniques enable the derivation of optimal clock synchronization algorithms under challenging scenarios.

Clock Synchronization of Wireless Sensor Networks

A display apparatus includes an image processor which processes an image to display an image content; a display unit which displays thereon an image content that is processed by the image processor; and a controller which displays a user interface (UI) menu including a plurality of UI items to search the image content, as one of a two-dimensional (2D) layout by which the plurality of UI items are arranged in a 2D manner, and a three-dimensional (3D) layout by which the plurality of UI items are arranged in a 3D manner , and changes displaying the one of the layouts to display the other of the layouts according to a user's command while maintaining a continuity of the arrangement of the plurality of UI items. Accordingly, search for an image content can be efficiently performed by using a UI menu.

Display apparatus and control method thereof

This letter proposes an energy-efficient clock synchronization scheme for Wireless Sensor Networks (WSNs) based on a novel time synchronization approach. Within the proposed synchronization approach, a subset of sensor nodes are synchronized by overhearing the timing message exchanges of a pair of sensor nodes. Therefore, a group of sensor nodes can be synchronized without sending any extra messages. This paper brings two main contributions: 1. Development of a novel synchronization approach which can be partially or fully applied for implementation of new synchronization protocols and for improving the performance of existing time synchronization protocols. 2. Design of a time synchronization scheme which significantly reduces the overall network-wide energy consumption without incurring any loss of synchronization accuracy compared to other well-known schemes.

/pdf/a-new-approach-for-time-synchronization-in-wireless-sensor-2h549pf069.pdf

A New Approach for Time Synchronization in Wireless Sensor Networks: Pairwise Broadcast Synchronization

The development of tiny, low-cost, low-power and multifunctional sensor nodes equipped with sensing, data processing, and communicating components, have been made possible by the recent advances in micro-electro-mechanical systems (MEMS) technology. Wireless sensor networks (WSNs) assume a collection of such tiny sensing devices connected wirelessly and which are used to observe and monitor a variety of phenomena in the real physical world. Many applications based on these WSNs assume local clocks at each sensor node that need to be synchronized to a common notion of time. This paper reviews the existing clock synchronization protocols for WSNs and the methods of estimating clock offset and clock skew in the most representative clock synchronization protocols for WSNs.

/pdf/clock-synchronization-in-wireless-sensor-networks-an-36yt1ulqc2.pdf

Clock Synchronization in Wireless Sensor Networks: An Overview

Time synchronization and localization are two important issues in wireless sensor networks. Although these two problems share many aspects in common, they are traditionally treated separately. In this paper, we present a unified framework to jointly solve time synchronization and localization problems at the same time. Furthermore, since the accuracy of synchronization and localization is very sensitive to the accuracy of anchor timings and locations, the joint time synchronization and localization problem with inaccurate anchors is also considered in this paper. For the case with accurate anchors, the joint maximum likelihood estimator and a more computationally efficient least squares (LS) estimator are proposed. When the anchor timings and locations are inaccurate, a generalized total least squares (GTLS) scheme is proposed. Crame?r-Rao lower bounds (CRLBs) and the analytical mean square error (MSE) expressions of the LS based estimators are derived for both accurate and inaccurate anchor cases. Results show that the proposed joint estimators exhibit performances close to their respective CRLBs and outperform the separate time synchronization and localization approach. Furthermore, the derived analytical MSE expressions predict the performances of the proposed joint estimators very well.

/pdf/joint-time-synchronization-and-localization-of-an-unknown-2h7qki592c.pdf

Joint Time Synchronization and Localization of an Unknown Node in Wireless Sensor Networks

With the help of recent technological advances in micro-electro-mechanical systems (MEMS) and wireless communications, low-cost, low-power, and multifunctional wireless sensing devices have been developed. When these devices are deployed over a wide geographical region, they can collect information about the environment and efficiently collaborate to process such information by forming a distributed communication network, called the wireless sensor network (WSN). WSN is a special case of wireless ad hoc network, and assumes a multihop communication framework with no common infrastructure, where the sensors spontaneously cooperate to deliver information by 13

Time Synchronization for Wireless Sensor Networks

In a first embodiment of the present invention, a method is provided comprising: receiving application data from a primary mobile device, wherein the application data is received via hooks designed to automatically send the application data received by or sent from an application on the primary mobile device; and sending the application data to one or more secondary mobile devices that are registered to the primary mobile device, wherein each of the secondary mobile devices are resource limited devices.

Secondary mobile device

Time synchronization for wireless sensor networks has been studied in recent years as a fundamental and critical design problem. This paper proposes an adaptive multi-hop timing synchronization (AMTS) which aims at minimizing overall network-wide energy consumption in timing synchronization. According to the current network status, AMTS determines the synchronization mode either the always on or sensor initiated mode, then adjusts the re-synchronization period to minimize energy consumption. Besides, it adapts a joint clock offset and skew estimation mechanism to achieve long term reliability of synchronization. AMTS has significant benefits in terms of energy-efficiency, and can be applied to various types of wireless sensor networks having different regulations.

Adaptive multi-hop timing synchronization for wireless sensor networks (invited paper)

Synchronization for Wireless Sensor Networks

A method and apparatus are provided for a multifunction remote control device, allows a user to display the contents of a mobile terminal on a larger screen, while retaining use of the mobile terminal's other functions. The method includes checking whether the mobile terminal is connected to the multifunction remote control device, running a multi-screen mode for composing a service environment in which control and call connection functions of the mobile terminal are executable, by implementing a wireless interface of the mobile terminal, and controlling basic functions and additional functions of the mobile terminal.

Kyoung-Lae Noh

Papers

Time Synchronization for Wireless Sensor Networks

Secondary mobile device

Adaptive multi-hop timing synchronization for wireless sensor networks (invited paper)

Synchronization for Wireless Sensor Networks

Multifunction remote control device for mobile terminal and method using the same