Re: [Make-wifi-fast] Wiring up a wireless testbed

[Bob McMahon <bob.mcmahon@broadcom.com>]

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A way I think about is to emulate the "system" in both range/power
(attenuation) and in mixing (phase shifts)   It's a diagonal matrix for
range feeding into an h-matrix for the mixing.  A butler matrix can be used
for the latter if variable phase control isn't required, e.g. you don't
care about spatial stream relative powers.

On adding energy for "random" noise, some knobs of concern are the energy
detect on the tx and signal floor for the rx.   These sources can be fed
into the same h-matrix through their own d-matrices.  This won't replace
field tests but helps get closer towards that while providing for repeat
ability.

Also, equally important by my judgment, though not related to wireless, is
to synchronize the clocks on the PCs.  An oven controlled oscillator and
PTP works well towards that goal.

Bob



On Fri, Nov 3, 2017 at 4:03 PM, Aaron Wood <woody77@gmail.com> wrote:

> What this setup also removes is random noise, which is good for
> repeatability, but bad for real-life testing. My experiences doing similar
> are that there isn’t much of a grey area between a “great”
> throughput/packet error rate and “nothing works”.
>
> It also removes the real-world crosstalk between the antennas.
>
> So good for some things, especially automated tests, but it’s not a
> replacement for real field tests in the presence of random noise.
>
> On Fri, Nov 3, 2017 at 15:51 Toke Høiland-Jørgensen <toke@toke.dk> wrote:
>
>> Since I had to (physically) move my wireless testbed recently, I had to
>> figure out a way to run reliable WiFi experiments in a cramped server
>> room. I ended up wiring everything up instead of running over the air,
>> and documented the process here, in case anyone wants to replicate it:
>>
>> https://blog.tohojo.dk/2017/11/building-a-wireless-
>> testbed-with-wires.html
>>
>> Also, if anyone sees any fatal flaw in that setup, please do let me know
>> :)
>>
>> -Toke
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