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digital compensation of FFO on PBCH symbols (works only for FFO less than 0.5)

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This commit is contained in:
Francesco Mani
2019-02-01 16:42:11 +01:00
parent 0234a5c21a
commit 832eb3dc50
1 changed files with 26 additions and 2 deletions
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openair1/PHY/NR_UE_TRANSPORT/nr_initial_sync.c
+26 -2
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@@ -39,6 +39,7 @@
//#include "SCHED/extern.h"
#include "common_lib.h"
#include <math.h>
#include "PHY/NR_REFSIG/pss_nr.h"
#include "PHY/NR_REFSIG/sss_nr.h"
@@ -55,6 +56,8 @@ int nr_pbch_detection(PHY_VARS_NR_UE *ue, runmode_t mode)
{
NR_DL_FRAME_PARMS *frame_parms=&ue->frame_parms;
int ret =-1;
int ar, n;
double im, re;
#ifdef DEBUG_INITIAL_SYNCH
LOG_I(PHY,"[UE%d] Initial sync: starting PBCH detection (rx_offset %d)\n",ue->Mod_id,
@@ -65,6 +68,27 @@ int nr_pbch_detection(PHY_VARS_NR_UE *ue, runmode_t mode)
int nb_prefix_samples0 = frame_parms->nb_prefix_samples0;
frame_parms->nb_prefix_samples0 = frame_parms->nb_prefix_samples;
// digital compensation of FFO for PBCH symbols
if(abs(2*ue->common_vars.freq_offset)<frame_parms->subcarrier_spacing){ // this FFO compensation seems to work only for FFO between -0.5 and 0.5
int size_wp = (frame_parms->ofdm_symbol_size+frame_parms->nb_prefix_samples0); // symbol size including prefix
double s_time = 1/(1.0e3*frame_parms->samples_per_subframe); // sampling time
double off_angle = -2*M_PI*s_time*(ue->common_vars.freq_offset); // offset rotation angle compensation per sample
int start = ue->ssb_offset + size_wp; // start for offset correction is one symbol after ssb_offset (pss time position), including prefix
int end = start + (3*size_wp); // loop over samples in 3 symbols, including prefix
for(n=start; n<end; n++){
for (ar=0; ar<frame_parms->nb_antennas_rx; ar++) {
re = ((double)(((short *)ue->common_vars.rxdata[ar]))[2*n]);
im = ((double)(((short *)ue->common_vars.rxdata[ar]))[2*n+1]);
((short *)ue->common_vars.rxdata[ar])[2*n] = (short)(round(re*cos(n*off_angle) - im*sin(n*off_angle)));
((short *)ue->common_vars.rxdata[ar])[2*n+1] = (short)(round(re*sin(n*off_angle) + im*cos(n*off_angle)));
}
}
}
//symbol 1
nr_slot_fep(ue,
1,
@@ -183,14 +207,14 @@ int nr_initial_sync(PHY_VARS_NR_UE *ue, runmode_t mode)
sync_pos = pss_synchro_nr(ue, NO_RATE_CHANGE);
sync_pos_slot = (fp->samples_per_subframe/fp->slots_per_subframe) - 10*(fp->ofdm_symbol_size + fp->nb_prefix_samples);
if (sync_pos >= fp->nb_prefix_samples){
ue->ssb_offset = sync_pos - fp->nb_prefix_samples;}
else{
ue->ssb_offset = sync_pos + (fp->samples_per_subframe * 10) - fp->nb_prefix_samples;}
ue->rx_offset = ue->ssb_offset - sync_pos_slot;
//write_output("rxdata1.m","rxd1",ue->common_vars.rxdata[0],10*fp->samples_per_subframe,1,1);
#ifdef DEBUG_INITIAL_SYNCH