On Feb 26, 2010, at 9:13 AM, Daniel Halperin wrote: > On Feb 26, 2010, at 8:45 AM, Luis R. Rodriguez wrote: > >>> Luis - can you comment on the MRC implementation? Is this entirely >>> invisible to ath9k, or is this implemented / supported in software? >> >> No, frankly this is the first time I read about MRC. >> I just poked a few guys here about MRC and got the clarification >> above. > > I'm confused about your goals, Galen? What is it you're trying to learn about > the chips? Do you want to understand the RF-level wireless processing, or > don't you? The answers are much easier to intuit if one understands the > underlying processing, and I don't see how your questions can return valuable > information if one does not :).
I understand a significant amount about the DSP and RF processing, but I'm no chip designer, nor have I any plans to be one. > MRC is a receiver-side technique that is entirely performed at the RF > processing layer (likely in the DSP) and as such should be opaque to the > driver-level software. It involves making the copies of signals received by > the different antennas coherent and adding them before doing the normal RF > processing that turns the electromagnetic signals into bits. This is simply > not the purpose of the software available on the host side, even in a > software HAL/MAC; this functionality is likely to be in DSP ASICs on the > chips themselves. I understand most of this function is probably in the DSP - but nothing documented to date had told me whether MRC was actually present. It looks like it's entirely invisible to software which is fine. > The only way I envision software having anything to do with MRC would be > (maybe) some software-side control of what relative power level thresholds to > use to decide when MRC is worth it. If antenna A has a signal that is 20 dB > (100x) stronger than antenna B, it's likely not worth combining A and B's > signals (and might take extra computation/power) and instead better to just > use A. Maybe the 20 dB is configurable in ath5k/9k as it is in iwlwifi. Other > than that, I'd expect there to be pretty much no software mention of MRC. > > Dan > > p.s. TxBF is still helpful with multiple spatial streams. You can combine > TxBF with fewer streams than (or equal) antennas, and there are (often > sizable) gains. Yes - I was looking around at this with Matlab simulations. But it seems like in a lot of cases with 2x2 configurations, by the time you have MRC and STBC involved, you tend to primarily extend your range more than increase your throughput in excellent to moderate SNR situations. > p.p.s. If you do want to learn more about the RF side of things and are > willing to tackle an explanation written for computer scientists without a > strong EE / RF signal processing background, you can check out our tutorial > called "802.11 with Multiple Antennas for Dummies." It's available from ACM > here (we kept the copyright, so it should be free) > <http://portal.acm.org/citation.cfm?id=1672308.1672313> or off my website > <http://www.cs.washington.edu/homes/dhalperi> direct PDF link: > <http://www.cs.washington.edu/homes/dhalperi/pubs/mimo_for_dummies.pdf> . > _______________________________________________ > ath9k-devel mailing list > ath9k-devel@lists.ath9k.org > https://lists.ath9k.org/mailman/listinfo/ath9k-devel _______________________________________________ ath9k-devel mailing list ath9k-devel@lists.ath9k.org https://lists.ath9k.org/mailman/listinfo/ath9k-devel
