BROWSING THE SENSOR WEB

Pervasive Access for Wide-area Wireless Sensor Networks

Jie Wan

, Michael J. O’Grady

, Gregory M. P. O’Hare

and Todor Colakov

CLARITY: Centre for Sensor Web Technologies, School of Computer Science and Informatics, University College Dublin

Dublin, Ireland

University of West Bohemia, Pilsen, Czech Republic

Keywords:

Sensor Web, Human Computer Interaction, Pervasive Computing.

Abstract:

Wireless Sensor Networks (WSNs) are almost exclusively regarded as data gathering entities. Various sensed

data elements are captured and routed back to a central server for processing, visualization and interpretation.

However, it can be realistically conjectured that scenarios will increasingly emerge that demand a facility

for ad-hoc interaction with individual sensor nodes. Moreover, such interaction will occur in the physical

environment in close proximity to where the sensor node is physically located. In this paper, the need for

in-situ ad-hoc interaction is motivated. A methodology for facilitating such interaction is presented, and the

implementation of a sensor browser is described.

1 INTRODUCTION

Pervasive Computing envisages a world of embed-

ded artifacts connected by pervasive networking tech-

nologies. Moreover, seamless and intuitive interac-

tion is perceived as a key characteristic of such sys-

tems. While Wireless Sensor Networks (WSNs) are a

fundamental enabling technology for pervasive com-

puting, and have been harnessed in a diverse range

of applications for example, surveillance and environ-

mental monitoring, access to such networks is inher-

ently centralized, and support for point-to-point ad-

hoc interaction with individual sensor nodes is lack-

ing. Cases where such interaction would be desirable

might include law enforcement where, after an inci-

dent, ofﬁcials at the scene could obtain instant access

to security cameras within their immediate vicinity.

Crowd-sourcing activities are another avenue where

such access would be useful. For the purposes of

this discussion, the practical issue of network main-

tenance in the ﬁeld is considered.

Section 2 outlines some documented approaches

to interaction with WSNs. In Section 3, the need for

ad-hoc interaction with WSNs is motivated through

a practical example in network Operation and Main-

tenance (O&M). A methodology for enabling ad-hoc

interaction is described in Section 4. A prototype sen-

sor browser is outlined in Section 5 after which the

paper is concluded.

2 RELATED RESEARCH

Interaction and visualization in WSN contexts are re-

ceiving increasing attention by the research commu-

nity. Initially, there is a focus on WSN management

issues, and a number of frameworks have been de-

scribed in this area. Examples include SNMS (Tolle

and Culler, 2005), TASK (Buonadonna et al., 2005),

Mote-View (Turon, 2005), SensibleDoctor (Cha et al.,

2008), Wireless Sensor Network Remote Interaction

Tool (Tirkawi and Fischer, 2008) and Octopus (Jur-

dak et al., 2008). Another approach describes how

Geographic Information Systems (GIS) and web tech-

nologies may be integrated to enable online visualiza-

tion (Fan and Biagioni, 2004). However in all these

cases, the predominant model is one of centralized ac-

cess and control.

Other researchers have considered issues relating

to WSN access while in the physical WSN environ-

ment. SensAR is an innovative approach that har-

nesses Augmented Reality (AR) for the visualiza-

tion of real-time environmental data using a hand-

held computer (Goldsmith et al., 2008). Likewise,

the speckled computing consortium harness AR as

an interaction paradigm for micro-sensor networks

(Leach and Benyon, 2006). Gauger et al explore dif-

ferent physical modalities for interaction with individ-

ual nodes, including gesture and light (Gauger et al.,

2009). Tricorder (Lifton et al., 2007) is a dedicated

device for browsing and navigating WSNs. It can

query local sensor nodes directly or remote sensor no-

109

Wan J., J. O’Grady M., M. P. O’Hare G. and Colakov T..

BROWSING THE SENSOR WEB - Pervasive Access for Wide-area Wireless Sensor Networks.

DOI: 10.5220/0003809601090112

In Proceedings of the 1st International Conference on Sensor Networks (SENSORNETS-2012), pages 109-112

ISBN: 978-989-8565-01-3

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

Figure 1: Topology of a ideal sensor ﬁeld.

des by issuing a multi-hop request. Using an em-

bedded compass for orientation, and a signal strength

indicator for position, it can be used in a point-and-

browse fashion while physically in the WSN. Tri-

corder is designed to operate with the Plug sensor net-

work. Such a network has potential in domestic or

occupational environments; however, it is not suitable

for wide area sensor networks of the kind used for

environmental monitoring. Ringwald et al (Ringwald

et al., 2006) have developed a tool for interactively

inspecting WSNs in the ﬁeld. It allows querying of

individual nodes and ﬁrmware upgrades on the nodes

as well as topology viewing. Extensive use is made of

Bluetooth, even at sensor level.

The Sensor Browser described in this paper com-

plements and builds upon these approaches, but is

more generic in its applicability in that it seeks to op-

erate on a range of popular smart phones, and support

a variety of sensor platforms.

3 CASE STUDY: OPERATIONS &

MAINTENANCE

The primary function of a sensor is to measure either

individual or multiple phenomena, and to report this

measurement to a dedicated sensor or base station.

This leads to the second key function: the routing of

data. Sensors may also serve as routers, routing data

from other sensors to the base station, or more likely,

to other sensors that are closer to the base station. A

failure in either of these functions would compromise

the operation of the WSN, requiring physical inter-

vention in the ﬁeld to correct the problem.

Figure 1 illustrates what an uniform WSN topol-

ogy might be expected to look like. Sensors are laid

out in the coverage area in a grid-like fashion, all

equidistant such that the entire area is covered from

a sensing and routing perspective. Each sensor has a

number of paths for routing data to the base station,

Figure 2: Topology of a realistic sensor ﬁeld.

Figure 3: Topology of a faulty sensor ﬁeld.

which in turn can either process it in situ or pass it

further up the network stack for further analysis.

Over time, a WSN will deteriorate, resulting in a

number of sensors no longer functioning (Figure 2).

However, the WSN itself is still functioning; data can

still be routed to the base station, and the gaps in

the sensing function may be estimated using various

modeling techniques.

A major problem arises when a combination of

sensors fail such that either the sensing or routing

function is seriously compromised for part of the

WSN coverage area. Figure 3 illustrates a case of

routing failure where part of the network is isolated

and cannot communicate with the base station. To

remedy this situation, physical intervention is re-

quired - this would frequently demand a capability for

in situ ad-hoc interaction with individual nodes.

4 ENABLING AD-HOC

INTERACTION

From a hardware perspective, three components are

necessary to realize a sensor browsing experience.

• Mobile phone - As the de facto standard for ubiq-

uitous communication, high-end mobile phones

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Figure 4: Sensor Browser: introduction screen.

and smart phones increasingly incorporate a suite

of technologies that enables them to host spe-

cialized third-party and custom-developed appli-

cations. In this case, a Nokia N97 was harnessed.

• Sensor platform - a Mica2 unit was adopted as it

was considered an archetypical sensor device, ca-

pable of sensing a number of common phenom-

ena. For communications it uses RF (868/916

MHz).

• Protocol Convertor - mobile phones and sensor

platforms use different communications technolo-

gies so it is necessary to enable a protocol con-

vertor through hardware. A base station was con-

structed using a second Mica2 mote mounted on

a PC Interface board. This was then augmented

with a BlueSnapXP Mobile Bluetooth RS-232

dongle from Serialio.com. This supports the stan-

dard Bluetooth Serial Port proﬁle.

All motes were programmed using NesC. The

browser itself on the mobile phone was developed in

Java ME.

5 THE SENSOR BROWSER

Figure 4 illustrates the introduction screen of the Sen-

sor Browser. This enables access to various function-

ality supported by the browser. In practice, a sensor

may support a multitude of sensed modalities, for ex-

ample, temperature, humidity, ambient noise levels

Figure 5: Sensor Browser: identifying the temperature, dust

and noise as the sensed values of interest.

Figure 6: Sensor Browser: trends are plotted on the individ-

ual faces of a rotating cube for the sensed phenomena under

investigation.

and so on. But users may only be interested in some of

these, depending on their need. Thus, they can spec-

ify multiple modalities that are interesting to them, for

example, temperature, dust and noise (Figure 5), and

visualize the sensed data via the browser. A number

of other modalities such as the battery level, air pol-

lution level can also be monitored while might not be

of interest for general users, additional data about the

network topology, link quality can be gathered if it is

available.

A key feature of the browser is that it continuously

records the required sensed values as they are encoun-

tered. In this way trends can be visualised. The sensor

BROWSING THE SENSOR WEB - Pervasive Access for Wide-area Wireless Sensor Networks

111

adopts a cube metaphor, showing the trends for each

required sensed parameter on an individual face (Fig-

ure 6).

6 FUTURE WORK

A number of improvements are planned for this ini-

tial prototype. Managing scalability and sensor het-

erogeneity are essential, thus the possibility of stan-

dardizing on SensorML or MoteML (Ali et al., 2011)

is being explored. This would also form the basis

for a more robust approach to conﬁguration and de-

bugging. Augmenting the user interface using GPS

and GoogleMaps would enable a realistic visualiza-

tion of the spatial relationship between the sensors.

Finally, until Zigbee and associated technologies are

integrated into mobile phones, it will be necessary to

support a protocol convertor. Mobile base stations of

the type described in (Angove et al., 2011) offer alter-

natives approaches in this instance.

7 CONCLUSIONS

This paper has presented an initial prototype of a

mobile sensor browser; in contrast with previous ap-

proaches, this browser implements a number of novel

features. The adoption of the dynamic cube metaphor

enables an intuitive tool for users to view various

sensed parameters. Furthermore, an adaptive person-

alization mechanism has been harnessed; with the

consideration of individual user’s proﬁle, user pref-

erences and physical environments attributes, select

sensor data can be gathered and visualized in a user-

speciﬁed manner. In addition, real-time sensing, data

collection and visualization have been implemented,

as well as short term historical data recording for

trend analysis.

ACKNOWLEDGEMENTS

This work is supported by Science Foundation Ireland

under grant 07/CE/I1147.

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