I agree that we don't want to make perfect the enemy of better.
A lot of the issues I'm calling out can be simulated/enhanced with different
power levels.
over wifi distances, I don't think time delays are going to be noticable (we're
talking 10s to low 100s of feet, not miles)
David Lang
On Mon, 2 Aug 2021, Bob McMahon wrote:
fair enough, but for this "RF emulator device" being able to support
distance matrices, even hollow symmetric ones, is much better than what's
typically done. The variable solid state phase shifters are 0-360 so don't
provide real time delays either.
This is another "something is better than nothing" type proposal. I think
it can be deployed at a relatively low cost which allows for more
standardized, automated test rigs and much less human interactions and
human errors.
Bob
On Mon, Aug 2, 2021 at 9:30 PM David Lang <da...@lang.hm> wrote:
symmetry is not always (or usually) true. stations are commonly heard at
much
larger distances than they can talk, mobile devices have much less
transmit
power (becuase they are operating on batteries) than fixed stations, and
when
you adjust the transmit power on a station, you don't adjust it's receive
sensitivity.
David Lang
On Mon, 2 Aug 2021, Bob McMahon wrote:
Date: Mon, 2 Aug 2021 20:23:06 -0700
From: Bob McMahon <bob.mcma...@broadcom.com>
To: David Lang <da...@lang.hm>
Cc: Ben Greear <gree...@candelatech.com>,
Luca Muscariello <muscarie...@ieee.org>,
Cake List <c...@lists.bufferbloat.net>,
Make-Wifi-fast <make-wifi-f...@lists.bufferbloat.net>,
Leonard Kleinrock <l...@cs.ucla.edu>, starl...@lists.bufferbloat.net,
co...@lists.bufferbloat.net,
cerowrt-devel <cerowrt-de...@lists.bufferbloat.net>,
bloat <bloat@lists.bufferbloat.net>
Subject: Re: [Cake] [Make-wifi-fast] [Starlink] [Cerowrt-devel] Due Aug
2:
Internet Quality workshop CFP for the internet architecture board
The distance matrix defines signal attenuations/loss between pairs. It's
straightforward to create a distance matrix that has hidden nodes because
all "signal loss" between pairs is defined. Let's say a 120dB
attenuation
path will cause a node to be hidden as an example.
A B C D
A - 35 120 65
B - 65 65
C - 65
D -
So in the above, AC are hidden from each other but nobody else is. It
does
assume symmetry between pairs but that's typically true.
The RF device takes these distance matrices as settings and calculates
the
five branch tree values (as demonstrated in the video). There are
limitations to solutions though but I've found those not to be an issue
to
date. I've been able to produce hidden nodes quite readily. Add the phase
shifters and spatial stream powers can also be affected, but this isn't
shown in this simple example.
Bob
On Mon, Aug 2, 2021 at 8:12 PM David Lang <da...@lang.hm> wrote:
I guess it depends on what you are intending to test. If you are not
going
to
tinker with any of the over-the-air settings (including the number of
packets
transmitted in one aggregate), the details of what happen over the air
don't
matter much.
But if you are going to be doing any tinkering with what is getting
sent,
and
you ignore the hidden transmitter type problems, you will create a
solution that
seems to work really well in the lab and falls on it's face out in the
wild
where spectrum overload and hidden transmitters are the norm (at least
in
urban
areas), not rare corner cases.
you don't need to include them in every test, but you need to have a way
to
configure your lab to include them before you consider any
settings/algorithm
ready to try in the wild.
David Lang
On Mon, 2 Aug 2021, Bob McMahon wrote:
We find four nodes, a primary BSS and an adjunct one quite good for
lots
of
testing. The six nodes allows for a primary BSS and two adjacent ones.
We
want to minimize complexity to necessary and sufficient.
The challenge we find is having variability (e.g. montecarlos) that's
reproducible and has relevant information. Basically, the distance
matrices
have h-matrices as their elements. Our chips can provide these
h-matrices.
The parts for solid state programmable attenuators and phase shifters
aren't very expensive. A device that supports a five branch tree and
2x2
MIMO seems a very good starting point.
Bob
On Mon, Aug 2, 2021 at 4:55 PM Ben Greear <gree...@candelatech.com>
wrote:
On 8/2/21 4:16 PM, David Lang 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
To add to this, I think you need lots of different station devices,
different capabilities (/n, /ac, /ax, etc)
different numbers of spatial streams, and different distances from the
AP. From download queueing perspective, changing
the capabilities may be sufficient while keeping all stations at same
distance. This assumes you are not
actually testing the wifi rate-ctrl alg. itself, so different
throughput
levels for different stations would be enough.
So, a good station emulator setup (and/or pile of real stations) and a
few
RF chambers and
programmable attenuators and you can test that setup...
From upload perspective, I guess same setup would do the job.
Queuing/fairness might depend a bit more on the
station devices, emulated or otherwise, but I guess a clever AP could
enforce fairness in upstream direction
too by implementing per-sta queues.
Thanks,
Ben
--
Ben Greear <gree...@candelatech.com>
Candela Technologies Inc http://www.candelatech.com
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