I have a GnuRadio modem I've developed and I'd like to reduce latency. It
does IP encapsulation and for testing, I use two USRPs to implement an OTA
connection between the modems.

I've reduced latency so far by 1) adding fill frames/bytes only at the very
last block before the USRP sink and 2) increasing the sample rate to the
device. This has gotten my slightly under 100 ms latency, which is good
compared to what I started with, but I think we can do better.

My assumption is that there is still some latency in the last buffer
between the last block and the USRP sink and perhaps some in the USRP USB
transport itself. I am using B200s in this case, BTW.

I suspect that what I really must do is now tweak the usrp buffer params
from here: https://files.ettus.com/manual/page_transport.html But, I have
no idea what they are set to by default (any way to tell)? And some naive
manipulation of them hasn't improved anything.

I also tried tweaking the mx output buffer size on the last block before
the USRP sink without any improvement.

Any advice from Ettus folks would be appreciated :) I am giving a talk at
GRCon that addresses the latency reduction work so far, so if we can get
any more, I'll throw that in as well.

- Dan
Very Respectfully,

Dan CaJacob
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