[Cerowrt-devel] Managed to break 802.11n (on a 3800)

[Robert Bradley]

On 16/01/2014 15:03, Aaron Wood wrote:
> All,
>
> I'm noting this here in case anyone is interested.  After I write this
> up, I'm going to start from scratch on the configuration, and
> factory-reset the router.
>
> =====
>
> The 5GHz radio on my 3800 seems to be in a very odd state.  I'm not
> quire sure what state it's in, but it seems to be only doing HT20 1x1.
>  And in a fairly broken manner at that.
>

<snip>

> And here are radio blocks from the current /etc/config/wireless:
>
> config wifi-device 'radio1'
> option type 'mac80211'
> option macaddr '28:c6:8e:bb:9a:49'
> list ht_capab 'SHORT-GI-40'
> list ht_capab 'TX-STBC'
> list ht_capab 'RX-STBC1'
> list ht_capab 'DSSS_CCK-40'
> option txpower '17'
> option distance '25'
> option channel '48'
> option country 'US'

That's interesting, since it's missing a few configuration options and
seems to be still using the US country code for the 5 GHz interface. 
For what it's worth, my router's configuration looks like this (with the
MAC address changed to match your configuration):

config wifi-device 'radio1'
        option type 'mac80211'
        option channel '36'
        option hwmode '11na'
        option macaddr '28:c6:8e:bb:9a:49'
        list ht_capab 'SHORT-GI-40'
        list ht_capab 'TX-STBC'
        list ht_capab 'RX-STBC1'
        list ht_capab 'DSSS_CCK-40'
        option disabled '0'
        option txpower '17'
        option country 'GB'
        option htmode 'HT40+'

I'm using channel 36 and HT40+ here at 17 dBm.  This is also from a
UK-based router, so you'll probably want to change the country code from
GB to FR.  I'm seeing about 270 Mb/s using Intel wireless (4965AGN) and
Windows 7 about 2.5 m away from the router with those settings.

> config wifi-device 'radio0'
> option type 'mac80211'
> option hwmode '11ng'
> option macaddr '28:c6:8e:bb:9a:47'
> option htmode 'HT20'
> list ht_capab 'SHORT-GI-40'
> list ht_capab 'TX-STBC'
> list ht_capab 'RX-STBC1'
> list ht_capab 'DSSS_CCK-40'
> option txpower '26'
> option country 'FR'
> option distance '15'
> option channel 'auto'
>

My settings for the 2.4 GHz side (deliberately limited to HT20 to avoid
interference):

config wifi-device 'radio0'
        option type 'mac80211'
        option hwmode '11ng'
        option macaddr '28:c6:8e:bb:9a:47'
        option htmode 'HT20'
        list ht_capab 'SHORT-GI-40'
        list ht_capab 'TX-STBC'
        list ht_capab 'RX-STBC1'
        list ht_capab 'DSSS_CCK-40'
        option disabled '0'
        option channel '1'
        option country 'GB'
        option txpower '20'

This time I'm using channel 1 at 20 dBm.  In both of these blocks I'm
leaving the distance option unspecified.

Hope this helps a bit!

-- 
Robert Bradley

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