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

siva sankar sankar.siva730 at gmail.com
Fri Apr 24 01:45:55 EDT 2015


Hey Marcus,

I am attaching the picture of the set up. The two receivers(Receiver 1 and
Receiver 2)  shown in the picture are on one USRP B210. We are trying to
calculate the angle of arrival using the TDOA.
These are the equations being used:
   Sin θ= S/L;
   S = (TDOA)*Speed of light(C);
   θ=arcsin(((TDOA)*C)/L);


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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>
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>
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-- 
Thanks and regards
Siva Sankar.
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