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Add noise reduction in PSS before estimating CFO

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master
Ismael Gomez 7 years ago
parent d34ce74419
commit 0d7af88822
2 changed files with 94 additions and 68 deletions
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16
lib/include/srslte/phy/sync/pss.h
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@ -70,9 +70,7 @@
/* Low-level API */
typedef struct SRSLTE_API {
srslte_dft_plan_t dftp_input;
#ifdef CONVOLUTION_FFT
srslte_conv_fft_cc_t conv_fft;
srslte_filt_cc_t filter;
@ -87,16 +85,22 @@ typedef struct SRSLTE_API {
uint32_t N_id_2;
uint32_t fft_size;
cf_t *pss_signal_freq_full[3];
cf_t *pss_signal_time[3];
cf_t pss_signal_freq[3][SRSLTE_PSS_LEN]; // One sequence for each N_id_2
cf_t *tmp_input;
cf_t *conv_output;
float *conv_output_abs;
float ema_alpha;
float ema_alpha;
float *conv_output_avg;
float peak_value;
srslte_dft_plan_t dftp_input;
srslte_dft_plan_t idftp_input;
cf_t tmp_fft[SRSLTE_SYMBOL_SZ_MAX];
cf_t yr[SRSLTE_PSS_LEN];
}srslte_pss_synch_t;
typedef enum { PSS_TX, PSS_RX } pss_direction_t;

146
lib/src/phy/sync/pss.c
Unescape Escape View File

@ -137,9 +137,15 @@ int srslte_pss_synch_init_fft_offset_decim(srslte_pss_synch_t *q,
}
srslte_dft_plan_set_mirror(&q->dftp_input, true);
srslte_dft_plan_set_dc(&q->dftp_input, true);
srslte_dft_plan_set_norm(&q->dftp_input, true);
q->tmp_input = srslte_vec_malloc((buffer_size + frame_size*(q->decimate - 1)) * sizeof(cf_t));
if (srslte_dft_plan(&q->idftp_input, fft_size, SRSLTE_DFT_BACKWARD, SRSLTE_DFT_COMPLEX)) {
fprintf(stderr, "Error creating DFT plan \n");
goto clean_and_exit;
}
srslte_dft_plan_set_mirror(&q->idftp_input, true);
srslte_dft_plan_set_dc(&q->idftp_input, true);
q->tmp_input = srslte_vec_malloc((buffer_size + frame_size*(q->decimate - 1)) * sizeof(cf_t));
if (!q->tmp_input) {
fprintf(stderr, "Error allocating memory\n");
goto clean_and_exit;
@ -167,7 +173,7 @@ int srslte_pss_synch_init_fft_offset_decim(srslte_pss_synch_t *q,
}
bzero(q->conv_output_abs, sizeof(float) * buffer_size);
#endif
for (N_id_2=0;N_id_2<3;N_id_2++) {
q->pss_signal_time[N_id_2] = srslte_vec_malloc(buffer_size * sizeof(cf_t));
if (!q->pss_signal_time[N_id_2]) {
@ -178,14 +184,14 @@ int srslte_pss_synch_init_fft_offset_decim(srslte_pss_synch_t *q,
if (srslte_pss_synch_init_N_id_2(q->pss_signal_freq[N_id_2], q->pss_signal_time[N_id_2], N_id_2, fft_size, offset)) {
fprintf(stderr, "Error initiating PSS detector for N_id_2=%d fft_size=%d\n", N_id_2, fft_size);
goto clean_and_exit;
}
}
bzero(&q->pss_signal_time[N_id_2][q->fft_size], q->frame_size * sizeof(cf_t));
}
}
#ifdef CONVOLUTION_FFT
for(N_id_2=0; N_id_2<3; N_id_2++)
q->pss_signal_freq_full[N_id_2] = srslte_vec_malloc(buffer_size * sizeof(cf_t));
q->pss_signal_freq_full[N_id_2] = srslte_vec_malloc(buffer_size * sizeof(cf_t));
if (srslte_conv_fft_cc_init(&q->conv_fft, frame_size, fft_size)) {
fprintf(stderr, "Error initiating convolution FFT\n");
@ -194,15 +200,15 @@ int srslte_pss_synch_init_fft_offset_decim(srslte_pss_synch_t *q,
for(int i=0; i<3; i++) {
srslte_dft_run_c(&q->conv_fft.filter_plan, q->pss_signal_time[i], q->pss_signal_freq_full[i]);
}
#endif
srslte_pss_synch_reset(q);
ret = SRSLTE_SUCCESS;
}
clean_and_exit:
clean_and_exit:
if (ret == SRSLTE_ERROR) {
srslte_pss_synch_free(q);
}
@ -298,7 +304,7 @@ void srslte_pss_synch_free(srslte_pss_synch_t *q) {
}
#ifdef CONVOLUTION_FFT
srslte_conv_fft_cc_free(&q->conv_fft);
#endif
if (q->tmp_input) {
free(q->tmp_input);
@ -312,9 +318,10 @@ void srslte_pss_synch_free(srslte_pss_synch_t *q) {
if (q->conv_output_avg) {
free(q->conv_output_avg);
}
srslte_dft_plan_free(&q->dftp_input);
srslte_dft_plan_free(&q->idftp_input);
if(q->decimate > 1)
{
srslte_filt_decim_cc_free(&q->filter);
@ -323,7 +330,7 @@ void srslte_pss_synch_free(srslte_pss_synch_t *q) {
}
bzero(q, sizeof(srslte_pss_synch_t));
bzero(q, sizeof(srslte_pss_synch_t));
}
}
@ -379,7 +386,7 @@ void srslte_pss_put_slot(cf_t *pss_signal, cf_t *slot, uint32_t nof_prb, srslte_
void srslte_pss_get_slot(cf_t *slot, cf_t *pss_signal, uint32_t nof_prb, srslte_cp_t cp) {
int k;
k = (SRSLTE_CP_NSYMB(cp) - 1) * nof_prb * SRSLTE_NRE + nof_prb * SRSLTE_NRE / 2 - 31;
memcpy(pss_signal, &slot[k], SRSLTE_PSS_LEN * sizeof(cf_t));
memcpy(pss_signal, &slot[k], SRSLTE_PSS_LEN * sizeof(cf_t));
}
@ -398,34 +405,34 @@ int srslte_pss_synch_set_N_id_2(srslte_pss_synch_t *q, uint32_t N_id_2) {
/* Sets the weight factor alpha for the exponential moving average of the PSS correlation output
*/
void srslte_pss_synch_set_ema_alpha(srslte_pss_synch_t *q, float alpha) {
q->ema_alpha = alpha;
q->ema_alpha = alpha;
}
/** Performs time-domain PSS correlation.
/** 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 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 &&
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
*
*
* We do not reverse time-domain PSS signal because it's conjugate is symmetric.
* The conjugate operation on pss_signal_time has been done in srslte_pss_synch_init_N_id_2
* This is why we can use FFT-based convolution
@ -442,7 +449,7 @@ int srslte_pss_synch_find_pss(srslte_pss_synch_t *q, cf_t *input, float *corr_pe
{
conv_output_len = srslte_conv_fft_cc_run_opt(&q->conv_fft, q->tmp_input, q->pss_signal_freq_full[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
@ -450,19 +457,19 @@ int srslte_pss_synch_find_pss(srslte_pss_synch_t *q, cf_t *input, float *corr_pe
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;
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
if (q->ema_alpha < 1.0 && q->ema_alpha > 0.0) {
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_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);
} else {
@ -470,43 +477,43 @@ int srslte_pss_synch_find_pss(srslte_pss_synch_t *q, cf_t *input, float *corr_pe
}
/* 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
// save absolute value
q->peak_value = q->conv_output_avg[corr_peak_pos];
#ifdef SRSLTE_PSS_RETURN_PSR
#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 ++;
pl_ub ++;
}
// Find end of peak lobe to the left
int pl_lb;
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 --;
}
pl_lb --;
}
} else {
pl_lb = 0;
pl_lb = 0;
}
int sl_distance_right = conv_output_len-1-pl_ub;
int sl_distance_right = conv_output_len-1-pl_ub;
if (sl_distance_right < 0) {
sl_distance_right = 0;
sl_distance_right = 0;
}
int sl_distance_left = pl_lb;
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]);
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;
if (*corr_peak_value < 10)
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,
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
@ -514,7 +521,7 @@ int srslte_pss_synch_find_pss(srslte_pss_synch_t *q, cf_t *input, float *corr_pe
*corr_peak_value = q->conv_output_avg[corr_peak_pos];
}
#endif
if(q->decimate >1)
{
int decimation_correction = (q->filter.num_taps - 2);
@ -524,23 +531,23 @@ int srslte_pss_synch_find_pss(srslte_pss_synch_t *q, cf_t *input, float *corr_pe
if (q->frame_size >= q->fft_size) {
ret = (int) corr_peak_pos;
ret = (int) corr_peak_pos;
} else {
ret = (int) corr_peak_pos + q->fft_size;
}
}
}
return ret;
}
/* Computes frequency-domain channel estimation of the PSS symbol
* input signal is in the time-domain.
* ce is the returned frequency-domain channel estimates.
/* Computes frequency-domain channel estimation of the PSS symbol
* input signal is in the time-domain.
* ce is the returned frequency-domain channel estimates.
*/
int srslte_pss_synch_chest(srslte_pss_synch_t *q, cf_t *input, cf_t ce[SRSLTE_PSS_LEN]) {
int ret = SRSLTE_ERROR_INVALID_INPUTS;
cf_t input_fft[SRSLTE_SYMBOL_SZ_MAX];
if (q != NULL &&
if (q != NULL &&
input != NULL)
{
@ -548,31 +555,46 @@ int srslte_pss_synch_chest(srslte_pss_synch_t *q, cf_t *input, cf_t ce[SRSLTE_PS
fprintf(stderr, "Error finding PSS peak, Must set N_id_2 first\n");
return SRSLTE_ERROR;
}
/* Transform to frequency-domain */
srslte_dft_run_c(&q->dftp_input, input, input_fft);
/* Compute channel estimate taking the PSS sequence as reference */
srslte_vec_prod_conj_ccc(&input_fft[(q->fft_size-SRSLTE_PSS_LEN)/2], q->pss_signal_freq[q->N_id_2], ce, SRSLTE_PSS_LEN);
ret = SRSLTE_SUCCESS;
}
return ret;
return ret;
}
#define CLEAN_NOISE_DFT
//#define PSS_CFO_FREQ
/* 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 srslte_pss_synch_cfo_compute(srslte_pss_synch_t* q, cf_t *pss_recv) {
cf_t y0, y1, yr;
cf_t y0, y1;
#ifdef PSS_CFO_FREQ
srslte_vec_prod_conj_ccc(&q->tmp_fft[q->fft_size/2-SRSLTE_PSS_LEN/2], q->pss_signal_freq[q->N_id_2], q->yr, SRSLTE_PSS_LEN);
y0 = srslte_vec_acc_cc(q->yr, SRSLTE_PSS_LEN/2);
y1 = srslte_vec_acc_cc(&q->yr[SRSLTE_PSS_LEN/2], SRSLTE_PSS_LEN/2);
#else
#ifdef CLEAN_NOISE_DFT
// Eliminate noise
srslte_dft_run_c(&q->dftp_input, pss_recv, q->tmp_fft);
bzero(q->tmp_fft, sizeof(cf_t)*(q->fft_size/2-SRSLTE_PSS_LEN/2));
bzero(&q->tmp_fft[q->fft_size/2+SRSLTE_PSS_LEN/2], sizeof(cf_t)*(q->fft_size/2-SRSLTE_PSS_LEN/2));
srslte_dft_run_c(&q->idftp_input, q->tmp_fft, pss_recv);
#endif
y0 = srslte_vec_dot_prod_ccc(q->pss_signal_time[q->N_id_2], pss_recv, q->fft_size/2);
y1 = srslte_vec_dot_prod_ccc(&q->pss_signal_time[q->N_id_2][q->fft_size/2], &pss_recv[q->fft_size/2], q->fft_size/2);
yr = conjf(y0) * y1;
return atan2f(__imag__ yr, __real__ yr) / M_PI;
#endif
return carg(conjf(y0) * y1)/M_PI;
}

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