<div dir="ltr">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.<br><br>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.<br><br>Bob</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Aug 7, 2021 at 9:35 PM Dick Roy <<a href="mailto:dickroy@alum.mit.edu">dickroy@alum.mit.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
<br>
-----Original Message-----<br>
From: Starlink [mailto:<a href="mailto:starlink-bounces@lists.bufferbloat.net" target="_blank">starlink-bounces@lists.bufferbloat.net</a>] On Behalf Of<br>
David Lang<br>
Sent: Monday, August 2, 2021 9:31 PM<br>
To: Bob McMahon<br>
Cc: <a href="mailto:starlink@lists.bufferbloat.net" target="_blank">starlink@lists.bufferbloat.net</a>; Make-Wifi-fast; Cake List;<br>
<a href="mailto:codel@lists.bufferbloat.net" target="_blank">codel@lists.bufferbloat.net</a>; cerowrt-devel; bloat<br>
Subject: Re: [Starlink] [Cake] [Make-wifi-fast] [Cerowrt-devel] Due Aug 2:<br>
Internet Quality workshop CFP for the internet architecture board<br>
<br>
symmetry is not always (or usually) true. <br>
[RR] There is a big difference between "symmetric RF channels" and "balanced<br>
RF links". Be careful not to confuse the two.<br>
<br>
stations are commonly heard at much <br>
larger distances than they can talk, mobile devices have much less transmit <br>
power (becuase they are operating on batteries) than fixed stations, and<br>
when <br>
you adjust the transmit power on a station, you don't adjust it's receive <br>
sensitivity.<br>
<br>
[RR] Not quite true. Rx sensitivity is a function of MCS (the modulation and<br>
coding scheme) and those levels can be adjusted, both up and down, by<br>
changing the MCS. This is in fact one of the major tools that needs to be<br>
integrated into wireless systems today. It's generally overlooked, though<br>
not always! Starlink should be doing this if they are not already BTW!<br>
<br>
David Lang<br>
<br>
On Mon, 2 Aug 2021, Bob McMahon wrote:<br>
<br>
> Date: Mon, 2 Aug 2021 20:23:06 -0700<br>
> From: Bob McMahon <<a href="mailto:bob.mcmahon@broadcom.com" target="_blank">bob.mcmahon@broadcom.com</a>><br>
> To: David Lang <<a href="mailto:david@lang.hm" target="_blank">david@lang.hm</a>><br>
> Cc: Ben Greear <<a href="mailto:greearb@candelatech.com" target="_blank">greearb@candelatech.com</a>>,<br>
> Luca Muscariello <<a href="mailto:muscariello@ieee.org" target="_blank">muscariello@ieee.org</a>>,<br>
> Cake List <<a href="mailto:cake@lists.bufferbloat.net" target="_blank">cake@lists.bufferbloat.net</a>>,<br>
> Make-Wifi-fast <<a href="mailto:make-wifi-fast@lists.bufferbloat.net" target="_blank">make-wifi-fast@lists.bufferbloat.net</a>>,<br>
> Leonard Kleinrock <<a href="mailto:lk@cs.ucla.edu" target="_blank">lk@cs.ucla.edu</a>>, <a href="mailto:starlink@lists.bufferbloat.net" target="_blank">starlink@lists.bufferbloat.net</a>,<br>
> <a href="mailto:codel@lists.bufferbloat.net" target="_blank">codel@lists.bufferbloat.net</a>,<br>
> cerowrt-devel <<a href="mailto:cerowrt-devel@lists.bufferbloat.net" target="_blank">cerowrt-devel@lists.bufferbloat.net</a>>,<br>
> bloat <<a href="mailto:bloat@lists.bufferbloat.net" target="_blank">bloat@lists.bufferbloat.net</a>><br>
> Subject: Re: [Cake] [Make-wifi-fast] [Starlink] [Cerowrt-devel] Due Aug 2:<br>
> Internet Quality workshop CFP for the internet architecture board<br>
> <br>
> The distance matrix defines signal attenuations/loss between pairs. It's<br>
> straightforward to create a distance matrix that has hidden nodes because<br>
> all "signal loss" between pairs is defined. Let's say a 120dB<br>
attenuation<br>
> path will cause a node to be hidden as an example.<br>
><br>
> A B C D<br>
> A - 35 120 65<br>
> B - 65 65<br>
> C - 65<br>
> D -<br>
><br>
> So in the above, AC are hidden from each other but nobody else is. It does<br>
> assume symmetry between pairs but that's typically true.<br>
><br>
> The RF device takes these distance matrices as settings and calculates the<br>
> five branch tree values (as demonstrated in the video). There are<br>
> limitations to solutions though but I've found those not to be an issue to<br>
> date. I've been able to produce hidden nodes quite readily. Add the phase<br>
> shifters and spatial stream powers can also be affected, but this isn't<br>
> shown in this simple example.<br>
><br>
> Bob<br>
><br>
> On Mon, Aug 2, 2021 at 8:12 PM David Lang <<a href="mailto:david@lang.hm" target="_blank">david@lang.hm</a>> wrote:<br>
><br>
>> I guess it depends on what you are intending to test. If you are not<br>
going<br>
>> to<br>
>> tinker with any of the over-the-air settings (including the number of<br>
>> packets<br>
>> transmitted in one aggregate), the details of what happen over the air<br>
>> don't<br>
>> matter much.<br>
>><br>
>> But if you are going to be doing any tinkering with what is getting sent,<br>
>> and<br>
>> you ignore the hidden transmitter type problems, you will create a<br>
>> solution that<br>
>> seems to work really well in the lab and falls on it's face out in the<br>
>> wild<br>
>> where spectrum overload and hidden transmitters are the norm (at least in<br>
>> urban<br>
>> areas), not rare corner cases.<br>
>><br>
>> you don't need to include them in every test, but you need to have a way<br>
>> to<br>
>> configure your lab to include them before you consider any<br>
>> settings/algorithm<br>
>> ready to try in the wild.<br>
>><br>
>> David Lang<br>
>><br>
>> On Mon, 2 Aug 2021, Bob McMahon wrote:<br>
>><br>
>>> We find four nodes, a primary BSS and an adjunct one quite good for lots<br>
>> of<br>
>>> testing. The six nodes allows for a primary BSS and two adjacent ones.<br>
>> We<br>
>>> want to minimize complexity to necessary and sufficient.<br>
>>><br>
>>> The challenge we find is having variability (e.g. montecarlos) that's<br>
>>> reproducible and has relevant information. Basically, the distance<br>
>> matrices<br>
>>> have h-matrices as their elements. Our chips can provide these<br>
>> h-matrices.<br>
>>><br>
>>> The parts for solid state programmable attenuators and phase shifters<br>
>>> aren't very expensive. A device that supports a five branch tree and 2x2<br>
>>> MIMO seems a very good starting point.<br>
>>><br>
>>> Bob<br>
>>><br>
>>> On Mon, Aug 2, 2021 at 4:55 PM Ben Greear <<a href="mailto:greearb@candelatech.com" target="_blank">greearb@candelatech.com</a>><br>
>> wrote:<br>
>>><br>
>>>> On 8/2/21 4:16 PM, David Lang wrote:<br>
>>>>> If you are going to setup a test environment for wifi, you need to<br>
>>>> include the ability to make a fe cases that only happen with RF, not<br>
>> with<br>
>>>> wired networks and<br>
>>>>> 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.<br>
>>>> station A can hear that station B is transmitting, but not with a<br>
strong<br>
>>>> enough signal to<br>
>>>>> decode the signal (yes in theory you can work around interference, but<br>
>>>> in practice interference is still a real thing)<br>
>>>>><br>
>>>>> David Lang<br>
>>>>><br>
>>>><br>
>>>> To add to this, I think you need lots of different station devices,<br>
>>>> different capabilities (/n, /ac, /ax, etc)<br>
>>>> different numbers of spatial streams, and different distances from the<br>
>>>> AP. From download queueing perspective, changing<br>
>>>> the capabilities may be sufficient while keeping all stations at same<br>
>>>> distance. This assumes you are not<br>
>>>> actually testing the wifi rate-ctrl alg. itself, so different<br>
throughput<br>
>>>> levels for different stations would be enough.<br>
>>>><br>
>>>> So, a good station emulator setup (and/or pile of real stations) and a<br>
>> few<br>
>>>> RF chambers and<br>
>>>> programmable attenuators and you can test that setup...<br>
>>>><br>
>>>> From upload perspective, I guess same setup would do the job.<br>
>>>> Queuing/fairness might depend a bit more on the<br>
>>>> station devices, emulated or otherwise, but I guess a clever AP could<br>
>>>> enforce fairness in upstream direction<br>
>>>> too by implementing per-sta queues.<br>
>>>><br>
>>>> Thanks,<br>
>>>> Ben<br>
>>>><br>
>>>> --<br>
>>>> Ben Greear <<a href="mailto:greearb@candelatech.com" target="_blank">greearb@candelatech.com</a>><br>
>>>> Candela Technologies Inc <a href="http://www.candelatech.com" rel="noreferrer" target="_blank">http://www.candelatech.com</a><br>
>>>><br>
>>><br>
>>><br>
>><br>
><br>
><br>
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