Thursday, March 17, 2005

WiMAX - IEEE 802.16

IEEE 802.16 is working group number 16 of IEEE 802, specialising in point-to-multipoint broadband wireless access. It also is known as WiMAX, an acronym that stands for Worldwide Interoperability for Microwave Access.

The current 802.16 standard is 802.16d-2004, which was approved late 2004. It obsoletes the previous (and first) version 802.16-2001, and its amendments 802.16a and 802.16c. The 802.16d standard only addresses 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.

Similar technologies
What differentiates WiMAX from earlier broadband wireless access (BWA) iterations is standardization. Chipsets are currently custom-built for each broadband wireless access vendor, adding time and cost to the process.

Its 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.

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.

Technical advantages
WiMAX does not conflict with WiFi but complements it. 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. So the comment about complementarity to WiFi also includes all flavors of wired ethernet (802.3), token ring (802.5) and non-IEEE standards that use the same LLC including FDDI and cable modem (DOCSIS).

WiMAX is a wireless metropolitan area network (MAN) technology that will connect IEEE 802.11(WiFi) 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 than in WiFi (and ethernet from which WiFi is derived). In WiFi, 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. 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 803.11). 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.

What is important for business using this technology is to ensure that it is managed correctly.

WiMAX is referred to as "WiFi on steroids". It has the potential to enable even more millions to access the Internet wirelessly, cheaply and easily. Proponents say that WiMAX wireless coverage will be measured in square kilometers/miles while that of WiFi is measured in square meters/yards. 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 WiFi. The 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, respresents, at best, a theoretical maximum under ideal circumstances. The technical merit of this claim has yet to be tested in the real world. No test has demonstrated the technical or practical feasibility of this number.

WiMAX standard relies mainly on spectrum in the 2 to 11 GHz range. The WiMAX specification improves upon many of the limitations of the WiFi 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.

Product release
Products are expected to be announced second quarter of 2005. As of 2004, major cities such as Los Angeles , New York , Boston , Providence RI, Seattle in the U.S.,and Dalian and Chengdu in China are already implementing WiMax.

Beyond the metro area rollouts (prev paragraph), WiMax is like WiFi in that you can 'roll your own'. Several vendors have some form of product now (2004), usually in a pre-standards-compliance stage so you can't reasonably expect multivendor interoperability within a single network segment. 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.


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