srsRAN_4G/lte/phy/lib/sync/src/pss.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 <strings.h>
#include <string.h>
#include <stdlib.h>
#include <complex.h>
#include <math.h>

#include "liblte/phy/sync/pss.h"
#include "liblte/phy/utils/dft.h"
#include "liblte/phy/utils/vector.h"
#include "liblte/phy/utils/convolution.h"

#define NOT_SYNC  0xF0F0F0F0

/* Initializes the object. subframe_size is the size, in samples, of the 1ms subframe
 *
 */
int pss_synch_init(pss_synch_t *q, int frame_size) {
  int ret = -1;
  bzero(q, sizeof(pss_synch_t));

  q->pss_signal_freq = vec_malloc((PSS_LEN_FREQ + frame_size) * sizeof(cf_t));
  if (!q->pss_signal_freq) {
    fprintf(stderr, "Error allocating memory\n");
    goto clean_and_exit;
  }
  q->conv_abs = vec_malloc((PSS_LEN_FREQ + frame_size) * sizeof(float));
  if (!q->conv_abs) {
    fprintf(stderr, "Error allocating memory\n");
    goto clean_and_exit;
  }
  q->tmp_input = vec_malloc((PSS_LEN_FREQ + frame_size) * sizeof(cf_t));
  if (!q->tmp_input) {
    fprintf(stderr, "Error allocating memory\n");
    goto clean_and_exit;
  }
  q->frame_buffer = vec_malloc(4 * frame_size * sizeof(cf_t));
  if (!q->frame_buffer) {
    fprintf(stderr, "Error allocating memory\n");
    goto clean_and_exit;
  }
  q->conv_output = vec_malloc((PSS_LEN_FREQ + frame_size) * sizeof(cf_t));
  if (!q->conv_output) {
    fprintf(stderr, "Error allocating memory\n");
    goto clean_and_exit;
  }

#ifdef CONVOLUTION_FFT
  if (conv_fft_cc_init(&q->conv_fft, frame_size, PSS_LEN_FREQ)) {
    fprintf(stderr, "Error initiating convolution FFT\n");
    goto clean_and_exit;
  }
#endif

  q->correlation_threshold = DEFAULT_CORRELATION_TH;
  q->nosync_timeout_frames = DEFAULT_NOSYNC_TIMEOUT;
  q->cfo_auto = true;
  q->N_id_2 = -1;
  q->frame_size = frame_size;
  q->frame_start_idx = NOT_SYNC;
  q->fb_wp = 0;

  ret = 0;
  clean_and_exit: if (ret == -1) {
    pss_synch_free(q);
  }
  return ret;
}

void pss_synch_free(pss_synch_t *q) {
  if (q->pss_signal_freq) {
    free(q->pss_signal_freq);
  }
  if (q->conv_abs) {
    free(q->conv_abs);
  }
  if (q->tmp_input) {
    free(q->tmp_input);
  }
  if (q->frame_buffer) {
    free(q->frame_buffer);
  }
  if (q->conv_output) {
    free(q->conv_output);
  }

#ifdef CONVOLUTION_FFT
  conv_fft_cc_free(&q->conv_fft);
#endif

  bzero(q, sizeof(pss_synch_t));
}

/**
 * This function calculates the Zadoff-Chu sequence.
 * @param signal Output array.
 */
int pss_generate(cf_t *signal, int N_id_2) {
  int i;
  float arg;
  const float root_value[] = { 25.0, 29.0, 34.0 };
  int root_idx;

  int sign = -1;

  if (N_id_2 < 0 || N_id_2 > 2) {
    fprintf(stderr, "Invalid N_id_2 %d\n", N_id_2);
    return -1;
  }

  root_idx = N_id_2;

  for (i = 0; i < PSS_LEN / 2; i++) {
    arg = (float) sign * M_PI * root_value[root_idx]
        * ((float) i * ((float) i + 1.0)) / 63.0;
    __real__ signal[i] = cosf(arg);
    __imag__ signal[i] = sinf(arg);
  }
  for (i = PSS_LEN / 2; i < PSS_LEN; i++) {
    arg = (float) sign * M_PI * root_value[root_idx]
        * (((float) i + 2.0) * ((float) i + 1.0)) / 63.0;
    __real__ signal[i] = cosf(arg);
    __imag__ signal[i] = sinf(arg);
  }
  return 0;
}

/** 36.211 10.3 section 6.11.1.2
 */
void pss_put_slot(cf_t *pss_signal, cf_t *slot, int nof_prb, lte_cp_t cp) {
  int k;
  k = (CP_NSYMB(cp) - 1) * nof_prb * RE_X_RB + nof_prb * RE_X_RB / 2 - 31;
  memset(&slot[k - 5], 0, 5 * sizeof(cf_t));
  memcpy(&slot[k], pss_signal, PSS_LEN * sizeof(cf_t));
  memset(&slot[k + PSS_LEN], 0, 5 * sizeof(cf_t));
}

/** Sets the current N_id_2 value. Initializes the object for this PSS sequence
 * Returns -1 on error, 0 otherwise
 */
int pss_synch_set_N_id_2(pss_synch_t *q, int N_id_2) {
  q->N_id_2 = N_id_2;

  dft_plan_t plan;
  cf_t pss_signal_pad[PSS_LEN_FREQ];
  cf_t pss_signal_time[PSS_LEN];

  if (N_id_2 < 0 || N_id_2 > 2) {
    fprintf(stderr, "Invalid N_id_2 %d\n", N_id_2);
    return -1;
  }

  pss_generate(pss_signal_time, N_id_2);

  memset(pss_signal_pad, 0, PSS_LEN_FREQ * sizeof(cf_t));
  memset(q->pss_signal_freq, 0, PSS_LEN_FREQ * sizeof(cf_t));
  memcpy(&pss_signal_pad[33], pss_signal_time, PSS_LEN * sizeof(cf_t));

  if (dft_plan(&plan, PSS_LEN_FREQ - 1, COMPLEX_2_COMPLEX, BACKWARD)) {
    return -1;
  }
  plan.options = DFT_MIRROR_PRE | DFT_DC_OFFSET;

  dft_run_c2c(&plan, pss_signal_pad, q->pss_signal_freq);

  vec_sc_prod_cfc(q->pss_signal_freq, (float) 1 / (PSS_LEN_FREQ - 1),
      pss_signal_pad, PSS_LEN_FREQ);

  vec_conj_cc(pss_signal_pad, q->pss_signal_freq, PSS_LEN_FREQ);

  q->N_id_2 = N_id_2;

  dft_plan_free(&plan);

  return 0;
}

/** Returns the index of the PSS correlation peak in a subframe.
 * The frame starts at corr_peak_pos-subframe_size/2.
 * The value of the correlation is stored in corr_peak_value.
 *
 * Input buffer must be subframe_size long.
 */
int pss_synch_find_pss(pss_synch_t *q, cf_t *input, float *corr_peak_value,
    float *corr_mean_value) {
  int corr_peak_pos;
  int conv_output_len;

  memset(&q->pss_signal_freq[PSS_LEN_FREQ], 0, q->frame_size * sizeof(cf_t));
  memcpy(q->tmp_input, input, q->frame_size * sizeof(cf_t));
  memset(&q->tmp_input[q->frame_size], 0, PSS_LEN_FREQ * sizeof(cf_t));

#ifdef CONVOLUTION_FFT
  conv_output_len = conv_fft_cc_run(&q->conv_fft, q->tmp_input,
      q->pss_signal_freq, q->conv_output);
#else
  conv_output_len = conv_cc(input, q->pss_signal_freq, q->conv_output, q->frame_size, PSS_LEN_FREQ);
#endif

  vec_abs_cf(q->conv_output, q->conv_abs, conv_output_len);
  corr_peak_pos = vec_max_fi(q->conv_abs, conv_output_len);
  if (corr_peak_value) {
    *corr_peak_value = q->conv_abs[corr_peak_pos];
  }
  if (corr_mean_value) {
    *corr_mean_value = vec_acc_ff(q->conv_abs, conv_output_len)
        / conv_output_len;
  }

  return (int) corr_peak_pos;
}

/* Returns the CFO estimation given a PSS received sequence
 *
 * Source: An Efficient CFO Estimation Algorithm for the Downlink of 3GPP-LTE
 *       Feng Wang and Yu Zhu
 */
float pss_synch_cfo_compute(pss_synch_t* q, cf_t *pss_recv) {
  cf_t y0, y1, yr;
  cf_t y[PSS_LEN_FREQ - 1];

  vec_prod_ccc_unalign(q->pss_signal_freq, pss_recv, y, PSS_LEN_FREQ - 1);

  y0 = vec_acc_cc(y, (PSS_LEN_FREQ - 1) / 2);
  y1 = vec_acc_cc(&y[(PSS_LEN_FREQ - 1) / 2], (PSS_LEN_FREQ - 1) / 2);
  yr = conjf(y0) * y1;

  return atan2f(__imag__ yr, __real__ yr) / M_PI;
}

/** This function is designed to be called periodically on a subframe basis.
 * The function finds the PSS correlation peak and computes (does not adjust) CFO automatically as defined by
 * pss_synch_set_cfo_mode().
 *
 * If the PSS sequence is not found, returns 0 writes nothing to the output buffer.
 * If the PSS sequence is found, aligns the beginning of the subframe to the output buffer and returns the number of samples
 * written to the output buffer.
 * If synchronized, subsequent calls to this function align the input buffer to the subframe beginning.
 */
int pss_synch_frame(pss_synch_t *q, cf_t *input, cf_t *output, int nsamples) {
  int max_idx, tmp_start_idx;
  int retval;
  float max_value;

  if (nsamples != q->frame_size) {
    fprintf(stderr, "Configured for frame size %d but got %d samples\n",
        q->frame_size, nsamples);
    return -1;
  }

  if (q->N_id_2 < 0) {
    fprintf(stderr,
        "N_id_2 must be configured before calling pss_synch()\n");
    return -1;
  }

  max_idx = pss_synch_find_pss(q, input, &max_value, NULL);
  if (max_value > q->correlation_threshold) {
    tmp_start_idx = max_idx - nsamples / 2;
    if (q->frame_start_idx != tmp_start_idx) {
      printf("Re-synchronizing: new index is %d, old was %d\n",
          tmp_start_idx, q->frame_start_idx);
    }
    q->frame_start_idx = tmp_start_idx;
  } else {
    if (q->nosync_timeout_frames > 0) {
      q->nof_nosync_frames++;
      if (q->nof_nosync_frames >= q->nosync_timeout_frames) {
        q->frame_start_idx = NOT_SYNC;
      }
    }
  }

  if (q->frame_start_idx == NOT_SYNC) {

    memcpy(q->frame_buffer, input, nsamples * sizeof(cf_t));
    retval = 0;

  } else if (q->frame_start_idx > 0) {

    if (q->fb_wp) {
      memcpy(&q->frame_buffer[(nsamples - q->frame_start_idx)], input,
          q->frame_start_idx * sizeof(cf_t));
      memcpy(output, q->frame_buffer, nsamples * sizeof(cf_t));
      retval = nsamples;
    } else {
      retval = 0;
    }
    memcpy(q->frame_buffer, &input[q->frame_start_idx],
        (nsamples - q->frame_start_idx) * sizeof(cf_t));
    q->fb_wp = 1;

  } else {

    memcpy(output, &q->frame_buffer[nsamples + q->frame_start_idx],
        (-q->frame_start_idx) * sizeof(cf_t));
    memcpy(&output[-q->frame_start_idx], input,
        (nsamples + q->frame_start_idx) * sizeof(cf_t));
    memcpy(&q->frame_buffer[nsamples + q->frame_start_idx],
        &input[nsamples + q->frame_start_idx],
        (-q->frame_start_idx) * sizeof(cf_t));
    retval = nsamples;
  }

  if (q->frame_start_idx != NOT_SYNC && q->cfo_auto && retval) {
    q->current_cfo = pss_synch_cfo_compute(q,
        &output[q->frame_size / 2 - PSS_LEN_FREQ + 1]);
  }

  return retval;
}

void pss_synch_set_timeout(pss_synch_t *q, int nof_frames) {
  q->nosync_timeout_frames = nof_frames;
}

void pss_synch_set_threshold(pss_synch_t *q, float threshold) {
  q->correlation_threshold = threshold;
}

void pss_synch_set_cfo_mode(pss_synch_t *q, bool cfo_auto) {
  q->cfo_auto = cfo_auto;
}

float pss_synch_get_cfo(pss_synch_t *q) {
  return q->current_cfo;
}

int pss_synch_get_frame_start_idx(pss_synch_t *q) {
  return q->frame_start_idx;
}

/** High-level API */

int pss_synch_initialize(pss_synch_hl* h) {
  int fs = h->init.frame_size;
  if (!fs) {
    fs = DEFAULT_FRAME_SIZE;
  }
  if (pss_synch_init(&h->obj, fs)) {
    return -1;
  }
  if (h->init.unsync_nof_pkts) {
    pss_synch_set_timeout(&h->obj, h->init.unsync_nof_pkts);
  }

  pss_synch_set_N_id_2(&h->obj, h->init.N_id_2);
  if (h->init.do_cfo) {
    pss_synch_set_cfo_mode(&h->obj, true);
  } else {
    pss_synch_set_cfo_mode(&h->obj, false);
  }
  return 0;
}

int pss_synch_work(pss_synch_hl* hl) {

  if (hl->ctrl_in.correlation_threshold) {
    pss_synch_set_threshold(&hl->obj, hl->ctrl_in.correlation_threshold);
  }

  hl->out_len = pss_synch_frame(&hl->obj, hl->input, hl->output, hl->in_len);

  return 0;
}

int pss_synch_stop(pss_synch_hl* hl) {
  pss_synch_free(&hl->obj);
  return 0;
}