TP-Link agrees to allow third-party firmware in FCC settlement

Posted Aug 2, 2016 9:55 UTC (Tue) by farnz (subscriber, #17727)
In reply to: TP-Link agrees to allow third-party firmware in FCC settlement by rcochran
Parent article: TP-Link agrees to allow third-party firmware in FCC settlement

Because, for the purposes of 802.11, radar is only something you're supposed to notice in the 5 GHz band, not the 2.4 GHz band.

802.11 devices are only supposed to worry about radar when using bands where radar is the primary licensed user, and WLAN is a secondary permitted use; in the 2.4 GHz band, there's no primary licensed user, so 802.11 does not need to worry about interfering with the primary user. In the 5 GHz band, there are chunks where radar is the primary licensed user, and WLAN is permitted to use the spectrum as long as it does not interfere with radar operations; 802.11 has interpreted this as "when you detect radar on a channel, do not use it".

Thus, any radar detection on 2.4 GHz is wrong - the spec for 802.11 says to only do radar detection in the 5 GHz band; further, only 5 GHz devices are required to support channel change notifications and channel blacklisting, so reacting to radar detection in the 2.4 GHz band is not possible (you can't be confident that everything will respect the radar detection).