Performance v/s signal quality graph.

Bart Jooris Bart.Jooris at
Tue Aug 5 08:15:58 PDT 2014

Hi Ben,

I enjoyed watching your graph already a few times now ;-)

I have a few questions related to your experiment:
-about the setup, the cards have 3x3 MIMO so the attenuator has probably 
also three channels which are attenuated in parallel?
-based on the datasheet of the QCA9880 VHT80_MCS9 reception should break 
around -68dBm. On your graph it breaks around -52dBm, which is not 
within the described tolerances. Do you have any idea what could be 
causing this? Is the noise level higher than expected? Or did I made the 
wrong conclusions? I will try to verify on our setup.
-my million dollar question to you is related to the approx. 810Mbps UDP 
goodput :-) I already did some experiments over 3 coax cables, I noticed 
the same UDP goodput as over the air, which is around 640Mbps. Watching 
the sniffer I've noticed MCS=9, Data rate=1299.9 Mbps and block ACKs 
every (in avg.) 10 frames. So what is the key to the higher goodput?
-related to the hot signal, without having proof I've noticed that  it 
is easier to have higher goodputs with a low tx-power set, like 1 dBm. 
But probably more related to our setup... Which tx-power did you use 
during your experiments? Would you be able to get the same results 
(point break around -52dBm) with another tx-power set?



On 07/26/2014 01:15 AM, Ben Greear wrote:
> Some time back, I ran some tests, and someone (sorry, can't remember or find the email)
> suggested my signal might be too hot.  I was using a 30 db fixed attenuator inline with the SMA
> cables.
> I set up a test today with E5 processor system as station, and a fast i7 processor
> system as AP, with the two systems cabled through our variable attenuator.  Open authentication,
> channel 149, other wifi equipment in area on 5ghz was (mostly) idle or powered down.
> Kernel is 3.14.13+, latest ath10k CT (10.1.467 based) firmware on both systems
> (though I don't think that matters much for throughput tests).  10 virtual stations
> configured on station machine, but only one was actively doing traffic.
> Here is a udp download v/s rx-signal graph as the attenuator is stepped from 0 to 95.5
> db attenuation in .5 db steps.
> The rx-signal axis is the left hand side.  The green graph is the station's (ie netdev)
> rx bps, the black is UDP goodput.
> It seems ath10k (WLE900VX) has no real trouble with hot signals, and runs best between
> -15 and -52 rx signal level (as reported by the station device).
> Our systems are not perfectly isolated, so the maximum attenuation is around -85.
> Enjoy,
> Ben

Bart Jooris
Department of Information Technology
Internet Based Communication Networks and Services (IBCN)
Ghent University - iMinds
Gaston Crommenlaan 8 (Bus 201), B-9050 Gent, Belgium
E-mail: bart.jooris at
M: +32 474 59 53 42
Tel. +32 9 33 14900
Fax +32 9 33 14899

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