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@ -35,12 +35,34 @@
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#include "srslte/config.h"
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#include "srslte/ch_estimation/chest_common.h"
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#include "srslte/ch_estimation/chest_dl.h"
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#include "srslte/utils/vector.h"
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#include "srslte/utils/convolution.h"
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#define ESTIMATE_NOISE_LS_PSS
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//#define DEFAULT_FILTER_LEN 3
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#ifdef DEFAULT_FILTER_LEN
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static void set_default_filter(srslte_chest_dl_t *q, int filter_len) {
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float fil[SRSLTE_CHEST_DL_MAX_SMOOTH_FIL_LEN];
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for (int i=0;i<filter_len/2;i++) {
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fil[i] = i+1;
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fil[i+filter_len/2+1]=filter_len/2-i;
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}
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fil[filter_len/2]=filter_len/2+1;
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float s=0;
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for (int i=0;i<filter_len;i++) {
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s+=fil[i];
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}
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for (int i=0;i<filter_len;i++) {
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fil[i]/=s;
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}
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srslte_chest_dl_set_smooth_filter(q, fil, filter_len);
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}
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#endif
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/** 3GPP LTE Downlink channel estimator and equalizer.
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* Estimates the channel in the resource elements transmitting references and interpolates for the rest
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@ -101,6 +123,8 @@ int srslte_chest_dl_init(srslte_chest_dl_t *q, srslte_cell_t cell)
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goto clean_exit;
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}
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q->noise_alg = SRSLTE_NOISE_ALG_PSS;
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q->smooth_filter_len = 3;
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srslte_chest_dl_set_smooth_filter3_coeff(q, 0.1);
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@ -139,14 +163,21 @@ void srslte_chest_dl_free(srslte_chest_dl_t *q)
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}
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/* Uses the difference between the averaged and non-averaged pilot estimates */
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float estimate_noise_pilots(srslte_chest_dl_t *q, uint32_t port_id)
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static float estimate_noise_pilots(srslte_chest_dl_t *q, uint32_t port_id)
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{
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int nref=SRSLTE_REFSIGNAL_NUM_SF(q->cell.nof_prb, port_id);
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float power = srslte_chest_estimate_noise_pilots(q->pilot_estimates,
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q->pilot_estimates_average,
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q->tmp_noise,
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nref);
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/* Substract noisy pilot estimates */
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srslte_vec_sub_ccc(q->pilot_estimates_average, q->pilot_estimates, q->tmp_noise, nref);
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#ifdef FREQ_SEL_SNR
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/* Compute frequency-selective SNR */
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srslte_vec_abs_square_cf(q->tmp_noise, q->snr_vector, nref);
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srslte_vec_abs_square_cf(q->pilot_estimates, q->pilot_power, nref);
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srslte_vec_div_fff(q->pilot_power, q->snr_vector, q->snr_vector, nref);
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srslte_vec_fprint_f(stdout, q->snr_vector, nref);
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#endif
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/* Compute average power. Normalized for filter len 3 using matlab */
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float norm = 1;
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if (q->smooth_filter_len == 3) {
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@ -154,10 +185,10 @@ float estimate_noise_pilots(srslte_chest_dl_t *q, uint32_t port_id)
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float norm3 = 6.143*a*a+0.04859*a-0.002774;
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norm /= norm3;
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}
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return norm*q->cell.nof_ports*power;
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float power = norm*q->cell.nof_ports*srslte_vec_avg_power_cf(q->tmp_noise, nref);
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return power;
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}
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#ifdef ESTIMATE_NOISE_LS_PSS
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static float estimate_noise_pss(srslte_chest_dl_t *q, cf_t *input, cf_t *ce)
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{
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/* Get PSS from received signal */
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@ -177,9 +208,6 @@ static float estimate_noise_pss(srslte_chest_dl_t *q, cf_t *input, cf_t *ce)
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return power;
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}
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#else
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/* Uses the 5 empty transmitted SC before and after the SSS and PSS sequences for noise estimation */
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static float estimate_noise_empty_sc(srslte_chest_dl_t *q, cf_t *input) {
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int k_sss = (SRSLTE_CP_NSYMB(q->cell.cp) - 2) * q->cell.nof_prb * SRSLTE_NRE + q->cell.nof_prb * SRSLTE_NRE / 2 - 31;
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@ -192,8 +220,6 @@ static float estimate_noise_empty_sc(srslte_chest_dl_t *q, cf_t *input) {
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return noise_power;
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}
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#endif
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#define cesymb(i) ce[SRSLTE_RE_IDX(q->cell.nof_prb,i,0)]
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@ -251,16 +277,25 @@ void srslte_chest_dl_set_smooth_filter(srslte_chest_dl_t *q, float *filter, uint
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}
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}
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void srslte_chest_dl_set_smooth_filter3_coeff(srslte_chest_dl_t* q, float w) {
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srslte_chest_set_smooth_filter3_coeff(q->smooth_filter, w);
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q->smooth_filter_len = 3;
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void srslte_chest_dl_set_noise_alg(srslte_chest_dl_t *q, srslte_chest_dl_noise_alg_t noise_estimation_alg) {
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q->noise_alg = noise_estimation_alg;
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}
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static void average_pilots(srslte_chest_dl_t *q, cf_t *input, cf_t *output, uint32_t port_id)
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void srslte_chest_dl_set_smooth_filter3_coeff(srslte_chest_dl_t* q, float w)
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{
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q->smooth_filter_len = 3;
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q->smooth_filter[0] = w;
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q->smooth_filter[2] = w;
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q->smooth_filter[1] = 1-2*w;
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}
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static void average_pilots(srslte_chest_dl_t *q, cf_t *input, cf_t *output, uint32_t port_id) {
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uint32_t nsymbols = srslte_refsignal_cs_nof_symbols(port_id);
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uint32_t nref = 2*q->cell.nof_prb;
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srslte_chest_average_pilots(input, output, q->smooth_filter, nref, nsymbols, q->smooth_filter_len);
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for (int l=0;l<nsymbols;l++) {
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srslte_conv_same_cf(&input[l*nref], q->smooth_filter, &output[l*nref], nref, q->smooth_filter_len);
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}
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}
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float srslte_chest_dl_rssi(srslte_chest_dl_t *q, cf_t *input, uint32_t port_id) {
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@ -283,26 +318,29 @@ int srslte_chest_dl_estimate_port(srslte_chest_dl_t *q, cf_t *input, cf_t *ce, u
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/* Use the known CSR signal to compute Least-squares estimates */
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srslte_vec_prod_conj_ccc(q->pilot_recv_signal, q->csr_signal.pilots[port_id/2][sf_idx],
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q->pilot_estimates, SRSLTE_REFSIGNAL_NUM_SF(q->cell.nof_prb, port_id));
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if (ce != NULL) {
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if (q->smooth_filter_len > 0) {
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average_pilots(q, q->pilot_estimates, q->pilot_estimates_average, port_id);
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interpolate_pilots(q, q->pilot_estimates_average, ce, port_id);
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/* If averaging, compute noise from difference between received and averaged estimates */
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q->noise_estimate[port_id] = estimate_noise_pilots(q, port_id);
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} else {
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/* Smooth estimates (if applicable) and interpolate */
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if (q->smooth_filter_len == 0 || (q->smooth_filter_len == 3 && q->smooth_filter[0] == 0)) {
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interpolate_pilots(q, q->pilot_estimates, ce, port_id);
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/* If not averaging, compute noise from empty subcarriers */
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#ifdef ESTIMATE_NOISE_LS_PSS
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} else {
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average_pilots(q, q->pilot_estimates, q->pilot_estimates_average, port_id);
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interpolate_pilots(q, q->pilot_estimates_average, ce, port_id);
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}
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/* Estimate noise power */
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if (q->noise_alg == SRSLTE_NOISE_ALG_REFS && q->smooth_filter_len > 0) {
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q->noise_estimate[port_id] = estimate_noise_pilots(q, port_id);
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} else if (q->noise_alg == SRSLTE_NOISE_ALG_PSS) {
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if (sf_idx == 0 || sf_idx == 5) {
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q->noise_estimate[port_id] = estimate_noise_pss(q, input, ce);
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}
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#else
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q->noise_estimate[port_id] = estimate_noise_empty_sc(q, input);
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#endif
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} else {
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if (sf_idx == 0 || sf_idx == 5) {
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q->noise_estimate[port_id] = estimate_noise_empty_sc(q, input);
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}
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}
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}
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/* Compute RSRP for the channel estimates in this port */
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@ -338,8 +376,6 @@ float srslte_chest_dl_get_snr(srslte_chest_dl_t *q) {
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#endif
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}
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float srslte_chest_dl_get_rssi(srslte_chest_dl_t *q) {
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return 4*q->rssi[0]/q->cell.nof_prb/SRSLTE_NRE;
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}
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Ismael Gomez
9 years ago