[Make-wifi-fast] SmallNetBuilder article: Does OFDMA Really Work?

[Bob McMahon]

I haven't looked closely at OFDMA but these latency numbers seem way too
high for it to matter.  Why is the latency so high?  It suggests there may
be queueing delay (bloat) unrelated to media access.

Also, one aspect is that OFDMA is replacing EDCA with AP scheduling per
trigger frame.  EDCA kinda sucks per listen before talk which is about 100
microseconds on average which has to be paid even when no energy detect.
This limits the transmits per second performance to 10K (1/0.0001.). Also
remember that WiFi aggregates so transmissions have multiple packets and
long transmits will consume those 10K tx ops. One way to get around
aggregation is to use voice (VO) access class which many devices won't
aggregate (mileage will vary.). Then take a packets per second
measurement with small packets.  This would give an idea on the frame
scheduling being AP based vs EDCA.

Also, measuring ping time as a proxy for latency isn't ideal. Better to
measure trip times of the actual traffic.  This requires clock sync to a
common reference. GPS atomic clocks are available but it does take some
setup work.

I haven't thought about RU optimizations and that testing so can't really
comment there.

Also, I'd consider replacing the mechanical turn table with variable phase
shifters and set them in the MIMO (or H-Matrix) path.  I use model 8421
from Aeroflex
<https://www.apitech.com/globalassets/documents/products/rf-microwave-microelectronics-power-solutions/rf-components/phase-shifter-subsystem/wmod84208421.pdf>.
Others make them too.

Bob

On Thu, May 14, 2020 at 9:43 AM Tim Higgins <tim at smallnetbuilder.com> wrote:

> Hi folks,
>
> I decided to publish some details of the hoops I've been jumping through
> to try to find benefit from OFDMA.
> It's proving very hard to do.
>
>
> https://www.smallnetbuilder.com/wireless/wireless-features/33222-does-ofdma-really-work-part-1
>
> I'll publish results from real devices next. But I'm still trying
> different things to get SOMETHING to show an improvement from OFDMA.
>
> Suggestions are welcome.
> ===========
> Tim
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> Make-wifi-fast at lists.bufferbloat.net
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