802.11h – the one that played nice with radar

next up: IEEE Std 802.11h-2003 – Amendment 5. came out in 2003 and was mostly aimed at making 5 GHz Wi-Fi legal and friendly in Europe. no fancy “Task Group H” tag on this one either, just more behind-the-scenes work from the 802.11 machine.

so what did it do? basically, 802.11h added spectrum etiquette to the mix. the 5 GHz band was shared with radar systems and other sensitive equipment, and 802.11a (which also ran at 5 GHz) didn’t really care. so Europe stepped in and said: if you wanna use that band, you need to behave. thus, 802.11h was born.

this amendment introduced two big things: Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC). DFS meant your Wi-Fi gear had to scan for radar signals and hop to another channel if one showed up. no radar crashing allowed. TPC made sure your device didn’t blast more power than it needed – keeping interference low and battery life high.

the TPC side was especially clever. it allowed stations to negotiate their transmit power levels, respect local/regional limits, and adjust based on path loss and link margin estimates. basically: talk just loud enough, but not more. quiet, efficient, and compliant – very European.

as with the others, 11h got pulled into the 802.11-2007 revision and stuck around through 2012, 2016, and 2020. it doesn’t get much credit, but it’s the reason your router doesn’t get into a fistfight with airport radar.

in short: 802.11h made 5 GHz Wi-Fi smarter, safer, and legal in places that cared about shared airspace. it’s the protocol equivalent of putting your phone on silent in a theater – polite and necessary.