Leslie Overs

Long-duration solar-powered wireless sensor networks

This paper discusses hardware design principles for long-term solar-powered wireless sensor networks. We argue that the assumptions and principles appropriate for long-term operation from primary cells are quite different from the solar power case with its abundant energy and regular charging cycles. We present data from a long-term deployment that illustrates the use of solar energy and rechargeable batteries to achieve 24x7 operation for over two years, since March 2005.

secFleck: A Public Key Technology Platform for Wireless Sensor Networks

We describe the design and implementation of a public-key platform, secFleck, based on a commodity Trusted Platform Module (TPM) chip that extends the capability of a standard node. Unlike previous software public-key implementations this approach provides E-Commerce grade security; is computationally fast, energy efficient; and has low financial cost -- all essential attributes for secure large-scale sensor networks. We describe the secFleck message security services such as confidentiality, authenticity and integrity, and present performance results including computation time, energy consumption and cost. This is followed by examples, built on secFleck, of symmetric key management, secure RPC and secure software update.

Design and Deployment of a Remote Robust Sensor Network: Experiences from an Outdoor Water Quality Monitoring Network

This paper investigates a wireless sensor network deployment - monitoring water quality, e.g. salinity and the level of the underground water table - in a remote tropical area of northern Australia. Our goal is to collect real time water quality measurements together with the amount of water being pumped out in the area, and investigate the impacts of current irrigation practice on the environments, in particular underground water salination. This is a challenging task featuring wide geographic area coverage (mean transmission range between nodes is more than 800 meters), highly variable radio propagations, high end-to-end packet delivery rate requirements, and hostile deployment environments. We have designed, implemented and deployed a sensor network system, which has been collecting water quality and flow measurements, e.g., water flow rate and water flow ticks for over one month. The preliminary results show that sensor networks are a promising solution to deploying a sustainable irrigation system, e.g., maximizing the amount of water pumped out from an area with minimum impact on water quality.

Fleck - A platform for real-world outdoor sensor networks

This paper presents the design of the Fleck platform for building real-world outdoor sensor networks. Fleck1 and Fleck2 have been successfully deployed in several long-term outdoor sensor networks. The Fleck3 is the latest member of the platform. The power input stage of the Fleck3 has been simplified and now provides the ability to compute both the energy coming in and the energy being consumed. This makes possible the implementation of sophisticated distributed energy-aware applications. Both rechargeable batteries (with over-charge protection) and super-capacitors can be used as the primary source of power. The Fleck3 incorporates a real-time clock. At the expense of a small current drain, the real-time clock provides several advantages. It allows the Fleck3 to be placed into very deep sleep, reducing the overall energy consumption down to 30 micro-Amps. It also allows the network as a whole to maintain a better sense of time and reduces the time-keeping overhead on the micro-controller. The Fleck3 incorporates a packet-based radio from Nordic. This radio is more energy efficient than earlier generations and significantly reduces the communications overhead on the micro-controller. It also provides a better radio front-end, with a range of about 1 km with normal, zero-gain quarter-wavelength antennas in the 915 MHz band. The Fleck platform supports a large variety of sensor interface boards, including a companion board incorporating a TPM chip from Atmel for applications where security is important. These features make the Fleck platform a very strong candidate for outdoor sensor networks.

New ways of measuring intake, efficiency and behaviour of grazing livestock

Wireless sensor networks (WSN) offer a novel method for measuring important livestock phenotypes in commercial grazing environments. This information can then be used to inform genetic parameter estimation and improve precision livestock management. Arguably, these technologies are well suited for such tasks due to their small, non-intrusive form, which does not constrain the animals from expressing the genetic drivers for traits of interest. There are many technical challenges to be met in developing WSN technologies that can function on animals in commercial grazing environments. This paper discusses the challenges of the software development required for the collection of data from multiple types of sensors, the management and analyses of the very large volumes of data, determination of which sensing modalities are sufficient and/or necessary, and the management of the constrained power source. Assuming such challenges can be met however, validation of the sensor accuracy against benchmark data for specific traits must be performed before such a sensor can be confidently adopted. To achieve this, a pasture intake research platform is being established to provide detailed estimates of pasture intake by individual animals through chemical markers and biomass disappearance, augmented with highly annotated video recordings of animal behaviours. This provides a benchmark against which any novel sensor can be validated, with a high degree of flexibility to allow experiments to be designed and conducted under continually differing environmental conditions. This paper also discusses issues underlying the need for new and novel phenotyping methods and in the establishment of the WSN and pasture intake research platforms to enable prediction of feed intake and feed efficiency of individual grazing animals.

A public key technology platform for wireless sensor networks

Communication security for wireless sensor networks (WSN) is a challenge due to the limited computation and energy resources available at nodes. We describe the design and implementation of a public-key (PK) platform based on a standard Trusted Platform Module (TPM) chip that extends the capability of a standard node. The result facilitates message security services such as confidentiality, authenticity and integrity. We present results including computation time, energy consumption and cost.

Intra-ruminal gas-sensing in real time: a proof-of-concept

An intra-rumen (IR) gas-sensing system incorporating commercially available gas sensors [methane (CH4), carbon dioxide (CO2) and hydrogen (H2)] and a wireless sensor network was developed to measure rumen gas concentrations of grazing animals in real-time. The IR gas-sensing devices also measure temperature and pressure near the sensors and the design isolates the electronics and battery from exposure to gases. Membranes were developed that allow the desired gases to diffuse through to the sensors while excluding corrosive hydrogen sulfide (H2S). Performance of the prototype IR devices was tested in cattle and sheep fed once a day as a proof-of-concept. Concentrations of expired gases from respiration chambers were compared with the concentrations obtained by the IR gas-sensing device within the rumen digesta. Direct measurements of rumen gas cap samples demonstrate a similar gas profile to that observed with the IR gas-sensing device with the ratio of CO2 : CH4 peaking shortly after feeding and CO2 levels nearly 2.5 times greater than those of CH4. The gas ratio then declines over time to a point when at 23 h post-feeding the concentration of CH4 exceeds that of CO2. The H2 gas concentration in the rumen varied throughout the day reaching maximum levels of 2500 ppm after feeding and declining to 250 ppm over the day. Although the IR device was able to detect H2 in the rumen throughout the entire day, expired H2 was often below the limits of detection in the respiration chamber. Current work is focussed on extending the longevity of the devices in the rumen so that replicated trials can be performed on the accuracy and precision of the measurements.

Towards a framework for a versatile wireless multimedia sensor network platform

We describe our current work towards a framework that establishes a hierarchy of devices (sensors and actuators) within a wireless multimedia node and uses frequent sampling of cheaper devices to trigger the activation of more energy-hungry devices. Within this framework, we consider the suitability of servos for Wireless Multimedia Sensor Networks (WMSNs) by examining their functional characteristics and energy consumption [2].