WiMax rolls interop guidelines for 802.16a

The 802.16 Working Group has developed common design para-meters within 802.16a while at the same time accommodating technical differentiation. Manufacturers can now preserve unique approaches for traffic scheduling, smart antennas and per-subscriber link optimization without sacrificing standards compliance.

The approach avoids setting lowest-common-denominator specifications, which prevent manufacturers from differentiating their product features. While it obviates that traditional concern, however, it does open the door to interoperability issues.

Luckily, a means of reducing the risk of interoperability has already been outlined. In much the same way as the Wi-Fi Alliance helped ensure interoperability between IEEE 802.11-based wireless-LAN devices, the Worldwide Interoperability for Microwave Access (WiMax) Forum will certify standards compliance and test product interoperability for 802.16-based devices. The upshot will be to create high-volume opportunities for silicon suppliers, free equipment vendors from developing proprietary silicon and give service providers multisourcing options at lower prices.

Each 802.16 physical layer (PHY) is optimized to support numerous different link conditions such as line of sight, obstructed line of sight and nonline of sight. By supporting per-subscriber link adaptation, systems can use different modulation rates or coding schemes to increase overall channel efficiency while maintaining robust links to each subscriber. The PHY layer also supports flexible channel bandwidths (required for licensed or license-exempt frequency bands) and multiple duplexing schemes, including both half- and full-duplex frequency-domain duplexing and time-domain duplexing.

Interoperability profiles

The media access control (MAC) is designed to carry transport protocols such as Internet Protocol or asynchronous transfer mode seamlessly. Mechanisms in the 802.16 (also known as WirelessMAN) MAC provide for differentiated quality-of-service to support dissimilar applications, such as voice and video, which require low latency but tolerate some error rate, and generic data applications, which tolerate latency but not error. The standard accommodates all transmissions via appropriate features in the MAC layer. This is more efficient than doing so via control layers overlaid on the MAC.

To ensure vendor product interoperability for all .16a applications, system profiles must be created. The profiles specify appropriate features within the PHY and MAC as mandatory or optional, targeting specific feature requirements within a particular market where the products will be sold. That allows interoperability based on an established set of features, rather than the entire set of specifications. Each has a number of subprofiles. For example, ProfM3 is a MAC profile for packet-based point-to-multipoint networks. ProfP3 is a PHY profile for orthogonal frequency-division multiplexing in the 3.5-MHz band for countries that follow European Telecommunications Standards Institute (ETSI) channelizations.

ProfP3's subprofile selects time-division duplexing and a power class profile, ProfC1, which describes the maximum transmit power from the radio (< 20 dBm).

Completion of the first system profiles is planned for the fourth quarter and will include several MAC profiles and a major PHY profile for each of the three PHY layers, with subprofiles for each channel bandwidth. All profiles are developed by the IEEE 802.16 Working Group and counterpart ETSI HiperMAN members. WiMax serves as liaison between the two groups, to ensure development of globally interoperable products.

Once system profiles are established, test specifications must be developed. The 802.16 Working Group follows ISO/IEC 9646 guidelines for test specification development and will produce the following documents:

Protocol Implementation Conformance Statements Proforma, per ISO/IEC 9646-7, describing mandatory and optional features for each system profile, enabling developers to state support for features;
the Test Suite Structure and Test Purposes per ISO/IEC 9646-2; and
the Abstract Test Suite specification per ISO/IEC 9646-2.

These specifications ensure that equipment and systems that are claimed to comply with 802.16a undergo sufficient testing to demonstrate compliance. They also help guarantee that equipment from various vendors is tested the same way, so that independent certification labs can run the tests. Test specifications will be completed by the 802.16 Working Group and ETSI HiperMAN and will be jointly coordinated through WiMax. Completion is expected by the third quarter of 2004.

After completing the test specs, WiMax will certify one or more independent labs to test product conformance to system profiles and interoperability among certified systems. The first fully interoperable 802.16a products should be available by the end of 2004.

While standards and interoperability guidelines would appear to limit vendors' ability to differentiate their products, the opposite is true with 802.16a. Since the PHY and MAC layers specify a mix of mandatory and optional features, silicon manufacturers can focus on solutions for those layers, allowing equipment suppliers to incorporate innovation at different layers.

Suppliers can introduce product differentiation as follows:

Application and services. Some products support data only; others support data, voice and video.
Networking, higher-layer protocols. These include support for VLANs, Point-to-Point Protocol over Ethernet, routing and network address translation.
Network management.
Customer-premises equipment installation. Products may be optimized for quick CPE installation with one or no truck rolls (to encourage lower costs).
Basestations. Options include number of sectors supported, redundancy and support for different frequency bands in the same platform.
Antennas. Support for numerous antenna implementations, to optimize coverage in any environment.

For more information on the IEEE 802.16a standards, go to ieee802.org/ or wirelessman.org/. For more on the WiMax Forum, see www.wimaxforumorg.

For more information on the ETSI HiperMAN organization, go to portal.etsi.org/Portal_Common/home.asp and click on the BRAN link.

Dean Chang is director of product management and Subir Varma is vice president of technology at Aperto Networks (Axtell, Nebraska).

http://www.eet.com