srsLTE/lte/phy/lib/phch/src/pdcch.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 "liblte/phy/phch/dci.h"
#include "liblte/phy/phch/regs.h"
#include "liblte/phy/phch/pdcch.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"

#define PDCCH_NOF_FORMATS 			4
#define PDCCH_FORMAT_NOF_CCE(i)		(1<<i)
#define PDCCH_FORMAT_NOF_REGS(i) 	((1<<i)*9)
#define PDCCH_FORMAT_NOF_BITS(i) 	((1<<i)*72)

#define NOF_COMMON_FORMATS	2
const dci_format_t common_formats[NOF_COMMON_FORMATS] = { Format1A, Format1C };

#define NOF_UE_FORMATS	2
const dci_format_t ue_formats[NOF_UE_FORMATS] = { Format0, Format1 }; // 1A has the same payload as 0

#define MIN(a,b) ((a>b)?b:a)

/**
 * 36.213 9.1
 */
int gen_common_search(dci_candidate_t *c, int nof_cce, int nof_bits,
    unsigned short rnti) {
  int i, l, L, k;
  k = 0;
  for (l = 3; l > 1; l--) {
    L = (1 << l);
    for (i = 0; i < MIN(nof_cce,16) / (L); i++) {
      c[k].L = l;
      c[k].nof_bits = nof_bits;
      c[k].rnti = rnti;
      c[k].ncce = (L) * (i % (nof_cce / (L)));
      INFO("Common SS Candidate %d: RNTI: 0x%x, nCCE: %d, Nbits: %d, L: %d\n",
          k, c[k].rnti, c[k].ncce, c[k].nof_bits, c[k].L);
      k++;
    }
  }
  return k;
}

/**
 * 36.213 9.1
 */
int gen_ue_search(dci_candidate_t *c, int nof_cce, int nof_bits,
    unsigned short rnti, int subframe) {
  int i, l, L, k, m;
  unsigned int Yk;
  const int S[4] = { 6, 12, 8, 16 };
  k = 0;
  if (!subframe) {
    INFO("UE-specific candidates for RNTI: 0x%x, NofBits: %d, NofCCE: %d\n",
        rnti, nof_bits, nof_cce);
    if (VERBOSE_ISINFO())
      printf("[INFO]: ");
  }
  for (l = 3; l >= 0; l--) {
    L = (1 << l);
    for (i = 0; i < MIN(nof_cce / L, 16 / S[l]); i++) {
      c[k].L = l;
      c[k].nof_bits = nof_bits;
      c[k].rnti = rnti;
      Yk = rnti;
      for (m = 0; m < subframe; m++) {
        Yk = (39827 * Yk) % 65537;
      }
      c[k].ncce = L * ((Yk + i) % (nof_cce / L));
      if (!subframe) {
        if (VERBOSE_ISINFO()) {
          printf("(%d, %d), ", c[k].ncce, c[k].L);
        }
      }
      k++;
    }
  }
  if (!subframe) {
    if (VERBOSE_ISINFO())
      printf("\n");
  }
  return k;
}

void pdcch_init_common(pdcch_t *q, pdcch_search_t *s, unsigned short rnti) {
  int k, i;
  s->nof_candidates = NOF_COMMON_FORMATS
      * (MIN(q->nof_cce,16) / 4 + MIN(q->nof_cce,16) / 8);
  if (s->nof_candidates) {
    s->candidates[0] = malloc(sizeof(dci_candidate_t) * s->nof_candidates);
    dci_candidate_t *c = s->candidates[0];
    s->nof_candidates = 0;
    if (c) {
      // Format 1A and 1C L=4 and L=8, 4 and 2 candidates, only if nof_cce > 16
      k = 0;
      for (i = 0; i < NOF_COMMON_FORMATS; i++) {
        k += gen_common_search(&c[k], q->nof_cce,
            dci_format_sizeof(common_formats[i], q->nof_prb), SIRNTI);
        s->nof_candidates++;
      }
    }
  }
}

/** 36.213 v9.3 Table 7.1-1: System Information DCI messages
 * Expect DCI formats 1C and 1A in the common search space
 */
void pdcch_init_search_si(pdcch_t *q) {
  pdcch_init_common(q, &q->search_mode[SEARCH_SI], SIRNTI);
  q->current_search_mode = SEARCH_SI;
}

/** 36.213 v9.3 Table 7.1-5
 * user-specific search space. Currently supported transmission Mode 1:
 * DCI Format 1A and 1 + PUSCH scheduling format 0
 */
void pdcch_init_search_ue(pdcch_t *q, unsigned short c_rnti) {
  int l, n, k, i;
  pdcch_search_t *s = &q->search_mode[SEARCH_UE];
  s->nof_candidates = 0;
  for (l = 0; l < 3; l++) {
    s->nof_candidates += NOF_UE_FORMATS * (MIN(q->nof_cce,16) / (1 << l));
  }
  INFO(
      "Initiating %d candidate(s) in the UE-specific search space for C-RNTI: 0x%x\n",
      s->nof_candidates, c_rnti);
  if (s->nof_candidates) {
    for (n = 0; n < NSUBFRAMES_X_FRAME; n++) {
      s->candidates[n] = malloc(sizeof(dci_candidate_t) * s->nof_candidates);
      dci_candidate_t *c = s->candidates[n];

      if (c) {
        // Expect Formats 1, 1A, 0
        k = 0;
        for (i = 0; i < NOF_UE_FORMATS; i++) {
          k += gen_ue_search(&c[k], q->nof_cce,
              dci_format_sizeof(ue_formats[i], q->nof_prb), c_rnti, n);
        }
      }
    }
  }
  q->current_search_mode = SEARCH_UE;
}

/** 36.213 v9.3 Table 7.1-3
 * Expect DCI formats 1C and 1A in the common search space
 */
void pdcch_init_search_ra(pdcch_t *q, unsigned short ra_rnti) {
  pdcch_init_common(q, &q->search_mode[SEARCH_RA], ra_rnti);
  q->current_search_mode = SEARCH_RA;
}

void pdcch_set_search_si(pdcch_t *q) {
  q->current_search_mode = SEARCH_SI;
}
void pdcch_set_search_ue(pdcch_t *q) {
  q->current_search_mode = SEARCH_UE;
}
void pdcch_set_search_ra(pdcch_t *q) {
  q->current_search_mode = SEARCH_RA;
}

/** Initializes the PDCCH transmitter and receiver */
int pdcch_init(pdcch_t *q, regs_t *regs, int nof_prb, int nof_ports,
    int cell_id, lte_cp_t cp) {
  int ret = -1;
  int i;

  if (cell_id < 0) {
    return -1;
  }
  if (nof_ports > MAX_PORTS_CTRL) {
    fprintf(stderr, "Invalid number of ports %d\n", nof_ports);
    return -1;
  }
  bzero(q, sizeof(pdcch_t));
  q->cell_id = cell_id;
  q->cp = cp;
  q->regs = regs;
  q->nof_ports = nof_ports;
  q->nof_prb = nof_prb;
  q->current_search_mode = SEARCH_NONE;

  q->nof_regs = (regs_pdcch_nregs(q->regs) / 9) * 9;
  q->nof_cce = q->nof_regs / 9;
  q->nof_symbols = 4 * q->nof_regs;
  q->nof_bits = 2 * q->nof_symbols;

  INFO("Init PDCCH: %d CCEs (%d REGs), %d bits, %d symbols, %d ports\n",
      q->nof_cce, q->nof_regs, q->nof_bits, q->nof_symbols, q->nof_ports);

  if (modem_table_std(&q->mod, LTE_QPSK, true)) {
    goto clean;
  }
  if (crc_init(&q->crc, LTE_CRC16, 16)) {
    goto clean;
  }

  demod_soft_init(&q->demod);
  demod_soft_table_set(&q->demod, &q->mod);
  demod_soft_alg_set(&q->demod, APPROX);

  for (i = 0; i < NSUBFRAMES_X_FRAME; i++) {
    if (sequence_pdcch(&q->seq_pdcch[i], 2 * i, q->cell_id, q->nof_bits)) {
      goto clean;
    }
  }

  int poly[3] = { 0x6D, 0x4F, 0x57 };
  if (viterbi_init(&q->decoder, viterbi_37, poly, DCI_MAX_BITS + 16, true)) {
    goto clean;
  }

  q->pdcch_e = malloc(sizeof(char) * q->nof_bits);
  if (!q->pdcch_e) {
    goto clean;
  }

  q->pdcch_llr = malloc(sizeof(float) * q->nof_bits);
  if (!q->pdcch_llr) {
    goto clean;
  }

  q->pdcch_d = malloc(sizeof(cf_t) * q->nof_symbols);
  if (!q->pdcch_d) {
    goto clean;
  }

  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->pdcch_x[i] = malloc(sizeof(cf_t) * q->nof_symbols);
    if (!q->pdcch_x[i]) {
      goto clean;
    }
    q->pdcch_symbols[i] = malloc(sizeof(cf_t) * q->nof_symbols);
    if (!q->pdcch_symbols[i]) {
      goto clean;
    }
  }
  ret = 0;
  clean: if (ret == -1) {
    pdcch_free(q);
  }
  return ret;
}

void pdcch_free(pdcch_t *q) {
  int i, j;

  for (i = 0; i < PDCCH_NOF_SEARCH_MODES; i++) {
    for (j = 0; j < NSUBFRAMES_X_FRAME; j++) {
      if (q->search_mode[i].candidates[j]) {
        free(q->search_mode[i].candidates[j]);
      }
    }
  }
  if (q->pdcch_e) {
    free(q->pdcch_e);
  }
  if (q->pdcch_llr) {
    free(q->pdcch_llr);
  }
  if (q->pdcch_d) {
    free(q->pdcch_d);
  }
  for (i = 0; i < MAX_PORTS_CTRL; i++) {
    if (q->ce[i]) {
      free(q->ce[i]);
    }
    if (q->pdcch_x[i]) {
      free(q->pdcch_x[i]);
    }
    if (q->pdcch_symbols[i]) {
      free(q->pdcch_symbols[i]);
    }
  }

  for (i = 0; i < NSUBFRAMES_X_FRAME; i++) {
    sequence_free(&q->seq_pdcch[i]);
  }

  modem_table_free(&q->mod);
  viterbi_free(&q->decoder);
}

/** 36.212 5.3.3.2 to 5.3.3.4
 *
 * Returns XOR between parity and remainder bits
 *
 * TODO: UE transmit antenna selection CRC mask
 */
unsigned short dci_decode(pdcch_t *q, float *e, char *data, int E, int nof_bits) {

  float tmp[3 * (DCI_MAX_BITS + 16)];
  unsigned short p_bits, crc_res;
  char *x;

  assert(nof_bits < DCI_MAX_BITS);

  /* unrate matching */
  rm_conv_rx(e, E, tmp, 3 * (nof_bits + 16));

  DEBUG("Viterbi input: ", 0);
  if (VERBOSE_ISDEBUG()) {
    vec_fprint_f(stdout, tmp, 3 * (nof_bits + 16));
  }

  /* viterbi decoder */
  viterbi_decode_f(&q->decoder, tmp, data, nof_bits + 16);

  if (VERBOSE_ISDEBUG()) {
    bit_fprint(stdout, data, nof_bits + 16);
  }

  x = &data[nof_bits];
  p_bits = (unsigned short) bit_unpack(&x, 16);
  crc_res = ((unsigned short) crc_checksum(&q->crc, data, nof_bits) & 0xffff);
  DEBUG("p_bits: 0x%x, crc_res: 0x%x, tot: 0x%x\n", p_bits, crc_res,
      p_bits ^ crc_res);
  return (p_bits ^ crc_res);
}

int pdcch_decode_candidate(pdcch_t *q, float *llr, dci_candidate_t *c,
    dci_msg_t *msg) {
  unsigned short crc_res;
  DEBUG("Trying Candidate: Nbits: %d, E: %d, nCCE: %d, L: %d, RNTI: 0x%x\n",
      c->nof_bits, PDCCH_FORMAT_NOF_BITS(c->L), c->ncce, c->L, c->rnti);
  crc_res = dci_decode(q, &llr[72 * c->ncce], msg->data,
      PDCCH_FORMAT_NOF_BITS(c->L), c->nof_bits);

  if (c->rnti == crc_res) {
    memcpy(&msg->location, c, sizeof(dci_candidate_t));
    INFO("FOUND Candidate: Nbits: %d, E: %d, nCCE: %d, L: %d, RNTI: 0x%x\n",
        c->nof_bits, PDCCH_FORMAT_NOF_BITS(c->L), c->ncce, c->L, c->rnti);
    return 1;
  }
  return 0;
}

int pdcch_extract_llr(pdcch_t *q, cf_t *slot_symbols, cf_t *ce[MAX_PORTS_CTRL],
    float *llr, int nsubframe, float ebno) {

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

  if (nsubframe < 0 || nsubframe > NSUBFRAMES_X_FRAME) {
    fprintf(stderr, "Invalid subframe %d\n", nsubframe);
    return -1;
  }

  if (ebno == 0.0) {
    fprintf(stderr, "EbNo is Zero\n");
    return -1;
  }

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

  /* extract symbols */
  int n = regs_pdcch_get(q->regs, slot_symbols, q->pdcch_symbols[0]);
  if (q->nof_symbols != n) {
    fprintf(stderr, "Expected %d PDCCH symbols but got %d symbols\n",
        q->nof_symbols, n);
    return -1;
  }

  /* extract channel estimates */
  for (i = 0; i < q->nof_ports; i++) {
    n = regs_pdcch_get(q->regs, ce[i], q->ce[i]);
    if (q->nof_symbols != n) {
      fprintf(stderr, "Expected %d PDCCH symbols but got %d symbols\n",
          q->nof_symbols, n);
      return -1;
    }
  }

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

  DEBUG("pdcch d symbols: ", 0);
  if (VERBOSE_ISDEBUG()) {
    vec_fprint_c(stdout, q->pdcch_d, q->nof_symbols);
  }

  /* demodulate symbols */
  demod_soft_sigma_set(&q->demod, ebno);
  demod_soft_demodulate(&q->demod, q->pdcch_d, q->pdcch_llr, q->nof_symbols);

  DEBUG("llr: ", 0);
  if (VERBOSE_ISDEBUG()) {
    vec_fprint_f(stdout, q->pdcch_llr, q->nof_bits);
  }

  /* descramble */
  scrambling_f_offset(&q->seq_pdcch[nsubframe], llr, 0, q->nof_bits);

  return 0;
}

int pdcch_decode_current_mode(pdcch_t *q, float *llr, dci_t *dci, int subframe) {
  int k, i;

  if (q->current_search_mode == SEARCH_UE) {
    k = subframe;
  } else {
    k = 0;
  }

  for (i = 0;
      i < q->search_mode[q->current_search_mode].nof_candidates
          && dci->nof_dcis < dci->max_dcis; i++) {
    if (pdcch_decode_candidate(q, q->pdcch_llr,
        &q->search_mode[q->current_search_mode].candidates[k][i],
        &dci->msg[dci->nof_dcis])) {
      dci->nof_dcis++;
    }
  }
  return dci->nof_dcis;
}

int pdcch_decode_si(pdcch_t *q, float *llr, dci_t *dci) {
  pdcch_set_search_si(q);
  return pdcch_decode_current_mode(q, llr, dci, 0);
}
int pdcch_decode_ra(pdcch_t *q, float *llr, dci_t *dci) {
  pdcch_set_search_ra(q);
  return pdcch_decode_current_mode(q, llr, dci, 0);
}
int pdcch_decode_ue(pdcch_t *q, float *llr, dci_t *dci, int nsubframe) {
  pdcch_set_search_ue(q);
  return pdcch_decode_current_mode(q, llr, dci, nsubframe);
}

/* Decodes PDCCH channels
 *
 * dci->nof_dcis is the size of the dci->msg buffer (ie max number of messages)
 *
 * Returns number of messages stored in dci
 */
int pdcch_decode(pdcch_t *q, cf_t *slot_symbols, cf_t *ce[MAX_PORTS_CTRL],
    dci_t *dci, int nsubframe, float ebno) {

  if (pdcch_extract_llr(q, slot_symbols, ce, q->pdcch_llr, nsubframe, ebno)) {
    return -1;
  }

  if (q->current_search_mode != SEARCH_NONE) {
    return pdcch_decode_current_mode(q, q->pdcch_llr, dci, nsubframe);
  }

  return 0;
}

void crc_set_mask_rnti(char *crc, unsigned short rnti) {
  int i;
  char mask[16];
  char *r = mask;

  INFO("Mask CRC with RNTI 0x%x\n", rnti);

  bit_pack(rnti, &r, 16);
  for (i = 0; i < 16; i++) {
    crc[i] = (crc[i] + mask[i]) % 2;
  }
}

/** 36.212 5.3.3.2 to 5.3.3.4
 * TODO: UE transmit antenna selection CRC mask
 */
void dci_encode(pdcch_t *q, char *data, char *e, int nof_bits, int E,
    unsigned short rnti) {
  convcoder_t encoder;
  char tmp[3 * (DCI_MAX_BITS + 16)];

  assert(nof_bits < DCI_MAX_BITS);

  int poly[3] = { 0x6D, 0x4F, 0x57 };
  encoder.K = 7;
  encoder.R = 3;
  encoder.tail_biting = true;
  memcpy(encoder.poly, poly, 3 * sizeof(int));

  crc_attach(&q->crc, data, nof_bits);
  crc_set_mask_rnti(&data[nof_bits], rnti);

  convcoder_encode(&encoder, data, tmp, nof_bits + 16);

  DEBUG("CConv output: ", 0);
  if (VERBOSE_ISDEBUG()) {
    vec_fprint_b(stdout, tmp, 3 * (nof_bits + 16));
  }

  rm_conv_tx(tmp, 3 * (nof_bits + 16), e, E);
}

/** Converts the set of DCI messages to symbols mapped to the slot ready for transmission
 */
int pdcch_encode(pdcch_t *q, dci_t *dci, cf_t *slot_symbols[MAX_PORTS_CTRL],
    int nsubframe) {
  int i;
  /* Set pointers for layermapping & precoding */
  cf_t *x[MAX_LAYERS];

  if (nsubframe < 0 || nsubframe > NSUBFRAMES_X_FRAME) {
    fprintf(stderr, "Invalid subframe %d\n", nsubframe);
    return -1;
  }

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

  /* should add <NIL> elements? Or maybe random bits to facilitate power estimation */
  bzero(q->pdcch_e, q->nof_bits);

  /* Encode DCIs */
  for (i = 0; i < dci->nof_dcis; i++) {
    /* do some sanity checks */
    if (dci->msg[i].location.ncce + PDCCH_FORMAT_NOF_CCE(dci->msg[i].location.L)
        > q->nof_cce || dci->msg[i].location.L > 3
        || dci->msg[i].location.nof_bits > DCI_MAX_BITS) {
      fprintf(stderr, "Illegal DCI message %d\n", i);
      return -1;
    }
    INFO("Encoding DCI %d: Nbits: %d, E: %d, nCCE: %d, L: %d, RNTI: 0x%x\n", i,
        dci->msg[i].location.nof_bits,
        PDCCH_FORMAT_NOF_BITS(dci->msg[i].location.L),
        dci->msg[i].location.ncce, dci->msg[i].location.L,
        dci->msg[i].location.rnti);

    dci_encode(q, dci->msg[i].data, &q->pdcch_e[72 * dci->msg[i].location.ncce],
        dci->msg[i].location.nof_bits,
        PDCCH_FORMAT_NOF_BITS(dci->msg[i].location.L),
        dci->msg[i].location.rnti);
  }

  scrambling_b_offset(&q->seq_pdcch[nsubframe], q->pdcch_e, 0, q->nof_bits);

  mod_modulate(&q->mod, q->pdcch_e, q->pdcch_d, q->nof_bits);

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

  /* mapping to resource elements */
  for (i = 0; i < q->nof_ports; i++) {
    regs_pdcch_put(q->regs, q->pdcch_symbols[i], slot_symbols[i]);
  }
  return 0;
}