http://www.maths.qmul.ac.uk/%7Elatora/report_06.pdf

Complex networks: Structure and dynamics

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.

/pdf/fine-grained-network-time-synchronization-using-reference-3go0i1u94g.pdf

Fine-grained network time synchronization using reference broadcasts

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.

/pdf/timing-sync-protocol-for-sensor-networks-53aov77qpj.pdf

Timing-sync protocol for sensor networks

The Internet of Things (IoT) makes smart objects the ultimate building blocks in the development of cyber-physical smart pervasive frameworks. The IoT has a variety of application domains, including health care. The IoT revolution is redesigning modern health care with promising technological, economic, and social prospects. This paper surveys advances in IoT-based health care technologies and reviews the state-of-the-art network architectures/platforms, applications, and industrial trends in IoT-based health care solutions. In addition, this paper analyzes distinct IoT security and privacy features, including security requirements, threat models, and attack taxonomies from the health care perspective. Further, this paper proposes an intelligent collaborative security model to minimize security risk; discusses how different innovations such as big data, ambient intelligence, and wearables can be leveraged in a health care context; addresses various IoT and eHealth policies and regulations across the world to determine how they can facilitate economies and societies in terms of sustainable development; and provides some avenues for future research on IoT-based health care based on a set of open issues and challenges.

The Internet of Things for Health Care: A Comprehensive Survey

IEEE Transactions on Pattern Analysis and Machine Intelligence

In this demo, we showcase a generic cross-technologycommunication scheme allowing bidirectional communication between off-the-shelf IoT devices operating in the 2.4 GHz band. In particular, we make use of and extend the X-Burst framework to enable communication between devices embedding a Wi-Fi, BLE, or IEEE 802.15.4 radio. X-Burst encodes data in the duration of energy bursts by transmitting legitimate frames with different payload length. Devices with incompatible physical layer, but operating on overlapping channels, can detect the energy bursts and decode information by sampling the received signal strength at a high frequency. As the transmission of frames with variable size and energy detection are features available in most off-the-shelf IoT devices, X-Burst is not technology-specific and allows to broadcast cross-technology frames to multiple devices using diverse technologies simultaneously.

Demo: Cross-Technology Broadcast Communication between Off-The-Shelf Wi-Fi, BLE, and IEEE 802.15.4 Devices

Proceedings of the Third European conference on Wireless Sensor Networks

Clock synchronization in distributed IoT systems is a necessary feature to allow a coherent data collection and event detection. This task is challenging, as today's IoT systems often consist of heterogeneous wireless devices using incompatible technologies. Because of this, existing solutions often make use of multi-radio gateways, which allow an indirect synchronization across heterogeneous devices, but increase end-to-end delays and suffer from an increased overhead. In this work, we present X-Sync, a novel approach allowing a direct and bidirectional clock synchronization among off-the-shelf wireless IoT devices with incompatible physical layer. X-Sync leverages cross-technology communication to convey timing information among heterogeneous devices and presents novel techniques to compensate for the inaccuracies in reliably detecting the start of a cross-technology frame. We seamlessly integrate X-Sync into the Contiki-NG operating system and evaluate its performance experimentally on off-the-shelf Bluetooth Low Energy and IEEE 802.15.4 devices, showing that X-Sync achieves a μs-level synchronization accuracy.

X-Sync: Cross-Technology Clock Synchronization Among Off-the-Shelf Wireless IoT Devices

Wireless technologies suffer from physical and man-made impairments (e.g., multipath propagation and interference from competing transmissions, as well as from the effect of temperature variations and other environmental properties): this impairs the reliability, timeliness, and availability of IoT systems. At the same time, we see a wave of new safety-critical IoT applications that require performance guarantees. This chapter surveys methods to increase the dependability of the IoT, specifically focusing, first, on increasing the frequency bandwidth from narrowband, over wideband, towards ultra-wideband to better handle multipath effects and interference. Second, the chapter focuses on increasing the adaptability such that a networked system can compensate disturbances also dynamically, eventually striving for cognitive abilities. A distinguishing feature of this chapter is its comprehensive treatment of dependability issues across multiple layers, from signal processing, over microwave engineering, and to networking.

Dependable Wireless Communication and Localization in the Internet of Things

The collaborative activities of a diverse range of partners have resulted in a variety of assets directed towards trustworthy IoT and its integration into autonomous driving and Industry 4.0 applications. This paper strays away from technical development. Its motive is to establish a process and define an adequate set of high-level generic measures that could be implemented to support digital transformation beyond the project’s closing phase. The focus is placed on successful exploitation with a sustainable outlook for the project results in a quest to maximise benefits for a range of stakeholders. To that extent, the paper considers the realistic maximisation of benefits through the implementation of a strategy to improve the value proposition. These activities are prolonging and maximising the impact of the project.

Kay Römer

Papers

Demo: Cross-Technology Broadcast Communication between Off-The-Shelf Wi-Fi, BLE, and IEEE 802.15.4 Devices

Proceedings of the Third European conference on Wireless Sensor Networks

X-Sync: Cross-Technology Clock Synchronization Among Off-the-Shelf Wireless IoT Devices

Dependable Wireless Communication and Localization in the Internet of Things

Steering Drivers of Change: Maximising Benefits of Trustworthy IoT.