Self-Synchronization in Duty-cycled Internet of Things (IoT) Applications

In recent years, the networks of low-power devices have gained popularity. Typically these devices are wireless and interact to form large networks such as the Machine to Machine (M2M) networks, Internet of Things (IoT), Wearable Computing, and Wireless Sensor Networks. The collaboration among these devices is a key to achieving the full potential of these networks. A major problem in this field is to guarantee robust communication between elements while keeping the whole network energy efficient. In this paper, we introduce an extended and improved emergent broadcast slot (EBS) scheme, which facilitates collaboration for robust communication and is energy efficient. In the EBS, nodes communication unit remains in sleeping mode and are awake just to communicate. The EBS scheme is fully decentralized, that is, nodes coordinate their wake-up window in partially overlapped manner within each duty-cycle to avoid message collisions. We show the theoretical convergence behavior of the scheme, which is confirmed through real test-bed experimentation.Comment: 12 Pages, 11 Figures, Journa

Ultra-Low-Power Uwb Impulse Radio Design: Architecture, Circuits, And Applications

Recent advances in home healthcare, environmental sensing, and low power computing have created a need for wireless communication at very low power for low data rate applications. Due to higher energy/bit requirements at lower data -rate, achieving power levels low enough to enable long battery lifetime (~10 years) or power-harvesting supplies have not been possible with traditional approaches. Dutycycled radios have often been proposed in literature as a solution for such applications due to their ability to shut off the static power consumption at low data rates. While earlier radio nodes for such systems have been proposed based on a type of sleepwake scheduling, such implementations are still power hungry due to large synchronization uncertainty (~1[MICRO SIGN]s). In this dissertation, we utilize impulsive signaling and a pulse-coupled oscillator (PCO) based synchronization scheme to facilitate a globally synchronized wireless network. We have modeled this network over a widely varying parameter space and found that it is capable of reducing system cost as well as providing scalability in wireless sensor networks. Based on this scheme, we implemented an FCC compliant, 3-5GHz, timemultiplexed, dual-band UWB impulse radio transceiver, measured to consume only 20[MICRO SIGN]W when the nodes are synchronized for peer-peer communication. At the system level the design was measured to consume 86[MICRO SIGN]W of power, while facilitating multi- hop communication. Simple pulse-shaping circuitry ensures spectral efficiency, FCC compliance and ~30dB band-isolation. Similarly, the band-switchable, ~2ns turn-on receiver implements a non-coherent pulse detection scheme that facilitates low power consumption with -87dBm sensitivity at 100Kbps. Once synchronized the nodes exchange information while duty-cycling, and can use any type of high level network protocols utilized in packet based communication. For robust network performance, a localized synchronization detection scheme based on relative timing and statistics of the PCO firing and the timing pulses ("sync") is reported. No active hand-shaking is required for nodes to detect synchronization. A self-reinforcement scheme also helps maintain synchronization even in the presence of miss-detections. Finally we discuss unique ways to exploit properties of pulse coupled oscillator networks to realize novel low power event communication, prioritization, localization and immediate neighborhood validation for low power wireless sensor applications

Bio-Inspired Synchronization of Pulse-Coupled Oscillators and its Application to Wireless Sensor Networks

Precise synchronization among networked agents is responsible for phenomena as diverse as coral spawning and consistency in stock market transactions. The importance of synchronization in biological and engineering systems has triggered an avalanche of studies analyzing the emergence of a synchronized behavior within a network of, possibly heterogeneous, agents. In particular, synchronization of networks of coupled oscillators has received great attention since limit cycle oscillators are a natural abstraction for systems where periodicity is a distinctive property. Examples of such systems include circadian rhythms and alternate-current power generators. This work deals with synchronization of pulse-coupled limit cycle oscillators (PCOs). A reverse engineering approach is taken with the objective of obtaining an abstraction for PCO networks able to capture the key properties observed in the classical biological PCO model, to finally implement it in an en gineering system. To this end, we first reformulate the PCO model as a hybrid system, able to integrate in a smooth manner the continuous-time dynamics of the individual oscillators and the impulsive effect of the coupling. Using our new model, we analyze the existence and stability of synchronization in a variety of PCO network topologies, starting from the simplest all-to-all network where global synchronization is proven to exist, to end giving synchronization conditions in the general strongly connected network case. Inspired by the strong synchronization properties of PCO networks we design a PCO-inspired time synchronization protocol for wireless sensor networks that enjoys all the advantages of our optimized PCO setup. A pilot implementation is presented going from a simulation stage to a hardware implementation in Gumstix development boards and industrial acoustic sensors. To test the potential of the protocol in a real application, we implement the PCO-based time synchronization protocol in a distributed acoustic event detection system, where a sensor network combines local measurements over an infrastructure-free wireless network to find the source of an acoustic event. An evaluation by simulation is given to illustrate the advantages of using the pulse-coupled synchronization strategy.The contributions of this thesis range from the theoretical synchronization conditions for a variety of PCO networks to the design and implementation of a synchronization strategy for wireless sensor networks that seems to be the natural choice when using an infrastructure-free wireless network due to its simple formulation and natural scalability

Energy-Aware Decentralised Medium Access Control for Wireless Sensor Networks

The success of future Internet-of-Things (IoT) based application deployments depends on the ability of wireless sensor platforms to sustain uninterrupted operation based on: (i) environmental energy harvesting and optimised coupling with the platform’s energy consumption when processing and transmitting/receiving data; (ii) spontaneous adaptation to changes in the local network topology without requiring central coordination. To address the first aspect, starting from practical deployments of a multi-transducer platform for photovoltaic and piezoelectric energy harvesting and the associated modelling and analysis, data-driven probability models are derived to facilitate the optimal coupling of energy production and consumption when processing and transmitting data. To address the second aspect (adaptability), the new concept of decentralised time-synchronised channel swapping (DT-SCS) is proposed – a novel protocol for the medium access control (MAC) layer of IEEE 802.15.4-based wireless sensor networks (WSNs). Simulation results reveal that DT-SCS comprises an excellent candidate for completely decentralised MAC layer coordination in WSNs by providing quick convergence to steady state, high bandwidth utilisation, high connectivity, robustness to interference and low energy consumption. Moreover, performance results via a Contiki-OS based deployment on TelosB motes reveal that DT-SCS comprises an excellent candidate for a decentralised multichannel MAC layer

Security and Privacy for Ubiquitous Mobile Devices

We live in a world where mobile devices are already ubiquitous. It is estimated that in the United States approximately two thirds of adults own a smartphone, and that for many, these devices are their primary method of accessing the Internet. World wide, it is estimated that in May of 2014 there were 6.9 billion mobile cellular subscriptions, almost as much as the world population. of these 6.9 billion, approximately 1 billion are smart devices, which are concentrated in the developed world. In the developing world, users are moving from feature phones to smart devices as a result of lower prices and marketing efforts. Because smart mobile devices are ubiquitous, security and privacy are primary concerns. Threats such as mobile malware are already substantial, with over 2500 different types identified in 2010 alone. It is likely that, as the smart device market continues to grow, so to will concerns about privacy, security, and malicious software. This is especially true, because these mobile devices are relatively new. Our research focuses on increasing the security and privacy of user data on smart mobile devices. We propose three applications in this domain: (1) a service that provides private, mobile location sharing; (2) a secure, intuitive proximity networking solution; and (3) a potential attack vector in mobile devices, which utilizes novel covert channels. We also propose a first step defense mechanism against these covert channels. Our first project is the design and implementation of a service, which provides users with private and secure location sharing. This is useful for a variety of applications such as online dating, taxi cab services, and social networking. Our service allows users to share their location with one another with trust and location based access controls. We allow users to identify if they are within a certain distance of one another, without either party revealing their location to one another, or any third party. We design this service to be practical and efficient, requiring no changes to the cellular infrastructure and no explicit encryption key management for the users. For our second application, we build a modem, which enables users to share relatively small pieces of information with those that are near by, also known as proximity based networking. Currently there are several mediums which can be used to achieve proximity networking such as NFC, bluetooth, and WiFi direct. Unfortunately, these currently available schemes suffer from a variety of drawbacks including slow adoption by mobile device hardware manufactures, relatively poor usability, and wide range, omni-directional propagation. We propose a new scheme, which utilizes ultrasonic (high frequency) audio on typical smart mobile devices, as a method of communication between proximal devices. Because mobile devices already carry the necessary hardware for ultrasound, adoption is much easier. Additionally, ultrasound has a limited and highly intuitive propagation pattern because it is highly directional, and can be easily controlled using the volume controls on the devices. Our ultrasound modem is fast, achieving several thousand bits per second throughput, non-intrusive because it is inaudible, and secure, requiring attackers with normal hardware to be less than or equal to the distance between the sender and receiver (a few centimeters in our tests). Our third work exposes a novel attack vector utilizing physical media covert channels on smart devices, in conjunction with privilege escalation and confused deputy attacks. This ultimately results in information leakage attacks, which allow the attacker to gain access to sensitive information stored on a user\u27s smart mobile device such as their location, passwords, emails, SMS messages and more. Our attack uses our novel physical media covert channels to launder sensitive information, thereby circumventing state of the art, taint-tracking analysis based defenses and, at the same time, the current, widely deployed permission systems employed by mobile operating systems. We propose and implement a variety of physical media covert channels, which demonstrate different strengths such as high speed, low error rate, and stealth. By proposing several different channels, we make defense of such an attack much more difficult. Despite the challenging situation, in this work we also propose a novel defense technique as a first step towards research on more robust approaches. as a contribution to the field, we present these three systems, which together enrich the smart mobile experience, while providing mobile security and keeping privacy in mind. Our third approach specifically, presents a unique attack, which has not been seen in the wild , in an effort to keep ahead of malicious efforts

Performance of new GNSS satellite clocks

In Global Navigation Satellite Systems (GNSS), the on-board clocks are a key component from which timing and navigation signals are generated. This thesis reviews the performance of the first Passive Hydrogen Maser (PHM) launched by the Galileo system in 2008; and demonstrates how the new PHM can be consider as the best clock in space, pushing the physical clock error contribution below the noise floor of geodetic time transfer capabilities. Furthermore, overall GNSS clock peformance is reviewe

NASA Tech Briefs, June 1991

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