A State-Based Programming Model for Wireless Sensor Networks

28 Chapter 2. Wireless Sensor Networks
poses of embedded systems are monitoring or controlling the devices they are
embedded in, performing computational operations on behalf of them, as well
as providing interfaces to other systems, the environment (through sensors and
actuators), and users. Often multiple embedded systems are networked, such as
in automobiles and aircrafts.
2.4.2 Diversity of Embedded Systems
Embedded systems are very diverse, both in their application domains as
well as in their requirements. Examples of embedded-system applications are
industrial-machine controllers, cruise-controls and airbag controllers in automobiles,
medical equipment, digital video and still cameras, controllers in washingmachines
and other household appliances, fly-by-wire systems, vending machines,
toys, and sensing (typically wired) monitoring systems. Depending on
the application domain, embedded systems can have very diverse requirements,
such as high reliability (e.g., in medical systems), high-performance data processing
(e.g., image processing in cameras), low cost (e.g., in commodity devices
such as remote controls), and real-time behavior (e.g., in fly-by-wire systems and
airbag controllers). In fact, there does not seem to be a single set of requirements
applicable to all variants of embedded systems. For example, a digital-camera
controller typically requires high performance at a very low cost and low power
consumption. In contrast, medical systems require high reliability and real-time
behavior while performance, low cost, and low power consumption may not be
an issue.
2.4.3 Wireless Sensor Nodes
Sensor nodes have also been considered embedded systems. Though there are
some differences to traditional embedded systems, they also share many characteristics
and use very similar technology. The two most obvious differences
are that firstly, sensor nodes are typically not embedded into other machines
or devices but are autonomous and self contained. And secondly, traditional
distributed embedded systems typically use wired communication as it is more
reliable.
Apart from that, sensor nodes perform tasks similar to embedded systems and
have similar characteristics. Just like embedded systems, sensor nodes perform
various monitoring and control tasks and often perform significant data processing.
Sensor nodes also provide interfaces (to other nodes and the backend
for tasking), typically through the air interface. As we have argued in Sect. 3.1,
most applications of wireless sensor nodes do share a common set of requirements,
probably the most important of which are resource-efficiency, reliability,
and reactivity.
2.5 Summary and Outlook
In this chapter we have presented various applications of WSNs and their requirements
on a technical hard and software solution. Often the size and cost