<div dir="ltr">Another thing to keep in mind is we're using a poor man's version of emulating "passive channels" so the device transmit powers can provide power asymmetry. The distance matrix is about the h-matrices (as shown early in the slides.) Even with that though, the h-matrix elements aren't likely symmetric but it's a reasonable starting point to assume they are. Also being able to switch them in near realtime allows for some forms of transmit and receive asymmetry in the emulated channels as well.<br><br>Bob</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Aug 2, 2021 at 9:44 PM David Lang <<a href="mailto:david@lang.hm">david@lang.hm</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">I agree that we don't want to make perfect the enemy of better.<br>
<br>
A lot of the issues I'm calling out can be simulated/enhanced with different <br>
power levels.<br>
<br>
over wifi distances, I don't think time delays are going to be noticable (we're <br>
talking 10s to low 100s of feet, not miles)<br>
<br>
David Lang<br>
<br>
On Mon, 2 Aug 2021, Bob McMahon wrote:<br>
<br>
> fair enough, but for this "RF emulator device" being able to support<br>
> distance matrices, even hollow symmetric ones, is much better than what's<br>
> typically done. The variable solid state phase shifters are 0-360 so don't<br>
> provide real time delays either.<br>
><br>
> This is another "something is better than nothing" type proposal. I think<br>
> it can be deployed at a relatively low cost which allows for more<br>
> standardized, automated test rigs and much less human interactions and<br>
> human errors.<br>
><br>
> Bob<br>
><br>
> On Mon, Aug 2, 2021 at 9:30 PM David Lang <<a href="mailto:david@lang.hm" target="_blank">david@lang.hm</a>> wrote:<br>
><br>
>> symmetry is not always (or usually) true. stations are commonly heard at<br>
>> much<br>
>> larger distances than they can talk, mobile devices have much less<br>
>> 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>
>> 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<br>
>> 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<br>
>> does<br>
>>> assume symmetry between pairs but that's typically true.<br>
>>><br>
>>> The RF device takes these distance matrices as settings and calculates<br>
>> 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<br>
>> 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<br>
>> 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<br>
>> 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<br>
>> 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<br>
>> 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<br>
>> 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,<br>
>> 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>
>><br>
><br>
><br>
</blockquote></div>
<br>
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