Re: B2xx round trip delay

[jmfriedt]

In https://www.youtube.com/watch?v=B_fs9fWPTWw I discuss time of flight
measurement referenced to a local loopback channel (B210 for coherent
dual input receiver) to get rid of the data transfer and general purpose
computation time and only consider the communication delay. The
correlation phase can improve the resolution but oversampling the
correlation peak already strongly improves the resolution by a factor
equal to the SNR.

Best, JM

> By the way, if instead of time, we concentrate on the phase change on
> the correlation peaks,
> can we get to a better measure to relate it to RTD? For instance, we
> can send two sequences
> of the same type and track the correlation peaks phase change and
> relate it to the RTD?
> Thank you!
> 
> On Sun, Aug 13, 2023 at 8:15 AM Marcus D. Leech
> <patchvonbraun@gmail.com> wrote:
> 
> > On 13/08/2023 00:36, Ali G. Dezfuli wrote:
> > > Hi all,
> > > I'd like to measure the round-trip delay (RTD) between two B200
> > > USRPs. For that, I send a raised-cosined-filtered, BPSK modulated
> > > PN-sequence, and as soon as
> > > I get this signal at the receiver, send back the same sequence
> > > from the Rx to the Tx, and by correlation, I find the RTD.
> > > The question is that the measured RTD is not fixed. I wonder how
> > > can I make it fixed when the distance between the two USRPs is
> > > fixed. After that (A -> B -> A) I want to do that in reverse
> > > order (B -> A -> B) and expect to have the same RTD.
> > > Thanks
> > In your scenario, the latency will necessarily be variable--after
> > all your samples are entering a computer program where those
> >    samples are processed and then sent back in the other direction.
> > Since computer software on a general-purpose operating
> >    system cannot have fixed latency at fine-grained levels, this is
> > completely expected.
> >
> > This document may help:
> >
> > https://kb.ettus.com/Synchronizing_USRP_Events_Using_Timed_Commands_in_UHD
> >
> >
> >
> >



-- 
JM Friedt, FEMTO-ST Time & Frequency, 26 rue de l'Epitaphe, 25000
Besancon, France