srsRAN_4G/lte/phy/lib/phch/src/pbch.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 <stdint.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
#include <math.h>

#include "prb.h"
#include "liblte/phy/phch/pbch.h"
#include "liblte/phy/common/base.h"
#include "liblte/phy/utils/bit.h"
#include "liblte/phy/utils/vector.h"
#include "liblte/phy/utils/debug.h"

const char crc_mask[4][16] = {
    { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, { 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1 }, { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0 }, { 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1 } };

bool pbch_exists(int nframe, int nslot) {
  return (!(nframe % 5) && nslot == 1);
}

int pbch_cp(cf_t *input, cf_t *output, int nof_prb, lte_cp_t cp, int cell_id,
    bool put) {
  int i;
  cf_t *ptr;
  assert(cell_id >= 0);
  if (put) {
    ptr = input;
    output += nof_prb * RE_X_RB / 2 - 36;
  } else {
    ptr = output;
    input += nof_prb * RE_X_RB / 2 - 36;
  }

  /* symbol 0 & 1 */
  for (i = 0; i < 2; i++) {
    prb_cp_ref(&input, &output, cell_id % 3, 4, 6, put);
  }
  /* symbols 2 & 3 */
  if (CP_ISNORM(cp)) {
    for (i = 0; i < 2; i++) {
      prb_cp(&input, &output, 6);
    }
  } else {
    prb_cp(&input, &output, 6);
    prb_cp_ref(&input, &output, cell_id % 3, 4, 6, put);
  }
  if (put) {
    return input - ptr;
  } else {
    return output - ptr;
  }
}

/**
 * Puts PBCH in slot number 1
 *
 * Returns the number of symbols written to slot1_data
 *
 * 36.211 10.3 section 6.6.4
 */
int pbch_put(cf_t *pbch, cf_t *slot1_data, int nof_prb, lte_cp_t cp,
    int cell_id) {
  return pbch_cp(pbch, slot1_data, nof_prb, cp, cell_id, true);
}

/**
 * Extracts PBCH from slot number 1
 *
 * Returns the number of symbols written to pbch
 *
 * 36.211 10.3 section 6.6.4
 */
int pbch_get(cf_t *slot1_data, cf_t *pbch, int nof_prb, lte_cp_t cp,
    int cell_id) {
  return pbch_cp(slot1_data, pbch, nof_prb, cp, cell_id, false);
}

/** Initializes the PBCH transmitter and receiver */
int pbch_init(pbch_t *q, int nof_prb, int cell_id, lte_cp_t cp) {
  int ret = -1;
  if (cell_id < 0) {
    return -1;
  }
  bzero(q, sizeof(pbch_t));
  q->cell_id = cell_id;
  q->cp = cp;
  q->nof_prb = nof_prb;

  if (modem_table_std(&q->mod, LTE_QPSK, true)) {
    goto clean;
  }
  demod_soft_init(&q->demod);
  demod_soft_table_set(&q->demod, &q->mod);
  demod_soft_alg_set(&q->demod, APPROX);
  if (sequence_pbch(&q->seq_pbch, q->cp, q->cell_id)) {
    goto clean;
  }

  int poly[3] = { 0x6D, 0x4F, 0x57 };
  if (viterbi_init(&q->decoder, viterbi_37, poly, 40, true)) {
    goto clean;
  }
  if (crc_init(&q->crc, LTE_CRC16, 16)) {
    goto clean;
  }
  q->encoder.K = 7;
  q->encoder.R = 3;
  q->encoder.tail_biting = true;
  memcpy(q->encoder.poly, poly, 3 * sizeof(int));

  q->nof_symbols = (CP_ISNORM(q->cp)) ? PBCH_RE_CPNORM : PBCH_RE_CPEXT;

  q->pbch_d = malloc(sizeof(cf_t) * q->nof_symbols);
  if (!q->pbch_d) {
    goto clean;
  }
  int i;
  for (i = 0; i < MAX_PORTS_CTRL; i++) {
    q->ce[i] = malloc(sizeof(cf_t) * q->nof_symbols);
    if (!q->ce[i]) {
      goto clean;
    }
    q->pbch_x[i] = malloc(sizeof(cf_t) * q->nof_symbols);
    if (!q->pbch_x[i]) {
      goto clean;
    }
    q->pbch_symbols[i] = malloc(sizeof(cf_t) * q->nof_symbols);
    if (!q->pbch_symbols[i]) {
      goto clean;
    }
  }
  q->pbch_llr = malloc(sizeof(float) * q->nof_symbols * 4 * 2);
  if (!q->pbch_llr) {
    goto clean;
  }
  q->temp = malloc(sizeof(float) * q->nof_symbols * 4 * 2);
  if (!q->temp) {
    goto clean;
  }
  q->pbch_rm_f = malloc(sizeof(float) * 120);
  if (!q->pbch_rm_f) {
    goto clean;
  }
  q->pbch_rm_b = malloc(sizeof(float) * q->nof_symbols * 4 * 2);
  if (!q->pbch_rm_b) {
    goto clean;
  }
  q->data = malloc(sizeof(char) * 40);
  if (!q->data) {
    goto clean;
  }
  q->data_enc = malloc(sizeof(char) * 120);
  if (!q->data_enc) {
    goto clean;
  }

  ret = 0;
  clean: if (ret == -1) {
    pbch_free(q);
  }
  return ret;
}

void pbch_free(pbch_t *q) {
  if (q->pbch_d) {
    free(q->pbch_d);
  }
  int i;
  for (i = 0; i < MAX_PORTS_CTRL; i++) {
    if (q->ce[i]) {
      free(q->ce[i]);
    }
    if (q->pbch_x[i]) {
      free(q->pbch_x[i]);
    }
    if (q->pbch_symbols[i]) {
      free(q->pbch_symbols[i]);
    }
  }
  if (q->pbch_llr) {
    free(q->pbch_llr);
  }
  if (q->temp) {
    free(q->temp);
  }
  if (q->pbch_rm_f) {
    free(q->pbch_rm_f);
  }
  if (q->pbch_rm_b) {
    free(q->pbch_rm_b);
  }
  if (q->data_enc) {
    free(q->data_enc);
  }
  if (q->data) {
    free(q->data);
  }
  sequence_free(&q->seq_pbch);
  modem_table_free(&q->mod);
  viterbi_free(&q->decoder);
}

/** Unpacks MIB from PBCH message.
 * msg buffer must be 24 byte length at least
 */
void pbch_mib_unpack(char *msg, pbch_mib_t *mib) {
  int bw, phich_res;

  bw = bit_unpack(&msg, 3);
  switch (bw) {
  case 0:
    mib->nof_prb = 6;
    break;
  case 1:
    mib->nof_prb = 15;
    break;
  default:
    mib->nof_prb = (bw - 1) * 25;
    break;
  }
  if (*msg) {
    mib->phich_length = PHICH_EXT;
  } else {
    mib->phich_length = PHICH_NORM;
  }
  msg++;

  phich_res = bit_unpack(&msg, 2);
  switch (phich_res) {
  case 0:
    mib->phich_resources = R_1_6;
    break;
  case 1:
    mib->phich_resources = R_1_2;
    break;
  case 2:
    mib->phich_resources = R_1;
    break;
  case 3:
    mib->phich_resources = R_2;
    break;
  }
  mib->sfn = bit_unpack(&msg, 8) << 2;
}

/** Unpacks MIB from PBCH message.
 * msg buffer must be 24 byte length at least
 */
void pbch_mib_pack(pbch_mib_t *mib, char *msg) {
  int bw, phich_res = 0;

  bzero(msg, 24);

  if (mib->nof_prb <= 6) {
    bw = 0;
  } else if (mib->nof_prb <= 15) {
    bw = 1;
  } else {
    bw = 1 + mib->nof_prb / 25;
  }
  bit_pack(bw, &msg, 3);

  *msg = mib->phich_length == PHICH_EXT;
  msg++;

  switch (mib->phich_resources) {
  case R_1_6:
    phich_res = 0;
    break;
  case R_1_2:
    phich_res = 1;
    break;
  case R_1:
    phich_res = 2;
    break;
  case R_2:
    phich_res = 3;
    break;
  }
  bit_pack(phich_res, &msg, 2);
  bit_pack(mib->sfn >> 2, &msg, 8);
}

void pbch_mib_fprint(FILE *stream, pbch_mib_t *mib) {
  printf(" - Nof ports:       %d\n", mib->nof_ports);
  printf(" - PRB:             %d\n", mib->nof_prb);
  printf(" - PHICH Length:    %s\n",
      mib->phich_length == PHICH_EXT ? "Extended" : "Normal");
  printf(" - PHICH Resources: ");
  switch (mib->phich_resources) {
  case R_1_6:
    printf("1/6");
    break;
  case R_1_2:
    printf("1/2");
    break;
  case R_1:
    printf("1");
    break;
  case R_2:
    printf("2");
    break;
  }
  printf("\n");
  printf(" - SFN:             %d\n", mib->sfn);
}

void pbch_decode_reset(pbch_t *q) {
  q->frame_idx = 0;
}

void crc_set_mask(char *data, int nof_ports) {
  int i;
  for (i = 0; i < 16; i++) {
    data[24 + i] = (data[24 + i] + crc_mask[nof_ports - 1][i]) % 2;
  }

}

/* Checks CRC after applying the mask for the given number of ports.
 *
 * The bits buffer size must be at least 40 bytes.
 *
 * Returns 0 if the data is correct, -1 otherwise
 */
int pbch_crc_check(pbch_t *q, char *bits, int nof_ports) {
  char data[40];
  memcpy(data, bits, 40 * sizeof(char));
  crc_set_mask(data, nof_ports);
  return crc_checksum(&q->crc, data, 40);
}

int pbch_decode_frame(pbch_t *q, pbch_mib_t *mib, int src, int dst, int n,
    int nof_bits, int nof_ports) {
  int j;

  memcpy(&q->temp[dst * nof_bits], &q->pbch_llr[src * nof_bits],
      n * nof_bits * sizeof(float));

  /* descramble */
  scrambling_f_offset(&q->seq_pbch, &q->temp[dst * nof_bits], dst * nof_bits,
      n * nof_bits);

  for (j = 0; j < dst * nof_bits; j++) {
    q->temp[j] = RX_NULL;
  }
  for (j = (dst + n) * nof_bits; j < 4 * nof_bits; j++) {
    q->temp[j] = RX_NULL;
  }

  /* unrate matching */
  rm_conv_rx(q->temp, 4 * nof_bits, q->pbch_rm_f, 120);

  /* FIXME: If channel estimates are zero, received LLR are NaN. Check and return error */
  for (j = 0; j < 120; j++) {
    if (isnan(q->pbch_rm_f[j]) || isinf(q->pbch_rm_f[j])) {
      return 0;
    }
  }

  /* decode */
  viterbi_decode_f(&q->decoder, q->pbch_rm_f, q->data, 40);

  int c = 0;
  for (j = 0; j < 40; j++) {
    c += q->data[j];
  }
  if (!c) {
    c = 1;
  }

  if (!pbch_crc_check(q, q->data, nof_ports)) {
    /* unpack MIB */
    pbch_mib_unpack(q->data, mib);

    mib->nof_ports = nof_ports;
    mib->sfn += dst - src;

    return 1;
  } else {
    return 0;
  }
}

/* Decodes the PBCH channel
 *
 * The PBCH spans in 40 ms. This function is called every 10 ms. It tries to decode the MIB
 * given the symbols of the slot #1 of each radio frame. Successive calls will use more frames
 * to help the decoding process.
 *
 * Returns 1 if successfully decoded MIB, 0 if not and -1 on error
 */
int pbch_decode(pbch_t *q, cf_t *slot1_symbols, cf_t *ce[MAX_PORTS_CTRL],
    float ebno, pbch_mib_t *mib) {
  int src, dst, res, nb;
  int nant_[3] = { 1, 2, 4 };
  int na, nant;

  /* Set pointers for layermapping & precoding */
  int i;
  int nof_bits = 2 * q->nof_symbols;
  cf_t *x[MAX_LAYERS];

  /* number of layers equals number of ports */
  for (i = 0; i < MAX_PORTS_CTRL; i++) {
    x[i] = q->pbch_x[i];
  }
  memset(&x[MAX_PORTS_CTRL], 0, sizeof(cf_t*) * (MAX_LAYERS - MAX_PORTS_CTRL));

  /* extract symbols */
  if (q->nof_symbols
      != pbch_get(slot1_symbols, q->pbch_symbols[0], q->nof_prb, q->cp,
          q->cell_id)) {
    fprintf(stderr, "There was an error getting the PBCH symbols\n");
    return -1;
  }

  /* extract channel estimates */
  for (i = 0; i < MAX_PORTS_CTRL; i++) {
    if (q->nof_symbols
        != pbch_get(ce[i], q->ce[i], q->nof_prb, q->cp, q->cell_id)) {
      fprintf(stderr, "There was an error getting the PBCH symbols\n");
      return -1;
    }
  }

  q->frame_idx++;
  res = 0;

  /* Try decoding for 1 to 4 antennas */
  for (na = 0; na < 3 && !res; na++) {
    nant = nant_[na];

    INFO("Trying %d TX antennas with %d frames\n", nant, q->frame_idx);

    /* in conctrol channels, only diversity is supported */
    if (nant == 1) {
      /* no need for layer demapping */
      predecoding_single_zf(q->pbch_symbols[0], q->ce[0], q->pbch_d,
          q->nof_symbols);
    } else {
      predecoding_diversity_zf(q->pbch_symbols[0], q->ce, x, nant,
          q->nof_symbols);
      layerdemap_diversity(x, q->pbch_d, nant, q->nof_symbols / nant);
    }

    /* demodulate symbols */
    demod_soft_sigma_set(&q->demod, ebno);
    demod_soft_demodulate(&q->demod, q->pbch_d,
        &q->pbch_llr[nof_bits * (q->frame_idx - 1)], q->nof_symbols);

    /* We don't know where the 40 ms begin, so we try all combinations. E.g. if we received
     * 4 frames, try 1,2,3,4 individually, 12, 23, 34 in pairs, 123, 234 and finally 1234.
     * We know they are ordered.
     *
     * FIXME: There are unnecessary checks because 2,3,4 have already been processed in the previous
     * calls.
     */
    for (nb = 0; nb < q->frame_idx && !res; nb++) {
      for (dst = 0; (dst < 4 - nb) && !res; dst++) {
        for (src = 0; src < q->frame_idx - nb && !res; src++) {
          DEBUG("Trying %d blocks at offset %d as subframe mod4 number %d\n",
              nb + 1, src, dst);
          res = pbch_decode_frame(q, mib, src, dst, nb + 1, nof_bits, nant);
        }
      }
    }
  }

  /* If not found, make room for the next packet of radio frame symbols */
  if (q->frame_idx == 4) {
    memmove(q->pbch_llr, &q->pbch_llr[nof_bits], nof_bits * 3 * sizeof(float));
    q->frame_idx = 3;
  }
  return res;
}

/** Converts the MIB message to symbols mapped to SLOT #1 ready for transmission
 */
void pbch_encode(pbch_t *q, pbch_mib_t *mib,
    cf_t *slot1_symbols[MAX_PORTS_CTRL], int nof_ports) {
  int i;
  int nof_bits = 2 * q->nof_symbols;

  assert(nof_ports <= MAX_PORTS_CTRL);

  /* Set pointers for layermapping & precoding */
  cf_t *x[MAX_LAYERS];

  /* number of layers equals number of ports */
  for (i = 0; i < nof_ports; i++) {
    x[i] = q->pbch_x[i];
  }
  memset(&x[nof_ports], 0, sizeof(cf_t*) * (MAX_LAYERS - nof_ports));

  if (q->frame_idx == 0) {
    /* pack MIB */
    pbch_mib_pack(mib, q->data);

    /* encode & modulate */
    crc_attach(&q->crc, q->data, 24);
    crc_set_mask(q->data, nof_ports);

    convcoder_encode(&q->encoder, q->data, q->data_enc, 40);

    rm_conv_tx(q->data_enc, 120, q->pbch_rm_b, 4 * nof_bits);

  }

  scrambling_b_offset(&q->seq_pbch, &q->pbch_rm_b[q->frame_idx * nof_bits],
      q->frame_idx * nof_bits, nof_bits);
  mod_modulate(&q->mod, &q->pbch_rm_b[q->frame_idx * nof_bits], q->pbch_d,
      nof_bits);

  /* layer mapping & precoding */
  if (nof_ports > 1) {
    layermap_diversity(q->pbch_d, x, nof_ports, q->nof_symbols);
    precoding_diversity(x, q->pbch_symbols, nof_ports,
        q->nof_symbols / nof_ports);
  } else {
    memcpy(q->pbch_symbols[0], q->pbch_d, q->nof_symbols * sizeof(cf_t));
  }

  /* mapping to resource elements */
  for (i = 0; i < nof_ports; i++) {
    pbch_put(q->pbch_symbols[i], slot1_symbols[i], q->nof_prb, q->cp,
        q->cell_id);
  }
  q->frame_idx++;
  if (q->frame_idx == 4) {
    q->frame_idx = 0;
  }
}