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WiMax is  more robust standard for high-speed broadband wireless delivery to laptops and desktops has been launched.

"WiMAX" is an acronym that stands for Worldwide Interoperability for Microwave Access.

It is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL. WiMAX will provide fixed , nomadic, portable and, eventually, 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.

Since equipment being developed by WiMAX Forum members can operate in different configurations (e.g. TDD or FDD), have different channel bandwidths or operate in different spectrum bands, discussion are ongoing in CWG, as well as in other working groups, regarding profiles that the Forum would use for WiMAX Forum Certification. The main focus is on three bands – 5.8GHz, 3.5GHz and 2.5GHz.

The first generation of WiMAX Forum Certified CPEs is expected to be outdoor-installable subscriber stations akin to a small satellite dish. These are expected to be available in late 2005/early 2006 and priced around $350 in volume. The second generation of CPEs will be indoor self-installable modems similar to a cable or DSL modem and will be priced around $250 in volume and are expected to be available in 2006. Third-generation CPEs will be integrated into laptops and other portable devices, are expected to initially cost approximately $100 and will be available in the 2006-2007 timeframe

One of the main objectives of the WiMAX Forum is to create a single interoperable standard from the IEEE 802.16 and ETSI HiperMAN standards. This is achieved by the creation of System Profiles. Based upon what the WiMAX Forum sees in terms of service provider and vendor equipment plans, the WiMAX Forum has decided to focus first on profiles for the 256 OFDM PHY mode of the 802.16-2004 standard, which was ratified by the IEEE in June 2004. This physical layer (PHY) will be combined with a single media access controller (MAC), ensuring a uniform base for all WiMAX implementations.

Compliance with the 802.16 standard does not mean equipment is WiMAX Forum Certified or that it is interoperable with other vendors’ equipment. However, if a piece of equipment has earned the WiMAX Forum Certified designation, it is both compliant with the 802.16 standard and interoperable with other vendors’ equipment that is also WiMAX Forum Certified.

The position of the 802.16a standard today parallels that of WLAN technology in the late 1990 s, when the market finally grew as 802.11 price vs. performance gains converted WLAN from a niche to mass  market. In the very near future, 802.16a will also achieve important price and performance points.
 

The WiMAX Forum™ is working to facilitate the deployment of broadband wireless networks based on the IEEE 802.16 standard by helping to ensure the compatibility and inter-operability of broadband wireless access equipment. The organization is a nonprofit association formed in June of 2001by equipment and component suppliers to promote the adoption of IEEE 802.16 compliant equipment by operators of broadband wireless access systems.

The WiMAX Forum is comprised of industry leaders who are committed to the open interoperability of all products used for broadband wireless access.

• Support IEEE 802.16 standard
• Propose and promote access profiles for their IEEE 802.16 standard
• Certify interoperability levels both in network and the cell
• Achieve global acceptance
• Promote use of broadband wireless access overall

Under the current conditions, 802.16a could emulate 802.11 s rise several years from now.

Many chip and equipment vendors ignored the chance to get into the 802.11 market early and create market share due to market-size limitations created by high equipment costs, a much smaller potential audience and no need for all things Internet and Intranet yet. WiMAX offers these technology companies a fresh start.

802.16a is considered the next step beyond WiFi because it is optimized for broadband operation, fixed and later mobile, in the wide area network. It already includes numerous advances that are slated for introduction into the 802.11 standard, such as quality of service, enhanced security, higher data rates, and mesh and smart antenna technology allowing better utilization of the spectrum.

The study, 802.16/WiMAX Technologies: World Market Forecasts 2003-2008, finds WiMAX and WiFi complementary as the two technologies address different segments of the market and are optimized for different tasks; local vs. metropolitan area networking. Last mile access will be the first application for 802.16a but mobility will follow via 802.16e.

WiMAX is considered a migration path to 4G, but more likely to be used
by holders of BWA spectrum rather than mobile carriers. 802.16a is also  expected to play a role in outdoor and private networks, the extension
of hot spots, and backhaul applications that lack line-of -sight.

The opportunity for 802.16a equipment is forecast to reach a value of approximately $1 billion in 2008, the study finds, with growth accelerating late in the period. The study provides global forecasts for
802.16a/e equipment and chipset shipments and revenues as well as the  technology s penetration in the overall global BWA market.
 

Wimax Technical Specification:
The IEEE 802.16 Air Interface Standard is truly a state-of-the-art specification for fixed broadband wireless access systems employing a point-to-multipoint (PMP) architecture. The initial version was developed with the goal of meeting the requirements of a vast array of deployment scenarios for BWA systems operating between 10 and 66 GHz. As a result, only a subset of the functionality is needed for typical deployments directed at specific markets. A revision to the base IEEE 802.16 standard targeting sub 11 GHz is near completion with a publishing target date of July 2004. This revision will include the amendments from Task Group c, Task Group a, and Task Group d.

The IEEE process stops short of providing conformance standards and test specifications. In order to ensure interoperability between vendors equipment, the WiMAX technical working groups have completed the work for 10 to 66 GHz and has started work for the sub 11 GHz part of the standard. The working groups develop a set of system profiles, Protocol Implementation Conformance Statement Proforma, Test Suite Structure & Test Purposes, and Abstract Test Suite specifications for 10 to 66 GHz and sub 11 GHz, all according to the ISO/IEC 9464 series (equivalent to ITU-T x.290 series) of conformance testing standards.

Overview of IEEE 802.16

The IEEE 802.16 Working Group has developed point-to-multipoint broadband wireless access standard for systems in the frequency ranges 10-66 GHz and sub 11 GHz. The standard covers both the Media Access Control (MAC) and the physical (PHY) layers.

A number of PHY considerations were taken into account for the target environment. At higher frequencies, line of sight is a must. This requirement eases the effect of multipath, allowing for wide channels, typically greater than 10 MHz in bandwidth. This gives IEEE 802.16 the ability to provide very high capacity links on both the uplink and the downlink. For sub 11 GHz non line of sight capability is a requirement. The original IEEE 802.16 MAC was enhanced to accommodate different PHYs and services, which address the needs of different environments. The standard is designed to accommodate either Time Division Duplexing (TDD) or Frequency Division Duplexing (FDD) deployments, allowing for both full and half-duplex terminals in the FDD case.

The MAC was designed specifically for the PMP wireless access environment. It supports higher layer or transport protocols such as ATM, Ethernet or Internet Protocol (IP), and is designed to easily accommodate future protocols that have not yet been developed. The MAC is designed for very high bit rates (up to 268 mbps each way) of the truly broadband physical layer, while delivering ATM compatible Quality of Service (QoS); UGS, rtPS, nrtPS, and Best Effort.

The frame structure allows terminals to be dynamically assigned uplink and downlink burst profiles according to their link conditions. This allows a trade-off between capacity and robustness in real-time, and provides roughly a two times increase in capacity on average when compared to non-adaptive systems, while maintaining appropriate link availability.

The 802.16 MAC uses a variable length Protocol Data Unit (PDU) along with a number of other concepts that greatly increase the efficiency of the standard. Multiple MAC PDUs may be concatenated into a single burst to save PHY overhead. Additionally, multiple Service Data Units (SDU) for the same service may be concatenated into a single MAC PDU, saving on MAC header overhead. Fragmentation allows very large SDUs to be sent across frame boundaries to guarantee the QoS of competing services. And, payload header suppression can be used to reduce the overhead caused by the redundant portions of SDU headers.

The MAC uses a self-correcting bandwidth request/grant scheme that eliminates the overhead and delay of acknowledgements, while simultaneously allowing better QoS handling than traditional acknowledged schemes. Terminals have a variety of options available to them for requesting bandwidth depending upon the QoS and traffic parameters of their services. They can be polled individually or in groups. They can steal bandwidth already allocated to make requests for more. They can signal the need to be polled, and they can piggyback requests for bandwidth.

The Interoperability Challenge

Plethora of Options
From the preceding overview, it is clear that the IEEE 802.16 Air Interface Specification is a very capable, while complex, specification. There are allowances for a number of physical layers for different frequency bands and region-by-region frequency regulatory rules. There are features that allow an IP centric system or an ATM centric system depending upon the needs of customers. The specification is designed to cover application to diverse markets from very high bandwidth businesses to SOHO and residential users.

Because of the wealth of options available, an implementer currently faces a tough decision. To address this issue WiMAX undertaken the development of System Profiles.

The purpose of these system profiles is to specify which features are mandatory or optional for the various MAC or PHY scenarios that are most likely to arise in the deployment of real systems. This allows vendors addressing the same market to build systems for that market that are interoperable while not requiring the implementation of absolutely every feature.

No Test Specifications
Another issue facing IEEE 802.16 developers is an artifact of the IEEE standards process concentrating primarily on requirements. The output of the IEEE 802.16 working group is a standard, that is to say, a requirement specification. The working group will continue to expand the standard to cover additional markets, through amendments and revisions to the base standard. In the past, there was no work item in IEEE 802.16 to address the creation of test specifications. Test specifications are necessary to:

• Ensure that equipment and systems claiming compliance to the standard or a profile have been sufficiently tested to demonstrate that compliance.
• Guarantee that equipment from multiple vendors has been tested the same way, to the same interpretation of the standard, increasing the interoperability of the equipment.
• Enable independent conformance testing, giving further credibility to the previous two items.

This test specification initiative is an area where ETSI has an official process and is typically more complete than the IEEE process. ETSI follows the guidelines of the ISO/IEC 9646 series (ITU-T X.29x series). The Test Suite Structure and Test Purposes (TSS&TP) document and the Abstract Test Suite (ATC) specification, both described in ISO/IEC 9646-2 (ITU-T X.291), suit the purpose particularly well.

No Conformance Statements
Having profiles is only part of the interoperability challenge. There must be a standard method of identifying which profiles a device or system complies with and which optional features are implemented so that system integrators can make educated decisions about specific features to provide to customers and to aid in the selection of equipment.

To address the IEEE short-coming, WiMAX initiated the development of a set of conformance documents, in accordance with ISO/IEC recommendations, to be submitted to the IEEE 802.16 Working Group. These include Protocol Implementation Conformance Statement (PICS), TSS&TP, and ATS.