[ath9k-devel] why is bitrate of 65.0 MBit/s MCS 7 appropriate for signal strength of -93 dBm?

[Felix Fietkau <nbd@openwrt.org>]

On 2011-04-06 4:17 PM, Larry Vaden wrote:
> On Wed, Apr 6, 2011 at 5:26 AM, Mohammed Shafi<shafi.ath9k@gmail.com>  wrote:
>>  On Wed, Apr 6, 2011 at 3:28 PM, Larry Vaden<vaden@texoma.net>  wrote:
>>>  Mindful that we are all ignorant, just about different things, I ask
>>>  the ? in the subject line.
>>>
>>>  Would that not influence the success ratio and the performance?
>>
>>  ath9k rate control is based on PER(packet error rate), but previously
>>  it is based on RSSI.
>>  But i doubt you are using minstrel rate control, for that please read
>>  http://wireless.kernel.org/en/developers/Documentation/mac80211/RateControl/minstrel
>
> With all due respect, I do not think your answer is responsive to the
> question and the data presented.
>
>>>          tx packets:     45
>>>          tx retries:     308
>>>          tx failed:      23
>
> Note a FAILURE RATE of 50% and retries ~ 700%.
Simple packet/retry/fail counters are completely misleading when it 
comes to debugging wireless issues.

> So, why is 65.0 MBit/s MCS 7 even on the table if rate control is based on PER?
Because the assumption that lower rates always work better than higher 
rates is a bad one to make in a rate control algorithm.

> Is it possible that some code other than ath9k is jacking with the
> data rates (read: I am ignorant about what protections OpenWrt might
> have)?
You can find better statistics with much more meaningful output in
/sys/kernel/debug/ieee80211/phy0/netdev:wlan0/stations/*/rc_stats

- Felix