Information Technology Reference
In-Depth Information
the encoding of the data will allow the recovery of the information. This is very
much the case with pure noise interference. At any given time, a noise pulse may be
present on a particular discrete frequency, but it is unlikely that it will reoccur on
subsequent hops to that frequency.
Ideally, the operation of the wireless NIC would be such that if the circuitry
determines that a particular frequency is unavailable, because of a constant interfer-
ing signal, the frequency could simply be avoided, thus lowering the data through-
put. Unfortunately, regulations governing spread spectrum do not allow this
adaptive interference-avoidance, although some of the WLAN technologies handle
it better than others.
Interference and distance can limit the ability of a WLAN signal to reach the
higher data rates. Fortunately, standard operating procedure allows for graceful fall-
back of the operating data rate to allow for these conditions. In addition, some wire-
less manufacturers offer advanced signal processing techniques to reduce the
degradation caused by multipath interference, and one of the techniques, OFDM, is
inherently less susceptible.
Several WLAN standards are in current use. Each wireless standard has been devel-
oped to provide certain applications with the level of connectivity required. All of
these standards are evolving, and are changing as new technologies and applications
are developed.
IEEE 802.11 Standard Operation
The IEEE 802.11 committee was formed to implement standards for operating
Ethernet networks over wireless connections. The standard, as usual, embraces sev-
eral competing modes of operation, while lending interoperability and order to
future developments. The Wireless LAN Interoperability Forum and the IEEE both
participate in bringing forth operating and protocol standards for this service. IEEE
802.11 networks operate at 1 to 108 Mbps nominal data rates.
IEEE 802.11 is also often referred to as WiFi, an acronym for wireless fidelity.
The WiFi name has become so universally recognized that the originator of the term,
the Wireless Ethernet Compatibility Alliance (WECA), changed its name to the Wi-
Fi Alliance. The Wi-Fi Alliance offers the WiFi certification to manufacturers to
ensure compatibility and interoperability.
The 11 Mbps rate (with a new 5.5 Mbps fall-back) was added in the IEEE
802.11b supplement. It is roughly comparable in speed to the wired Ethernet at
