From mboxrd@z Thu Jan  1 00:00:00 1970
From: Felix <ic.felix@gmail.com>
Date: Mon, 27 Sep 2010 12:25:36 -0700
Subject: [ath9k-devel] [AR9160]: 3 RX chain operation in 11abg
 legacy-only mode?
In-Reply-To: <20100927181952.GC2429@tux>
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	<20100927181952.GC2429@tux>
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On Mon, 2010-09-27 at 11:19 -0700, Luis R. Rodriguez wrote:
> On Sat, Sep 25, 2010 at 08:14:43PM -0700, Adrian Chadd wrote:
> > Hi,
> > 
> > FreeBSD's AR9160 support enables all three RX chains in legacy mode.
> > The ath9k codebase doesn't - it calibrates all three chains, but the
> > ADC calibration results in legacy mode give all 0x0's for chain 1 and 2.
> > (And seemingly invalid results for chain 0 in 11g mode, but that's another
> > issue which I am hoping someone will comment on.)
> > 
> > Is there any benefit or detriment to leaving RX chains 1 and 2 enabled
> > when in 11a/11bg mode? Does the unit do any kind of multipath
> > discrimination?
Leaving all RX chains enabled will give a huge gain for all OFDM rates,
they get MRC combined
(http://en.wikipedia.org/wiki/Maximal-ratio_combining) in the frequency
domain(after the FFT).

  Felix

> Good question, not sure, but I can see the benefit of enabling other
> chains for selection diversity for legacy, perhaps we just never
> bothered implementing that on ath9k on Linux.
> 
>   Luis