checkKi.c

/**************************************************************************
 *
 * checkKi()
 *
 * Purpose: Calculates the value of Ki, with MCS table entry and Kt.
 *
 *          (ki = kt - k0,i) and k0,i. is found in the MCS table.
 *
 * Args:    UeConfig_t*    - pointer to UE configuration structure
 *          HarqData_t*    - pointer to HARQ data structure
 *          bool           - whether the UE supports 16QAM.
 *          uint16_t       - MCS combination, 0..29.
 *          uint16_t       - Number of HS-PDSCH code.for this combination.
 *          uint16_t       - Kt
 *
 * Returns: bool           - whether a Ki was successfully derived.
 *
 ***************************************************************************/
static bool checkKi(
  const UeConfig_t *thisUe, HarqData_t *thisHarq, const McsTable_t *mcsTable,
  uint16_t kt, int supportsQam)
{
  int     tempKi = 0;
  uint8_t idx = 0;
  uint8_t numCodes = MIN(thisHarq->nCodes, MCS_TABLE_SZ);

  if (numCodes == 0)
  {
    return false;
  }

  for ( ; numCodes; numCodes = idx)
  {
    // ki  = 0..63
    // kt  = 1..254  (137..27952 bits)
    // Koi = 153..1  (QPSK  combinations)
    // Koi = 192..40 (16QAM combinations)
    idx    = numCodes - 1;
    tempKi = kt - mcsTable->a[idx];

    // Reject this combo if Ki is out of range.
    // If too big, then quit now because it gets bigger each iteration.
    if (tempKi > MAX_KI)
    {
      return false;
    }

    if (tempKi < 0)
    {
      continue;
    }

    // Check whether we're checking for QPSK combinations or 16QAM.

    // 4800  <= (codingBlockSize) <=  28800
    // Coding block size = (480 symbols per TTI)*(numCodes)*(M symbols per bit)
    const uint32_t codingBlkSize = (uint32_t)SYMBOLS_PER_TTI * numCodes * mcsTable->bitsPerModSym;

    // Reject this combo if it requires too much buffering.
    // (bufferSize) = {4800..28800}
    if (codingBlkSize > ueCategory[thisUe->ueCategory].nIr)
    {
      continue;
    }

    // Check code rate is out of range for 16QAM capable users checking
    // QPSK combinations.
    if (supportsQam && mcsTable->mod == MOD_QPSK)
    {
      /* TBS 1..27952, i.e. needs 16 bits                                     */

      /* Coding rate <= 0.75                                                  */
      /* (TBS + Coder CRC + Tail Bits)/ Coding Block Size <= 0.75             */
      uint32_t codeRateValue = 
                (thisHarq->machsFrameSz + CODER_CRC_SZ + NUM_TURBO_TAIL_BITS)
                * (uint32_t)MAX_QPSK_CODING_RATE_DENOMINATOR;     //lint !e776

      uint32_t codeRate = MAX_QPSK_CODING_RATE_NUMERATOR * codingBlkSize;

      /* Reject this combo if the coding rate is too high.                    */
      if (codeRateValue > codeRate)
      {
        continue;
      }
    }

    break;
  }

  thisHarq->ki     = tempKi;
  thisHarq->nCodes = numCodes;
  thisHarq->mod    = mcsTable->mod;

  return true;
}