[srslte-users] Issue on SI / SIB messages

[Cedric Roux]

see 3gpp document 36.331, 5.2.1.1, they say:
"NOTE 1: The physical layer imposes a limit to the maximum size a SIB 
can take. When DCI format 1C is used the
         maximum allowed by the physical layer is 1736 bits (217 bytes) 
while for format 1A the limit is 2216 bits
         (277 bytes), see TS 36.212 [22] and TS 36.213 [23]. For BL UEs 
and UEs in CE, the maximum SIB and
         SI message size is 936 bits, see TS 36.213 [23]. For NB-IoT, 
the maximum SIB and SI message size is
         680 bits, see TS 36.213 [23]."

On 2021-02-22 18:23, Taillefer Simon wrote:
> Hello srsLTE team,
> 
> Basically, we are encountering an issue on the RRC protocol. We want to 
> send long SI / SIB messages but when the size is higher than 277 bytes, 
> some errors are raised.
> 
> More precisely, the errors are:
> 
> -Error("Computing DL grant\n"); from /srsLTE/srsenb/src/phy/cc_worker.cc 
> /file, around line 519 (depending on the srsLTE version and added code 
> on our side)
> 
> -ERROR("Configuring TB Info\n"); from /srsLTE/lib/src/phy/phch/ra_dl.c 
> /file, around line 627.
> 
> We found that these errors are coming from the 
> /grants[i].dci.tb[0].mcs_idx/ variable which has a value of -1 
> (4294967295exactly) instead of an unsigned integer. Then, we suppose 
> that the size of the corresponding transport block cannot be found in 
> the tbs_table (/srsLTE/lib/src/phy/phch/tbs_tables.h/file, line 38) and 
> this is why we have errors raised.
> 
> So our questions are:
> 
> -How this /grants[i].dci.tb[0].mcs_idx/variable is calculated?
> 
> -Do you know why its value is -1 (4294967295) when the size of the SI / 
> SIB messages is longer than 277 bytes?
> 
> -Maybe we are on the wrong way so do you know how it is possible to send 
> long SI / SIB messages?
> 
> Thank you for your help,
> 
> *Simon Taillefer***
> 
> 
> 
> 
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