Set the primary channel in HT40 mode

[Michal Kazior]

On 27 June 2016 at 10:58, Gaurang Ramesh Naik <gaurang at vt.edu> wrote:
> Hi All,
>
> I have some difficulty in understanding how HT40, HT40- and HT40+
> modes work. My objective is to set a particular 20 MHz channel as the
> primary channel when channel bonding is enabled. From what I
> understand, HT40- means secondary channel is below the primary, while
> HT40+ means secondary channel is above the primary channel. I am
> particularly dealing with channels 149, 153, 157 and 161.

http://securityuncorked.com/wordpress/wp-content/uploads/2013/11/graphic-80211-acChannels-all.png


> When I set the channel to say 157, whether I use HT40+ or HT40-, the
> primary channel is always set to channel 161. I am inferring this
> because when I scan using iwlist scan, my SSID shows on Channel 161.
> Does ath10k not set the primary and secondary channel in this manner?

ath10k doesn't care. hostapd can do a channel swap if it detects OBSS.
Not sure how much OpenWRT scripts mingle in (I'm guessing you're using
`uci`, hence the mention).


> If not, is there a mechanism by which I can explicitly mention which
> channel must be primary, and which must be secondary?

You can't. OBSS can still end up swapping your primary and extension channels.


> Also, how is the
> primary channel decided for VHT80 mode?

VHT80 is backward compat for HT40 and HT20 clients. See the channel
allocation link above.


Michał