Wireless Systems Design

WiMAX Calls For Broadband Revolution

The past year has seen renewed interest and activity in the broadband-wireless-access (BWA) industry. This flurry of activity has begun to spill over into the more mainstream networking world. It provides tantalizing glimpses of the new features and functionality contained in the IEEE 802.16-2004 specification. Coupled with that document's initial ratification in June of 2002 has been the launch of the WiMAX Forum (www.wimaxforum.org). This industry forum is dedicated to promoting interoperability and conformance testing among all BWA systems worldwide.

BWA has been around for over 10 years. Yet it has struggled to find its place as the third leg of a cable/DSL triad for delivering broadband in the last mile. Well over 10 years ago, companies like Tetherless Access Limited (TAL) and Cylink delivered the first BWA systems. They took off-the-shelf radios and added limited and proprietary point-to-multipoint protocols and an Ethernet interface to them. The demand for such systems did exist. But these first- and even second-generation systems failed to prosper for several reasons:

  • BWA systems are extremely complex. To deliver the minimal functionality required, demands are placed on every system segment. The startups that designed these initial systems had limited, in-house R&D budgets. They were forced to focus on a single system element, such as the modem or medium-access-controller (MAC) protocol. They thus sacrificed key areas like management and quality of service (QoS). The net result was a bevy of proprietary offerings—none of which provided a complete solution.
  • Because all of the systems were proprietary, manufacturing scales were impossible to achieve. Vendors couldn't build in volumes that would reduce costs enough to trigger broad industry adoption.
  • Although regional or national service providers did attempt large-scale deployments, they proved unsuccessful. They used a single supplier with 50 to 100 employees. The system vendor ended up declaring bankruptcy, putting an end to the rollout.
  • Last year, several events drove the rebirth of BWA. In January of 2003, the IEEE ratified and approved the 802.16a specification. That document covers BWA systems that are designed to operate between 2 and 11 GHz. With this adoption, the WiMAX Forum shifted its focus from systems above 11 GHz to the lower frequency offered by 802.16a (and revised in June 2004 to be called 802.16-2004).

    The WiMAX Forum's purpose is:

    1. To promote a common BWA standard based on IEEE 802.16 specifications.

    2. To ensure interoperability among vendor systems. Customers will then know that their CPE will work wherever a WiMAX-Forum-certified network is in operation.

    3. To develop conformance testing to narrow and focus all of the options within the specification to a small set of market-driven solutions.

    With such high-profile members as Intel, Fujitsu, and Alcatel, the WiMAX Forum has attracted over 100 new members in the past year. It also expanded its message and scope. Within the forum, Technical Working Groups have been developing test scenarios and testing protocols—the nuts and bolts of the interoperability testing that every WiMAX-Forum-certified system must pass.

    The WiMAX Forum's value proposition shares key elements with the Wi-Fi Alliance (www.wi-fi.org). Few remember that the original 802.11 standard included frequency hopping and infrared. The Wi-Fi Alliance took that standard and focused its efforts on a subset of features, which ensured interoperability and essentially launched the Wi-Fi market. The WiMAX Forum is focusing on a specific implementation of the IEEE 802.16-2004 specification based on market requirements.

    Scales of manufacturing are a natural outcome of standards. But the question remains: How does 802.16-2004 solve the limited functionality of BWA? Among the key attributes of 802.16-2004 are error correction and a burst-OFDM waveform, which helps adjust to multipath while providing rapid upstream response for delay-sensitive traffic. Dynamic FEC and modulation maximize every RF pipe between a subscriber station and a base station for the most bits. At the same time, they ensure a robust connection.

    To support flow-based queuing, 802.16-2004 includes a deterministic, TDM/TDMA protocol. It also flaunts encryption and security, which are more necessary with a standardized approach than with proprietary systems. Lastly, true QoS is enforced by hooks for scheduling algorithms. These hooks control parameters like minimum/maximum bandwidth, latency, jitter, and packet loss.

    These features improve performance, reliability, and security. They also reduce truck rolls by enabling some subscriber stations to be customer installed. Service providers can offer and support service-level agreements (SLAs) as well as premium service (and fees) for special applications like gaming, voice over IP, or videoconferencing. WiMAX-Forum-certified solutions also will be able to offer economical and higher-speed backhaul for hot spots. These attributes will enable 802.16-2004-based BWA solutions to succeed where previous efforts failed.

    Over the next year, silicon vendors will begin shipping MAC/modem ASICs based on 802.16-2004. Vendors will follow with the delivery of complete systems. Yet the future of BWA doesn't stop with 802.16-2004. BWA will continue to evolve as it adapts to market demands with offerings like 802.16e—an initiative that adds mobility to the standard.

    TAGS: Intel
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