>> Right - so the MRC functionality is in the chip's DSP and entirely >> invisible to the software? Yes? Just being 100% clear here... > > Beats me. I haven't dealt with MRC at all in software so I guess. > >>>> And to be clear, you think the 802.11n chipsets before the >>>> AR9300 *do not* include TxBF at all? Not that it simply isn't >>>> supported by the drivers? >>> >>> Only a legacy (802.11g) end of life'd device had some form >>> of Tx beamforming, but that's not even supported and its easier >>> to just assume no chipset supports it other than the shiny >>> new AR93xx family. >> >> Right - and as discussed, TxBF has less benefit than with 802.11n. > > Oh?
This is a typo. But my point is that when you have 2x2:2, MRC, multiple spatial streams, etc. adding TxBF to the equation doesn't achieve the same kinds of gains for mid to high bitrate situations you see when you drop a TxBF 802.11g system into place. At least that's my understanding... I haven't actually modeled all of these variables together into a full system. >> Since then, I have looked at some Matlab simulations here and seeing >> that 2 antenna MRC can slightly outperform 2 antenna TxBF. > > Good to know, can you publish your results while at it. I was only playing with MRC versus TxBF in 2x2 configurations. My data isn't conclusive enough to be published and didn't look at them in combination. Mostly, I was trying to answer the question, why would they drop TxBF from 802.11n chipsets? Did we end up with a worse performing product? And the conclusion was that MRC probably equals or beats TxBF. e.g. client with MRC connected to non-TxBF AP should achieve similar to slightly better performance than a non-MRC client with a TxBF AP, resulting in significant reception gains for virtually all stations versus a non-MRC chipset. Conversely, TxBF would only help with transmit, which is usually much less data intensive than receive for most users (e.g. station mode client radios in notebooks, desktops, phones, etc.) I also suspect that MRC makes it easier to deal with cheap / crappy hardware implementations - cheap amplifiers, suboptimal antennas, etc. So if you want a fast performing chipset and have a time/dollar/power/complexity budget to meet, MRC is a better choice for most of your customers most of the time. Or at least that's my take on it. All that said, AR9003 will still be warmly welcomed. I'm not arguing that TxBF is useless, just not quite as overwhelmingly valuable as it once was. (This is highly context sensitive though, as 3x3 802.11n APs with 802.11g clients will probably see big gains, but 3x3 802.11n to 3x3 802.11n will not see as much, and at extreme range, the TxBF may also keep a very slow connection alive longer.) It's pretty hard to encapsulate all this effectively into text, and I don't know that I have the time or expertise to build out and publish extensive simulations.... but I hope this makes some sense. -Galen _______________________________________________ ath9k-devel mailing list ath9k-devel@lists.ath9k.org https://lists.ath9k.org/mailman/listinfo/ath9k-devel
