Image Processing Reference
In-Depth Information
Star network
Hybrid mesh network
Mesh network
S
S
S
S
S
R
R
S
S
S
S
S
S
S
S
G
G
G
R
R
S
S
S
S
S
S
R
S
S
S
S
S
Gateway
Sensor
Router
Sensor with router
G
S
R
S
FIGURE .
WSNtopologies.(FromAakvaag,N.andFrey,J.-E.,
ABB Rev
., , , . With permission.)
Industrial automation environments are characterized by
•
Harsh environments
: Extreme temperature, moisture, vibration, hazardous envi-
ronments, steel constructions, and (moving) obstructions. Issues facing wireless
communication in such environments are heavy multipath fading, fast/slow fading,
coverage quality (due to reflection), and local variations in received power.
•
EMI
: Electromagnetic interference from electrical activity such as drives and welding,
which cause noise in radio frequency bands.
•
Other users
: Disturbance by occupation of frequencies over time (WLAN, Bluetooth,
ZigBee, etc.).
The following sections will elaborate more on the implications of these severe conditions on the
embedded design of WSN devices.
27.2.3.2 Typical WSN Applications
The requirements of any WSN solution will always depend heavily on the particular application in
mind. There are many promising applications for wireless technologies in industrial automation,
ranging from monitoring of process parameters to mission-critical control applications. Interna-
tional Society of Automation (ISA []) defines six usage classes of wireless communication based
on the criticality of the application, which directly governs the importance of the message response
time (see Table .).
WSNs in the traditional sense (i.e., low power, multi-hop, mesh networks) are today usually
deployed in class - applications. This is logical since most WSN solutions are usually optimized
for low-power consumption to increase battery's lifetime, and this stands in direct conflict with short
and deterministic response times.
However, in real life, the boundaries between these classes are not always that clearly
defined/identified. It is common that from a user's point of view, the application is a mixture of
monitoring and control, making the requirements on message delay hard to specify. Defining a suit-
able wireless communication solution can thus be difficult unless we provide means to influence the
network forming and optimization criterions.
