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Technology Summaries:
Bluetooth™
Bluetooth (Official
Bluetooth Website 2002; Bhagwat 2001; Bluetooth SIG Inc. 2001) is a
royalty-free technology specification for short-range wireless
communication among devices. It uses the 2.4 GHz industrial,
scientific, and medical (ISM) radio band, which is available for
license-free use worldwide (FCC, Part 15, 1998). In the U.S. and
most other countries, this band extends from 2400 MHz to 2483.5 MHz.
The protocol uses a frequency-hopping spread spectrum technique, where the
radio hops through the 79 channels in a pseudo-random sequence at a rate
of 1600 hops per second. This provides excellent immunity to
interference and contributes to security of the transmissions. The
maximum data rate is 781 kbps. The maximum transmission range for a
home environment is 10 meters and for an outside environment can reach 30
meters.
Bluetooth devices
can form small ad hoc nets known as piconets. A piconet consists of
up to eight Bluetooth devices. Communication can be extended to more
devices by interconnecting piconets.
The intended
purpose of Bluetooth is to provide a universal standard for connecting a
broad set of wireless devices. Bluetooth includes definitions for a
set of application-level profiles for 13 applications, which are necessary
to implement user functions. These include among others cordless
telephone, LAN access, FAX, and serial-cable emulation. The latter
is likely to serve building sensor data acquisition in the near-term.
The Bluetooth radio is intended to be a low-cost device, which will become
even lower cost when deployed in billions of units (which is projected
over the next 5 years).
For more
Information please go to
http://www.bluetooth.com.
About Bluetooth™ Trademark
IEEE
802.11b
The IEEE 802.11
(IEEE 1997) is a family of standards for wireless local area networks
(LANs) operating in the 2.4 GHz frequency band. Standard IEEE
802.11b (IEEE 1999) is an extension to 802.11 covering wireless LANs
transmitting at up to 11 Mbps in the 2.4 GHz band.
IEEE 802.11b
devices may connect in ad hoc networks (i.e., networks requiring no base
station) or in infrastructure mode with a fixed access point, which
connects to a stationary LAN. Roaming is provided between multiple
access points. LAN connections are available in some hotels,
airports, restaurants, and other locations. Devices using 802.11b
have a maximum range of about 500 meters outdoors at a data rate of 1
Mbps. Maximum ranges at higher data rates are more typically 100
meters outdoors and about 50 meters indoors.
The data rates
provided by 802.11b far exceed the requirements of most building data
collection needs. As a result, 802.11b-based devices have much
larger bandwidth and greater electrical power consumption than required
for wireless data acquisition. Unless the cost of wireless LAN
systems becomes competitive with alternative wireless communication, they
are unlikely to see use for this purpose.
For more
information please go to
http://grouper.ieee.org/groups/802/11/.
Wireless
Serial Communication
Wireless data
acquisition for industrial and agricultural applications is currently
provided primarily with serial communication. Communication is at much
lower bandwidth than wireless LAN systems but is generally sufficient for
data collection from most sensors. Data rates range up to 115.3 kbps,
although most wireless serial units operate at 19.2 kbps and lower. A
number of different license-free bands are used (some having greater
limitations than others), including 300 MHz, 433 MHz, 900 MHz, and 2.4
GHz. Maximum transmission distances vary from about 100 feet to many miles
(Fern and Tietsworth 1999). Generally, lower bandwidth and less
sophisticated modulation schemes are used to lower costs when compatible
with the installation environment and data transfer needs. In many cases,
a sensor may need to be polled only once every several minutes, with each
transmission requiring only a few bits; therefore significant cost
reductions can be achieved by matching the wireless technology used with
the specific application.
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