[USRP-users] Time of arrival of first sample in a 2 Rx setup

siva sankar sankar.siva730 at gmail.com
Fri Apr 24 02:00:55 EDT 2015


Hey Laurent,

Thanks for the suggestion infact this is what we initially tried to do but
we are not able to give the offset as we require high sampling rate which
on giving is throwing a sequence of L's(LLLLLLL...) .

Regards
Siva.

On Thu, Apr 23, 2015 at 7:38 PM, LOUF Laurent <laurent.louf at thalesgroup.com>
wrote:

> Hi,
>
>
>
> If you just want the time difference, you may want to compute the
> correlation between the two signals for different offsets (unit : samples)
> and find the offset that gives you the maximum of correlation (and then
> translate the number of samples into a time difference with the sampling
> frequency). If receivers are not too far away one from the other, I guess
> that could be a solution (to be investigated).
>
>
>
> Regards,
>
> Laurent.
>
>
>
>
>
> *De :* USRP-users [mailto:usrp-users-bounces at lists.ettus.com] *De la part
> de* siva sankar via USRP-users
> *Envoyé :* jeudi 23 avril 2015 14:54
> *À :* Marcus Müller
> *Cc :* usrp-users at lists.ettus.com
> *Objet :* Re: [USRP-users] Time of arrival of first sample in a 2 Rx setup
>
>
>
> Hey Marcus,
>
> Thanks for the reply.
> The receivers here are at different distances from the transmitter and we
> are looking for the time difference of arrival of the samples at the
> receive buffers.
>
> How do we proceed with this ?
>
> Regards
> Siva
>
> Hello Siva,
> recv() will do an aligned reception, i.e. the first samples of both
> streams were received at the same time.
>
> Often, you don't want to *know* *afterwards* the time of reception, you
> want to *define* it beforehand. You can do that by using a stream_cmd
> with a stream_now = false and a timespec to allow you to define when the
> reception is going to take place.
>
> Greetings,
> Marcus
>
> On 04/23/2015 12:28 PM, siva sankar via USRP-users wrote:
>
> Hello List,
>
>
>
> I am using USRP B210 and the UHD version is 003.008.000. We are
> transmitting on one channel and receiving simultaneously on both the
> channels and what we want is the time of arrival of the first sample in
> both the receive buffers.
>
>
>
> We have used the "time_spec_t" to get the time of the first sample but we
> don't know if the time that we are getting is for both the channels or for
> one of the receiver buffers.
>
>
>
> We have tried using two "recv" commands one for each buffer hoping we
> could calculate the time from each metadata parameter passed to the "recv"
> command in one thread  but it throws "multi channel alignment" error and
> stops running.
>
>
>
> We also tried to create individual threads for both the rx channels and
> pass different metadata parameters and hence know the time of first sample
> for each buffer. However, this throws segmentation fault.
>
>
>
> Any help on how to calculate the time of first sample for each receive
> buffer will be appreciated.
>
>
>
> Thanks
>
> Siva.
>
>
>
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-- 
Thanks and regards
Siva Sankar.
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