wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

A Survey of Wireless Sensor Networks for Industrial Applications 12-5
It is possible to achieve reliable operation of wireless networks, even in harsh environments, by
employing redundant paths, self-healing algorithms, and retransmissions of lost data packets.
12.4.3 Battery Lifetime
One of the main benefits of using WSNs is the fact that they do not require any cabling. However, this
means that the power needed to operate the wireless sensor must come from a local power source, in
most cases a battery. This makes it important to keep the power consumption of a wireless sensor as
low as possible in order to increase the battery lifetime. With the expectation that possibly hundreds or
even thousands of wireless sensors could be deployed in a facility, exchanging batteries can be a timeconsuming
and costly maintenance task, especially if the wireless sensors are installed in hazardous
areas. Wireless sensors should therefore be able to provide a battery lifetime in excess of a few years.
Due to the multi-hop mesh network topologies and the self-configuring and self-healing capabilities
often present in WSNs, the power consumption of a wireless sensor node is usually nondeterministic.
Measurements in [PDA08] have shown that the power consumption of a node in a mesh network
depends on the amount of packets it has to forward for other nodes in the network. With constant
changes in the RF environment due to climatic changes, RF noise/interference, and moving personnel
or equipment, the routing paths in a WSN are dynamic and are subject to change over time. This means
that the power consumption of the nodes in a network will change accordingly.
A way to eliminate the need for batteries is to have self-powered wireless sensors. This can be achieved
through energy harvesting, where a wireless sensor captures and stores energy from its environment.
Energy harvesting can either replace or augment the battery usage of a wireless sensor, depending on the
amount of harvested energy. The power generation capability of the harvesting methods are at the time
of writing 40.μW/cm 3 for thermoelectric, 116.μW/cm 3 for vibration, and 330.μW/cm 3 for piezoelectric
harvesting [CC08].
12.4.4 Friendly Coexistence with Wireless Local Area Networks
Wireless local area networks (WLANs) based on the IEEE 802.11 family of standards [802.11], [802.11n],
which provide access to intranet/Internet from the field, are becoming increasingly popular in industrial
plants and facilities. To enable the possibility of deploying both WSN and WLAN in the same
facility, which represents a highly relevant scenario, it is imperative that the two technologies are able to
coexist in a friendly manner. This means no critical degradation of either WSN or WLAN performance
when they are operating in the same area.
Coexistence between WSNs and WLAN are discussed in more detail in Section 12.5.5.
12.4.5 Security
The data in a WSN are transmitted over the air, which makes it more susceptible to eavesdropping and
other security breaches compared to wired communication. Privacy and access violations are the most
common threats to a wireless network.
For WSNs, encryption techniques are employed to protect the privacy of the transmitted data in
the network. Transmitter authentication and data consistency tools are used to combat and counteract
access threats.
12.4.6 Operation in Harsh and Hazardous Environments
WSNs are a viable solution for noncritical monitoring applications for practically any industrial plant or
facility worldwide. The environment in which the wireless sensors can be deployed will thus vary greatly
from site to site, ranging from cold winter conditions with snow and ice in arctic regions, to heat and
© 2011 by Taylor and Francis Group, LLC