The changes in wireless technology for data networks over the
past five years have been more dramatic than the changes in
radio itself in the century since Guglielmo Marconi sent the
first telegraph signal across the Atlantic from Cornwall in the
U.K. to St. Johns, Newfoundland, on December 12, 1901. The
progress in commercial radio transmission from telegraphy to
voice to television was measured in decades. Commercial digital
wireless transmission began in the mid-1990s when cellular
digital telephony-known as PCS for Personal Communications
Service-replaced advanced mobile phone service
(AMPS), the then dominant analog voice transmission protocol.
Digital wireless telephony technology was then split into
two competing technologies: time division multiple access
(TDMA) and code division multiple access (CDMA). TDMA is
still used by AT&T but is being phased out in favor of global
system mobile (GSM), a standard version of TDMA used by
most European and Asian carriers as well as by T-Mobile and
AT&T. CDMA is used by some Japanese carriers as well as by
Sprint and Verizon. TDMA, GSM, and CDMA are not interoperable.

The wireless local area network (LAN) began to emerge in the
late 1990s, when it became obvious that there was a need for
wireless data networking. Wireless LANs required faster data
transmission than was possible with cellular PCS (of any technology),
and eventually industry settled upon using digital
spread spectrum as defined by the IEEE 802.11 standards.
Spread spectrum was originally developed for the U.S. military
so wireless transmissions could be made in the presence of
strong jamming signals. This work by the military was based
on the spread spectrum patent US 2,292,387, which had origi-
nally been granted to Hollywood actress Hedy Lamarr and her
partner George Antheil.

Frequency hopping spread spectrum (FHSS) and direct
sequence spread spectrum (DSSS), both operating up to 2.0
Mbps, were the first two IEEE 802.11 technologies. Neither is
commercially available today. These initial technologies were
improved upon until, in rapid succession, IEEE 802.11b (operating
at up to 11 Mbps) and 802.11a and 802.11g (both operating
up to 54 Mbps) emerged. All of these are called Wi-Fi
(wireless fidelity) after the name of the supporting industry
association, the Wi-Fi Alliance, but 802.11b has become a commercially
successful technology with a large installed base.
Both 802.11a and 802.11g are rapidly penetrating the market,
essentially displacing 802.11b. For the sake of simplicity, I will
continue using 802.11a, 802.11b, and 802.11g to designate each
of the IEEE 802 standards, but the marketplace calls these technologies
Wireless-A, Wireless-B, and Wireless-G, respectively.