float compute_peak_sidelobe(srslte_pss_t *q, uint32_t corr_peak_pos, uint32_t conv_output_len) { // Find end of peak lobe to the right int pl_ub = corr_peak_pos+1; while(q->conv_output_avg[pl_ub+1] <= q->conv_output_avg[pl_ub] && pl_ub < conv_output_len) { pl_ub ++; } // Find end of peak lobe to the left int pl_lb; if (corr_peak_pos > 2) { pl_lb = corr_peak_pos-1; while(q->conv_output_avg[pl_lb-1] <= q->conv_output_avg[pl_lb] && pl_lb > 1) { pl_lb --; } } else { pl_lb = 0; } int sl_distance_right = conv_output_len-1-pl_ub; if (sl_distance_right < 0) { sl_distance_right = 0; } int sl_distance_left = pl_lb; int sl_right = pl_ub+srslte_vec_max_fi(&q->conv_output_avg[pl_ub], sl_distance_right); int sl_left = srslte_vec_max_fi(q->conv_output_avg, sl_distance_left); float side_lobe_value = SRSLTE_MAX(q->conv_output_avg[sl_right], q->conv_output_avg[sl_left]); return q->conv_output_avg[corr_peak_pos]/side_lobe_value; }
/** Performs time-domain PSS correlation. * 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 srslte_pss_synch_find_pss(srslte_pss_synch_t *q, cf_t *input, float *corr_peak_value) { int ret = SRSLTE_ERROR_INVALID_INPUTS; if (q != NULL && input != NULL) { uint32_t corr_peak_pos; uint32_t conv_output_len; if (!srslte_N_id_2_isvalid(q->N_id_2)) { fprintf(stderr, "Error finding PSS peak, Must set N_id_2 first\n"); return SRSLTE_ERROR; } /* Correlate input with PSS sequence */ if (q->frame_size >= q->fft_size) { #ifdef CONVOLUTION_FFT memcpy(q->tmp_input, input, q->frame_size * sizeof(cf_t)); conv_output_len = srslte_conv_fft_cc_run(&q->conv_fft, q->tmp_input, q->pss_signal_time[q->N_id_2], q->conv_output); #else conv_output_len = srslte_conv_cc(input, q->pss_signal_time[q->N_id_2], q->conv_output, q->frame_size, q->fft_size); #endif } else { for (int i=0;i<q->frame_size;i++) { q->conv_output[i] = srslte_vec_dot_prod_ccc(q->pss_signal_time[q->N_id_2], &input[i], q->fft_size); } conv_output_len = q->frame_size; } #ifdef SRSLTE_PSS_ABS_SQUARE srslte_vec_abs_square_cf(q->conv_output, q->conv_output_abs, conv_output_len-1); #else srslte_vec_abs_cf(q->conv_output, q->conv_output_abs, conv_output_len-1); #endif srslte_vec_sc_prod_fff(q->conv_output_abs, q->ema_alpha, q->conv_output_abs, conv_output_len-1); srslte_vec_sc_prod_fff(q->conv_output_avg, 1-q->ema_alpha, q->conv_output_avg, conv_output_len-1); srslte_vec_sum_fff(q->conv_output_abs, q->conv_output_avg, q->conv_output_avg, conv_output_len-1); /* Find maximum of the absolute value of the correlation */ corr_peak_pos = srslte_vec_max_fi(q->conv_output_avg, conv_output_len-1); // save absolute value q->peak_value = q->conv_output_avg[corr_peak_pos]; #ifdef SRSLTE_PSS_RETURN_PSR // Find second side lobe // Find end of peak lobe to the right int pl_ub = corr_peak_pos+1; while(q->conv_output_avg[pl_ub+1] <= q->conv_output_avg[pl_ub] && pl_ub < conv_output_len) { pl_ub ++; } // Find end of peak lobe to the left int pl_lb; if (corr_peak_pos > 2) { pl_lb = corr_peak_pos-1; while(q->conv_output_avg[pl_lb-1] <= q->conv_output_avg[pl_lb] && pl_lb > 1) { pl_lb --; } } else { pl_lb = 0; } int sl_distance_right = conv_output_len-1-pl_ub; if (sl_distance_right < 0) { sl_distance_right = 0; } int sl_distance_left = pl_lb; int sl_right = pl_ub+srslte_vec_max_fi(&q->conv_output_avg[pl_ub], sl_distance_right); int sl_left = srslte_vec_max_fi(q->conv_output_avg, sl_distance_left); float side_lobe_value = SRSLTE_MAX(q->conv_output_avg[sl_right], q->conv_output_avg[sl_left]); if (corr_peak_value) { *corr_peak_value = q->conv_output_avg[corr_peak_pos]/side_lobe_value; DEBUG("peak_pos=%2d, pl_ub=%2d, pl_lb=%2d, sl_right: %2d, sl_left: %2d, PSR: %.2f/%.2f=%.2f\n", corr_peak_pos, pl_ub, pl_lb, sl_right,sl_left, q->conv_output_avg[corr_peak_pos], side_lobe_value,*corr_peak_value); } #else if (corr_peak_value) { *corr_peak_value = q->conv_output_avg[corr_peak_pos]; } #endif if (q->frame_size >= q->fft_size) { ret = (int) corr_peak_pos; } else { ret = (int) corr_peak_pos + q->fft_size; } } return ret; }