[srslte-users] Problem with decoding SIB2 using cell_measurement example

[Laura Flueratoru]

Hi everyone,

I am trying to decode SIB2 using the cell_measurement example. I have
already decoded the information regarding the location of the SI
messages from SIB1, and the periodicity of SIB2 should be RF8 (same as
for SIB3) and the SI Window Length is 3.

>From this, I compute the subframe number, the periodicity and the
offset according to 36.331 and try to search for the SIB2 in a loop as
in the code snippet below:

    if ((srslte_ue_sync_get_sfidx(&ue_sync) == si_loc[0].subframe) &&
         (sfn % si_loc[0].period) == si_loc[0].mod_sfn) {
        n = srslte_ue_dl_decode(&ue_dl, data, 0,
                  sfn*10+srslte_ue_sync_get_sfidx(&ue_sync), acks);

where:
    - si_loc[0].subframe is SIB2's subframe number and has the value 0
    - si_loc[0].period is SIB2's periodicity and has the value 8 (RF8)
    - si_loc[0].mod_sfn is SIB2's offset and has the value 0

It does find something at that location and an example payload is
[40 48 a0 03 06 50 11 84 60 88 19 31 80 81 84 4c 23 61 23 18 00 00 63
9e 9d 00 00 00 00 00 00 00 65 2b 44 7c ef ]
whereas the payload of SIB1 was
[40 48 a0 03 06 50 11 84 60 88 19 31 80 81 84 4c 23 61 23 18 00 00 ]

So I find it weird that the first part of the payload I get for SIB2
would be exactly the same as for SIB1, so I think there's something
wrong with the way I try to retrieve SIB2's data.

Can you please tell me if there's something wrong with the way I
search for the SI message? I tried to look in
rrc::run_si_acquisition_procedure which seems to be computing the same
location, but it seems to me that I'm doing almost the same thing here
(minus specifying the window length in which to search for the SI
message). Any help would be greatly appreciated. Thank you!

Best regards,
Laura