[srslte-users] srslte_pss_synch_find_pss returns peak position greater than the subframe size

Felipe Augusto Pereira de Figueiredo zz4fap at gmail.com
Mon May 15 12:23:21 UTC 2017


Dear Andre,

Thanks for your reply.

That's not the case I'm testing, I saw that during some initial phase you
check a 5 miliseconds long frame, however, now I'm seeing those peaks
greater than a subframe after that initial phase, when you only read a 1ms
(i.e., 5760 samples) long subframe.

Do you think that might be a bug in the PSS find function (
srslte_conv_fft_cc_run)?

Thanks and Best regards,

Felipe Augusto



On Mon, May 15, 2017 at 2:16 PM, Andre Puschmann <
andre.puschmann at softwareradiosystems.com> wrote:

> Hey Felipe,
>
>
> On 11.05.2017 19:34, Felipe Augusto Pereira de Figueiredo wrote:
> > Dear srsLTE group,
> >
> > I'm studying the srsLTE code and I`m confused by one thing I've found
> out.
> >
> > I observed that the function: srslte_pss_synch_find_pss from pss.c
> > sometimes returns a peak position that is greater than the subframe,
> > i.e., 5760 in the case of 5 MHz and using the sampling rate of 5.76 MHz.
>
> During the initial find phase, we capture 5 subframes at once to make
> sure the samples contain one PSS sequence. Note that the PSS is
> transmitted twice in every frame, i.e. every 5ms. So running the PSS
> search on this set of samples may return a PSS position that is _after_
> the first subframe, since it is not known where exactly the PSS started
> (otherwise we would already be in sync).
>
> Hope that helps.
>
> Cheers
> Andre
>
>
>
> >
> > I've checked and that function uses convolution FFT to do the
> > correlation, see below:
> > conv_output_len = srslte_conv_fft_cc_run(&q->conv_fft, q->tmp_input,
> > q->pss_signal_time[q->N_id_2], q->conv_output);
> >
> > If the peak is used to align the subframe how can it be greater than the
> > subframe? Is this behavior correct?
> >
> > Thanks in advance and Best Regards,
> >
> > Felipe Augusto
> >
> >
> >
> >
> >
> > _______________________________________________
> > srslte-users mailing list
> > srslte-users at lists.softwareradiosystems.com
> > http://www.softwareradiosystems.com/mailman/listinfo/srslte-users
> >
>
>
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