bi241@scn.org hath wroth:

>i played with the linksys WRT54G for a while and somehow got stuck in
>DD-WRT concept of diversity antenna. and also i am skeptical about the
>MIMO title that the Ralink chipset is advertised, after all, the
>AWLL5025 is still within 802.11G specs, while MIMO seems to belong to
>draft-N or whatever...

Correct. The marketting baloney that accompanies the Buffalo
WHR-HP-54G is disgusting. They use the term MIMO because it's the
latest and greatest, while there's nothing even remotely related to
MIMO inside the box. What Buffalo is pushing is that you'll get the
same performance as MIMO with their high power transmitter, and offer
some un-reproduceable tests to prove it. It makes me sick to see a
good product polluted by such technically inept marketing.
<http://www.buffalotech.com/technology/our-technology/high-power/>


>but yeah in true MIMO design, diversity mean multiple RX antennas, (and
>mulltiple TX antennas too)
>i often see draft-N wireless adpaters with three antennas, just like
>the 802.11G AWLH5025 PCI adapter, but i was too lazy to learn about the
>antenna configurations.

MIMO is not diversity. What "real" MIMO does is send data from 2 or
more antennas. The data arrives at corresponding antennas and
receivers, but delayed very slightly. The DSP is able to seperate out
the various delays and extract seperate data streams for each delay.
The result is a doubling in available bandwidth. See:
<http://www.airgonetworks.com/mimo/how/>

There's also a skool of thought that claims that MIMO is also adaptive
antenna patterns. This is where the access point contains a smart
antenna system that adds more gain where it's needed, and installs
nulls where it detects interference. See Ruckus Beamflex at:
<http://www.ruckuswireless.com/technology/beamflex.php>
I have a good laugh on this one. The system works, but Netgear
advertises their various routers mounted in the vertical (tower)
position, where the beam forming can't work.

If you're interested in reading about non-MIMO diversity reception
see:
<http://www.commsdesign.com/design_corner/showArticle.jhtml?articleID=16500279>
<http://www.commsdesign.com/design_corner/showArticle.jhtml?articleID=16501888>
<http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml>

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558