Performance v/s signal quality graph.

Bartosz Markowski bartosz.markowski at
Tue Aug 5 08:25:10 PDT 2014

On 5 August 2014 17:15, Bart Jooris <Bart.Jooris at> wrote:
> 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?

Did you platform not suffer from lack of resources? On less powerfull
devices (e.g. ARM based routers) the main blocker for higher
throughput were the host CPU.. On high end x86 laptops I was getting
around 900Mbps UDP in cabled environment some time ago.

Also what mode are you testing AP / STA? Is your DUT bridged or has to
generate the traffic also?

> -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?
> Thanks,
> Bart
> 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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