[Starlink] [Cake] [Make-wifi-fast] [Cerowrt-devel] Due Aug 2: Internet Quality workshop CFP for the internet architecture board
Bob McMahon
bob.mcmahon at broadcom.com
Sun Aug 8 01:04:35 EDT 2021
The four nodes being connected per a five branch tree using variable
attenuators on the branches can produce hidden nodes quite readily. The
solutions for the attenuations are straight forward per being given the
desired distance matrices.
The challenging part is supporting distance matrices that have h-matrices
as the elements. The solid state variable phase shifters combined with
chips that can dump the h-matrix works fairly well per running monte carlos
and grabbing such a distance matrix. Mapping these distance matrices,
matrices with h-matrices as the elements, to "real world" conditions is not
so easy. But having the ability to do so at a reasonable price and in a
reproducible way is very worthwhile to automated testing systems.
Bob
On Sat, Aug 7, 2021 at 9:35 PM Dick Roy <dickroy at alum.mit.edu> wrote:
>
>
> -----Original Message-----
> From: Starlink [mailto:starlink-bounces at lists.bufferbloat.net] On Behalf
> Of
> David Lang
> Sent: Monday, August 2, 2021 9:31 PM
> To: Bob McMahon
> Cc: starlink at lists.bufferbloat.net; Make-Wifi-fast; Cake List;
> codel at 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
>
> symmetry is not always (or usually) true.
> [RR] There is a big difference between "symmetric RF channels" and
> "balanced
> RF links". Be careful not to confuse the two.
>
> 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.
>
> [RR] Not quite true. Rx sensitivity is a function of MCS (the modulation
> and
> coding scheme) and those levels can be adjusted, both up and down, by
> changing the MCS. This is in fact one of the major tools that needs to be
> integrated into wireless systems today. It's generally overlooked, though
> not always! Starlink should be doing this if they are not already BTW!
>
> David Lang
>
> On Mon, 2 Aug 2021, Bob McMahon wrote:
>
> > Date: Mon, 2 Aug 2021 20:23:06 -0700
> > From: Bob McMahon <bob.mcmahon at broadcom.com>
> > To: David Lang <david at lang.hm>
> > Cc: Ben Greear <greearb at candelatech.com>,
> > Luca Muscariello <muscariello at ieee.org>,
> > Cake List <cake at lists.bufferbloat.net>,
> > Make-Wifi-fast <make-wifi-fast at lists.bufferbloat.net>,
> > Leonard Kleinrock <lk at cs.ucla.edu>, starlink at lists.bufferbloat.net,
> > codel at lists.bufferbloat.net,
> > cerowrt-devel <cerowrt-devel at lists.bufferbloat.net>,
> > bloat <bloat at 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 <david at 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 <greearb at 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 <greearb at candelatech.com>
> >>>> Candela Technologies Inc http://www.candelatech.com
> >>>>
> >>>
> >>>
> >>
> >
> >
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>
>
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