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

Analytic Conditions for Energy Neutrality in Uniformly-Formed Wireless Sensor Networks

Future deployments of wireless sensor network (WSN) infrastructures for environmental or event monitoring are expected to be equipped with energy harvesters (e.g. piezoelectric, thermal, photovoltaic) in order to substantially increase their autonomy. In this paper we derive conditions for energy neutrality, i.e. perpetual energy autonomy per sensor node, by balancing the node's expected energy consumption with its expected energy harvesting capability. Our analysis assumes a uniformly-formed WSN, i.e. a network comprising identical transmitter sensor nodes and identical receiver/relay sensor nodes with a balanced cluster-tree topology. The proposed framework is parametric to: (i) the duty cycle for the network activation; (ii) the number of nodes in the same tier of the cluster-tree topology; (iii) the consumption rate of the receiver node(s) that collect (and possibly relay) data along with their own; (iv) the marginal probability density function (PDF) characterizing the data transmission rate per node; (v) the expected amount of energy harvested by each node. Based on our analysis, we obtain the number of nodes leading to the minimumenergy harvestingrequirement for each tier of the WSN cluster-tree topology. We also derive closed-form expressions for the difference in the minimum energy harvesting requirements between four transmission rate PDFs in function of the WSN parameters. Our analytic results are validated via experiments using TelosB sensor nodes and an energy measurement testbed. Our framework is useful for feasibility studies on energy harvesting technologies in WSNs and for optimizing the operational settings of hierarchical WSN-based monitoring infrastructures prior to time-consuming testing and deployment within the application environment

Energy consumption of visual sensor networks: impact of spatio-temporal coverage

Wireless visual sensor networks (VSNs) are expected to play a major role in future IEEE 802.15.4 personal area networks (PANs) under recently established collision-free medium access control (MAC) protocols, such as the IEEE 802.15.4e-2012 MAC. In such environments, the VSN energy consumption is affected by a number of camera sensors deployed (spatial coverage), as well as a number of captured video frames of which each node processes and transmits data (temporal coverage). In this paper we explore this aspect for uniformly formed VSNs, that is, networks comprising identical wireless visual sensor nodes connected to a collection node via a balanced cluster-tree topology, with each node producing independent identically distributed bitstream sizes after processing the video frames captured within each network activation interval. We derive analytic results for the energy-optimal spatiooral coverage parameters of such VSNs under a priori known bounds for the number of frames to process per sensor and the number of nodes to deploy within each tier of the VSN. Our results are parametric to the probability density function characterizing the bitstream size produced by each node and the energy consumption rates of the system of interest. Experimental results are derived from a deployment of TelosB motes and reveal that our analytic results are always within 7%of the energy consumption measurements for a wide range of settings. In addition, results obtained via motion JPEG encoding and feature extraction on a multimedia subsystem (BeagleBone Linux Computer) show that the optimal spatiooral settings derived by our framework allow for substantial reduction of energy consumption in comparison with ad hoc settings

Interim report drawn up on behalf of the Committee on Budgetary Control on control problems in the olive oil sector. Working Documents 1983-1984, Document 1-1537/83, 12 March 1983

Desynchronization is a fundamental approach in wireless sensor networks that allows for convergence to time-division multiple access (TDMA) of the medium without the need for clock synchronization and centralized coordination. The method is based on the concept of reactive listening of periodic fre message broadcasts between nodes sharing the given spectrum. We propose a novel framework to estimate the required iterations for convergence to fair TDMA scheduling. Unlike previous conjectures or bounds found in the literature, our estimation framework is based on a stochastic modeling approach. Experiments via imote2 TinyOS nodes and simulations demonstrate that the proposed estimates characterize the experimental desynchronization convergence iterations signifcantly better than existing conjectures or bounds

Energy Consumption of Visual Sensor Networks: Impact of Spatio-Temporal Coverage Based on Single-Hop Topologies

Wireless visual sensor networks (VSNs) are expected to play a major role in future IEEE 802.15.4 personal area networks (PAN) under recently-established collision-free medium access control (MAC) protocols. In such environments, the trade-off between the number of camera sensors to deploy (spatial coverage) and the frame rate to use for each camera sensor (temporal coverage) plays a major role in the VSN energy consumption. In this paper, we address this aspect for single-hop VSNs, i.e. networks comprising independent and identical wireless visual sensor nodes connected to a collection node via a star topology. We derive analytic results for the energy-optimal spatio-temporal coverage parameters of such VSNs under a-priori known bounds for the minimum frame rate per sensor and the minimum and maximum possible number of nodes to deploy. Our results are parametric to the probability density function characterizing the data-production rate per node and the energy consumption parameters of the system of interest. Experimental results using TelosB motes under: a collision-free transmission protocol, the IEEE 802.15.4 PAN physical layer (CC2420 transceiver) and Monte-Carlo-generated data sets, reveal that our analytic results are within 7% of the energy consumption measurements for a wide range of settings. In addition, results obtained via a multimedia subsystem performing visual feature extraction in video frames show that the optimal spatio-temporal settings derived by the proposed framework allow for up to 48% of reduction of energy consumption in comparison to ad-hoc settings. As such, our analytic modeling is useful for early-stage studies of possible VSN deployments under collision-free MAC protocols prior to costly and time-consuming experiments in the field

Energy Consumption Of Visual Sensor Networks: Impact Of Spatio--Temporal Coverage

Wireless visual sensor networks (VSNs) are expected to play a major role in future IEEE 802.15.4 personal area networks (PAN) under recently-established collision-free medium access control (MAC) protocols, such as the IEEE 802.15.4e- 2012 MAC. In such environments, the VSN energy consumption is affected by the number of camera sensors deployed (spatial coverage), as well as the number of captured video frames out of which each node processes and transmits data (temporal coverage). In this paper, we explore this aspect for uniformlyformed VSNs, i.e., networks comprising identical wireless visual sensor nodes connected to a collection node via a balanced clustertree topology, with each node producing independent identicallydistributed bitstream sizes after processing the video frames captured within each network activation interval. We derive analytic results for the energy-optimal spatio–temporal coverage parameters of such VSNs under a-priori known bounds for the number of frames to process per sensor and the number of nodes to deploy within each tier of the VSN. Our results are parametric to the probability density function characterizing the bitstream size produced by each node and the energy consumption rates of the system of interest. Experimental results derived from a deployment of TelosB motes under: a collisionfree transmission protocol, the IEEE 802.15.4 PAN physical layer (CC2420 transceiver) and Monte-Carlo–generated data sets, reveal that our analytic results are always within 7% of the energy consumption measurements for a wide range of settings. In addition, results obtained via a multimedia subsystem (BeagleBone Linux Computer) performing differential Motion JPEG encoding and local visual feature extraction from video frames show that the optimal spatio–temporal settings derived by the proposed framework allow for substantial reduction of energy consumption in comparison to ad-hoc settings. As such, our analytic modeling is u- eful for early-stage studies of possible VSN deployments under collision-free MAC protocols prior to costly and time-consuming experiments in the field