DFS TESTER -- RADAR SIGNAL PATTERN SIMULATOR
WifiMETRIX includes a 6 GHz radio module, amplifier and filters that are used to generate and transmit RF pulses that simulate radar patterns. When an AP is configured to use a DFS channel then the simulated radar pattern is detected as a radar event and the AP begins broadcasting a sequence of packets in preparation to switch channels.
WifiMETRIX’s DFS Tester functionality can be used to confirm that an AP switches channels and follows 802.11 guidelines to ensure the move to the new channel occurs gracefully for the associated clients. Also, not only do DFS-triggered channel changes impact client connectivity, they may also degrade performance across a larger network if APs are not properly configured or do not follow 802.11 guidelines.
WifiMETRIX makes it easy to test and validate an AP's behavior and a WLAN's response to a radar event. Being able to make use of the 16 DFS channels in the 5 GHz band nearly triples the number of available channels and can be a big win in your WLAN's channel allocation scheme. Here we show DFS Testing Is Easy.
DFS requirements pose channel-assignment complications for enterprise networks that deploy 802.11ac. If any part of a channel touches a defined DFS frequency, then that channel is off-limits if a radar event is detected. Wider channels mean more opportunity to overlap a DFS frequency -- which is why the 802.11ac standard with its wide channels creates additional complications with DFS compared to previous standards that employ more narrow channels.
Considering the additional complications posed by DFS, it’s no surprise there was a time when AP vendors recommended that Wi-Fi architects avoid DFS channels when deploying 5 GHz wireless systems. However, without the use of DFS-enabled Wi-Fi channels a new problem emerges -- without DFS channels 802.11ac has an extremely limited number of available channels for use. This presents a problem when attempting to stagger non-overlapping channels in an enterprise environment. This channel limitation on 802.11ac is reminiscent of the problems encountered when deploying wireless for 2.4 GHz and its meager, three non-overlapping channels.
In the United States the frequency bands from 5.25 to 5.35 GHz and from 5.47 to 5.725 GHz are reserved for radar applications. As demand for additional bandwidth has grown for the Unlicensed National Information Infrastructure (U-NII), the FCC ruled these bands may also be used for other wireless applications if, and only if, they comply to standard FCC-06-96A1. (The mechanism required to comply to standard FCC-06-96A1 is called Dynamic Frequency Selection -- DFS). The idea behind DFS is siimple -- switch to a different channel whenever a radar event is detected on the channel currently in use.
The FCC has defined 6 radar test waveforms -- radar types 0 - 5. WifiMETRIX supports all 6 radar types. A pulse pattern is defined by 2 properties -- the width of a pulse (in uSec) and the interval between pulses (in uSec). See FCC radar test waveforms.