[srslte-users] Low Leve PHY sync method usage

[Andre Puschmann]

Hi Sylvain,

On 14/9/19 9:03, Sylvain Munaut wrote:
> For instance,  srslte_pss_init_fft takes a frame_size argument, but
> turns out it's actually half the frame size you need to give it
> AFAICT.
> Also, I'm still not sure exactly what the offset that's return
> corresponds to. It seems to be to the first sample after where the PSS
> is found, which isn't exactly obvious (I would have expected the first
> sample of the PSS or the first sample of the frame/half-frame).

Yes, it would return the first sample after the PSS. Since the PSS is
sent in the 7th OFDM symbol of the first and the sixth subframe, you get
the start of the 8th symbol of either the first or the sixth subframe.

By default we only receive a half frame because we can assume that we
received at least one PSS (or at least a fraction of it).

We usually initial sync and MIB decoding at 1.92 MHz sample rate but
then switch to the actual bandwidth of the cell. So it works with full
bandwidth too.

I don't think you need it for the PSS sync if you pass the FFT size
manually but as your signal is using 30.72 MHz, you need to make sure to
also use the default LTE FFT sizes. Have you passed the CMake flag
accordingly or have you set the static variable "bool use_standard_rates
= true;"?

Maybe you can also share a minimal non-working example.

Cheers
Andre