srsLTE/srslte/lib/phch/pbch.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 <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_dl.h"
#include "srslte/phch/pbch.h"
#include "srslte/common/phy_common.h"
#include "srslte/utils/bit.h"
#include "srslte/utils/vector.h"
#include "srslte/utils/debug.h"

#define PBCH_RE_CP_NORM    240
#define PBCH_RE_CP_EXT     216


const uint8_t srslte_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 srslte_pbch_exists(int nframe, int nslot) {
  return (!(nframe % 5) && nslot == 1);
}

cf_t *offset_original;

int srslte_pbch_cp(cf_t *input, cf_t *output, srslte_cell_t cell, bool put) {
  int i;
  cf_t *ptr;
  
  offset_original = input; 
  
  if (put) {
    ptr = input;
    output += cell.nof_prb * SRSLTE_NRE / 2 - 36;
  } else {
    ptr = output;
    input += cell.nof_prb * SRSLTE_NRE / 2 - 36;
  }
  
  /* symbol 0 & 1 */
  for (i = 0; i < 2; i++) {
    prb_cp_ref(&input, &output, cell.id % 3, 4, 4*6, put);
    if (put) {
      output += cell.nof_prb * SRSLTE_NRE - 2*36 + (cell.id%3==2?1:0);      
    } else {
      input += cell.nof_prb * SRSLTE_NRE - 2*36 + (cell.id%3==2?1:0);
    }
  }
  /* symbols 2 & 3 */
  if (SRSLTE_CP_ISNORM(cell.cp)) {
    for (i = 0; i < 2; i++) {
      prb_cp(&input, &output, 6);
      if (put) {
        output += cell.nof_prb * SRSLTE_NRE - 2*36;
      } else {
        input += cell.nof_prb * SRSLTE_NRE - 2*36;
      }
    }
  } else {
    prb_cp(&input, &output, 6);
    if (put) {
      output += cell.nof_prb * SRSLTE_NRE - 2*36;
    } else {
      input += cell.nof_prb * SRSLTE_NRE - 2*36;
    }
    prb_cp_ref(&input, &output, cell.id % 3, 4, 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 srslte_pbch_put(cf_t *pbch, cf_t *slot1_data, srslte_cell_t cell) {
  return srslte_pbch_cp(pbch, slot1_data, cell, true);
}

/**
 * Extracts PBCH from slot number 1
 *
 * Returns the number of symbols written to pbch
 *
 * 36.211 10.3 section 6.6.4
 */
int srslte_pbch_get(cf_t *slot1_data, cf_t *pbch, srslte_cell_t cell) {
  return srslte_pbch_cp(slot1_data, pbch, cell, false);
}

/** Initializes the PBCH transmitter and receiver. 
 * At the receiver, the field nof_ports in the cell structure indicates the 
 * maximum number of BS transmitter ports to look for.  
 */
int srslte_pbch_init(srslte_pbch_t *q, srslte_cell_t cell) {
  int ret = SRSLTE_ERROR_INVALID_INPUTS;

  if (q                       != NULL &&
      srslte_cell_isvalid(&cell))
  {
    ret = SRSLTE_ERROR;

    bzero(q, sizeof(srslte_pbch_t));
    
    if (cell.nof_ports == 0) {
      q->search_all_ports = true; 
      cell.nof_ports = SRSLTE_MAX_PORTS; 
    } else {
      q->search_all_ports = false; 
    }
    
    q->cell = cell;
    q->nof_symbols = (SRSLTE_CP_ISNORM(q->cell.cp)) ? PBCH_RE_CP_NORM : PBCH_RE_CP_EXT;
    
    if (srslte_modem_table_lte(&q->mod, SRSLTE_MOD_QPSK)) {
      goto clean;
    }
    if (srslte_sequence_pbch(&q->seq, q->cell.cp, q->cell.id)) {
      goto clean;
    }

    int poly[3] = { 0x6D, 0x4F, 0x57 };
    if (srslte_viterbi_init(&q->decoder, SRSLTE_VITERBI_37, poly, 40, true)) {
      goto clean;
    }
    if (srslte_crc_init(&q->crc, SRSLTE_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->d = srslte_vec_malloc(sizeof(cf_t) * q->nof_symbols);
    if (!q->d) {
      goto clean;
    }
    int i;
    for (i = 0; i < q->cell.nof_ports; i++) {
      q->ce[i] = srslte_vec_malloc(sizeof(cf_t) * q->nof_symbols);
      if (!q->ce[i]) {
        goto clean;
      }
      q->x[i] = srslte_vec_malloc(sizeof(cf_t) * q->nof_symbols);
      if (!q->x[i]) {
        goto clean;
      }
      q->symbols[i] = srslte_vec_malloc(sizeof(cf_t) * q->nof_symbols);
      if (!q->symbols[i]) {
        goto clean;
      }
    }
    q->llr = srslte_vec_malloc(sizeof(float) * q->nof_symbols * 4 * 2);
    if (!q->llr) {
      goto clean;
    }
    q->temp = srslte_vec_malloc(sizeof(float) * q->nof_symbols * 4 * 2);
    if (!q->temp) {
      goto clean;
    }
    q->rm_b = srslte_vec_malloc(sizeof(float) * q->nof_symbols * 4 * 2);
    if (!q->rm_b) {
      goto clean;
    }
    ret = SRSLTE_SUCCESS;
  }
clean: 
  if (ret == SRSLTE_ERROR) {
    srslte_pbch_free(q);
  }
  return ret;
}

void srslte_pbch_free(srslte_pbch_t *q) {
  if (q->d) {
    free(q->d);
  }
  int i;
  for (i = 0; i < q->cell.nof_ports; i++) {
    if (q->ce[i]) {
      free(q->ce[i]);
    }
    if (q->x[i]) {
      free(q->x[i]);
    }
    if (q->symbols[i]) {
      free(q->symbols[i]);
    }
  }
  if (q->llr) {
    free(q->llr);
  }
  if (q->temp) {
    free(q->temp);
  }
  if (q->rm_b) {
    free(q->rm_b);
  }
  srslte_sequence_free(&q->seq);
  srslte_modem_table_free(&q->mod);
  srslte_viterbi_free(&q->decoder);

  bzero(q, sizeof(srslte_pbch_t));

}


/** Unpacks MIB from PBCH message.
 * msg buffer must be 24 byte length at least
 */
void srslte_pbch_mib_unpack(uint8_t *msg, srslte_cell_t *cell, uint32_t *sfn) {
  int phich_res;

  cell->bw_idx = srslte_bit_pack(&msg, 3);
  switch (cell->bw_idx) {
  case 0:
    cell->nof_prb = 6;
    break;
  case 1:
    cell->nof_prb = 15;
    break;
  default:
    cell->nof_prb = (cell->bw_idx - 1) * 25;
    break;
  }
  if (*msg) {
    cell->phich_length = SRSLTE_PHICH_EXT;
  } else {
    cell->phich_length = SRSLTE_PHICH_NORM;
  }
  msg++;

  phich_res = srslte_bit_pack(&msg, 2);
  switch (phich_res) {
  case 0:
      cell->phich_resources = SRSLTE_PHICH_R_1_6;
    break;
  case 1:
      cell->phich_resources = SRSLTE_PHICH_R_1_2;
    break;
  case 2:
      cell->phich_resources = SRSLTE_PHICH_R_1;
    break;
  case 3:
      cell->phich_resources = SRSLTE_PHICH_R_2;
    break;
  }
  if (sfn) {
    *sfn = srslte_bit_pack(&msg, 8) << 2;    
  }
}

/** Unpacks MIB from PBCH message.
 * msg buffer must be 24 byte length at least
 */
void srslte_pbch_mib_pack(srslte_cell_t *cell, uint32_t sfn, uint8_t *msg) {
  int bw, phich_res = 0;

  bzero(msg, 24);

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

  *msg = cell->phich_length == SRSLTE_PHICH_EXT;
  msg++;

  switch (cell->phich_resources) {
  case SRSLTE_PHICH_R_1_6:
    phich_res = 0;
    break;
  case SRSLTE_PHICH_R_1_2:
    phich_res = 1;
    break;
  case SRSLTE_PHICH_R_1:
    phich_res = 2;
    break;
  case SRSLTE_PHICH_R_2:
    phich_res = 3;
    break;
  }
  srslte_bit_unpack(phich_res, &msg, 2);
  srslte_bit_unpack(sfn >> 2, &msg, 8);
}

void srslte_pbch_decode_reset(srslte_pbch_t *q) {
  q->frame_idx = 0;
}

void srslte_crc_set_mask(uint8_t *data, int nof_ports) {
  int i;
  for (i = 0; i < 16; i++) {
    data[SRSLTE_BCH_PAYLOAD_LEN + i] = (data[SRSLTE_BCH_PAYLOAD_LEN + i] + srslte_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
 */
uint32_t srslte_pbch_crc_check(srslte_pbch_t *q, uint8_t *bits, uint32_t nof_ports) {
  uint8_t data[SRSLTE_BCH_PAYLOADCRC_LEN];
  memcpy(data, bits, SRSLTE_BCH_PAYLOADCRC_LEN * sizeof(uint8_t));
  srslte_crc_set_mask(data, nof_ports);
  int ret = srslte_crc_checksum(&q->crc, data, SRSLTE_BCH_PAYLOADCRC_LEN);
  if (ret == 0) {
    uint32_t chkzeros=0;
    for (int i=0;i<SRSLTE_BCH_PAYLOAD_LEN;i++) {
      chkzeros += data[i];
    }
    if (chkzeros) {
      return 0;
    } else {
      return SRSLTE_ERROR;
    }
  } else {
    return ret; 
  }
}

int decode_frame(srslte_pbch_t *q, uint32_t src, uint32_t dst, uint32_t n,
    uint32_t nof_bits, uint32_t nof_ports) {
  int j;
  
  memcpy(&q->temp[dst * nof_bits], &q->llr[src * nof_bits],
      n * nof_bits * sizeof(float));

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

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

  /* unrate matching */
  srslte_rm_conv_rx(q->temp, 4 * nof_bits, q->rm_f, SRSLTE_BCH_ENCODED_LEN);
  
  /* Normalize LLR */
  srslte_vec_sc_prod_fff(q->rm_f, 1.0/((float) 2*n), q->rm_f, SRSLTE_BCH_ENCODED_LEN);
  
  /* decode */
  srslte_viterbi_decode_f(&q->decoder, q->rm_f, q->data, SRSLTE_BCH_PAYLOADCRC_LEN);

 if (!srslte_pbch_crc_check(q, q->data, nof_ports)) {
    return 1;
  } else {
    return SRSLTE_SUCCESS;
  }
}

/* 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 a subframe (1 ms). Successive calls will use more subframes
 * to help the decoding process.
 *
 * Returns 1 if successfully decoded MIB, 0 if not and -1 on error
 */
int srslte_pbch_decode(srslte_pbch_t *q, cf_t *slot1_symbols, cf_t *ce_slot1[SRSLTE_MAX_PORTS], float noise_estimate, 
                 uint8_t bch_payload[SRSLTE_BCH_PAYLOAD_LEN], uint32_t *nof_tx_ports, int *sfn_offset) 
{
  uint32_t src, dst, nb;
  uint32_t nant;
  int i;
  int nof_bits;
  cf_t *x[SRSLTE_MAX_LAYERS];
  
  int ret = SRSLTE_ERROR_INVALID_INPUTS;
  
  if (q                 != NULL &&
      slot1_symbols     != NULL)
  {
    for (i=0;i<q->cell.nof_ports;i++) {
      if (ce_slot1[i] == NULL) {
        return SRSLTE_ERROR_INVALID_INPUTS;
      } 
    }

    /* Set pointers for layermapping & precoding */
    nof_bits = 2 * q->nof_symbols;

    /* number of layers equals number of ports */
    for (i = 0; i < SRSLTE_MAX_PORTS; i++) {
      x[i] = q->x[i];
    }
    memset(&x[SRSLTE_MAX_PORTS], 0, sizeof(cf_t*) * (SRSLTE_MAX_LAYERS - SRSLTE_MAX_PORTS));
    
    /* extract symbols */
    if (q->nof_symbols != srslte_pbch_get(slot1_symbols, q->symbols[0], q->cell)) {
      fprintf(stderr, "There was an error getting the PBCH symbols\n");
      return SRSLTE_ERROR;
    }

    /* extract channel estimates */
    for (i = 0; i < q->cell.nof_ports; i++) {
      if (q->nof_symbols != srslte_pbch_get(ce_slot1[i], q->ce[i], q->cell)) {
        fprintf(stderr, "There was an error getting the PBCH symbols\n");
        return SRSLTE_ERROR;
      }
    }

    q->frame_idx++;
    ret = 0;

    /* Try decoding for 1 to cell.nof_ports antennas */
    if (q->search_all_ports) {
      nant = 1; 
    } else {
      nant = q->cell.nof_ports; 
    }
    do {
      if (nant != 3) {
        DEBUG("Trying %d TX antennas with %d frames\n", nant, q->frame_idx);

        /* in control channels, only diversity is supported */
        if (nant == 1) {
          /* no need for layer demapping */
          srslte_predecoding_single(q->symbols[0], q->ce[0], q->d, q->nof_symbols, noise_estimate);
        } else {
          srslte_predecoding_diversity(q->symbols[0], q->ce, x, nant,
              q->nof_symbols);
          srslte_layerdemap_diversity(x, q->d, nant, q->nof_symbols / nant);
        }

        /* demodulate symbols */
        srslte_demod_soft_demodulate(SRSLTE_MOD_QPSK, q->d, &q->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.
        */
        for (nb = 0; nb < q->frame_idx; nb++) {
          for (dst = 0; (dst < 4 - nb); dst++) {
            for (src = 0; src < q->frame_idx - nb; src++) {
              ret = decode_frame(q, src, dst, nb + 1, nof_bits, nant);     
              if (ret == 1) {
                if (sfn_offset) {
                  *sfn_offset = (int) dst - src + q->frame_idx - 1;
                }
                if (nof_tx_ports) {
                  *nof_tx_ports = nant; 
                }
                if (bch_payload) {
                  memcpy(bch_payload, q->data, sizeof(uint8_t) * SRSLTE_BCH_PAYLOAD_LEN);      
                }
                INFO("Decoded PBCH: src=%d, dst=%d, nb=%d, sfn_offset=%d\n", src, dst, nb+1, (int) dst - src + q->frame_idx - 1);
                return 1; 
              }
            }
          }
        }
      }
      nant++;
    } while(nant <= q->cell.nof_ports); 
    
    /* If not found, make room for the next packet of radio frame symbols */
    if (q->frame_idx == 4) {
      memmove(q->llr, &q->llr[nof_bits], nof_bits * 3 * sizeof(float));
      q->frame_idx = 3;
    }
  }
  return ret;
}

/** Converts the MIB message to symbols mapped to SLOT #1 ready for transmission
 */
int srslte_pbch_encode(srslte_pbch_t *q, uint8_t bch_payload[SRSLTE_BCH_PAYLOAD_LEN], cf_t *slot1_symbols[SRSLTE_MAX_PORTS]) {
  int i;
  int nof_bits;
  cf_t *x[SRSLTE_MAX_LAYERS];
  
  if (q                 != NULL &&
      bch_payload               != NULL)
  {
    for (i=0;i<q->cell.nof_ports;i++) {
      if (slot1_symbols[i] == NULL) {
        return SRSLTE_ERROR_INVALID_INPUTS;
      } 
    }
    /* Set pointers for layermapping & precoding */
    nof_bits = 2 * q->nof_symbols;

    /* number of layers equals number of ports */
    for (i = 0; i < q->cell.nof_ports; i++) {
      x[i] = q->x[i];
    }
    memset(&x[q->cell.nof_ports], 0, sizeof(cf_t*) * (SRSLTE_MAX_LAYERS - q->cell.nof_ports));
    
    if (q->frame_idx == 0) {
      memcpy(q->data, bch_payload, sizeof(uint8_t) * SRSLTE_BCH_PAYLOAD_LEN);

      /* encode & modulate */
      srslte_crc_attach(&q->crc, q->data, SRSLTE_BCH_PAYLOAD_LEN);
      srslte_crc_set_mask(q->data, q->cell.nof_ports);
      
      srslte_convcoder_encode(&q->encoder, q->data, q->data_enc, SRSLTE_BCH_PAYLOADCRC_LEN);

      srslte_rm_conv_tx(q->data_enc, SRSLTE_BCH_ENCODED_LEN, q->rm_b, 4 * nof_bits);
    }

    srslte_scrambling_b_offset(&q->seq, &q->rm_b[q->frame_idx * nof_bits],
        q->frame_idx * nof_bits, nof_bits);
    srslte_mod_modulate(&q->mod, &q->rm_b[q->frame_idx * nof_bits], q->d,
        nof_bits);

    /* layer mapping & precoding */
    if (q->cell.nof_ports > 1) {
      srslte_layermap_diversity(q->d, x, q->cell.nof_ports, q->nof_symbols);
      srslte_precoding_diversity(x, q->symbols, q->cell.nof_ports,
          q->nof_symbols / q->cell.nof_ports);
    } else {
      memcpy(q->symbols[0], q->d, q->nof_symbols * sizeof(cf_t));
    }

    /* mapping to resource elements */
    for (i = 0; i < q->cell.nof_ports; i++) {
      srslte_pbch_put(q->symbols[i], slot1_symbols[i], q->cell);
    }
    q->frame_idx++;
    if (q->frame_idx == 4) {
      q->frame_idx = 0;
    }
    return SRSLTE_SUCCESS;
  } else {
    return SRSLTE_ERROR_INVALID_INPUTS;
  }
}