Dynamic Bandwidth in hw rate control

Dave Taht dave.taht at gmail.com
Thu Jun 16 13:06:31 PDT 2016

On Thu, Jun 16, 2016 at 12:57 PM, Gaurang Ramesh Naik <gaurang at vt.edu> wrote:
> Hi Ben,
> Thanks for your reply.
> I wanted to know if the dynamic bandwidth option implemented in ath10k
> is the same as that mentioned in the standard, or does it deviate? I
> tried to look for any documentation on ath10k dynamic bandwidth, but
> could not find any.

So far as I know "rate control" is one of the major handwaves in the
standard and differs from vendor to vendor and 802.11 standard to

The pieces of how 802.11ac should fall back to narrower channels,  I
think you've correctly identified below (as for width)...

but actually choosing a MCS rate, number of retries, formatting an
aggregate... and other factors, are... different.

I've tried to point at the first and best paper that shows how
minstrel works here:


(and minstrel's known problems) but that's not what ath10k uses.

I would *welcome* full documentation (or code!) on how ath10k choses
its rates. Or any other wifi chipset's blob, frankly.

> If I am not wrong, on the secondary channel, the sender senses the
> channel for PIFS interval of time immediately preceding the start of
> the TXOP ( in the standard). In the static mode, if the
> secondary channel is sensed busy, the sender waits until all channels
> become idle; but in the dynamic mode, the sender sends on the primary
> and (adjacent) secondary channel that are not busy.
> However, the documentation for dynamic bandwidth in ath10k/mac.c seems
> to suggest that the transmission retries are carried over narrower
> bandwidth in dynamic mode. Does this mean the same as what is given in
> the standard? Or is the dynamic mode implemented differently? Any help
> is appreciated.
> Thanks,
> Gaurang.
> On Thu, Jun 9, 2016 at 1:23 AM, Ben Greear <greearb at candelatech.com> wrote:
>> On 06/08/2016 08:10 PM, Gaurang Ramesh Naik wrote:
>>> Hi,
>>> I needed a small clarification related to dynamic bandwidth setup. The
>>> documentation in wmi.h says " When enabled HW rate control tries
>>> different bandwidths when retransmitting frames."
>>> Does this mean that each packet is first always tried over VHT80 and
>>> if that fails it goes to HT40 and then to HT20? I tried this with one
>>> AP-Sta operating in VHT80 and one AP operating in its first secondary
>>> channel. When I check the rx rate info using "iw dev wlanx station
>>> dump", the bandwidth seems to sometimes alternate between 20 and 80,
>>> but sometimes it stays fixed at 20. Hence, I was wondering what really
>>> happens.
>> For one thing, if the hardware detects interference on secondary channels,
>> then it may decide to transmit a 20Mhz encoding.
>> The rate-ctrl algs in the firmware differ from release to release, but
>> the general goal is to transmit with the fastest encoding rate.
>> Thanks,
>> Ben
>>> Thanks,
>>> Gaurang.
>>> _______________________________________________
>>> ath10k mailing list
>>> ath10k at lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/ath10k
>> --
>> Ben Greear <greearb at candelatech.com>
>> Candela Technologies Inc  http://www.candelatech.com
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Dave Täht
Let's go make home routers and wifi faster! With better software!

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