Wi-Fi Systems

Wi-Fi based-systems may be used to provide broadband wireless. Wi-Fi is
based on the research 802.11 family of standards and is primarily a local area networking (LAN)
technology designed to provide in-building broadband coverage. Current Wi-Fi systems based
on research 802.11a/g support a peak physical-layer data rate of 54Mbps3 and typically provide
indoor coverage over a distance of 100 feet. Wi-Fi has become the defacto standard for “last
feet” broadband connectivity in homes, offices, and public hotspot locations. In the past couple
of years, a number of municipalities and local communities around the world have taken the initiative
to get Wi-Fi systems deployed in outdoor settings to provide broadband access to city
centers and metrozones as well as to rural and underserved areas. It is this application of Wi-Fi
that overlaps with the fixed and nomadic application space of WiMAX.
Metro-area Wi-Fi deployments rely on higher power transmitters that are deployed on lampposts
or building tops and radiating at or close to the maximum allowable power limits for operating
in the license-exempt band. Even with high power transmitters, Wi-Fi systems can typically
provide a coverage range of only about 1,000 feet from the access point. Consequently, metro-
Wi-Fi applications require dense deployment of access points, which makes it impractical for
large-scale ubiquitous deployment. Nevertheless, they could be deployed to provide broadband
access to hotzones within a city or community. Wi-Fi offers remarkably higher peak data rates
than do 3G systems, primarily since it operates over a larger 20MHz bandwidth. The inefficient
CSMA (carrier sense multiple access) protocol used by Wi-Fi, along with the interference constraints
of operating in the license-exempt band, is likely to significantly reduce the capacity of
outdoor Wi-Fi systems. Further, Wi-Fi systems are not designed to support high-speed mobility.
One significant advantage of Wi-Fi over WiMAX and 3G is the wide availability of terminal
devices. A vast majority of laptops shipped today have a built-in Wi-Fi interface. Wi-Fi interfaces
are now also being built into a variety of devices, including personal data assistants (PDAs), cordless
phones, cellular phones, cameras, and media players. The large embedded base of terminals
makes it easy for consumers to use the services of broadband networks built using Wi-Fi. As with
3G, the capabilities of Wi-Fi are being enhanced to support even higher data rates and to provide
better QoS support. In particular, using multiple-antenna spatial multiplexing technology, the
emerging research 802.11n standard will support a peak layer 2 throughput of at least 100Mbps.
research 802.11n is also expected to provide significant range improvements through the use of
transmit diversity and other advanced techniques.