Unlicensed National Information Infrastructure

Background

The U-NII band was established by the FCC under Part 15 of the CFR Title 47, specifically Subpart E, which governs Unlicensed National Information Infrastructure Devices. It originally consisted of four ranges for 5 GHz WLAN (U-NII 1 through 4), with U-NII 2 further divided into three subsections. In 2003, the FCC added the U-NII-2C (Worldwide) range to align U.S. bands with international allocations. By March 2021, the band expanded to eight ranges, with U-NII 5 through 8 allocated for 6 GHz WLAN (802.11ax).

Power limits and usage rules vary by sub-band. U-NII-1 (Low) was originally limited to indoor use with an integrated antenna and 50 mW power, but rules changed in 2014 to permit outdoor operation with higher power limits, though strict out-of-band emission rules constrain practical point-to-point power. U-NII-2A and U-NII-2C require Dynamic Frequency Selection (DFS) to avoid radar interference. U-NII-3 overlaps with the ISM band and allows user-installable antennas, with power limited to 1 W in the U.S. and 25 mW in the European Union. U-NII-4 is currently reserved for Dedicated Short Range Communications Service (DSRC) and licensed amateur radio operators, though the FCC has considered it for unlicensed use.

In 2007, the FCC mandated DFS for devices on channels 52, 56, 60, and 64 to avoid radar bands. In 2014, new rules were issued due to interference with government weather radar systems, with fines and equipment seizure as penalties for non-compliance. Many other countries use similar bands due to a shared IEEE standard, but regulatory details may differ.