static void interpolate_pilots(srslte_chest_ul_t *q, cf_t *ce, uint32_t nrefs, uint32_t n_prb[2])
{
uint32_t L1 = SRSLTE_REFSIGNAL_UL_L(0, q->cell.cp);
uint32_t L2 = SRSLTE_REFSIGNAL_UL_L(1, q->cell.cp);
uint32_t NL = 2*SRSLTE_CP_NSYMB(q->cell.cp);
/* Interpolate in the time domain between symbols */
srslte_interp_linear_vector3(&q->srslte_interp_linvec,
&cesymb(L2), &cesymb(L1), &cesymb(L1), &cesymb(L1-1), (L2-L1), L1, false, nrefs);
srslte_interp_linear_vector3(&q->srslte_interp_linvec,
&cesymb(L1), &cesymb(L2), NULL, &cesymb(L1+1), (L2-L1), (L2-L1)-1, true, nrefs);
srslte_interp_linear_vector3(&q->srslte_interp_linvec,
&cesymb(L1), &cesymb(L2), &cesymb(L2), &cesymb(L2+1), (L2-L1), (NL-L2)-1, true, nrefs);
}
static void average_pilots(srslte_chest_ul_t *q, cf_t *input, cf_t *ce, uint32_t nrefs, uint32_t n_prb[2]) {
for (int i=0;i<2;i++) {
srslte_chest_average_pilots(&input[i*nrefs],
&ce[SRSLTE_REFSIGNAL_UL_L(i, q->cell.cp)*q->cell.nof_prb*SRSLTE_NRE+n_prb[i]*SRSLTE_NRE],
q->smooth_filter, nrefs, 1, q->smooth_filter_len);
}
}
int srslte_chest_ul_estimate(srslte_chest_ul_t *q, cf_t *input, cf_t *ce,
uint32_t nof_prb, uint32_t sf_idx, uint32_t cyclic_shift_for_dmrs, uint32_t n_prb[2])
{
if (!q->dmrs_signal_configured) {
fprintf(stderr, "Error must call srslte_chest_ul_set_cfg() before using the UL estimator\n");
return SRSLTE_ERROR;
}
if (!srslte_dft_precoding_valid_prb(nof_prb)) {
fprintf(stderr, "Error invalid nof_prb=%d\n", nof_prb);
return SRSLTE_ERROR_INVALID_INPUTS;
}
int nrefs_sym = nof_prb*SRSLTE_NRE;
int nrefs_sf = nrefs_sym*2;
/* Get references from the input signal */
srslte_refsignal_dmrs_pusch_get(&q->dmrs_signal, input, nof_prb, n_prb, q->pilot_recv_signal);
/* Use the known DMRS signal to compute Least-squares estimates */
srslte_vec_prod_conj_ccc(q->pilot_recv_signal, q->dmrs_pregen.r[cyclic_shift_for_dmrs][sf_idx][nof_prb],
q->pilot_estimates, nrefs_sf);
if (n_prb[0] != n_prb[1]) {
printf("ERROR: intra-subframe frequency hopping not supported in the estimator!!\n");
}
if (ce != NULL) {
if (q->smooth_filter_len > 0) {
average_pilots(q, q->pilot_estimates, ce, nrefs_sym, n_prb);
interpolate_pilots(q, ce, nrefs_sym, n_prb);
/* If averaging, compute noise from difference between received and averaged estimates */
q->noise_estimate = estimate_noise_pilots(q, ce, nrefs_sym, n_prb);
} else {
// Copy estimates to CE vector without averaging
for (int i=0;i<2;i++) {
memcpy(&ce[SRSLTE_REFSIGNAL_UL_L(i, q->cell.cp)*q->cell.nof_prb*SRSLTE_NRE+n_prb[i]*SRSLTE_NRE],
&q->pilot_estimates[i*nrefs_sym],
nrefs_sym*sizeof(cf_t));
}
interpolate_pilots(q, ce, nrefs_sym, n_prb);
q->noise_estimate = 0;
}
}
// Estimate received pilot power
q->pilot_power = srslte_vec_avg_power_cf(q->pilot_recv_signal, nrefs_sf);
return 0;
}
/* Uses the difference between the averaged and non-averaged pilot estimates */
static float estimate_noise_pilots(srslte_chest_ul_t *q, cf_t *ce, uint32_t nrefs, uint32_t n_prb[2])
{
float power = 0;
for (int i=0;i<2;i++) {
power += srslte_chest_estimate_noise_pilots(&q->pilot_estimates[i*nrefs],
&ce[SRSLTE_REFSIGNAL_UL_L(i, q->cell.cp)*q->cell.nof_prb*SRSLTE_NRE+n_prb[i]*SRSLTE_NRE],
q->tmp_noise,
nrefs);
}
power/=2;
if (q->smooth_filter_len == 3) {
// Calibrated for filter length 3
float w=q->smooth_filter[0];
float a=7.419*w*w+0.1117*w-0.005387;
return (power/(a*0.8));
} else {
return power;
}
}