[OpenWrt-Devel] [OpenWrt] 2.4Ghz limited to 50mW in DFS-ETSI

Wed Jul 29 04:43:02 EDT 2015

Hi,

I have this strange behaviour down below, for which I also opened a
ticket because I think this should not be like that ;)

Does anyone have an idea where the problem could originate from and how
to fix it?

Thanks
Nico

On 07/29/2015 12:37 AM, OpenWrt wrote:
> #20222: 2.4Ghz limited to 50mW in DFS-ETSI
> ----------------------+----------------------------------
>  Reporter:  nicoduck  |      Owner:  developers
>      Type:  defect    |     Status:  new
>  Priority:  normal    |  Milestone:  Chaos Calmer (trunk)
> Component:  kernel    |    Version:  Trunk
>  Keywords:  wndr3800  |
> ----------------------+----------------------------------
>  I have got a Netgear WNDR 3800 running with openwrt since quite a while.
>  I now upgraded to the latest version (trunk) and wanted to use WLAN within
>  the regulations here in Germany but also wanted to max out the output
>  power (within the regulations).
>  Switching the country to Germany limits the maximum output power to 17dBm,
>  although it does show as being limited on 20dBm:
>  root at OpenWrt:/# iwinfo wlan0 txpower
>     0 dBm (   1 mW)
>     1 dBm (   1 mW)
>     2 dBm (   1 mW)
>     3 dBm (   1 mW)
>     4 dBm (   2 mW)
>     5 dBm (   3 mW)
>     6 dBm (   3 mW)
>     7 dBm (   5 mW)
>     8 dBm (   6 mW)
>     9 dBm (   7 mW)
>    10 dBm (  10 mW)
>    11 dBm (  12 mW)
>    12 dBm (  15 mW)
>    13 dBm (  19 mW)
>    14 dBm (  25 mW)
>    15 dBm (  31 mW)
>    16 dBm (  39 mW)
>  * 17 dBm (  50 mW)
>    18 dBm (  63 mW)
>    19 dBm (  79 mW)
>    20 dBm ( 100 mW)
> 
>  What I did: reset the device, flash it with various builts from trunk and
>  try to figure out what was going on.
>  I now modified my regdb and was able to isolate the source of the problem:
>  country DE: DFS-ETSI
>          # entries 279004 and 280006
>          (2400 - 2483.5 @ 40), (100 mW)
>          # entry 303005
>          (5150 - 5250 @ 80), (200 mW), NO-OUTDOOR, AUTO-BW
>          # entries 304002 and 305002
>          (5250 - 5350 @ 80), (100 mW), NO-OUTDOOR, DFS, AUTO-BW
>          # entries 308002, 309001 and 310003
>          (5470 - 5725 @ 160), (500 mW), DFS
>          # 60 gHz band channels 1-4, ref: Etsi En 302 567
>          (57000 - 66000 @ 2160), (40)
>  Thas does not work and has the mentioned behaviour, 2.4Ghz is limited at
>  17dBm. It also does not depend on which values are set in the regulatory
>  database for the 2.4Ghz channels, anything over 17dBm will be limited to
>  17dBm.
>  running "iw phy phy0 set txpower fixed 2000" gives no error but does not
>  change it to 20dBm. Changing the value to anything below 17dBm works
>  though.
> 
>  country DE: DFS-FCC
>          # entries 279004 and 280006
>          (2400 - 2483.5 @ 40), (100 mW)
>          # entry 303005
>          (5150 - 5250 @ 80), (200 mW), NO-OUTDOOR, AUTO-BW
>          # entries 304002 and 305002
>          (5250 - 5350 @ 80), (100 mW), NO-OUTDOOR, DFS, AUTO-BW
>          # entries 308002, 309001 and 310003
>          (5470 - 5725 @ 160), (500 mW), DFS
>          # 60 gHz band channels 1-4, ref: Etsi En 302 567
>          (57000 - 66000 @ 2160), (40)
> 
>  Thad does work. The only change to the entry above is "DFS-FCC" instead of
>  "DFS-ETSI". I can now select any powerlevel between 1 and 20dBm and it is
>  also reported as being used:
>  root at OpenWrt:/# iwinfo wlan0 txpower
>     0 dBm (   1 mW)
>     1 dBm (   1 mW)
>     2 dBm (   1 mW)
>     3 dBm (   1 mW)
>     4 dBm (   2 mW)
>     5 dBm (   3 mW)
>     6 dBm (   3 mW)
>     7 dBm (   5 mW)
>     8 dBm (   6 mW)
>     9 dBm (   7 mW)
>    10 dBm (  10 mW)
>    11 dBm (  12 mW)
>    12 dBm (  15 mW)
>    13 dBm (  19 mW)
>    14 dBm (  25 mW)
>    15 dBm (  31 mW)
>    16 dBm (  39 mW)
>    17 dBm (  50 mW)
>    18 dBm (  63 mW)
>    19 dBm (  79 mW)
>  * 20 dBm ( 100 mW)
> 
> 
>  I have no idea why but there seems to be a bug in the code parsing the DFS
>  regulations, limiting 2.4Ghz to lot lower values than allowed. Changing it
>  to DFS-FCC works for using the applicaple output power but does not seem
>  to be in compliance which German law.
> 
>  Do you have an idea where the problem could be? I'm happy to try out more
>  builds and future versions.
> 
>  Also (kind of off-topic): Do you know why 5Ghz channels 36-48 are forced
>  to be 17dBm only on the WNDR3800? I found two possible explanations:
>  either because of the factory calibration (is it possible to get them in a
>  human readable form somehow? The hexdump is not really readable and I have
>  not been able to find the code which pases them) or because these channels
>  are considered as "edge-channels" and someone thought it would be safe to
>  limit the power, to not disturb any other systems running on even lower
>  channels. The latter explanation is kind of weird because it would make no
>  sense to limit these 4 channels but no other ones. I find it especially
>  strange because that is typically the job of regulatory authorities, to
>  define those power levels.
> 
> --
> Ticket URL: <https://dev.openwrt.org/ticket/20222>
> OpenWrt <http://openwrt.org>
> Opensource Wireless Router Technology
> 
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