FCC Redefines 5GHz 802.11n\a Channels
The recent ruling by the Federal Communications Commission (FCC) has affects on Wireles LAN (WLAN) equipment operation in the 5Ghz spectrum. This ruling is only applicable to users operating under the FCC 5Ghz frequencies in the US and other countries utilizing 5GHz operating frequencies. This does not apply to other regulatory domains.
The new ruling is based around Dynamic Frequency Selection (DFS2) and is being required to allow the coexistence of military and weather radar systems in the 5GHz band. The new ruling requires that Unlicensed National Information Infrastructure (UNII) devices operating in the 5.25 - 5.35 GHz and 5.47 - 5.725 GHz bands shall employ a DFS radar detection mechanism to detect the presence of radar systems and to avoid co-channel operation with radar systems. This regulation mandates that equipment operating in these spectrum’s must now use DFS to avoid in-use spectrum, and transmit power control (TPC) which throttles power to the minimum necessary for given communication.
About 18 months ago the FCC quietly added a new frequency band, UNII-3, which operates in the 5.47 - 5.725 GHz frequencies. This is an additional 255 MHz that will allow for approximately 8 more channels in the 5GHz spectrum for WLAN devices. This comes as a result of compromise between the Department of Defense and the “industry”. This will be advantageous as the 5GHz spectrum is likely to be used in the early profiles for WiMax.
What this means to us is that most of our WLAN equipment vendors are going to have to do some changes to accommodate this new regulation. Some older equipment will be exempt from this ruling but I would expect most vendors to offer software upgrades. My vendor, Extreme Networks, has already begun developing software to fix this issue and will be providing upgrades to that software in the near future. This ruling became effective July, 20 2007.References