A.3 DFS and TPC
DFS and TPC for 5 GHz Channels
Many channels in the 5 GHz band are subject to regulations that require active avoidance of interference
with weather radar and other radars (Dynamic Frequency Selection aka DFS). In many countries, regula-
tions also require lower transmit power for nearby wireless connections (Transmit Power Control aka
TPC) on the same channels. These DFS channels may be available for use in some countries on
BreadCrumbs with 5 GHz radios that provide hardware support for radar detection.
The list of 5 GHz channels that are subject to DFS and TPC depends on the regulatory domain of the re-
gion of operation. In many regions any available channels from 5260-5700 MHz require DFS, or DFS and
TPC. In some regions, additional channels require DFS and TPC.
DFS channels will not be available immediately upon startup and will become non-operational for a fixed
period of time aer radar or any radar-like pulse of noise is detected.
BreadCrumb DFS Behavior
Aer power-on or restart, all transmits on a DFS channel will be disabled for 1 minute (typical)
while the radio pre-checks for radar on that channel (the Channel Availability Check aka CAC). If the
1 minute completes without detecting radar, the radio can then start normal operation on the chan-
nel while still continuously checking for radar. Note: Channels from 5600 MHz to 5650 MHz, if avail-
able, may have a 10 minute CAC period.
If radar detection is triggered on a DFS channel, that radio will stop transmitting for 30 minutes
(the Non-Occupancy period aka NOP). Warning code 382 “Radar detection paused radio: wlanN
(wlanN …)” will be displayed in BC|Commander if the affected unit was able to report its warning
status over another radio or over ethernet.
When the 30 minute NOP period of not transmitting completes, before reusing the DFS chan-
nel, the radio must not transmit for 1 additional minute (may be 10 minutes for 5600-5650 MHz)
while pre-checking for radar (a CAC period). If no radar is detected during the CAC period, normal ra-
dio operation is resumed with continuous checking for radar.
When resuming normal operation aer a radar detection, the radar detection warning 382 will be
removed from the radio and a warning 383 “Radio resumed from radar pause: wlanN (wlanN, …)”
will be added. This 383 “unpaused” warning will remain up for 12 hours so that personnel will know
what radios were affected by DFS stoppages. Warning 383 will be removed when all listed radios
have been aged out.
About Radar Detection
Radar is detected as pulses (spikes) of radio frequency (RF) noise. If pulses of noise make it past several
range checks, and the pattern of pulses is sufficiently similar to a radar pattern, a radar detection event
will occur. False detections may be caused by anything that creates RF interference including electrical
equipment, improperly positioned antennas, nearby wireless radio devices and RF reflections caused by
antennas too close to the ground, walls or other RF-reflecting surfaces.
If possible, use of DFS channels should be avoided for critical network paths, especially if the
BreadCrumb has no other wired or wireless network connections to the mesh.
DFS Additional Antenna Separation
DFS Additional Antenna Separation
For 5 GHz transceivers using channels that require DFS radar detection, it is recommended to mount
For 5 GHz transceivers using channels that require DFS radar detection, it is recommended to mount
each antenna for a DFS channel at least 2 feet from any other 5 GHz transceiver’s antenna.
each antenna for a DFS channel at least 2 feet from any other 5 GHz transceiver’s antenna.
Note: Two new DFS-related fields can be examined in BCAPI Explorer. For wireless DFS channels, these
fields will indicate the count of RF interference pulses encountered as well as a count of how many were
deemed sufficiently similar to radar by the radar pattern detector.
state.wireless[n].stats.pulseEvents – Raw count of interference pulses detected by the radio
state.wireless[n].stats.radarDetections – Count of pulses that triggered radar detector
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