Principles and technologies of local area networks - Intelligent Buildings and Building Automation - page 69

4.6.5 Application of wireless technologies in BAS
Field level: The wireless sensor network needs less bandwidth than the con-
troller network. One can select other lower frequencies to support lower data
rates. The devices include sensors and actuators. Power is supplied to wireless
sensors by battery, so they must be power-efficient devices. Their capabilities
mainly include reporting of value changes and responses to querying. Most
of the time they are idle or sleeping to enable power saving. The power of
actuators is not an issue as it is usually supplied by AC line power.
Automation level: The wireless controller network needs wider bandwidth
to transmit more data than a wireless sensor network. It likely requires the
use of a higher frequency band to support higher data rates. The controllers
usually are installed where AC line power is available. So power supply is
not an issue for the applications at this level. The wireless devices can real-
ize more functions in this level, such as routing messages from one node to
another node.
Management level: This level involves computers, network controllers,
or other Ethernet-ready devices. The devices at this level usually commu-
nicate based on Ethernet. Due to its high traffic and TCP/IP compatibility,
Wi-Fi standard can be implemented to establish a wireless connection of an
Ethernet-ready field panel to a facility's existing wired or wireless LAN.
Some manufacturers provide wireless BAS products based on Wi-Fi in the
management and automation levels. The BAS management level can share a
communication network with other information networks, both wired and
wireless. Wi-Fi networks are just the infrastructure of the entire building in
these cases, and are not specific for BAS in terms of technology and installa-
tion. BAS follows the ever-developing technology in the management level
in the IT field. Therefore the focus in the BAS field is on the development of
wireless networks at automation and field (sensor) levels.
When a large number of wireless sensors need to be networked, several
levels of networking may be combined. For example, an IEEE 802.11 (Wi-Fi)
mesh network comprised of high-end nodes, such as gateway units, can be
overlaid on a ZigBee sensor network to maintain a high level of network
performance. A remote application server can also be used in the field close
to a localized sensor network to manage the network, to collect localized
data, to host web-based applications, and other uses.
Recently in the market, there have been many wireless products applied
in BAS, from ICs, modules, sensors, actuators, thermostats, controllers,
gateways and transparent transmitters by tunnelling method to total sys-
tem solutions. The majority of them are compliant with ZigBee or IEEE
802.15.4.
Wireless technologies, particularly ZigBee, are going to have more impact
in the BAS industry and wireless building automation is going to be among
the practical options. However, they do not yet have a large range of