WiMAX, an acronym that stands for Worldwide Interoperability for Microwave Access
, is a certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards. IEEE 802.16 is working group number 16 of IEEE 802, specialising in point-to-multipoint broadband wireless access.
The WiMAX protocol is a way of networking computers together; for example to provide internet access, in a similar way to Wi-Fi.
WiMAX is both faster and has a longer range than Wi-Fi. However, WiMAX does not necessarily conflict with Wi-Fi, but is designed to interoperate with it and may indeed complement it. This complementarity to Wi-Fi also extends to all flavors of wired ethernet (IEEE 802.3), token ring (IEEE 802.5) and non-IEEE standards that use the same LLC including FDDI and cable modem (DOCSIS).
Early products are likely to be aimed at network service providers and businesses, not consumers. It has the potential to enable millions more to access the Internet wirelessly, cheaply and easily. Proponents say that WiMAX wireless coverage will be measured in square kilometers while that of Wi-Fi is measured in square meters. According to WiMAX promoters, a WiMAX base station would beam high-speed Internet connections to homes and businesses in a radius of up to 50 km (31 miles); these base stations will eventually cover an entire metropolitan area, making that area into a WMAN and allowing true wireless mobility within it, as opposed to hot-spot hopping required by Wi-Fi. Its proponents are hoping that the technology will eventually be used in notebook computers and PDAs. True roaming cell-like wireless broadband, however, is IEEE standard 802.20, which is compatible with WiMAX.
It should be duly noted that claims of 50 km (31 mile) range, especially claims that such distances can be achieved without line of sight, represent, at best, a theoretical maximum under ideal circumstances. The technical merit of these claims has yet to be tested in the real world.
WiMAX standard relies mainly on spectrum in the 2 to 11 GHz range. The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and stronger encryption. It also aims to provide connectivity to network endpoints without direct line of sight in some circumstances. The details of performance under non line of sight circumstances, however, are unclear, as they have yet to be demonstrated.
Note: A very rudimentary non-scientific test was done in Michigan on mostly flat land with 30% tree coverage. It suggests that distances of roughly 15 km can be achieved without line of sight. This, of course, can vary greatly depending on the land and weather.
Because IEEE 802.16 networks use the same Logical Link Controller (standardized by IEEE 802.2) as other LANs and WANs, it can be both bridged and routed to them.
WiMAX is a wireless metropolitan area network (MAN) technology that can connect IEEE 802.11(Wi-Fi) hotspots to the Internet and provide a wireless extension to cable and DSL for last mile (last km) broadband access. IEEE 802.16 provides up to 50 km (31 miles) of linear service area range and allows users connectivity without a direct line of sight to a base station. Note that this should not be taken to mean that users 50 km (31 miles) away without line of sight will have connectivity. The technology also provides shared data rates up to 70 Mbit/s, which, according to WiMAX proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and well over a thousand homes at 1Mbit/s DSL-level connectivity.
An important aspect of the IEEE 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings.
The MAC is significantly different from that of Wi-Fi (and ethernet from which Wi-Fi is derived). In Wi-Fi, the ethernet uses contention access -- all subscriber stations wishing to pass data through an access point are competing for the AP's attention on a random basis. This can cause distant nodes from the AP to be repeatedly interrupted by less sensitive, closer nodes, greatly reducing their throughput. By contrast, the 802.16 MAC is a scheduling MAC 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 constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and oversubscription (unlike 802.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations.
Products are expected to be announced second quarter of 2005. As of 2004, major cities such as Los Angeles, New York, Boston, Providence (Rhode Island), and Seattle in the U.S., as well as Dalian and Chengdu in China are already implementing pre-WiMAX networks that should be upgradable when certification testing begins in July 2005.
Beyond these metro area rollouts, WiMAX is like Wi-Fi in that you can "roll your own". Several vendors have some form of product now (2004), usually in a pre-standards-compliance stage so multivendor interoperability within a single network segment can't be reasonably expected. Several companies are planning rollouts of compliant chipsets in FPGAs in 2005 and ASICs the following year which will shrink the digital electronics suitable for PCMCIA type of form factors. Along with the physical shrinkage, we can reasonably expect some price shrinkage as economies of scale and amortization on non-recurrent engineering costs take place.
The current 802.16 standard is IEEE Std 802.16-2004, approved (http://www.ieee802.org/16/arc/802-16list2/msg01651.html
) in June 2004. It renders the previous (and 1st) version 802.16-2001 obsolete, along with its amendments 802.16a and 802.16c.
IEEE Std 802.16-2004 addresses only fixed systems. An amendment 802.16e is in the works which adds mobility components to the standard. This amendment is expected to be completed in mid 2005.
) IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems
) IEEE Recommended Practice for Local and metropolitan area networks -- Coexistence of Fixed Broadband Wireless Access Systems
802.16-2001 obsoleted by 802.16-2004
802.16a amendment, obsoleted by 802.16-2004
802.16c amendment, obsoleted by 802.16-2004
802.16e In progress. Adds mobility to the standard
The current IEEE 802.16 standards can be freely downloaded from the "Get IEEE 802"(tm) page http://standards.ieee.org/getieee802/802.16.html
Unlike earlier broadband wireless access (BWA) iterations WiMAX is highly standardized which should reduce costs. However, since Chipsets are custom-built for each broadband wireless access manufacturer, this adds time and cost to the process of bringing a product to market, and this won't be changed by WiMAX.
WiMAX's equivalent or competitor in Europe is HIPERMAN
. WiMAX Forum, the consortium behind the standardization, is working on methods to make 802.16 and HIPERMAN interoperate seamlessly. Products developed by the WiMAX Forum members need to comply to pass the certification process. The home page of WiMAX Forum is http://www.wimaxforum.org/home
Korea's telecoms industry has developed its own standard, WiBro. In late 2004, Intel and LG Electronics have agreed on interoperability between WiBro and WiMAX.