Re: [Cerowrt-devel] [Make-wifi-fast] [Starlink] [Cake] Due Aug 2: Internet Quality workshop CFP for the internet architecture board

[Aaron Wood <woody77@gmail.com>]

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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.

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.

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.

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).

On Sat, Aug 7, 2021 at 10:15 PM Bob McMahon via Make-wifi-fast <
make-wifi-fast@lists.bufferbloat.net> wrote:

> 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.
>
> Our real world test is using a real house that has been rented. Not cheap
> nor scalable.
>
> 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.
>
> Bob
>
> On Sat, Aug 7, 2021 at 10:07 PM Dick Roy <dickroy@alum.mit.edu> wrote:
>
>>
>>
>>
>> ------------------------------
>>
>> *From:* Starlink [mailto:starlink-bounces@lists.bufferbloat.net] *On
>> Behalf Of *Bob McMahon
>> *Sent:* Monday, August 2, 2021 6:24 PM
>> *To:* Leonard Kleinrock
>> *Cc:* starlink@lists.bufferbloat.net; Make-Wifi-fast; Cake List;
>> codel@lists.bufferbloat.net; cerowrt-devel; bloat
>> *Subject:* Re: [Starlink] [Cake] [Make-wifi-fast] [Cerowrt-devel] Due
>> Aug 2: Internet Quality workshop CFP for the internet architecture board
>>
>>
>>
>> I found the following talk relevant to distances between all the nodes.
>> https://www.youtube.com/watch?v=PNoUcQTCxiM
>>
>> 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.
>>
>> *[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?*
>>
>>
>>
>> Bob
>>
>>
>>
>> On Mon, Aug 2, 2021 at 5:37 PM Leonard Kleinrock <lk@cs.ucla.edu> wrote:
>>
>> These cases are what my student, Fouad Tobagi and I called the Hidden
>> Terminal Problem (with the Busy Tone solution) back in 1975.
>>
>> Len
>>
>>
>> > On Aug 2, 2021, at 4:16 PM, David Lang <david@lang.hm> wrote:
>> >
>> > 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
>> >
>> > 1. station A can hear station B and C but they cannot hear each other
>> > 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)
>> >
>> > David Lang
>> >
>>
>>
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>
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