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configuring SSL submodule in BCP

Aswathy Raj
Prodigy 210 points


  Hi,
We were verifying the functionalities of SSL submodule in BCP (only demodulation is enabled). Configurations are given below.
    pSslHdrCfg->local_hdr_len                  =   1;
    pSslHdrCfg->modeSelCfg.split_mode_en       =   0;
    pSslHdrCfg->modeSelCfg.jack_bit            =   0;
    pSslHdrCfg->modeSelCfg.lte_descrambler_en  =   0;
    pSslHdrCfg->modeSelCfg.mod_type_sel        =   (Bcp_ModulationType) (mod/2);
    pSslHdrCfg->modeSelCfg.cmux_ln             =   (Bcp_CmuxLength) (0);
    pSslHdrCfg->modeSelCfg.q_format            =   (Bcp_QFormat) (Qfmt)
    pSslHdrCfg->modeSelCfg.b_matrix_sel        =   0;
    pSslHdrCfg->modeSelCfg.rmux_ln_index       =   0;
    pSslHdrCfg->ri_ln                          =   0;
    pSslHdrCfg->ack_ln                         =   0;
 
    if (mod == 1 || mod == 2)   // BPSK or QPSK
        pSslHdrCfg->uva                 =   ((rms * 23170 + 0x4000) >> 15);
    else if (mod == 4)  // 16 QAM
        pSslHdrCfg->uva                 =   ((rms * 10362 + 0x4000) >> 15);
    else if (mod == 6)  // 64 QAM
        pSslHdrCfg->uva                 =   ((rms * 5056 + 0x4000) >> 15);
    else    // 256 QAM
        pSslHdrCfg->uva                 =   ((rms * 2513 + 0x4000) >> 15);
Input to SSL was 144 symbols and we selected modulation to be QPSK. So there would be 288 (144 * 2) demodulated soft bits (each soft bit is 8 bits long). But we are getting 280 soft bits only.  These soft bits are either '01' or 'FF'. So the result is like a hard decision. Can we use SSL for doing demodulation and descrambling alone??
 Is there anything missing in the configuration given above ??

Thanks and Regards,
Aswathy
  • 0
    TI__Mastermind 35645 points
    Hi,

    Moving your post to right forum to be better answered.

    Thanks & regards,
    Sivaraj K
  • 0 in reply to Sivaraj Kuppuraj
    TI__Guru* 81335 points
    What is DSP part number used?
  • 0
    TI__Mastermind 30405 points
    Hi Aswathy,

    You can use BCP SSL in WiMAX mode for demodulation only as mentioned in section 4.7, the descrambler (along with the de-interleaver and uplink control information handler) is bypassed in this mode so software will have to perform descrambling.

    Regards
    -Nitin
  • 0 in reply to Nitin Sakhuja
    Prodigy 210 points

    Thanks Nitin...

    We tried with the example given for wimax uplink.  Input   and output files are attached below (wimaxRx_sslIn.dat and ssloutputwi.dat). Same input file is used as given in the example project. Modulation format chosen is QPSK. There are 1056 symbols in the example file. So there should be 1056 * 2 = 2112 soft bits.. In the output file there are 264 words. So each soft bit is represented by 4 bits. With these observations we tried validating the result obtained. But we are unable to find out how to interpret the result.  In our output there are only 4 soft bits ('8','1','7' and 'F'). Looks like a hard decision is taken. Is this output correct for the given input ?? or we have change SSL or BCP global header configuration??

    bcpGlblHdrCfg.hdr_end_ptr = 6   // 2 (lobal header) + 2 (ssl) + 2(tm) and 2 words are added as filler bits for making the data to begin on the 128 bit boundary.

    Thanks and Regards,

    Aswathy

     ssloutputwi.datwimaxRx_sslIn.dat

  • 0 in reply to Aswathy Raj
    Prodigy 210 points

    still having the same issue. Any configuration to be changed ??

    thanks and regards,

    Aswathy

  • 0 in reply to Aswathy Raj
    Prodigy 210 points
    still having the same issue. Any configuration to be changed ??
    thanks and regards,
    Aswathy
  • 0 in reply to Aswathy Raj
    TI__Mastermind 30405 points
    Hi Ashwathy,

    In WiMax mode, each 32-bit symbol (16-bit I, 16-bit Q) has a noise scaling factor following it in the BCP input payload (BCP user guide, section 4.7.1.5). So the input file containing 1056 words has 528 symbols as every alternate 32-bit word is the noise scaling factor for the preceding symbol.

    The output of the SSL sub-module is 8-bit LLR soft bits so the output size in the example, i.e. 264 words, is correct as each 32 bit word contains 4 8-bit LLRs giving a total of 264 x 4 = 1056 LLRs

    (528 input symbols with QPSK modulation = 528 x 2 = 1056 soft-bits).

    Regards
    -Nitin
  • 0 in reply to Nitin Sakhuja
    Prodigy 210 points

    Thanks nitin..

    We verified the results with MATLAB. Its matching. Can we do the same in LTE mode (soft demodulation and descrambling with deinterleaving bypassed)??  We have to do the rate dematching in LTE mode.

    Thanks and Regards,

    Aswathy

  • 0 in reply to Aswathy Raj
    TI__Mastermind 30405 points
    Hi Ashwathy,

    In LTE, the de-interleaving is done on two stages. Stage 1, partial de-interleaving, which is done by the DSP (software or EDMA) and stage 2, which is done by the BCP SSL by the way of reading in the partially de-interleaved input data. While you can bypass stage-1 as it's software controlled, you cannot bypass stage-2 de-interleaving as it happens inside the BCP. In essence, it is not possible to use BCP SSL for only demodulation and de-scrambling of LTE symbols.

    Regards
    -Nitin