FCC Proposes Digital Modulation in Unlicensed 2.4 and 5 GHz Bands

The Federal Communications Commission (FCC) has proposed changes to the 2.4 and 5.7 GHz bands that could allow services and applications not currently permitted in these unlicensed bands. Changes include the elimination of processing gain requirements for direct sequence systems and the creation of digital transmission systems.

The new rules could become effective as early as April this year if FCC adopts the changes as written in a Further Notice of Proposed Rulemaking (FNPRM) issued in May 2001. The changes primarily affect devices that use digital modulation techniques such as WLAN (wireless local-area networks) and WOFDM (wireless orthogonal frequency division multiplexing).

"The proposed changes will be attractive to WLAN providers." —Tom Cokenias

"The proposed changes will undoubtedly be very attractive to WLAN and wireless ISP providers," says Tom Cokenias, of T. N. Cokenias Consulting (El Granada, CA). "For instance, the IEEE 802.11a specification supports up to 54 Mb/sec. It could theoretically be employed at 900 MHz and 2.4 GHz with the advantages of less-costly components and significant decreases in path loss when compared with 5 GHz."

The rule changes were prompted by petitions that cited studies indicating that adaptive-hopping techniques in the 2.4 GHz band would reduce the potential for interference with direct-sequence systems. The studies showed that the adaptive-hopping techniques would allow frequency-hopping systems to avoid transmitting on frequencies being used by collocated systems.

"In this FNPRM, FCC seeks to relax or eliminate requirements that would hinder a new technology or the efficient use of the radio-frequency spectrum," says Cokenias. "The proposed changes will hopefully remove unnecessary restriction to the successful deployment of systems with high data rates (20 Mb/sec or higher)."

As part of the FNPRM, FCC is waiving the restriction that limits operation of these devices. FCC is accepting applications and issuing grants for products meeting the requirements of the new rules as long as they comply with the maximum peak output power limit of 100 mW. These devices, however, will have to meet any rules ultimately adopted for digital modulation in the 2.4 GHz band.

Part 15 currently requires at least 75 hopping frequencies for narrow-bandwidth hopping channels. A minimum of 15 nonoverlapping channels, covering at least 75 MHz, are required for 1-MHz systems.

Under the new rules, 15 nonoverlapping channels could be used for systems that intelligently modify their hopsets at least once every 30 seconds. The new rules would specify a maximum occupancy of 0.4 seconds on any channel.

The new rules could make it less desirable to use the 5 GHz unlicensed national information infrastructure (UNII) band. "New digital technologies are very attractive for use in the 2.4 GHz band," says Cokenias. And, according to Cokenias, modulations such as OFDM previously could be employed only under U-NII band rules, which required that modulation be digital. "Under the proposed spread-spectrum rules, not only will 2.4 GHz devices be able to use the more advanced modulations, 5.7 GHz devices will be afforded advantages not available under the current U-NII regulations."

Under the proposed rules, digital transmission systems would have to meet the same emissions limits and requirements as direct-sequence spread-spectrum radios.

Bluetooth Not So Blue Bluetooth chip set shipments are on track to meet a previous 2001 forecast of 13 million units, according to Cahners In-Stat Group (San Jose). The high-tech market research firm reports that the excellent shipment results could double those of 802.11b. "Activity has moved forward in the mobile phone, notebook PC, and adapter space, with specialty adapters just beginning to show up for personal digital assistants," says Joyce Putscher, a director with In-Stat. "Once people are educated on what the benefits are, demand will rise for products that include Bluetooth connectivity, as long as prices of products are reasonable." In-Stat also reports that comments about Bluetooth in the past year have not significantly affected development or relationships between Bluetooth chip vendors and their customers. According to the report, wireless providers indicate that they are interested in evaluating deployment of Bluetooth access points and networks. Japan, South Korea, and Europe are ahead of the curve, with respect to carrier deployments and enterprise Bluetooth access-point deployment plans. The report, "Bluetooth Overtakes 802.11x with 2001 Shipments on Track" (#MM0118BW) provides an interim Bluetooth forecast update that looks at units, chip set integration, revenue, application, and geographic segmentations. For more information, go to http://www.instat.com/catalog/cat-mm.htm or contact Matthew Woods at 617-630-2139 or mwoods@instat.com.

Shared Spectrum and Stricter Limits: DoD Creates Spectrum Policy Office

The Department of Defense (DoD) has created an office to establish policy and provide direction for its frequency spectrum issues. Steven Price was named deputy assistant secretary of defense (DASD) for the new office, Spectrum and C3 Policy.

According to DoD, this is the first time that spectrum issues have been elevated to the DASD level. As DoD's use of the electromagnetic spectrum for communication grows, it increasingly runs into potential competition, interference, and coordination requirements for international and commercial frequencies.

DoD says its long-standing bands of spectrum are critical to "meeting the needs of the warfighter yet also are considered prime by investors in third-generation and ultrawideband device markets." According to DoD, the government has ceded 247 MHz of bandwidth —more than half in the desirable 3 GHz band—to industry over the past decade. "Maintenance of sufficient spectrum and bandwidth is essential to network-centric warfare and information superiority, two key transformational tenets of joint operations like Enduring Freedom," says DoD.

Price says his vision is to "help DoD build a global, secure, wideband network, with wireless access, for warriors in the field so that bandwidth does not limit or impede U.S. military capability."

"Transforming toward a network-centric military that decentralizes decision making by allowing access to information without concerns of bandwidth or interoperability will help create the flexible, reliable, and effective joint command and control systems that will be needed in the future," he says.

Shared Spectrum

In February of this year, DoD submitted a report to Congress regarding the feasibility of sharing the 138–144 MHz band with public safety users. A DoD Joint Spectrum Center engineering study identified ways to share the spectrum without interfering with DoD
operations.

"We believe it is possible to share portions of the 138–144 MHz band with public safety users on a limited, coordinated basis. DoD is willing to work with the National Telecommunications and Information Administration (NTIA), state and local governments, and first responders on a case-by-case basis to explore sharing the band for the common good," Price said.

DoD says that although the 138–144 MHz band continues to be critical to its operations, the department has found it helpful in emergencies to share communication systems with other first responders. A small number of channels may be shared on a regional basis when doing so mutually benefits DoD and public safety officials.

DoD operations that would be affected if this band were interrupted through heavy use of too many channels include air-surface-air, air traffic control, and ground support functions at military airfields.

The National Defense Authorization Act for fiscal 2000 reclaimed for federal use (primarily DoD) 3 MHz in the 138–144 MHz band. The frequency band was previously identified for reallocation for mixed federal government and nonfederal government uses. According to DoD, Congress understood the recovery of 3 MHz was crucial to fulfilling DoD's spectrum requirements. However, DoD was asked to provide a technical report assessing the feasibility of sharing the 138–144 MHz band with public safety users. In the fiscal 2001 authorization, Congress directed DoD, in cooperation with the Justice Department and NTIA, to provide for an engineering study.

Under direction of John Stenbit, assistant secretary of defense for Command, Control, Communications, and Intelligence (C3I), the DoD Joint Spectrum Center conducted the study. It showed that the areas of operation associated with the DoD frequency usage in the band encompasses nearly the entire continental United States. Large-distance separations would be required to prevent cochannel and adjacent-channel interference between DoD equipment and potential state and local public safety systems, particularly in the case of DoD air-ground-air radios.

FCC Limits Ultrawideband Devices

DoD says FCC's decision to authorize the use of ultrawideband (UWB) devices above 3.1 GHz and impose strict technical limits below 3.1 GHz protects spectrum-dependent military systems, including the global positioning satellite system.

"The department supports FCC's reasoned and balanced approach of protecting critical national security systems from frequency interference while allowing commercial deployment of new technologies," Price says. DoD concluded that FCC's technical restrictions on UWB devices would be sufficient to protect military systems. "Such restrictions were the minimum required to avoid interference with those systems."

DoD plans to monitor regulatory and market developments to ensure that national security is maintained and UWB devices, as deployed, do not jeopardize mission-critical operations supporting public safety and national security.