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

[Laura Flueratoru]

Hi Alejandro,

Thank you for the advice, I will also try that. But do you know why
this happens and is this the way it's done in srsue? I find it strange
to need to go through all of the payloads. I saw that in
rrc::run_si_acquisition_procedure (srsue/src/upper/rrc.cc) the
location of the SIBs is still computed, but I couldn't identify the
physical layer part that is accessing them.

Best,
Laura

On Tue, Apr 17, 2018 at 5:25 PM, ALEJANDRO BLANCO PIZARRO
<100283180 at alumnos.uc3m.es> wrote:
> Hi Laura,
>
> I had this issue and I finally realized that the position that it is
> obtained using the LTE standard could not be the same in real scenarios.
>
> My piece of advice: you should program a loop and go over the subframe id
> and the system frame number  showing all the payloads and the positions.
> With it, you are going to show all SIB payloads, afterwards, with
> http://www.marben-products.com/decoder-asn1-lte/ see what is the SIB2
> payload and see what are the system frame number and the subframe id
> relative to SIB2, to see if you made a mistake.
>
>  if ((srslte_ue_sync_get_sfidx(&ue_sync) == variable_loop1) &&   (sfn %
> si_loc[0].period) == variable_loop2)
>
> I know that this piece of advice is not really smart but is functional.
>
> Tell me if you need further information.
>
> Best,
> Alejandro
>
> 2018-04-17 17:16 GMT+02:00 Laura Flueratoru <flueratorulaura at gmail.com>:
>>
>> 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
>> >> _______________________________________________
>> >> srslte-users mailing list
>> >> srslte-users at lists.softwareradiosystems.com
>> >> http://www.softwareradiosystems.com/mailman/listinfo/srslte-users
>> >
>> >
>
>