Many wireless applications require a propagation model that describes the attenuation of the transmitted signal as a function of the distance between devices. Such channel models are derived commonly from signal strength measurements, and assume that the true distances between wireless terminals are known. In practice, however, the true distances may be unavailable or difficult to obtain, for instance in mobile scenarios or in the absence of line-of-sight. These conditions typically occur in forested environments, urban areas, etc. This paper addresses the problem of path loss model parameter estimation in presence of erroneous distance measurements, such as the ones derived from the GPS positions. We provide a model for the uncertainties, and study the impact of distance errors on the estimation of a log-distance channel model. Our main conclusion is that the path loss model can be estimated with a reasonable accuracy from unreliable distances, provided that the measurements are taken at distances beyond a few standard deviations of the GPS positioning error. In case the maximum communication range does not allow such large distances, we provide a method to correct the erroneous channel model. Real-world measurements are used in order to validate our approach.

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Impact of Position Errors on Path Loss Model Estimation for Device-to-Device Channels

Eucalyptus trees are among the most important sources of firebrands with potential to produce spot fires which are one of the most relevant manifestations of extreme fire behaviour. The mechanism of spot fires has several sequential phases starting in the release of a burning ember which is lofted and transported by the airflow, to land in a fuel bed causing a new ignition. In the present study, dedicated to the phase of firebrand release, an analysis of the firebrands released in a process of burning of eucalyptus trees is carried out. Barks of eucalyptus trees have a great potential to produce firebrands during a forest fire. Sometimes these fuels are lay down on the ground or are attached to the trunk and to large branches of the canopy. In this study, the number and size distribution of firebrands released during the burning of these fuels for different scenarios are analysed. Three tests were made varying the location of the barks (suspended and lay down on a fuel bed) and the orientation of suspended barks (vertical and horizontal). An additional similar test was performed with a fuel bed composed of shrubs. A particle image velocimetry system available in the Forest Fire Research Laboratory of ADAI was used to analyse the release of firebrands. Additionally, the convective up flow velocity and the temperature 2m above the tree, as well as the weight loss decay were measured. The final results among the several parameters controlled are compared.

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Advances in forest fire research

Current research suggests that firefighters are under high risks of cardiac attacks due to heat stress and high physiological exertion. Thus, it is very important to track the location of firefighters in a real fire scenario, so as to alert the fire crew chief during a medical emergency. In this paper, we use Wireless Body Area Sensor Networks (WBASN) to gather various physiological data from monitoring devices and constantly monitor the firefighters in training or in action. A fire disaster is also a source of potentially hazardous gases. Therefore, systems should be developed that can monitor the level of such gases in the vicinity of the firefighters and generate appropriate alarms if levels of such gases exceed the prescribed safe levels. We also propose to set up wireless sensor devices to monitor the mobility of the firefighters inside the crisis area by measuring the Received Signal Strength Indicator (RSSI) values received by these sensor motes strategically placed at different locations. We propose to develop a comprehensive location and monitoring system to be used by the firefighters while fighting fires. Our system would be ad-hoc, thus enabling it to be setup fairly quickly.

Comprehensive monitoring of firefighters by a Wireless Body Area Sensor Network

Fire rescue operation is one of the most critical public safety activities where the firefighters put their lives to direct risk in order to extinguish the fire and help save other humans. For the success of fire rescue operation it is very important that the incident commander and the firefighters in the fire field are completely aware of their surroundings. Situation awareness can be achieved by a firefighter monitoring system consisting of sensors implanted in the firefighter's uniform. Like any other sensor application, the sensor nodes should remain alive till the end of rescue operation and should send regular updates to the incident commander. In this paper we propose an energy aware sensing and transmission (EAST) scheme for the firefighter monitoring system. The proposed scheme computes the on-off scheduling scheme for the sensor nodes depending upon the expected maximum operation time, the residual energy and update period of the sensor nodes. Simulations are performed and comparisons are made in MATLAB. It is shown that the EAST scheme achieves the energy efficiency within the update period constraints when compared to other schemes.

Energy aware sensing and transmission (EAST) scheme for firefighter monitoring system

Data collection is a powerful application in scenarios where mobile and static agents work towards a common goal. Mobile and vehicular ad hoc networks (M/VANETs) are a steadfast platform over which such applications can be built. Static nodes interact with the M/VANET as data sinks that provide access to cloud-based services, or as sensor nodes that regard the mobile network as a dependable communication backhaul. The relevance of our target application – data collection applications over ad hoc networks with mobile and static nodes – motivates the development of network design solutions addressing scenario characterization, infrastructure planning and network operation. Our thesis aims to show that the design of such solutions can be improved by the use of measurements and datasets from the target scenario. The development of wireless applications requires an accurate characterization of the electromagnetic signal propagation. Empirical channel models aim to capture the behaviour of propagation from measurements of received signal strength and distance between wireless terminals. We address the problem of path loss model parameter estimation in presence of erroneous distance measurements, in particular those obtained from the GPS positions. Our main conclusion is that the path loss model can be estimated with a reasonable accuracy from unreliable distances, provided that the measurements are taken at distances beyond a few standard deviations of the GPS positioning error. In case the maximum communication range does not allow such large distances, we provide a method to correct the erroneous channel model. Field experiments were undertaken to collect measurement data in order to validate our approach. In a number of scenarios, static sensor nodes can harness vehicular backhauls for collecting data to a base station. Sensors and backhaul gateways can be interfaced by static communication hubs, and network designers can use mobility and connectivity datasets from the target scenario to place hubs ensuring service requirements and minimizing resources. We address the challenge of placing communication hubs over large areas (e.g. at city scale) and driven by infrastructureto-vehicle (I2V) service requirements, alongside constraints of other nature. Our solution strategy involves an model of I2V transfers estimation over large areas that builds on an experimental characterization of throughput and data transfers at the target scenario. Our placement strategy attains less 20% hubs than sensor nodes, and estimates of our model of I2V data transfers fall within one order of magnitude of measurements collected on site. The operation of protocols for data collection can harness base station-centric strategies such as beaconing. Protocols that set up structured routes (such as spanning trees) from beaconing are bound to suffer degraded performance as routing information at the nodes becomes outdated. We study an opportunistic design so that traffic does not become restrained to rigid routes. Given that link-level reliability becomes impractical, network coding is introduced to provide reliability. We set up a simulation framework over real-world connectivity traces and carry out extensive design-space exploration and benchmarking against a reference structured protocol. Our results support a number of design recommendations for a network coding-based protocol, and clarify the conditions in which our solution exhibits better resilience to routing information degradation.

Wireless protocols and channel estimation for data gathering with mobile nodes

Every day, thousands of first responders work to save the lives of others, sometimes without the adequate surveillance of health conditions. The VitalResponder is a project that aims at monitoring and control teams of first responders in emergency scenarios, using mobile technologies to capture and use real-time data to support real-time coordination. In this paper we present a system to capture, process, and display the vital signs of team members, which are made available to a first responders’ team leader, for coordination and monitoring. The system addresses specific requirements of the field action, such as the mobility of actors, combining two of the most recent mobile technologies: the iPad (for the coordination view) and Android OS-based smartphones (for real-time sensor data acquisition).

Diogo C. Teles

Papers

iVital: A Real Time Monitoring System for First Response Teams

iVital: A Real Time Monitoring System for First Response Teams