[FS#506] BT Home Hub 5: 5g WiFi jumps to channel 36 and stops working if stopped and restarted

[LEDE Bugs]

The following task has a new comment added:

FS#506 - BT Home Hub 5: 5g WiFi jumps to channel 36 and stops working if stopped and restarted
User who did this - Mauro Mozzarelli (ezplanet)

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I found the following documentation on line that summarizes DFS specifications:

DFS-enabled radios monitor the operating frequency for radar signals. If radar signals are detected on the channel, the wireless device takes these steps:
1) Blocks new transmissions on the channel.
2) Broadcasts an 802.11h channel-switch announcement.
3) Disassociates remaining client devices.
4) Access Point selects a different channel permitted within the regulatory domain.
5) After the DFS non-occupancy period has been reached for the original DFS channel, if no clients are associated it will move back to the original DFS channel and scan for 60 seconds. If there are no radar signals on the new channel, the wireless device enables beacons and accepts client associations. The non-occupancy period is defined by the regulatory domain but in most cases is 30 minutes. 

>From my observations the implementation of LEDE DFS:

a) assume (4) as ch 36 only whilst it could be any other permitted frequency
b) do not implement (5) because once switched, the router is stuck on ch 36 (in my sample I get very little radar detections)

And finally it crashes the WiFi device if I try to change the channel manually or disable re-enable the device, requiring a reboot to resume operations.

Also on BT Home Hub 5 DFS is reported as disabled but it appears to be taking place anyway.
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=506#comment1826