WiMAX (World Interoperability for Microwave Access, Inc.), based on the IEEE 802.16 standard, is expected to enable true broadband speeds over wireless networks at a cost point to enable mass market adoption. WiMAX is the only wireless standard today that has the ability to deliver true broadband speeds and help make the vision of pervasive connectivity a reality.
WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to wired broadband like cable and DSL. WiMAX provides fixed , nomadic, portable and, soon, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station. In a typical cell radius deployment of three to ten kilometers, WiMAX Forum Certified™ systems can be expected to deliver capacity of up to 40 Mbps per channel, for fixed and portable access applications. This is enough bandwidth to simultaneously support hundreds of businesses with T-1 speed connectivity and thousands of residences with DSL speed connectivity. Mobile network deployments are expected to provide up to 15 Mbps of capacity within a typical cell radius deployment of up to three kilometers. It is expected that WiMAX technology will be incorporated in notebook computers and PDAs by 2007, allowing for urban areas and cities to become “metro zones” for portable outdoor broadband wireless access.

Technical overview
WiMAX is a term coined to describe standard, interoperable implementations of IEEE 802.16 wireless networks, in a rather similar way to Wi-Fi being interoperable implementations of the IEEE 802.11 Wireless LAN standard. However, WiMAX is very different from Wi-Fi in the way it works.In Wi-Fi, the media access controller (”MAC”) uses contention access — all subscriber stations that wish to pass data through a wireless access point (”AP”) are competing for the AP’s attention on a random interrupt basis. This can cause distant nodes from the AP to be repeatedly interrupted by closer nodes, greatly reducing their throughput. This makes services such as Voice over IP (VoIP) or IPTV, which depend on a predetermined type of “quality of service” (QoS), difficult to maintain for large numbers of users.

In contrast, the 802.16 MAC uses a scheduling algorithm, where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and contract, but it remains assigned to the subscriber station, meaning that other subscribers cannot use it. This scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It can also be more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service parameters by balancing the time-slot assignments among the application needs of the subscriber stations.

The original WiMAX standard (IEEE 802.16) specified WiMAX in the 10 to 66 GHz range. 802.16a, updated in 2004 to 802.16-2004 (also known as 802.16d), added support for the 2 to 11 GHz range. 802.16d was updated to 802.16e in 2005. 802.16e uses scalable orthogonal frequency-division multiplexing (OFDM) as opposed to the non-scalable version in .16d. This brings potential benefits in terms of coverage, self installation, power consumption, frequency re-use and bandwidth efficiency. .16e also adds a capability for full mobility support.

Most interest will probably be in the 802.16d and .16e standards, since the lower frequencies suffer less from signal attenuation and therefore give improved range and in-building penetration.
The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and range and stronger encryption. It provides connectivity between network endpoints without need for direct line of sight in favourable circumstances. The non-line-of-sight propagation (NLOS) performance requires the .16d or .16e variants, since the lower frequencies are needed. It relies upon clever use of multi-path signals.

Uses for WiMAX
A commonly held misconception is that WiMAX will deliver 70 Mbit/s, over 70 miles. Each of these may be true individually, given ideal circumstances, but they are not simultaneously true. WiMAX has some similarities to DSL in this respect, where one can either have high bandwidth or long reach, but not both simultaneously. The other feature to consider with WiMAX is that the bandwidth is shared between users in a given radio sector, so if there are many active users in a single sector, each will get reduced bandwidth.

The bandwidth and reach of WiMAX make it suitable for the following potential applications:
Connecting Wi-Fi hotspots with each other and to other parts of the Internet
Providing a wireless alternative to cable and DSL for last mile (last km) broadband access.
Providing high-speed mobile data and telecommunications services (4G)
Broadband Access
Many cable and traditional telephone companies are closely examining or actively trialling the potential of WiMAX for “last mile” connectivity. This could result in better price-points for both home and business customers as based on the benefits of competition. In areas without pre-existing physical cable or telephone networks, WiMAX could allow broadband access that has hitherto been unavailable. Home units the size of a paperback book that provide both phone and network connection points are already available and easy to install.
http://www.wimax.com
http://www.wimaxforum.org/home/