[srslte-users] Low Leve PHY sync method usage

[Andre Puschmann]

Sylvain,

On 25/9/19 15:45, Sylvain Munaut wrote:
> I can see how that would save on CPU usage, however not really an
> option here. Even if I prototype on a USRP that can do that, the
> hardware I will end up using wouldn't be able to change rate and keep
> timestamp easily.

Sure. I was just explaining how we usually do it in pdsch_ue and srsUE.
It certainly doesn't mean you can sync at full rate ;-)


>> Maybe you can also share a minimal non-working example.
> 
> http://people.osmocom.org/tnt/lte/lte_be_796m_1536.cfile
> 
> This is an example capture. This is at 15.36Msps rather than
> 30.72Msps, but same difference, it's just a bit quicker to init.

I've downloaded the file and it looks like a valid LTE capture.


> 
> My understanding is that :
> 
> ./lib/examples/synch_file -s 1024 -l 76800 -i lte_be_796m_1536.cfi>
> should find the sync for it.
> 
> But it doesn't, and I don't understand why.


You're right. I've just tried with pss_file and that synced perfectly.
Note that you have to specify the N_id_2 here. Try with e.g.:

$ ./lib/src/phy/sync/test/pss_file -i 2 -f ~/tmp/lte_be_796m_1536.cfile
-s 1024

I've then checked synch_file which indeed doesn't work. I've noticed the
correlation threshold was a bit high, so reduce that with "-t 2". Also
I've noticed that internally, the synch_file example uses 128 as default
FFT size, so that can only work with 1.92 MHz sample rate, not with your
signal. Try to apply the attached patch. With that, it gives me the
expected results.

$ ./lib/examples/synch_file -i ~/tmp/lte_be_796m_1536.cfile -l 76800 -s
1024  -t 2
Initializing...done in 2 s 896 ms

        Fr.Cnt  N_id_2  N_id_1  Subf    PSS Peak/Avg    Idx     m0
m1      CFO

===============================================================================
        0       2       48      5       5.953           39973   20
18      0.004
        1       2       48      0       7.218           39973   18
20      -0.445
        2       2       48      5       8.275           39973   20
18      0.126
        3       2       48      0       7.313           39973   18
20      -0.887
        4       2       48      5       7.849           39973   20
18      -0.551
        5       2       48      0       7.492           39973   18
20      0.827
        6       2       48      5       7.913           39973   20
18      -0.579
        7       2       48      0       7.638           39973   18
20      0.272
        8       2       48      5       8.094           39973   20
18      -0.553
        9       2       48      0       7.658           39973   18
20      0.281
        10      2       48      5       8.182           39973   20
18      -0.496
        11      2       48      0       7.687           39973   18
20      0.045
        12      2       48      5       8.200           39973   20
18      -0.556
        13      2       48      0       7.686           39973   18
20      0.736
        14      2       48      5       8.127           39973   20
18      -0.734


Hope that works for you.

Thanks
Andre

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