central controller for up to seven other
devices who can now exchange data.
Forthcoming versions of Bluetooth
may also use a form of ultra wideband
(UWB). More about that later.
Wi-Fi means wireless fidelity. It is
the trade name of a wireless local
area networking (WLAN) technology
that has been standardized by the
IEEE as 802.11. There are several versions with different frequency bands
and data rates. The 802.11b version is
the oldest and most common. It operates using direct sequence spread
spectrum in the 2.4 GHz unlicensed
band, as well with a data rate up to 11
Mb/s at a range up to 100 meters.
The 802.11g version is the most
recent. It is backwards compatible with
802.11b. It too operates in the 2.4 GHz
band but the data rate is up to 54
Mb/s. This version uses orthogonal frequency division multiplexing (OFDM).
Another 54 Mb/s version using OFDM
is 802.11a. This version operates in the
5 GHz unlicensed band. There is far
less interference up there than in the
2.4 GHz band but the range is shorter,
only about 30 to 50 meters.
A newer version is under development. Called 802.11n, it promises
data rates from 100 to 600 Mb/s up to
100 meters. It too uses OFDM but also
a new technology called multiple
input multiple output (MIMO) with
two to four antennas and transceivers
that operate in parallel. It won’t be
officially available until late this year
or 2007. Some standard “pre-n”
versions are available now, but most
will wait on the formal standard that
will ensure interoperabilty.
Wi-Fi is used in companies to
form wireless extensions to their wired
Ethernet networks. A wireless access
point is set up to talk to PCs and
laptops containing a Wi-Fi transceiver
interface. No other Ethernet wiring is
needed making the process of moving
a PC fast and easy. It also allows you to
take your laptop into the conference
room, cafeteria, or someone else’s
office and still maintain a link.
Wi-Fi is also the most popular
form of wireless home network. With
no wiring to worry about, home
owners can set up a simple network so
that multiple computers can share a
fast cable TV or DSL broadband connection, a printer, or other common
device. But the most popular application is Internet access and email with a
laptop through hot spots — those
popular public access points in hotels,
airports, coffee shops, and elsewhere.
Some cities — notably Philadelphia —
are setting up total wireless coverage
around the town so that anyone can
access the Internet from any place.
Wi-Fi has been around a few years
now and is a highly developed technology. It is also used to form mesh networks to provide broadband access to
areas where no cable TV or DSL broadband connections are available. And it
is beginning to show up in consumer
devices like digital cameras and TV sets.
ZigBee is a short-range wireless
technology designed for monitoring
and control operations in commercial
buildings, home automation systems,
and industrial manufacturing or process
control settings. It is an IEEE standard
802.15.4 and a supplementary standard
developed by the ZigBee Alliance which
also does product testing and certification for interoperability.
There are several versions, but the
most widespread is one that operates in
the 2.4 GHz unlicensed band. It has a
maximum data rate of 250 kbps using
offset QPSK modulation. A 868 MHz version at 20 kbps is available for European
use and a 915 MHz version at 40 kbps for
US and other areas. While the data rate
is slow, it is more than sufficient for
basic monitor and control operations.
The transmission range is short —
usually less than 10 meters — but with
appropriate antennas, the range can be
extended to several hundred meters.
The most common application is
remote sensor readings. It can transmit digitized sensor info from temperature, pressure, flow, light, and other
sensors to a central monitoring point.
It can also send control signals to
devices to be operated such as turning
lights, motors, relays, valves, or solenoids off or on. In many cases, a wire-
less link is actually cheaper than a
wired link simply because of the high
cost of installing wiring these days.
ZigBee’s big claim to fame is the
ability to automatically form mesh networks. In a mesh network, each transceiver can send or receive data but also
act as a repeater to pick up and retransmit data from another source. With
such an arrangement, one transceiver
can link up with any nearby transceiver
and transmit its information over
longer distances by simply routing it
through other transceivers closer to the
destination. Mesh networks are more
reliable because if one transceiver fails,
the message can still get through the
network via an alternative path.
ZigBee is still new but look for first
products sometime this year. They will
show up in commercial and industrial
applications such as lighting, HVAC
monitoring and control, automatic
meter reading, and security systems.
You will see units available for home
use later this year and early next year.
ULTRA WIDEBAND (UWB)
UWB is the technology that
spreads the signal over a very wide
bandwidth at very low power. It was
originally developed for secure military communications and radar. But it
is now used for high speed data transmissions. Original versions used very
short pulses representing the data to
create a radio signal with a huge
bandwidth usually over 500 MHz
wide. Obviously, lots of spectrum
space is needed. In the US, the FCC
has allocated 3.1 to 10. 6 GHz for UWB.
Efforts to create an IEEE standard
have failed, but one version of UWB
has emerged as the winner in the standards battle. This version uses OFDM.
It transmits over 128 bands inside one
of three blocks that are each 528 MHz
wide. With such an arrangement, data
rates from 100 Mbps to 1 Gbps are
possible. The range is very short, however. Maximum range is very short,
typically only 10 meters and that is at
the lower 100 Mbps data rate. At a rate
of 500 Mbps to 1 Gbps, the range is
only a couple meters. The companies
belonging to the Wimedia Alliance
have agreed on this as a standard and
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