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Synchronize multiple gNBs by aliging to the slot boundary

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Currently, we derive frame and slot number based on `proc->timestamp_rx`
using
`proc->frame_rx    = (proc->timestamp_rx / (fp->samples_per_subframe*10))&1023;` and
`proc->tti_rx = get_slot_from_timestamp(proc->timestamp_rx, fp);`

This ignores the samples `proc->timestamp_rx % fp->samples_per_frame`
while computing the frame and slot number creating a mis-alignment with the slot boundaries.
We fix this alignment by compensating these samples during the first reception.
This commit is contained in:
Rakesh Mundlamuri
2026-01-30 12:04:55 +05:30
parent 520360a629
commit b1f32ea049
1 changed files with 19 additions and 0 deletions
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19
executables/nr-ru.c
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@@ -609,6 +609,25 @@ static void rx_rf(RU_t *ru, int *frame, int *slot)
proc->first_rx = 0;
*frame = proc->frame_rx;
*slot = proc->tti_rx;
// Align to slot boundary
uint64_t samples_to_slot_boundary = 0;
uint64_t sample_offset_within_frame = proc->timestamp_rx % fp->samples_per_frame;
uint64_t sample_offset_within_slot = sample_offset_within_frame - get_samples_slot_timestamp(fp, *slot);
if (sample_offset_within_slot > 0) {
samples_to_slot_boundary = get_samples_per_slot(*slot, fp) - sample_offset_within_slot;
LOG_A(NR_PHY, "Aligning to the slot boundary %lu\n", samples_to_slot_boundary);
// Read and discard the samples in the first_rx to align to the slot boundary
rxs = ru->rfdevice.trx_read_func(&ru->rfdevice, &ts, rxp, samples_to_slot_boundary, nb);
if (rxs != samples_to_slot_boundary)
LOG_E(PHY, "rx_rf: Asked for %ld samples, got %d from USRP\n", samples_to_slot_boundary, rxs);
proc->timestamp_rx += samples_to_slot_boundary;
if (*slot + 1 >= fp->slots_per_frame)
*frame = *frame + 1;
*slot = (*slot + 1) % fp->slots_per_frame;
}
}
metadata mt = {.slot = *slot, .frame = *frame};