1. technology and computing

Wireless Sensor Networks in Residential Layouts
D. Manjunath and S.V. Gopalaiah
Department of Electrical Communication Engineering,
Indian Institute of Science (IISc), Bangalore, INDIA 560 012
{manjunath,svg}@ece.iisc.ernet.in
In recent years, Wireless Sensor Networks (WSNs) have gathered a lot of attention as an important
research domain. A typical WSN is a multi-hop wireless network consisting of small sensor devices that
are capable of sensing, processing (computing), and communicating. These devices sense the environment
(temperature, pressure, vibration, acoustics, etc.), process the sensed data often in a distributed fashion,
and wirelessly communicates the outcome of processing to a base station. Figure 1 shows a diminutive
exemplar of a typical WSN.
The viability of WSNs is entirely depends on the small physical size and low cost of the sensor devices.
Consequently, sensor devices are severely constrained by the resources. A typical sensor node is built of a
8-bit microcontroller, 4-16 MHz crystal oscillator, few hundred Kbytes of program memory, 4-10 Kbytes
of data memory (RAM), radio-chip with data rates between 10-250 Kbps, typically a 10-bit ADC, and
two AA batteries. Because of these constraints, even simple protocols and algorithms may not perform to
the expectation when actually implemented on the sensor devices − this is the major challenge driving
all the current research in WSNs.
Fig. 1.
A typical Wireless Sensor Network
WSNs have been proposed for wide-variety of applications, however, most of these are confined to
military use and a very few commercial sensor applications have been explored till date. For WSNs to
be truly ubiquitous, many more commercial sensor applications are yet to be investigated. As an effort to
probe for such an application, we explore the potential of using WSNs for handling certain security and
safety issues in residential layouts.
A residential layout is a collection of domiciles generally built across a large geographical area, and
despite of existing manual security and safety measures, layouts are vulnerable to the problems such as
dacoity, fire accidents, environmental pollution, etc. In order to address such problems, we propose to
employ WSNs, as monitoring, an essence of WSNs makes them an appropriate candidate.
This article contemplates five important issues and proposes a Residential Wireless Sensor Network
(RWSN) and a Central Facility (CF) to handle them. RWSN is a wireless network of location-aware tiny
embedded sensor nodes (motes) placed at strategic positions within the residential layout, and it provides a
common networking infrastructure to deal with all the identified issues. The CF is a geographical location
where the information conveyed by RWSN is monitored. We separately consider each of the identified
issues and explicate how it can be addressed using WSNs. Furthermore, we also investigate the challenges
involved in realizing the proposed system.
1) Dacoity
2) Individual Domiciles Monitoring
3) Patients Surveillance
4) Children and Pets Tracking
5) Air Pollution Monitoring
DACOITY: Robbery by a gang of armed dacoits is a serious concern and it can be avoided by adding
human intrusion detection capability to RWSN. Detection, classification, and tracking of human targets
is a basic surveillance application, and has hence received a considerable amount of research interest.
In the past few years, number of human target detection and classification techniques (based on sensors
like vibration, acoustic, magnetic, etc.) have been proposed and by furnishing RWSN with one of these
techniques enables to detect the intrusion of dacoits.
For this solution to be robust, it is essential to differentiate between a bona fide resident and an intruder.
A wireless wearable mote having a very limited radio range can serve this purpose. Every resident
is provided with a wearable Identity Mote that periodically sends out a beacon containing an unique
identification code corresponding to the resident. On hearing to the beacon, a RWSN node forwards it to
CF so that simultaneous reception of human detection information and a valid identification code from
the same location confirms that the detected human is a bona fide resident.
The RWSN not only allows to detect the presence of dacoits, with the recent advancements in tracking
techniques, it is also possible to track their movement, which greatly assist in coordinating the act of
capturing dacoits.
I NDIVIDUAL D OMICILES M ONITORING : Using RWSN to remotely monitor individual domiciles is
of significant use. For example, equipping domiciles’ electricity and water billing meters with sensors
capable of sensing and transmitting allows a Meter Reader to collect meter readings at the CF, thereby
eliminating the need for visiting individual domiciles.
Similarly, by furnishing domiciles with the sensors capable of detecting fire accidents, LPG leakage,
etc. enables staff at CF to detect the respective events and take appropriate actions even in the absence
of domicile residents.
PATIENTS S URVEILLANCE : We propound to outfit residential patients with wearable medical sensors
capable of communicating with RWSN. This allows doctors of the layout’s Health Center to remotely and
continuously monitor the real-time physiological status of their patients, and also to react immediately in
the case of emergency (e.g., cardiac arrest). This is true irrespective of the location of doctors and patients
as long as both are in the vicinity of the RWSN. Furthermore, collecting and maintaining the physiological
database of the patients is remarkably useful in diagnosis, prognosis, and forestalling potential health
problems.
C HILDREN AND P ETS T RACKING : The children and pets can be tracked by outfitting them with wireless
wearable Identity Motes that periodically transmits a beacon consisting of an identification code specific
to the wearer (child or pet). On its reception, a RWSN node route beacon to the CF along with the node’s
location information. As Identity Motes are tuned to have a limited radio transmission range, the location
information conveyed in the beacon can be considered as location of the wearer corresponding to the
received identification code. This also allows to trace the trajectory of the movement of children and pets.
A IR P OLLUTION M ONITORING : The concerns increase on the level of air pollution being generated and
particularly over its deleterious effects on localized human health. As an attempt to control air pollution
and avoid consequent health hazards, we propose to add pollution monitoring capability to RWSN. By
equipping gas sensors (e.g., metal oxide sensors, electrochemical sensors, QCM sensors, etc.) on RWSN
enables to monitor air pollution levels and to take corrective actions in the case of pollution exceeding a
threshold level.
R EALIZATION C HALLENGES : As this article is the first one to take steps toward using WSNs in
residential layouts, the challenges that arise in realizing the proposed system are yet to be investigated.
Following is an overview of few such realization challenges.
• As RWSN is heterogeneous in nature, for an identified issue, only a specific type of sensor nodes
or some parts of the monitored environment may be relevant. So it is imperative to provide a means
to define groups of sensor nodes and limit the visibility of network messages sent within groups. A
system user must be able to select and communicate with a particular interested group of sensors
based on selection rules, such as selection based on node features, geographic coordinates, topology
information, etc.
• As WSNs edge towards widespread deployment, securing them becomes a central concern. One of
the common attacks on WSNs is node capture attack, where an adversary gains full control over
sensor nodes through direct physical access. It is a common notion that WSNs are highly susceptible
to node capture attack and we set out to verify this assumption with respect to RWSN. As one of the
goals of deploying RWSN is for intrusion detection, any unauthorized physical access to the sensor
nodes would be detected as intrusion and the same is conveyed to the CF. Consequently, it is not easy
for an adversary to physically capture the sensor nodes of RWSN. Moreover, since RWSN nodes are
placed at strategic positions, their physical access by an intruder is almost impractical.
• Methods for tight binding between the wearable Identity Mote and the wearer needs to be investigated.
One such simple and reliable method is to compel residents to inform the CF on loosing his/her
Identity Mote so that the pre-assigned identification code corresponding to the resident can be
deactivated.
• The employed network protocols of RWSN must support real-time requirements as for instance, in the
case of intrusion detection, invasion should be instantaneously notified to the CF and the collectedand-delivered intrusion data must still be valid at the time of acting, thereby demanding real-time
communication.
• As WSNs are severely constrained by power supply, it is compulsory to employ power-aware routing,
medium access, and physical layer protocols. Most of the network protocols proposed for WSNs
are associated with a well-known tradeoff between real-time requirements and power management,
therefore, it is necessary to choose well-balanced protocols that are appropriate to RWSN.
• It is crucial to decide when and how often identification beacons must be sent as high frequency is
both power and bandwidth consuming, where as low frequency increases the detection delay.
• The RWSN nodes must be location-aware, but it is not feasible to have a Global Positioning System
(GPS) receiver on every RWSN node as GPS is a expensive solution. In the past several years, a
number of location discovery schemes have been proposed to eliminate the need of having a GPS
receiver on individual sensor nodes. In the proposed RWSN, only the static backbone nodes are
to be aware of their location and moreover, only an approximate location information can serve
the application requirements. This enables to employ a location scheme that is easy-to-implement,
inexpensive, and reliable rather than an expensive, complex by incorporating support for mobile
nodes, and highly accurate solutions like GPS.
Finally, there is still a long way to be able to realize the proposed system, which needs comprehensive
investigation of system design, realization challenges, efficient algorithms, etc. This article has just explored
the potential of using WSNs for handling certain critical issues in residential layouts. We discussed the
issues and explained how the technology of Wireless Sensor Networking can be employed to handle them.
We also identified and described few challenges involved in realizing the system.