srsRAN_4G/lte/phy/lib/mimo/src/precoding.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 <stdio.h>
#include <assert.h>
#include <complex.h>
#include <string.h>
#include <math.h>

#include "liblte/phy/common/phy_common.h"
#include "liblte/phy/mimo/precoding.h"
#include "liblte/phy/utils/vector.h"

int precoding_single(cf_t *x, cf_t *y, int nof_symbols) {
  memcpy(y, x, nof_symbols * sizeof(cf_t));
  return nof_symbols;
}
int precoding_diversity(cf_t *x[MAX_LAYERS], cf_t *y[MAX_PORTS], int nof_ports,
    int nof_symbols) {
  int i;
  if (nof_ports == 2) {
    /* FIXME: Use VOLK here */
    for (i = 0; i < nof_symbols; i++) {
      y[0][2 * i] = x[0][i] / sqrtf(2);
      y[1][2 * i] = -conjf(x[1][i]) / sqrtf(2);
      y[0][2 * i + 1] = x[1][i] / sqrtf(2);
      y[1][2 * i + 1] = conjf(x[0][i]) / sqrtf(2);
    }
    return 2 * i;
  } else if (nof_ports == 4) {
    //int m_ap = (nof_symbols%4)?(nof_symbols*4-2):nof_symbols*4;
    int m_ap = 4 * nof_symbols;
    for (i = 0; i < m_ap / 4; i++) {
      y[0][4 * i] = x[0][i] / sqrtf(2);
      y[1][4 * i] = 0;
      y[2][4 * i] = -conjf(x[1][i]) / sqrtf(2);
      y[3][4 * i] = 0;

      y[0][4 * i + 1] = x[1][i] / sqrtf(2);
      y[1][4 * i + 1] = 0;
      y[2][4 * i + 1] = conjf(x[0][i]) / sqrtf(2);
      y[3][4 * i + 1] = 0;

      y[0][4 * i + 2] = 0;
      y[1][4 * i + 2] = x[2][i] / sqrtf(2);
      y[2][4 * i + 2] = 0;
      y[3][4 * i + 2] = -conjf(x[3][i]) / sqrtf(2);

      y[0][4 * i + 3] = 0;
      y[1][4 * i + 3] = x[3][i] / sqrtf(2);
      y[2][4 * i + 3] = 0;
      y[3][4 * i + 3] = conjf(x[2][i]) / sqrtf(2);
    }
    return 4 * i;
  } else {
    fprintf(stderr, "Number of ports must be 2 or 4 for transmit diversity\n");
    return -1;
  }
}

/* 36.211 v10.3.0 Section 6.3.4 */
int precoding_type(cf_t *x[MAX_LAYERS], cf_t *y[MAX_PORTS], int nof_layers,
    int nof_ports, int nof_symbols, lte_mimo_type_t type) {

  if (nof_ports > MAX_PORTS) {
    fprintf(stderr, "Maximum number of ports is %d (nof_ports=%d)\n", MAX_PORTS,
        nof_ports);
    return -1;
  }
  if (nof_layers > MAX_LAYERS) {
    fprintf(stderr, "Maximum number of layers is %d (nof_layers=%d)\n",
        MAX_LAYERS, nof_layers);
    return -1;
  }

  switch (type) {
  case SINGLE_ANTENNA:
    if (nof_ports == 1 && nof_layers == 1) {
      return precoding_single(x[0], y[0], nof_symbols);
    } else {
      fprintf(stderr,
          "Number of ports and layers must be 1 for transmission on single antenna ports\n");
      return -1;
    }
    break;
  case TX_DIVERSITY:
    if (nof_ports == nof_layers) {
      return precoding_diversity(x, y, nof_ports, nof_symbols);
    } else {
      fprintf(stderr,
          "Error number of layers must equal number of ports in transmit diversity\n");
      return -1;
    }
  case SPATIAL_MULTIPLEX:
    fprintf(stderr, "Spatial multiplexing not supported\n");
    return -1;
  }
  return 0;
}

/* ZF detector */
int predecoding_single_zf(cf_t *y, cf_t *ce, cf_t *x, int nof_symbols) {
  for (int i=0;i<nof_symbols;i++) {
    if (ce[i] == 0) {
      ce[i] = 0.01;
    }
  }
  vec_div_ccc(y, ce, x, nof_symbols);
  return nof_symbols;
}

/* ZF detector */
int predecoding_diversity_zf(cf_t *y, cf_t *ce[MAX_PORTS], cf_t *x[MAX_LAYERS],
    int nof_ports, int nof_symbols) {
  int i;
  cf_t h0, h1, h2, h3, r0, r1, r2, r3;
  float hh, hh02, hh13;
  if (nof_ports == 2) {
    /* TODO: Use VOLK here */
    for (i = 0; i < nof_symbols / 2; i++) {
      h0 = ce[0][2 * i];
      h1 = ce[1][2 * i];
      hh = crealf(h0) * crealf(h0) + cimagf(h0) * cimagf(h0)
          + crealf(h1) * crealf(h1) + cimagf(h1) * cimagf(h1);
      r0 = y[2 * i];
      r1 = y[2 * i + 1];
      if (hh == 0) {
        hh = 1e-2;
      }
      x[0][i] = (conjf(h0) * r0 + h1 * conjf(r1)) / hh * sqrt(2);
      x[1][i] = (-h1 * conj(r0) + conj(h0) * r1) / hh * sqrt(2);
    }
    return i;
  } else if (nof_ports == 4) {

    int m_ap = (nof_symbols % 4) ? ((nof_symbols - 2) / 4) : nof_symbols / 4;
    for (i = 0; i < m_ap; i++) {
      h0 = ce[0][4 * i];
      h1 = ce[1][4 * i + 2];
      h2 = ce[2][4 * i];
      h3 = ce[3][4 * i + 2];
      hh02 = crealf(h0) * crealf(h0) + cimagf(h0) * cimagf(h0)
          + crealf(h2) * crealf(h2) + cimagf(h2) * cimagf(h2);
      hh13 = crealf(h1) * crealf(h1) + cimagf(h1) * cimagf(h1)
          + crealf(h3) * crealf(h3) + cimagf(h3) * cimagf(h3);
      r0 = y[4 * i];
      r1 = y[4 * i + 1];
      r2 = y[4 * i + 2];
      r3 = y[4 * i + 3];

      x[0][i] = (conjf(h0) * r0 + h2 * conjf(r1)) / hh02 * sqrt(2);
      x[1][i] = (-h2 * conjf(r0) + conjf(h0) * r1) / hh02 * sqrt(2);
      x[2][i] = (conjf(h1) * r2 + h3 * conjf(r3)) / hh13 * sqrt(2);
      x[3][i] = (-h3 * conjf(r2) + conjf(h1) * r3) / hh13 * sqrt(2);

    }
    return i;
  } else {
    fprintf(stderr, "Number of ports must be 2 or 4 for transmit diversity\n");
    return -1;
  }
}

/* 36.211 v10.3.0 Section 6.3.4 */
int predecoding_type(cf_t *y, cf_t *ce[MAX_PORTS], cf_t *x[MAX_LAYERS],
    int nof_ports, int nof_layers, int nof_symbols, lte_mimo_type_t type) {

  if (nof_ports > MAX_PORTS) {
    fprintf(stderr, "Maximum number of ports is %d (nof_ports=%d)\n", MAX_PORTS,
        nof_ports);
    return -1;
  }
  if (nof_layers > MAX_LAYERS) {
    fprintf(stderr, "Maximum number of layers is %d (nof_layers=%d)\n",
        MAX_LAYERS, nof_layers);
    return -1;
  }

  switch (type) {
  case SINGLE_ANTENNA:
    if (nof_ports == 1 && nof_layers == 1) {
      return predecoding_single_zf(y, ce[0], x[0], nof_symbols);
    } else {
      fprintf(stderr,
          "Number of ports and layers must be 1 for transmission on single antenna ports\n");
      return -1;
    }
    break;
  case TX_DIVERSITY:
    if (nof_ports == nof_layers) {
      return predecoding_diversity_zf(y, ce, x, nof_ports, nof_symbols);
    } else {
      fprintf(stderr,
          "Error number of layers must equal number of ports in transmit diversity\n");
      return -1;
    }
    break;
  case SPATIAL_MULTIPLEX:
    fprintf(stderr, "Spatial multiplexing not supported\n");
    return -1;
  }
  return 0;
}