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

[Laura Flueratoru]

Hi Alejandro,

Yes, I know about the decoder, but my problem is that I don't know how
to find SIB2's location, even given the information from SIB1. The way
I tried to do it (explained in the email before) gives me a payload
for SIB2 that is interpreted by the decoder you mentioned as a SIB1
format. So the location I'm trying to access is clearly not the
location of SIB2.

So do you know how could I find the correct location of SIB2? Thank you!

Best,
Laura

On Tue, Apr 17, 2018 at 4:53 PM, ALEJANDRO BLANCO PIZARRO
<100283180 at alumnos.uc3m.es> wrote:
> Hi Laura,
>
> I do not completely understand your problem, but have you tried to decode
> the SIB2 payload by http://www.marben-products.com/decoder-asn1-lte/?
>
> Best!
> Alejandro
>
> 2018-04-17 13:46 GMT+02:00 Laura Flueratoru <flueratorulaura at gmail.com>:
>>
>> 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
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>
>