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From:   Ramon Fontes <ramonreisfontes@gmail.com>
Date:   Wed, 21 Nov 2018 09:26:41 -0300
Message-ID: <CAK8U23Yi-wa0yT_K2eazTBEsVH3kmYHpZEeMmoDEAdyamdSTqA@mail.gmail.com>
Subject: Re: mac80211_hwsim: multiple antennas
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     linux-wireless@vger.kernel.org
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Sorry. I meant throughput.

Let's considering GI=3D800ns - 20MHz:

Without setting the MCS value the throughput is around 18Mbps.
tx bitrate 58.5 MBit/s MCS 6
rx bitrate 48.0 MBit/s

Then I set the bitrate to ht-mcs-2.4 13, 14 and finally 15. Although
the tx bitrate increases as expected the maximum throughput is around
33Mbps
tx bitrate: 117.0 MBit/s MCS 14
rx bitrate: 54.0 MBit/s

I also tried the same with 40Mhz and the throughput doesn't change.
The maximum throughput is always ~33Mbps. Even when the tx bitrate is
300Mbps the maximum throughput is still ~33Mbps.

I noticed that the rx birate is related to the hwsim_rates from
mac80211_hwsim, however, increasing the value provided by hwsim_rates
doesn't change the throughput.

My topology consists of three nodes. 2 clients and one AP working with
hostapd. The hostapd config file includes ieee80211n=3D1 and
ht_capab=3D'[HT40+]'. Sometimes I can see that tx bitrate is working at
40Mhz. However, it doesn't work at 40Mhz when there are data traffic.
The RSSI of both clients is -60dBm, but I also tried with -50dBm and
-40dBm. Tested with both 2.4 and 5Ghz.

This is my per.c file
(https://github.com/ramonfontes/wmediumd/blob/ieee80211n/wmediumd/per.c).
I only check if the rate-flags =3D=3D IEEE80211_TX_RC_MCS and I force some
of the rateset added in my per.c.

Given this brief explanation I was wondering if it could be related to
the number of antennas.

Thank you in advance.
Ramon

Em qua, 21 de nov de 2018 =C3=A0s 06:11, Johannes Berg
<johannes@sipsolutions.net> escreveu:
>
> On Tue, 2018-11-20 at 16:33 -0300, Ramon Fontes wrote:
> > Would be possible to simulate (or even add support to) multiple
> > antennas? I was trying to extend wmediumd to 802.11n according the
> > rates provided by http://mcsindex.com/, but the maximum rate I get is
> > ~33Mbps, even if I set the MCS index to 15. Given the result, I
> > thought that it could be related to the number of antennas. Is my
> > assumption correct?
>
> I'm not sure what you mean by "the maximum rate I get is ~33Mbps".
>
> Are you trying to actually _measure_ it? Then, on a decent platform, you
> should probably get many *gigabits*.
>
> Or are you trying to look at the rate in "iw station dump" or in
> radiotap? Then you should see higher rates since hwsim is configured to
> pretend to have 4 spatial streams (IIRC)
>
> johannes
>