Unlicensed National Information Infrastructure (UNII) is a license-free radio technology in the 5 GHz range. The UNII range is divided into several frequency ranges. The lower frequency range between 5.17 GHz and 5.25 GHz is referred to as UNII Low, the one above that between 5.25 GHz and 5.33 GHz as UNII Mid, and the frequency range above that with frequencies between 5.490 GHz and 5.710 GHz as Worldwide.
The frequency ranges are 160 MHz wide. The upper frequency range can be used for both outdoor and indoor applications. Above the Worldwide range, there is also the Upper range with frequencies between 5.735 GHz and 5.815 GHz, but this is not released in Europe.
In the individual frequency ranges, transmission is only permitted at certain transmission powers. In UNII Low, the permissible transmission power is 50 mW, in UNII Mid and Worldwide, 250 mW may be transmitted, and in UNII Upper, a maximum of 1 W may be transmitted.
The frequency ranges of the Unlicensed National Information Infrastructure are used by WLANs according to 802.11a, 802 .11n and 802.11ac. The frequency range above 5.850 GHz is reserved for vehicle communication according to IEEE 802.11p.