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From: Daniel Halperin <dhalperi@cs.washington.edu>
Date: Wed, 29 Jun 2011 19:36:30 -0700
Message-ID: <BANLkTinQOWiddbSiyCDMhwu78fFUkw+seA@mail.gmail.com> (sfid-20110630_043655_000444_1E41E810)
Subject: Re: [ath9k-devel] STBC functionality details request
To: Fred Matthews <fredmm@hotmail.co.uk>
Cc: Adrian Chadd <adrian@freebsd.org>, ath9k-devel@venema.h4ckr.net,
	linux-wireless@vger.kernel.org
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On Wed, Jun 29, 2011 at 6:17 PM, Fred Matthews <fredmm@hotmail.co.uk> wrote:
>
> Hi,
> Thanks for replying Adrian,
>
> OK, just for clarity, you are saying for 1-stream STBC NICs
> (AR9380/9280), when I enable STBC from hostapd, the driver only
> transmits in STBC (transmits multiple copies of data to each antenna)
> if it sending at MCSs 0-7 (1 stream rates), due to low signal quality
> or via fixing the MCS to those values. For all other MCSs STBC is
> disabled.
>
> Does the rate adaptation (minstrel/ath9k) tell the driver to use STBC,
> or is this done at automatically at a lower level?
>
> Any other information about STBC would be appreciated.
>
You should really look at the 802.11n standard to understand how they
implement STBC. From the driver side, from what I can tell, there is
never a downside (rate-wise) to enabling STBC for transmissions at
MCS0--MCS7. Thus, minstrel_ht turns it on by default.

Dan