srsRAN_4G/lte/phy/lib/fec/src/rm_turbo.c

/**
 *
 * \section COPYRIGHT
 *
 * Copyright 2013-2014 The libLTE Developers. See the
 * COPYRIGHT file at the top-level directory of this distribution.
 *
 * \section LICENSE
 *
 * This file is part of the libLTE library.
 *
 * libLTE is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of
 * the License, or (at your option) any later version.
 *
 * libLTE 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 Lesser General Public License for more details.
 *
 * A copy of the GNU Lesser 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 <math.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdint.h>

#include "liblte/phy/fec/rm_turbo.h"

#define NCOLS 32
#define NROWS_MAX NCOLS

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


/* Turbo Code Rate Matching.
 * 3GPP TS 36.212 v10.1.0 section 5.1.4.1
 *
 * If rv_idx==0, the circular buffer w_buff is filled with all redundancy versions and 
 * the corresponding version of length out_len is saved in the output buffer.  
 * Otherwise, the corresponding version is directly obtained from w_buff and saved into output. 
 * 
 * Note that calling this function with rv_idx!=0 without having called it first with rv_idx=0
 * will produce unwanted results. 
 * 
 * TODO: Soft buffer size limitation according to UE category
 */
int rm_turbo_tx(char *w_buff, uint32_t w_buff_len, char *input, uint32_t in_len, char *output,
    uint32_t out_len, uint32_t rv_idx) {

  int ndummy, kidx; 
  int nrows, K_p;

  int i, j, k, s, N_cb, k0;

  nrows = (uint32_t) (in_len / 3 - 1) / NCOLS + 1;
  K_p = nrows * NCOLS;
  if (3 * K_p > w_buff_len) {
    fprintf(stderr,
        "Input too large. Max input length including dummy bits is %d (3x%dx32, in_len %d)\n",
        w_buff_len, nrows, in_len);
    return -1;
  }

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

  if (rv_idx == 0) {
    /* Sub-block interleaver (5.1.4.1.1) and bit collection */
    k = 0;
    for (s = 0; s < 2; s++) {
      for (j = 0; j < NCOLS; j++) {
        for (i = 0; i < nrows; i++) {
          if (s == 0) {
            kidx = k % K_p;
          } else {
            kidx = K_p + 2 * (k % K_p);
          }
          if (i * NCOLS + RM_PERM_TC[j] < ndummy) {
            w_buff[kidx] = TX_NULL;
          } else {
            w_buff[kidx] = input[(i * NCOLS + RM_PERM_TC[j] - ndummy) * 3 + s];
          }
          k++;
        }
      }
    }

    // d_k^(2) goes through special permutation
    for (k = 0; k < K_p; k++) {
      kidx = (RM_PERM_TC[k / nrows] + NCOLS * (k % nrows) + 1) % K_p;
      if ((kidx - ndummy) < 0) {
        w_buff[K_p + 2 * k + 1] = TX_NULL;
      } else {
        w_buff[K_p + 2 * k + 1] = input[3 * (kidx - ndummy) + 2];
      }
    }
  }

  /* Bit selection and transmission 5.1.4.1.2 */
  N_cb = 3 * K_p;       // TODO: Soft buffer size limitation

  k0 = nrows
      * (2 * (uint32_t) ceilf((float) N_cb / (float) (8 * nrows)) * rv_idx + 2);
  k = 0;
  j = 0;

  while (k < out_len) {
    if (w_buff[(k0 + j) % N_cb] != TX_NULL) {
      output[k] = w_buff[(k0 + j) % N_cb];
      k++;
    }
    j++;
  }
  return 0;
}

/* Undoes Turbo Code Rate Matching.
 * 3GPP TS 36.212 v10.1.0 section 5.1.4.1
 * 
 * If rv_idx==0, the w_buff circular buffer is initialized. Every subsequent call 
 * with rv_idx!=0 will soft-combine the LLRs from input with w_buff
 */
int rm_turbo_rx(float *w_buff, uint32_t w_buff_len, float *input, uint32_t in_len, float *output,
    uint32_t out_len, uint32_t rv_idx) {

  int nrows, ndummy, K_p, k0, N_cb, jp, kidx;
  int i, j, k;
  int d_i, d_j;
  bool isdummy;

  nrows = (uint32_t) (out_len / 3 - 1) / NCOLS + 1;
  K_p = nrows * NCOLS;
  if (3 * K_p > w_buff_len) {
    fprintf(stderr,
        "Input too large. Max output length including dummy bits is %d (3x%dx32, in_len %d)\n",
        w_buff_len, nrows, out_len);
    return -1;
  }

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

  if (rv_idx == 0) {
    for (i = 0; i < 3 * K_p; i++) {
      w_buff[i] = RX_NULL;
    }    
  }

  /* Undo bit collection. Account for dummy bits */
  N_cb = 3 * K_p;       // TODO: Soft buffer size limitation
  k0 = nrows
      * (2 * (uint32_t) ceilf((float) N_cb / (float) (8 * nrows)) * rv_idx + 2);

  k = 0;
  j = 0;
  while (k < in_len) {
    jp = (k0 + j) % N_cb;

    if (jp < K_p || !(jp % 2)) {
      if (jp >= K_p) {
        d_i = ((jp - K_p) / 2) / nrows;
        d_j = ((jp - K_p) / 2) % nrows;
      } else {
        d_i = jp / nrows;
        d_j = jp % nrows;
      }
      if (d_j * NCOLS + RM_PERM_TC[d_i] >= ndummy) {
        isdummy = false;
      } else {
        isdummy = true;
      }
    } else {
      uint32_t jpp = (jp - K_p - 1) / 2;
      kidx = (RM_PERM_TC[jpp / nrows] + NCOLS * (jpp % nrows) + 1) % K_p;
      if ((kidx - ndummy) < 0) {
        isdummy = true;
      } else {
        isdummy = false;
      }
    }

    if (!isdummy) {
      if (w_buff[jp] == RX_NULL) {
        w_buff[jp] = input[k];
      } else if (input[k] != RX_NULL) {
        w_buff[jp] += input[k]; /* soft combine LLRs */
      }
      k++;
    }
    j++;
  }

  /* 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++) {
      if (j != 2) {
        kidx = K_p * j + (j + 1) * (RM_PERM_TC[d_j] * nrows + d_i);
      } else {
        k = (i + ndummy - 1) % K_p;
        if (k < 0)
          k += K_p;
        kidx = (k / NCOLS + nrows * RM_PERM_TC[k % NCOLS]) % K_p;
        kidx = 2 * kidx + K_p + 1;
      }
      if (w_buff[kidx] != RX_NULL) {
        output[i * 3 + j] = w_buff[kidx];
      } else {
        output[i * 3 + j] = 0;
      }
    }
  }
  return 0;
}

/** High-level API */

int rm_turbo_initialize(rm_turbo_hl* h) {
  return 0;
}

/** This function can be called in a subframe (1ms) basis */
int rm_turbo_work(rm_turbo_hl* hl) {
  return 0;
}

int rm_turbo_stop(rm_turbo_hl* hl) {
  return 0;
}