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Edward F. Drocella Jr., Larry Brunson, and Charles T. Glass

Abstract: In 1997, the Federal Communications Commission (FCC) authorized the use of Unlicensed National Information Infrastructure (U-NII) devices in the 5150–5250 MHz, 5250–5350 MHz, and 5725–5825 MHz bands. The technical and operational requirements are different in each of these bands. Many of the devices presently operating under these rules are designed to meet the Institute of Electrical and Electronics Engineers (IEEE) 802.11(a) industry standard for wireless local area networks.

The World Radiocommunication Conference 2003 (WRC-03) considered allocations for wireless access systems including unlicensed radio local area networks (RLANs), radar systems, and other services in the 5 GHz region of the spectrum. In preparing for WRC-03, the National Telecommunications and Information Administration (NTIA), in conjunction with the FCC, the Department of Defense, and the National Aeronautics and Space Administration, and working closely with industry, agreed to require U-NII devices operating in the 5250–5350 MHz and 5470–5725 MHz band to employ dynamic frequency selection (DFS), a listen-before-transmit mechanism. DFS works by selecting an alternate operating frequency for the U-NII device when a radar signal is detected above a minimum threshold.

To determine the necessary DFS detection threshold, NTIA developed a computer model that calculated the aggregate interference level into a radar system from a population of RLANs. The model took into account RLAN transmit control of DFS to determine interference to four types of radar systems that operate in the 5 GHz frequency range. The types of radar included: ground-based scanning, ground-based tracking, airborne, and shipborne. Current and planned federal radar utilization of the 5 GHz frequency range was examined and characterized to study interactions between RLANs and the radars that operate at 5 GHz. Operational scenarios were developed that considered the operational deployments of unlicensed RLANs and typical deployments of radar systems representative of those that would operate in the band. These operational scenarios included physical placement factors, as well as technical characteristics of both the RLAN and radar systems. Link budget calculations were then performed to determine the effect of RLANs employing the DFS function and the aggregate level of RLAN signals that would be received by the different types of radar systems. The results of the NTIA analysis were used by the FCC to amend the Part 15 U-NII service rules.

NTIA is in the process of developing a handbook documenting the best practices in spectrum engineering for use by regulators, technology developers, manufacturers, and service providers. This “Best Practices Handbook” will bring together a common set of approaches for conducting engineering analyses and will develop a common set of criteria for performing technical studies to evaluate emerging technologies.

The objective of this technical memorandum is to document the analysis methodology that NTIA developed and used in assessing interference from RLANs to 5 GHz radar systems. NTIA will consider the analysis methodology and operational iii scenarios described in this technical memorandum as it develops the Best Practices Handbook.

For technical information concerning this report, contact:

Edward F. Drocella
National Telecommunications and Information Administration
(202) 482-2608

Disclaimer: Certain commercial equipment, components, and software may be identified in this report to specify adequately the technical aspects of the reported results. In no case does such identification imply recommendation or endorsement by the National Telecommunications and Information Administration, nor does it imply that the equipment or software identified is necessarily the best available for the particular application or uses.

For questions or information on this or any other NTIA scientific publication, contact the ITS Publications Office at or 303-497-3572.

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