UNII-4

Radio devices don’t transmit on arbitrary frequencies, but in fixed ranges allocated by authorities. Such ranges are called frequency bands. UNII-4 is the name of one of these bands, located at approximately 5.85 to 5.925 gigahertz. The abbreviation stands for “Unlicensed National Information Infrastructure,” meaning radio use without an expensive individual license. In the USA, part of this band has also been permitted for wireless home internet since 2020. This gives WLAN there an additional 45 megahertz of bandwidth, meaning extra space for transmission.

Why 45 additional megahertz determine speed

Radio works similarly to a road: the wider it is, the more vehicles fit on it at the same time. In WLAN, this width is called channel width and is measured in megahertz. A very wide channel of 160 megahertz transports significantly more data per second than a narrow one. The problem: in the existing 5-gigahertz range, there are only a few spots where such a wide channel even fits.

This is exactly where UNII-4 helps. The additional 45 megahertz border directly on the existing 5-gigahertz band. This creates new combinations for wide channels that were not possible before. In densely built residential areas with many networks, this space is especially valuable.

An important restriction: the release applies to the USA. Europe has not opened the band for WLAN in the same way, because here it remains designated for vehicular traffic radio. A router that supports UNII-4 therefore normally doesn’t use it in Germany.

How WLAN shares the band with vehicular radio

The range around 5.9 gigahertz was long reserved entirely for vehicles. Cars were meant to use it to warn each other about traffic jams, ice, or braking maneuvers. This technology was called DSRC and was barely used in the USA. The US regulatory authority FCC therefore decided in 2020 to hand over the lower part of the band to WLAN.

The upper part remained with traffic, now however using a newer technology called C-V2X. To ensure UNII-4 doesn’t interfere with warning messages between vehicles, strict rules apply. Devices may only operate there with limited transmission power, and outdoor WLAN use is more restricted than indoor use.

Technically, UNII-4 is not a standard of its own and not a successor to anything. It is simply additional space that existing standards such as Wi-Fi 6E and Wi-Fi 7 can make use of as well. A common misconception is confusing UNII-4 with the 6-gigahertz band. The latter, at around 1200 megahertz, is many times larger and was released around the same time.

Where the name appears in product descriptions

You rarely read UNII-4 on router packaging. It appears more often in technical data sheets, firmware notes, or test reports from specialist websites. There it usually shows up as a list, such as “UNII-1 through UNII-4 supported.” The numbers one through three refer to the older sections of the 5-gigahertz range.

In news reports, the term appears mainly in disputes over frequency allocation. Car manufacturers, mobile network operators, and the WLAN industry compete for the same scarce bands. UNII-4 is regarded as an example of how a reservation can be reversed if the planned use fails to materialize.

For everyday life in Germany, UNII-4 currently plays hardly any role. It becomes relevant if you import devices from the USA or compare data sheets from international manufacturers. In that case, the term explains why a model offers more channels there than it does here.