Low-PowerWireless Sensor Network Platforms - Signal Processing Systems - page 380

root of the tree in the tree topology, and can be located anywhere in the peer-to-peer
topology. ZigBee defines a wide range of application profiles targeted at home and
building automation, remote controls, and health care.
WirelessHART and ISA100.11a [ 20 ] are targeted at process industry applications
where process measurement and control applications have stringent requirements
for end-to-end communication delay, reliability, and security. The standards have
similar operating principle and the convergence of the standards is planned in
ISA100.12. Both standards build on top of the IEEE 802.15.4 physical layer and
utilize a TDMA MAC that employs network wide time synchronization, channel
hopping, channel blacklisting. A centralized network manager is responsible for
route updates and communication scheduling for entire network. However, as the
centralized control of TDMA schedules limits the network size and the tolerance
against network dynamics, the usability of the standards in WSNs is limited to static
networks.
Z-Wave is targeted for the control of building automation and entertainment
electronics. It has been developed by over 120 companies including Zensys, Intel
and Cisco. Supported network topologies are star and mesh. The maximum number
of nodes in a network is 232, although Z-wave networks can be inter-connected via
gateways.
Bluetooth Low Energy is an extension to the Bluetooth technology and is aimed
at low energy wireless devices. The first defined applications comprise watch,
Human Interface Device (HID), and sensor profiles. Compared to the traditional
Bluetooth, the main functional differences are the use of variable packet length,
entering power save mode automatically when a device is not transmitting, and the
exchange data in attribute/value pairs.
ANT developed by Dynastream Innovations is based on a star-topology, but more
complex topologies can be achieved by using several channels: each node can be
simultaneously a master and a slave on different channels. Master nodes always
receive, while slaves transmit when new data is provided. A practical limit for
network size is few thousands nodes. ANT+ is an extension to the ANT protocol
that includes profiles for data formats and channel parameters. The disadvantages
of ANT are high power consumption in master nodes and low scalability due to
random access transmissions.
DASH7 is based on ISO 18000-7 standard and is targeted at low data rate appli-
cations. Its main cited benefit stems from the 433 MHz operating frequency, which
provides longer communication ranges and less crowded wireless channel than the
typical 2.4 GHz frequency band [ 36 ] . DASH7 has the nominal communication range
of 250 m at 0 dBm transmission power level, compared to 75 m of ZigBee and 10 m
of Bluetooth (High Rate variant) [ 36 ] .
IEEE 1902.1 (RuBee) fills the gap between WSN and Radio Frequency IDen-
tification (RFID) technologies. It uses magnetic dipole antennas instead of electric
field signals. Thus, the signal is unaffected by water, while metals either enhance or
do not affect the signal. The small 1.2 kbps nominal data rate limits the applicability
of RuBee.