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Achieving Interoperability with IEEE 802 . 16-Compliant Systems

The IEEE 802.16 Air Interface Standard is truly a state-of-the-art specification for fixed broadband wireless access systems employing a point-tomultipoint (PMP) architecture. It was developed with the goal of meeting the requirements of a vast array of deployment scenarios, in particular those networks operating between 11 and 66 GHz frequencies. As a result, only a subset of the functionality is needed for typical deployments directed at specific markets. Additionally, the IEEE process stops short of providing conformance statements and test specifications. In order to ensure interoperability between vendors competing in the same market, a non-profit group was formed, the Worldwide Interoperability for Microwave Access (WiMAX) Forum, which was created by the leaders in above 11 GHz IEEE 802.16 technology. WiMAX addresses these issues by developing system profiles and by producing ICS proforma, Test Suite Structure and Test Purposes specifications and Abstract Test Suite specifications according to the ISO/IEC 9464 series of conformance testing standards. OVERVIEW OF IEEE 802.16 Task Group 1 of IEEE 802.16 was started approximately two and half years ago with the charter to develop a point–to-multipoint broadband wireless access standard for systems in the frequency range 11-66 GHz. The standard was to cover both the Media Access Control (MAC) and the physical (PHY) layers. The IEEE 802 process favors the submission of complete system proposals as a starting point for the creation of the standard. Initially, there were numerous proposals, but eventually it was narrowed down to two: a proposal based on wireless DOCSIS (also known as DOCSIS+) and a proposal based on Ensemble Communication’s proprietary technology, known as Adaptix (with notable input from Nokia and other companies). It became clear that neither the DOCSIS proposal based on cable technology, nor the Ensemble proposal based on a next-generation, state-of-the-art set of technologies would achieve the necessary 75 percent vote to become the sole basis for the standard. The proposals were already compatible in many basic aspects, and in May of 2000, the process of merging the two competing proposals began. The basic layering, bandwidth (BW) request scheme, ability to transport any application layer, and support of advanced physical layers were taken from the Ensemble proposal. The flexible message structure, authentication, and security were taken from the DOCSIS proposal. Over the course of the next year, the combined system specification was improved based on comments from a large number of sources. A number of PHY considerations were taken into account for the target environment. At the frequencies considered, 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. Adaptive burst profiles (modulation and forward error correction (FEC)) are used to further increase the typical capacity of 802.16 systems with respect to older technology. The PHY is also 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. Similarly, the MAC was designed specifically for the PMP wireless access environment. It is designed to seamlessly carry any higher layer or transport protocol 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 the very high bit rates (up to 268 mbps each way) of the truly broadband physical layer, while delivering ATM compatible Quality of Service (QoS) to ATM as well as non-ATM (MPLS, VoIP, etc.) service. The basic frame structure is shown in the following Figure.