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

A firefly-inspired scheme for energy-efficient transmission scheduling using a self-organizing method in a wireless sensor network

Various types of natural phenomena are regarded as primary sources of information for artificial occurrences that involve spontaneous synchronization. Among the artificial occurrences that mimic natural phenomena are Wireless Sensor Networks (WSNs) and the Pulse Coupled Oscillator (PCO), which utilizes firefly synchronization for attracting mating partners. However, the PCO model was not appropriate for wireless sensor networks because sensor nodes are typically not capable to collect sensor data packets during transmission (because of packet collision and deafness). To avert these limitations, this study proposed a self-organizing time synchronization algorithm that was adapted from the traditional PCO model of fireflies flashing synchronization. Energy consumption and transmission delay will be reduced by using this method. Using the proposed model, a simulation exercise was performed and a significant improvement in energy efficiency was observed, as reflected by an improved transmission scheduling and a coordinated duty cycling and data gathering ratio. Therefore, the energy-efficient data gathering is enhanced in the proposed model than in the original PCO-based wave-traveling model. The battery lifetime of the Sensor Nodes (SNs) was also extended by using the proposed model

EBS: decentralised slot synchronisation for broadcast messaging for low-power wireless embedded systems

In this paper, we present a decentralised scheme that facili- tates reliable network wide broadcast messaging without the requirement of strict time synchronisation, for duty-cycled low-power wireless embedded systems. In this emergent broadcast slot (EBS) scheme, devices coordinate their wake- up periods with their neighbours to exchange schedule infor- mation locally. This leads to the emergence of local slot syn- chronisation without the need for either network-wide syn- chronisation or a centralised time synchronisation element. We theoretically show that this scheme converges faster than similar emergent and gradient-based approaches, which we confirm by evaluation on real test-beds. We also show that our scheme exhibits lower overheads while being more tol- erant to disturbances caused by faulty nodes, wireless link failures, contention and interference in presence of deter- ministic propagation delays

Multichannel Distributed Coordination for Wireless Sensor Networks: Convergence Delay and Energy Consumption Aspects

This thesis develops new approaches for distributed coordination of data-intensive communications between wireless sensor nodes. In particular, the topic of synchronization, and its dual primitive, desynchronization at the Medium Access Control (MAC) or the Application (APP) layer of the OSI stack, is studied in detail. In Chapters 1 and 2, the related literature on the problem of synchronization is overviewed and the main approaches for distributed (de)synchronization at the MAC or APP layers are analyzed, designed and implemented on IEEE802.15.4- enabled wireless sensor nodes. Beyond the experimental validation of distributed (de)synchronization approaches, the three main contributions of this thesis, corresponding to the related publications found below, are: • establishing for the first time the expected time for convergence to distributed time division multiple access (TDMA) operation under the two main desynchronization models proposed in the literature and validating the derived estimates via a real-world implementation (Chapter 3); • proposing the extension of the main desynchronization models towards multi-hop and multi-channel operation; the latter is achieved by extending the concept of reactive listening to multi-frequency operation (Chapter 4 and 5). • analyzing the energy consumption of the distributed TDMA approach under different transmission probability density functions (Chapter 6 and 7). Conclusions and items for future work in relation to the proposals of this thesis are described in Chapter 8

Clock Synchronization for Many-Core Processors

In this dissertation we propose to develop, implement, and validate a software based clock synchronization algorithm in a many-core processor architecture, specifically the Kalray MPPA-256 architecture. This work was the objective of reducing the effect of clock skew in many-core architectures, so that we can take full advantage of this hardware type in real-time applications

Convergence of Desynchronization Primitives in Wireless Sensor Networks: A Stochastic Modeling Approach

Desynchronization approaches in wireless sensor networks converge to time-division multiple access (TDMA) of the shared medium without requiring clock synchronization amongst the wireless sensors, or indeed the presence of a central (coordinator) node. All such methods are based on the principle of reactive listening of periodic "fire" or "pulse" broadcasts: each node updates the time of its fire message broadcasts based on received fire messages from some of the remaining nodes sharing the given spectrum. In this paper, we present a novel framework to estimate the required iterations for convergence to fair TDMA scheduling. Our estimates are fundamentally different from previous conjectures or bounds found in the literature as, for the first time, convergence to TDMA is defined in a stochastic sense. Our analytic results apply to the Desync algorithm and to pulse-coupled oscillator algorithms with inhibitory coupling. The experimental evaluation via iMote2 TinyOS nodes (based on the IEEE 802.15.4 standard) as well as via computer simulations demonstrates that, for the vast majority of settings, our stochastic model is within one standard deviation from the experimentally-observed convergence iterations. The proposed estimates are thus shown to characterize the desynchronization convergence iterations significantly better than existing conjectures or bounds. Therefore, they contribute towards the analytic understanding of how a desynchronization-based system is expected to evolve from random initial conditions to the desynchronized steady state.Comment: to appear, IEEE Transactions on Signal Processing, 201

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

The Virtual Bus: A Network Architecture Designed to Support Modular-Redundant Distributed Periodic Real-Time Control Systems

The Virtual Bus network architecture uses physical layer switching and a combination of space- and time-division multiplexing to link segments of a partial mesh network together on schedule to temporarily form contention-free multi-hop, multi-drop simplex signalling paths, or 'virtual buses'. Network resources are scheduled and routed by a dynamic distributed resource allocation mechanism with self-forming and self-healing characteristics. Multiple virtual buses can coexist simultaneously in a single network, as the resources allocated to each bus are orthogonal in either space or time. The Virtual Bus architecture achieves deterministic delivery times for time-sensitive traffic over multi-hop partial mesh networks by employing true line-speed switching; delays of around 15ns at each switching point are demonstrated experimentally, and further reductions in switching delays are shown to be achievable. Virtual buses are inherently multicast, with delivery skew across multiple destinations proportional to the difference in equivalent physical length to each destination. The Virtual Bus architecture is not a purely theoretical concept; a small research platform has been constructed for development, testing and demonstration purposes