<div dir="ltr">My own experiments with this, in the past (5+ years ago), was that you absolutely had to use cabled setups for repeatability, but then didn't have enough randomness in the variability to really test anything that was problematic. We could create hidden nodes, or arbitrary meshes of devices, but they were always static.<div><br></div><div>We used N-way RF splitters and either direct coax in lieu of antennas, or isolation boxes with an antenna attached to a bulkhead fitting, with coax on the outside. One other problem we ran into was that unshielded radio front-ends could "hear" each other without isolation boxes.</div><div><br></div><div>I really wanted both variable attenuators, and points where I could inject RF noise, so that instead of broad-band attenuation, maybe we could just swamp the communications with other noise (which is also a common thing we were running into with both our 900Mhz (ZWave) and 2.4GHz (wifi) radios.</div><div><br></div><div>Less common, but something I still see, is that a moving station has continual issues staying in proper MIMO phase(s) with the AP. Or I think that's what's happening. Slow, continual movement of the two, relative to each other, and the packet rate drops through the floor until they stop having relative motion. And I assume that also applies to time-varying path-loss and path-distance (multipath reflections).</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Aug 7, 2021 at 10:15 PM Bob McMahon via Make-wifi-fast <<a href="mailto:make-wifi-fast@lists.bufferbloat.net">make-wifi-fast@lists.bufferbloat.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div dir="ltr">We have hundreds of test rigs in multiple labs all over geography. Each rig is shielded from the others using things like RF enclosures. We want reproducibility in the RF paths/channels as well as variability. Most have built fixed rigs using conducted equipment. This is far from anything real. A butler matrix produces great condition numbers but that makes it too easy for MIMO rate selection algorithms.<br><br>Our real world test is using a real house that has been rented. Not cheap nor scalable.<br><br>There is quite a gap between the two. A RF path device that supports both variable range and variable mixing is a step towards closing the gap.<br><br>Bob</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Aug 7, 2021 at 10:07 PM Dick Roy <<a href="mailto:dickroy@alum.mit.edu" target="_blank">dickroy@alum.mit.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal"><b><font size="2" face="Tahoma"><span style="font-size:10pt;font-family:Tahoma;font-weight:bold">From:</span></font></b><font size="2" face="Tahoma"><span style="font-size:10pt;font-family:Tahoma"> Starlink
[mailto:<a href="mailto:starlink-bounces@lists.bufferbloat.net" target="_blank">starlink-bounces@lists.bufferbloat.net</a>] <b><span style="font-weight:bold">On Behalf Of </span></b>Bob McMahon<br>
<b><span style="font-weight:bold">Sent:</span></b> Monday, August 2, 2021 6:24
PM<br>
<b><span style="font-weight:bold">To:</span></b> Leonard Kleinrock<br>
<b><span style="font-weight:bold">Cc:</span></b> <a href="mailto:starlink@lists.bufferbloat.net" target="_blank">starlink@lists.bufferbloat.net</a>;
Make-Wifi-fast; Cake List; <a href="mailto:codel@lists.bufferbloat.net" target="_blank">codel@lists.bufferbloat.net</a>; cerowrt-devel; bloat<br>
<b><span style="font-weight:bold">Subject:</span></b> Re: [Starlink] [Cake]
[Make-wifi-fast] [Cerowrt-devel] Due Aug 2: Internet Quality workshop CFP for
the internet architecture board</span></font><u></u><u></u></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">I found the following talk relevant to distances between all the
nodes. <a href="https://www.youtube.com/watch?v=PNoUcQTCxiM" target="_blank">https://www.youtube.com/watch?v=PNoUcQTCxiM</a>
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<br>
Distance is an abstract idea but applies to energy into a node as well as
phylogenetic trees. It's the same problem, i.e. fitting a distance matrix using
some sort of tree. I've found the five branch tree works well for four nodes.<font color="navy"><span style="color:navy"><u></u><u></u></span></font></span></font></p>
<p class="MsoNormal"><b><i><font size="2" color="navy" face="Arial"><span style="font-size:10pt;font-family:Arial;color:navy;font-weight:bold;font-style:italic">[RR] These trees are means for approximating a higher
dimensional real-world problem with a lower dimensional structure. You may be
doing this to save hardware when trying to cable up some complex test scenarios,
however I’m wondering why? Why not just put the STAs in the lab and turn them
on rather than cabling them?<u></u><u></u></span></font></i></b></p>
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Bob <u></u><u></u></span></font></p>
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<p class="MsoNormal"><font size="3" face="Times New Roman"><span style="font-size:12pt">On Mon, Aug 2, 2021 at 5:37 PM Leonard Kleinrock <<a href="mailto:lk@cs.ucla.edu" target="_blank">lk@cs.ucla.edu</a>> wrote:<u></u><u></u></span></font></p>
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<p class="MsoNormal" style="margin-bottom:12pt"><font size="3" face="Times New Roman"><span style="font-size:12pt">These cases are what my
student, Fouad Tobagi and I called the Hidden Terminal Problem (with the Busy
Tone solution) back in 1975.<br>
<br>
Len <br>
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<br>
> On Aug 2, 2021, at 4:16 PM, David Lang <<a href="mailto:david@lang.hm" target="_blank">david@lang.hm</a>> wrote:<br>
> <br>
> If you are going to setup a test environment for wifi, you need to include
the ability to make a fe cases that only happen with RF, not with wired
networks and are commonly overlooked<br>
> <br>
> 1. station A can hear station B and C but they cannot hear each other<br>
> 2. station A can hear station B but station B cannot hear station A 3.
station A can hear that station B is transmitting, but not with a strong enough
signal to decode the signal (yes in theory you can work around interference,
but in practice interference is still a real thing)<br>
> <br>
> David Lang<br>
> <u></u><u></u></span></font></p>
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