srsLTE/srslte/lib/fec/rm_conv.c

/**
 *
 * \section COPYRIGHT
 *
 * Copyright 2013-2015 Software Radio Systems Limited
 *
 * \section LICENSE
 *
 * This file is part of the srsLTE library.
 *
 * srsLTE is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of
 * the License, or (at your option) any later version.
 *
 * srsLTE is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * A copy of the GNU Affero General Public License can be found in
 * the LICENSE file in the top-level directory of this distribution
 * and at http://www.gnu.org/licenses/.
 *
 */

#include <string.h>
#include <stdio.h>
#include <stdint.h>

#include "srslte/fec/rm_conv.h"

#define NCOLS 32
#define NROWS_MAX NCOLS

uint8_t RM_PERM_CC[NCOLS] = { 1, 17, 9, 25, 5, 21, 13, 29, 3, 19, 11, 27,
    7, 23, 15, 31, 0, 16, 8, 24, 4, 20, 12, 28, 2, 18, 10, 26, 6, 22, 14, 30 };
uint8_t RM_PERM_CC_INV[NCOLS] =
    { 16, 0, 24, 8, 20, 4, 28, 12, 18, 2, 26, 10, 22, 6, 30, 14, 17, 1, 25, 9,
        21, 5, 29, 13, 19, 3, 27, 11, 23, 7, 31, 15 };

int srslte_rm_conv_tx(uint8_t *input, uint32_t in_len, uint8_t *output, uint32_t out_len) {

  uint8_t tmp[3 * NCOLS * NROWS_MAX];
  int nrows, ndummy, K_p;

  int i, j, k, s;

  nrows = (uint32_t) (in_len / 3 - 1) / NCOLS + 1;
  if (nrows > NROWS_MAX) {
    fprintf(stderr, "Input too large. Max input length is %d\n",
        3 * NCOLS * NROWS_MAX);
    return -1;
  }
  K_p = nrows * NCOLS;
  ndummy = K_p - in_len / 3;
  if (ndummy < 0) {
    ndummy = 0;
  }
  /* Sub-block interleaver 5.1.4.2.1 */
  k = 0;
  for (s = 0; s < 3; s++) {
    for (j = 0; j < NCOLS; j++) {
      for (i = 0; i < nrows; i++) {
        if (i * NCOLS + RM_PERM_CC[j] < ndummy) {
          tmp[k] = SRSLTE_TX_NULL;
        } else {
          tmp[k] = input[(i * NCOLS + RM_PERM_CC[j] - ndummy) * 3 + s];
        }
        k++;
      }
    }
  }
  /* Bit collection, selection and transmission 5.1.4.2.2 */
  k = 0;
  j = 0;
  while (k < out_len) {
    if (tmp[j] != SRSLTE_TX_NULL) {
      output[k] = tmp[j];
      k++;
    }
    j++;
    if (j == 3 * K_p) {
      j = 0;
    }
  }
  return 0;
}

/* Undoes Convolutional Code Rate Matching.
 * 3GPP TS 36.212 v10.1.0 section 5.1.4.2
 */
int srslte_rm_conv_rx(float *input, uint32_t in_len, float *output, uint32_t out_len) {

  int nrows, ndummy, K_p;
  int i, j, k;
  int d_i, d_j;

  float tmp[3 * NCOLS * NROWS_MAX];
  
  nrows = (uint32_t) (out_len / 3 - 1) / NCOLS + 1;
  if (nrows > NROWS_MAX) {
    fprintf(stderr, "Output too large. Max output length is %d\n",
        3 * NCOLS * NROWS_MAX);
    return -1;
  }
  K_p = nrows * NCOLS;

  ndummy = K_p - out_len / 3;
  if (ndummy < 0) {
    ndummy = 0;
  }

  for (i = 0; i < 3 * K_p; i++) {
    tmp[i] = SRSLTE_RX_NULL;
  }

  /* Undo bit collection. Account for dummy bits */
  k = 0;
  j = 0;
  while (k < in_len) {
    d_i = (j % K_p) / nrows;
    d_j = (j % K_p) % nrows;

    if (d_j * NCOLS + RM_PERM_CC[d_i] >= ndummy) {
      if (tmp[j] == SRSLTE_RX_NULL) {
        tmp[j] = input[k];
      } else if (input[k] != SRSLTE_RX_NULL) {
        tmp[j] += input[k]; /* soft combine LLRs */
      }
      k++;
    }
    j++;
    if (j == 3 * K_p) {
      j = 0;
    }
  }

  /* interleaving and bit selection */
  for (i = 0; i < out_len / 3; i++) {
    d_i = (i + ndummy) / NCOLS;
    d_j = (i + ndummy) % NCOLS;
    for (j = 0; j < 3; j++) {
      float o = tmp[K_p * j + RM_PERM_CC_INV[d_j] * nrows + d_i];
      if (o != SRSLTE_RX_NULL) {
        output[i * 3 + j] = o;
      } else {
        output[i * 3 + j] = 0;
      }
    }
  }
  return 0;
}