Sorry, you need to enable JavaScript to visit this website.
Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.

Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.

The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Lessons Learned from the Development and Deployment of 5 GHz Unlicensed National Information Infrastructure (U NII) Dynamic Frequency Selection (DFS) Devices

Report ID
Technical Report TR-20-544
December 01, 2019
Frank H. Sanders; Edward F. Drocella Jr.; Robert L. Sole; John E. Carroll

This report is a case-history of the development, deployment, and operational experiences associated with 5 GHz unlicensed national information infrastructure (U NII) devices that incorporate a detect-and-avoid approach to spectrum sharing. Such dynamic frequency selection (DFS) technology was authorized by the Federal Communications Commission (FCC) to accommodate co-band operation of U NII transmitters among other incumbent radio systems, specifically radars. DFS-equipped U NII systems are designed to detect frequencies occupied by radar transmissions and then command their own transmitters to avoid operation on those occupied frequencies. Examining the historical and technical aspects of the development and deployment of 5 GHz DFS-equipped U NIIs, this report focuses on issues encountered with the deployment of this nascent DFS technology, particularly with respect to two government radar systems that have experienced harmful interference: Terminal Doppler Weather Radars (TDWRs) and Range Instrumentation Radars (RIRs). These interference interactions and the likely underlying causes are described, along with steps that have already been taken in an effort to mitigate existing and potential future interference interactions. This report’s narrative summarizes the DFS experience and shares the Lessons Learned from these experiences that may be applied to future similar spectrum-sharing approaches.

Keywords: radar; electromagnetic compatibility (EMC); band sharing; spectrum sharing; radio interference; out-of-band (OOB) emissions; spectrum measurement; unlicensed national information infrastructure (U-NII); terminal Doppler weather radar (TDWR); dynamic frequency selection (DFS); emission limits; spurious emissions; 5 GHz band; access point (AP); detect and avoid; range instrumentation radar (RIR)