Biomedical Engineering Reference
In-Depth Information
Fig. 3
Typical multihop wireless sensor network architecture
3. Real-time and always on: Physiological and environmental data can be
monitored continuously, allowing real-time response by emergency or health
care workers. The data collected form a health journal, and are valuable for
filling in gaps in the traditional patient history. Although the network as a whole
is always on, individual sensors still must conserve energy through smart power
management and on-demand activation.
4. Reconfiguration and self-organization: Since there is no fixed installation,
adding and removing sensors instantly reconfigures the network. Doctors may
retarget the mission of the network as medical needs change. Sensors self-
organize to form routing paths, collaborate on data processing, and establish
hierarchies (Fig.
3
).
The WSN is built of ''nodes''—from a few to several hundreds or even thou-
sands, where each node is connected to one (or sometimes several) sensors. Each
such sensor network node has typically several parts: a radio transceiver with an
internal antenna or connection to an external antenna, a microcontroller, an
electronic circuit for interfacing with the sensors, and an energy source, usually a
battery or an embedded form of energy harvesting. A sensor node might vary in
size from that of a shoebox down to the size of a grain of dust, although func-
tioning ''motes'' of genuine microscopic dimensions have yet to be created. The
cost of sensor nodes is similarly variable, ranging from a few to hundreds of
dollars, depending on the complexity of the individual sensor nodes. Size and cost
constraints on sensor nodes result in corresponding constraints on resources such
as energy, memory, computational speed, and communications bandwidth. The
topology of the WSNs can vary from a simple star network to an advanced
multihop wireless mesh network. The propagation technique between the hops of
the network can be routing or flooding.
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