Rachel Cardell-Oliver

A Reactive Soil Moisture Sensor Network: Design and Field Evaluation

Wireless sensor network technology has the potential to reveal finegrained, dynamic changes in monitored variables of an outdoor landscape. But there are significant problems to be overcome in order to realize this vision in working systems. This paper describes the design and implementation of a reactive, event driven network for environmental monitoring of soil moisture and evaluates its effectiveness. A novel feature of our solution is its reactivity to the environment: when rain falls and soil moisture is changing rapidly, measurements are collected frequently, whereas during dry periods, between rainfall, measurements are collected less often. Field trials demonstrating the reactivity, robustness, and longevity of the network are presented and evaluated, and future improvements proposed.

Field testing a wireless sensor network for reactive environmental monitoring [soil moisture measurement]

Wireless sensor network technology promises to reveal fine-grained, dynamic changes in monitored variables of an outdoor landscape. But there are significant problems to be overcome in translating this vision to working systems. This paper describes the design and implementation of a reactive, event driven network for environmental monitoring of soil moisture and evaluates the effectiveness of this solution. A novel feature of our solution is its reactivity to the environment: when rain falls and soil moisture is changing rapidly, measurements are collected frequently, whereas during dry periods, between rainfall events, measurements are collected much less often. Reactivity allows us to focus on dynamic responses and limit the amount of useless data gathered, as well as improving robustness and network lifetime. The main contribution of the paper is to demonstrate that a reactive sensor network can deliver useful data on soil moisture responses to rainfall. Field trial results on the reactivity, robustness and longevity of the network are evaluated, and future improvements proposed.

FlexiTP: A Flexible-Schedule-Based TDMA Protocol for Fault-Tolerant and Energy-Efficient Wireless Sensor Networks

FlexiTP is a novel TDMA protocol that offers a synchronized and loose slot structure. Nodes in the network can build, modify, or extend their scheduled number of slots during execution, based on their local information. Nodes wake up for their scheduled slots; otherwise, they switch into power-saving sleep mode. This flexible schedule allows FlexiTP to be strongly fault tolerant and highly energy efficient. FlexiTP is scalable for a large number of nodes because its depth-first-search schedule minimizes buffering, and it allows communication slots to be reused by nodes outside each others interference range. Hence, the overall scheme of FlexiTP provides end-to-end guarantees on data delivery (throughput, fair access, and robust self-healing) while also respecting the severe energy and memory constraints of wireless sensor networks. Simulations in ns-2 show that FlexiTP ensures energy efficiency and is robust to network dynamics (faults such as dropped packets and nodes joining or leaving the network) under various network configurations (network topology and network density), providing an efficient solution for data-gathering applications. Furthermore, under high contention, FlexiTP outperforms 2-MAC in terms of energy efficiency and network performance.

Conformance Tests for Real-Time Systems with Timed Automata Specifications

Abstract. A method is introduced for testing the conformance of implemented real-time systems to timed automata specifications. Uppaal timed automata are transformed into testable timed transition systems (TTTSs) using a test view. Fault hypotheses and a test generation algorithm for TTTSs are defined. Results of applying the method are presented.

A Practical and Complete Algorithm for Testing Real-Time Systems

This paper presents a formal method for generating conformance tests for real-time systems. Our algorithm is complete in that, under a test hypothesis, if the system being tested passes every test generated then the tested system is bisimilar to its specification. Because the test algorithm has exponential worst case complexity and finite state automata models of real-time systems are typically very large, a judicious choice of model is critical for the successful testing of real-time systems. Developing such a model and demonstrating its effectiveness are the main contributions of this paper.

Conformance test experiments for distributed real-time systems

This paper introduces a new technique for testing that a distributed real-time system satisfies a formal timed automata specification. It outlines how to write test specifications in the language of Uppaal timed automata, how to translate those specifications into program code for executing the tests, and describes the results of test experiments on a distributed real-time system with limited hardware and software resources.

Formal specification and analysis of performance variation in sensor network diffusion protocols

Discovering a routing tree for gathering or disseminating streams of data is an important operation in many sensor network applications. However, protocols for tree discovery may have significant performance problems for certain configurations of a network and its application task.A Temporal Logic of Actions (TLA) specification of push and pull diffusion is introduced in order to analyse such problems. This specification can be used as a basis for implementation, for visualising protocol behaviours, for simulation experiments, and for formal verification of properties of the protocol.This short paper shows how such a specification is used to understand variations in the routing trees discovered by push and pull diffusion and the effect of their shape and size on protocol performance.

ROPE: a reactive, opportunistic protocol for environment monitoring sensor networks

The goal of sensor networks that monitor the environment is to detect and report the temporal and spatial dynamics of that environment and to run unattended for several months. Meeting all three of these requirements in real applications has proved to be a challenging task. The paper presents a novel protocol for data gathering that adapts opportunistically to changes in its environment. Each node compresses its gathered data locally, transmitting a burst of data when communication conditions are good. We report the design and analysis of the protocol and results of preliminary implementation tests using CSIRO Flecks and TinyOS.

Representation and recognition of situations in sensor networks

A situation is an abstraction for a pattern of observations made by a distributed system such as a sensor network. Situations have previously been studied in different domains, as composite events in distributed event based systems, service composition in multi-agent systems, and macro-programming in sensor networks. However, existing languages do not address the specific challenges posed by sensor networks. This article presents a novel language for representing situations in sensor networks that addresses these challenges. Three algorithms for recognizing situations in relevant fields are reviewed and adapted to sensor networks. In particular, distributed commitment machines are introduced and demonstrated to be the most suitable algorithm among the three for recognizing situations in sensor networks.

Evaluating the impact of limited resource on the performance of flooding in wireless sensor networks

Wireless sensor networks (WSNs) are large collections of resource limited nodes, densely deployed over a landscape. They gather and disseminate local data using multi-hop broadcasting. WSN design and deployment is hampered by currently limited knowledge of the performance characteristics of network nodes and protocols. Their systematic development, thus, requires a flexible simulation environment in which new models of specific node or network behaviours can be integrated easily. This paper introduces a loosely coupled, object oriented simulation environment for this task. The simulator is used to investigate the efficiency of flooding protocols in WSNs. For dense networks with noisy transmission, we show that using low transmission power maximizes time and resource efficiency and that the scalability of flooding for large networks is excellent. We demonstrate ways of improving flooding performance given specific deployment constraints.