LifeNet: an Ad-hoc Sensor Network and Wearable
System to Provide Firefighters with Navigation Support
Markus Klann1, Till Riedel 2, Hans Gellersen 3, Carl Fischer 3, Matt Oppenheim 3, Paul
Lukowicz 4, Gerald Pirkl 4, Kai Kunze 4, Monty Beuster 5, Michael Beigl 5, Otto Visser 6,Mirco Gerling1
31
Fraunhofer FIT, Germany; 2 TecO, University of Karlsruhe, Germany;
Computing Dept., Lancaster University, U.K.; 4 University of Passau, Germany;
5TU Braunschweig, Germany; 6 TU Delft, The Netherlands{markus.klann, mirco.gerling}@fit.fraunhofer.de; riedel@teco.uni-karlsruhe.de;{hwg, c.fischer, matt.oppenheim}@comp.lancs.ac.uk;{paul.lukowicz, gerald.pirkl, kai.kunze}@uni-passau.de{beuster, beigl}@ibr.cs.tu-bs.de; o.w.visser@tudelft.nl

Abstract. This paper describes a concept called LifeNet for using an ad-hoc
sensor network providing relative positioning and a wearable system to support
firefighters at indoor-navigation under impaired visibility. We describe theconcept and a first implementation.
Keywords: sensor networks, localization, navigation, wearable computing.

1 Introduction: The LifeNet Concept
When moving through a building structure under impaired visibility, firefighters use
ropes to mark the path they have taken. This helps them in finding their way back out
and helps other teams to take the same path. These ropes are called lifelines.
While this technique works reliably in many situations, there are also a number ofshortcomings that can become critical and in fact have let to fatalities in the past. In
particular, the lifeline can get stuck or be cut under doors or other objects, it canbecome entangled with furniture, railings etc. and it generally limits the operationalrange. Moreover, a lifeline always only offers one retreat path and communicates noor very little information on the firefighters to the outside.
The understanding of these difficulties was obtained through empirical researchwith the Paris Fire Brigade, including interviews, observations and participation indifferent trainings [1]. Based on this understanding we defined a concept called
LifeNet to address the difficulties. The concept proposes that• firefighters automatically deploy sensor nodes along their paths
effectively establishing an ad-hoc infrastructure for positioning, sensing
and communication.

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firefighters interact with this sensor network by way of wearable
computing equipment and receive navigational information on e.g. ahead-mounted display or over a headset.
While the LifeNet concept has some commonalities with the Siren sensor network
system proposed in [2], the main distinguishing feature is the proposed navigation
support under impaired visibility based on relative localisation.
What we consider as very interesting about the LifeNet concept is that theconcerned practice of indoor navigation by firefighters is a learned, skilful andcollaborative activity in an extended, only partially known, changing and dangerous
space and that the technology we are proposing interacts with this practice intimately
and on different levels. As such the concept affords a particularly interesting
opportunity to explore and investigate the usage conditions of an ad-hoc ubiquitouscomputing infrastructure.
In the next sections we describe a first implementation of the LifeNet. The system
consists of the sensor nodes that provide relative positioning and a wearable systemthat retrieves and processes the information from the sensor network and provides thesupport to the firefighters.

2 The Sensing Subsystem of LifeNet
The sensor system is based on nodes we refer to as RELATE Bricks (Fig 1, left), avariant of a RELATE sensor node as first introduced by Hazas et al. [3]. In contrast toHazas’ device, which was realized as a USB dongle for attachment to mobile
computers, the Brick is designed to function stand-alone. Core processing andcommunication for the Bricks is handled by a Particle Computer [4] sensor node with
an 8bit PIC18 micro controller and 868 MHz TR1001 radio front-end.
Communication and time synchronization primitives are provided by the AwareCon
network stack [5]. The sensor board consists of four 40 kHz narrow-band ultrasoundtransducers, a temperature sensor and power supply using AAAA batteries. We use
the transducers to act both as receivers and transmitters, for bi-directional ultrasonicsensing such that devices can measure their relative positions peer-to-peer. TheRELATE Brick also hosts an I²C expansion slot for adding further sensors, forinstance an accelerometer. A USB port is used as a command bridge to connect at any
point in the network to other devices like a portable or wearable computer.
Additionally, we fitted two of the nodes onto a pair of heavy duty boots similar tothe ones worn by firefighters (see Fig. 1, right). The transducers are attached to flying
leads and threaded through the lining of the boots. The body of the sensor node is
attached to the top of the boot and the transducers were placed on the toe, on the heel
and in the middle of both sides of the boot. Their placement is low to the ground, tobe in approximately the same plane as sensor nodes deployed on the floor. This isbecause the sensor system performs best in terms of accuracy when all nodes arelocated in the same plane.
The Logic of the LifeNet sensor subsystem is implemented on the sensor nodes assoftware modules using the RELATE Black Board architecture [6]. All modules areloosely coupled via a common blackboard interface that acts as a distributed shared125

Fig. 1. RELATE Brick sensor node with ultrasonic transducers on its four sides (left). Boots
augmented with RELATE sensor nodes, with transducers placed around the base (right).

memory system. Essential to the application scenario is the collaborative sensing
module, using ultrasonic measurements synchronized over RF. It is used to performspatial discovery (of nodes within a defined range) and to measure the distance andthe angle-of-arrival with respect to discovered nodes. The measurement range in thepresent implementation is about 2.5m, with distance estimates between neighbouring
nodes accurate to about 10cm, and angle-of-arrival accuracy of around 30º. On top of
the sensor measurements, a LifeNet module establishes virtual lifelines of sensor
nodes when these become deployed (i.e. dropped along the path of a firefighter).
In a setup phase after the deployment of a node, its LifeNet module tries to join alifeline of already deployed sensors. Lifelines are started by a dedicated node at theentrance of the building and then extended as nodes get dropped to the floor. Eachnode denotes its position in the lifeline and the distance towards the exit. If nodes are
already on the path (i.e. when a firefighter crosses an already deployed sensor trail),no new nodes get dropped but already deployed nodes join the lifeline (i.e. the samenode can be part of multiple lifelines). Once deployed, the LifeNet module
periodically scans along the line to detect missing links. If a lifeline is interrupted, thisinformation is propagated to the other participating nodes telling them that this path tothe exit is no longer available.

3 The Wearable System Components
The current wearable system prototype for use with the LifeNet consists of an OQO
micro PC that communicates with the sensor nodes through the USB bridge
mentioned above and that displays on a Carl Zeiss look-around head-mounted display
integrated with the breathing mask (Fig. 2). The PC runs an application that queries
the LifeNet sensing subsystem to provide navigation support to the firefighters.
Currently, the support consists in directional indications available alternatively as anarrow on the HMD, or as audio commands on the headset. Following theseindications, the firefighter is guided from one sensor node to the next on a trail126

leading out of the building. In case there are multiple
retreat paths, the firefighter may be rerouted if a shorter
path becomes available or the currently taken path
becomes unavailable. The questions that we explorewith this system is how the LifeNet needs to bedeployed, what functionality the individual nodes needto have and how the processed information needs to bepresented to the user for safe operation under thephysically and cognitively difficult circumstances of anintervention. Because of the size and casing of thesensor nodes, they are currently still deployed by hand.
But a device for automatic deployment and smaller
ruggedized sensor nodes are under development.
Acknowledgments
The presented research is supported by the European Fig. 2. HMD in breathing
Commission as part of the RELATE and mask and HMD interface
WearIT@Work projects (contract nos. 013790 and004216). We are grateful to the support of both projects for this collaborative effort
and to the Paris Fire Brigade for their participation as users in this research.

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