Trouble shooting low rate MCS9 in 802.11ac

[Bartosz Markowski]

On 17 July 2014 14:22, Vu Hai NGUYEN <vh.nguyen at actiasodielec.fr> wrote:
>>Did you use cables or measured OTA?
>
> My system is like this:
> PC1 - Device 1 (AP) <= Wifi => Device 2 (STA) - PC2
> Each PC connects to the device by a Gigabit Ethernet  cable.

I ment RF cables and attenuation to get around 30dBm signal lvl.

PC    ---(eth)---   [AP135 - APUT]ath10k    - - - (RF cable) - - -
[AP135]Station    ---(eth)---    PC

>>What platform it is?
> My platform is a PC built with an ARMv7 1.2GHz.
>
>> Did you use hostapd? Is it AP mode (bridge)?
> I'm using hostapd for AP and wpa_supplicant for STA. AP is in mode bridge
> but STA isn't (the official firmware crashed in bridge mode, I can set up bridged STA
> using the firmware of Candelatech but the rate is slower a little bit when I do iperf test.
>
>>(You did not provide basically any details on what exacly you've measured).
> Sorry, please feel free to ask me more details.
> I obtained that result table  when I did iperf test in TCP, option -w256K and 10 streams (-P10)
> If I did the test in UDP, with the same bandwidth (option -b),  I lost more packets
> in MCS 8 and 9 compared to MCS7, which also means that MCS7 has better performance.

So probably the air condition you have forces the rate control to pick
MCS7 as the most suitable rates.

>>In open AP mode (bridge), CUS223 HW (not WLE900VX however) and on
>>AP135 platform (customized openwrt SW + bleeding edge of
>>ath10k/wireless subsystem souces - private backports tarball).. for
>>UDP (last time I measured) I have around 820Mpbs for UCP both ways and
>>720Mbps TCP.
>
> This is in NSS3 -MCS9? Did you get better or worse rate if you clear the mask
> (iw wlanX set bitrates) cause if I don't config rate, from AP to STA I have the best rate
> (ie same as MCS7) but from STA to AP my rate is much lower than MCS7 (240 Mbps
> vs 370 Mbps in TCP).

Yes, NSS-3; Over the RF-cables I'm easily able to get MCS9 rates
transmitions without any forced settings (the rate control is picking
the highest rates).

-- 
Bartosz