In recent years, the wireless-local-area-network (WLAN) products based on the IEEE 802.11 standards have become wildly popular. In fact, products based on this technology—also known as Wi-Fi—have been listed among the most encouraging areas of high-tech growth. To date, most Wi-Fi products worldwide have been limited to spectrum in the 2.4-GHz band. 802.11a products, which utilize the 5-GHz band, have not achieved the same success. Mainly, this trend is due to the large variation in regulatory requirements and spectrum availability worldwide.

Recent events may alter this landscape and significantly increase the number of 802.11a products. The first is the harmonization of 5-GHz spectrum, which came about as a result of the World Radiocommunications Conference. Ratification of IEEE 802.11h—a standard to reduce interference in the 5-GHz band—stands as the other compelling event.

Together, these two achievements will allow products that utilize the 5-GHz band to achieve the same economies of scale that aided the success of earlier products in the 2.4-GHz band. Previously, manufacturers had to create an unwieldy array of products to match a patchwork environment. Now, they will be able to concentrate more efficiently on one standards-based solution.

Initial Wi-Fi adoption has been limited to products that use the 802.11b standard. Most recently, though, the products that utilize the 802.11g standard also have tasted success. Both of these technologies operate in the 2.400-to-2.4835-GHz band. This spectrum is allocated on a worldwide basis for mobile services including WLANs. Most countries allow WLAN products to operate on an unlicensed or license-exempt basis.

Allowing unlicensed devices to operate in the 2.4-GHz band has reduced the barriers to entry and encouraged innovation. This 83.5 MHz of unlicensed spectrum unleashed Wi-Fi and mobile computing. As Wi-Fi popularity has increased, however, the need for additional spectrum has become apparent.

The challenge of addressing the spectrum shortage fell to the International Telecommunication Union. From June 9 to July 4, 2003, member states sent official government delegations to the World Radiocommunication Conference (WRC) in Geneva. This effort was significant. After all, conferences to harmonize spectrum usage worldwide are only held every three to four years. Plus, the drafting and promoting of official positions is a lengthy and often arduous process.

During the conference, WLAN use in the 5-GHz band was one of the most contentious issues addressed. The delegates needed to balance WLAN equipment's popularity with the need to protect equipment already operating under previous primary allocation.

Debate over how best to achieve this balance lasted for months during pre-conference activities. Finally, the conference allocated the spectrum from 5.150 to 5.350 GHz and 5.470 to 5.725 GHz on a primary basis to the mobile service. It is to be used for the implementation of wireless access systems (WASs), including WLANs.

The conditions under which WLANs will be allowed to share the spectrum are defined in ITU Recommendation M.165. This document defines the agile radio techniques of dynamic frequency selection and transmit power control. Originally, these mechanisms were developed in response to European regulatory requirements, which governed WLAN use in the 5-GHz spectrum as embodied in ETSI EN 301 893 V1.2.2 (2003-2006).

For the basic conditions for spectrum sharing, look to TABLE 1. The resolution provides a win-win solution for incumbent spectrum users and WLAN users alike. Incumbent spectrum holders benefit from protection against interference with equipment like radar. At the same time, consumers worldwide will enjoy harmonized spectrum for Wi-Fi usage.

How does this resolution help the user? As countries around the world implement the WRC resolution, there will be a large increase in the amount of 5-GHz spectrum that is available for WLAN use by 802.11a products. This increase should encourage product development and innovation. In addition, the regulations governing WLAN use in 5 GHz should become very similar in many countries. Having common frequencies and spectrum-usage rules will free business travelers and others from having to purchase multiple product versions for use in different locations.

Take the United States, for example. The Federal Communications Commission (FCC) has already completed the process of rulemaking that would allow 802.11a products with 802.11h-based mitigation measures to operate in the 5.470-to-5.725-GHz band. Having an additional 255 MHz of spectrum means that 24 non-interfering channels are now available for use by 802.11a products in the U.S. By comparison, the 2.4-GHz band only has a total of three non-overlapping channels.

Yet spectrum harmonization alone is not enough. In order for manufacturers to achieve economies of scale, other regulatory requirements, such as mitigation measures, must be similar from region to region. FCC officials and their counterparts worldwide are starting to define the rules for WLAN use in the 5-GHz band. They must ensure that the other devices that are legally operating in that band do not suffer from harmful interference from WLAN products. To that end, it's desirable to harmonize mitigation measures and other requirements.

On September 19, 2003, the IEEE approved an amendment to the IEEE 802.11 WLAN standard to implement ITU-R Recommendation 1652. This amendment, IEEE 802.11h, has two main elements. They include dynamic frequency selection (DFS) and transmit power control (TPC). Dynamic frequency selection detects the presence of a primary service and switches the WLAN to a clear frequency. Transmit power control reduces the total power on a Wi-Fi network. The Wi-Fi Alliance plans to add interoperability testing for 802.11h mitigation measures to its certification program in 2004.