3.10 Vital Sign Monitoring
Wireless sensors are being used to monitor vital signs of patients
in a hospital environment [3]. Compared to conventional
approaches, solutions based on wireless sensors are
intended to improve monitoring accuracy whilst also being
more convenient for patients.
The system consists of four components: a patient identi-
fier, medical sensors, a display device, and a setup pen. The
patient identifier is a special sensor node containing patient
data (e.g., name) which is attached to the patient when he
or she enters the hospital. Various medical sensors (e.g.,
electrocardiogram) may be subsequently attached to the patient.
Patient data and vital signs may be inspected using a
display device. The setup pen is carried by medical personnel
to establish and remove associations between the various
devices. The pen emits a unique ID via infrared to limit
the scope to a single patient. Devices which receive this ID
form a body area network.
3.11 Power Monitoring
A WSN is being used to monitor power consumption in
large and dispersed office buildings [8]. The goal is to detect
locations or devices that are consuming a lot of power
to provide indications for potential reductions in power consumption.
The system consists of three major components: sensor
nodes, transceivers, and a central unit. Sensor nodes
are connected to the power grid (at outlets or fuse boxes)
to measure power consumption and for their own power
supply. Sensor nodes directly transmit sensor readings to
transceivers. The transceivers form a multi-hop network
and forward messages to the central unit. The central unit
acts as a gateway to the Internet and forwards sensor data to
a database system.
3.12 Parts Assembly
A WSN is being used to assist people during the assembly
of complex composite objects such as do-it-yourself furniture
[2]. This saves users from having to study and understand
complex instruction manuals, and prevents them from
making mistakes.
The furniture parts and tools are equipped with sensor
nodes. These nodes are equipped with a variety of different
sensors: force sensors (for joints), gyroscope (for screwdrivers),
and accelerometers (for hammers). The sensor
nodes form an ad hoc network for detecting certain actions
and sequences thereof and give visual feedback to the user
via LEDs integrated into the furniture parts.
3.13 Tracking Military Vehicles
A WSN is being used to track the path of military vehicles
(e.g., tanks) [19]. The sensor network should be unnotice-
7
able and difficult to destroy. Tracking results should be reported
within given deadlines.
Sensor nodes are deployed from an unmanned aerial
vehicle (UAV). Magnetometer sensors are attached to the
nodes in order to detect the proximity of tanks. Nodes collaborate
in estimating the path and velocity of a tracked
vehicle. Tracking results are transmitted to the unmanned
aerial vehicle.
3.14 Self-Healing Mine Field
Anti-tank landmines are being equipped with sensing and
communication capabilities to ensure that a particular area
remains covered even if the enemy tampers with a mine to
create a potential breach lane [12]. If tampering is detected
by the mine network, an intact mine hops into the breach
using a rocket thruster.
The mines form a multi-hop ad hoc network and monitor
radio link quality to detect failed mines. Nodes also estimate
their location and orientation using ultrasonic ranging.
When a node failure is detected, one of the mines is selected
to relocate itself using one of eight rocket thrusters.
3.15 Sniper Localization
A WSN is being used to locate snipers and the trajectory of
bullets [15], providing valuable clues for law enforcement.
The system consists of sensor nodes that measure the muzzle
blast and shock wave using acoustic sensors. The sensor
nodes form a multi-hop ad hoc network. By comparing the
time of arrival at distributed sensor nodes, the sniper can be
localized with an accuracy of about one meter, and with a latency
of under two seconds. The sensor nodes use an FPGA
chip to carry out the complex signal processing functions.
4 Conclusions
There are several important consequences of the design
space as discussed above. Clearly, a single hardware platform
will most likely not be sufficient to support the wide
range of possible applications. In order to avoid the development
of application-specific hardware, it would be desirable,
however, to have available a (small) set of platforms
with different capabilities that cover the design space. A
modular approach, where the individual components of a
sensor node can be easily exchanged, might help to partially
overcome this difficulty. Principles and tools for selecting
suitable hardware components for particular applications
would also be desirable.
As far as software is concerned, the situation becomes
even more complex. As with hardware, one could try to
cover the design space with a (larger) set of different protocols,
algorithms, and basic services. However, a system developer
would then still be faced with the complexity of the