a signal. Such is the case with Wi-Fi. A few of the attributes and elements of
Wi-Fi radios are as follows:
Transceiver: The ability to both transmit and receive as well as the abil-
ity to set and determine the circumstances under which each task is to
be performed.
Antenna: As with a CB radio, the antenna must be capable of both receiv-
ing and transmitting a signal in a specific bandwidth. Most antennas are
integrated into wireless cards, but in some cases, it's possible to add an
external antenna. (I talk more about antennas in Chapters 3 and 4.)
Code/Decode: Known as a codec, this is the method by which (among
other things) digital data is converted into a radio signal and vice versa.
Spread-spectrum signal: High-frequency radio signals used by Wi-Fi are
both low-powered and susceptible to interference. Wide-band, spread-
spectrum radio signals aren't as sensitive to interference as narrow-band
signals -- and they're quite efficient at getting the most out of the lim-
ited power. They also help in avoiding traffic jams among radio signals,
which makes it possible for several Wi-Fi transceivers to operate at the
same time.
Chapter 1: Taking the Wi-Fi Highway
What have an actress and composer
got to do with Wi-Fi?
For all of you who believe the abilities of enter-
tainers begin and end with their musical or
acting talents, read this: Just prior to the Amer-
ican entry into World War II, George Antheil,
an American composer, and Hedy Kiesler
Markey -- better known by her stage name,
Hedy Lamarr -- got into a discussion over
dinner regarding torpedo guidance. Seems like
standard entertainer table talk. Ms. Lamarr,
who'd been married to an Austrian arms mer-
chant, was interested in the problems sur-
rounding torpedo guidance, and Mr. Antheil
understood multichannel synchronization (It's
a long story, involving propellers and player
pianos). Together they developed -- and in
August 1942 were granted a patent for --
what they called a "Secret Communication
System." They hoped the SCS would eliminate,
through the use of "frequency hopping," the
possibility that the enemy might jam torpedo
radio-guidance systems.
Frequency-hopping technology, which couldn't
be used until radio technology caught up to
it in the early '60s, formed the foundation for the
spread-spectrum radio transmissions that all
the Wi-Fi standards use. The first 802.11 stan-
dard employed frequency-hopping spread spec-
trum (FHSS), and the 802.11b standard uses
direct-sequence spread spectrum (DSSS).
Building on these concepts, orthogonal
frequency-division multiplexing (OFDM), on
which the 802.11g standard is based, was devel-
oped and implemented. (Try saying
that five
times fast.)
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