Till this commit, the UE gets the position of SSB in frequency from
command line and does the syncronization by locating the SSB in time. It
does this by generating a PSS time signal during initialization with the
SSB offset given via command line. Then PSS detection is done by
correlation.
In this commit, the UE computes a list of GSCN in the current NR band
that falls within the current bandwidth for the set center frequency.
For each GSCN in the list, the UE starts a thread and performs the
following:
1. Generate PSS time signal with SSB offset for current GSCN.
2. Detect PSS, SSS and decode PBCH (this step remains the same).
After all threads finishes, the results are collected.
For now, only the first detected PBCH is used to proceed further. So
this PBCH is indicated to MAC and UE exits initial sync.
Future work: The cell search can be standalone feature where the UE
could scan for SSB in the entire NR band. This would require changing
radio's frequency on the fly as the UE's bandwidth would not cover an
entire NR band. The cell detection can futher be imporved by looking
for SIB1 for each decoded PBCH.
We access G_N at indexes that are not necessarily 32-byte aligned,
leading to segfaults. Use simde_mm256_loadu_si256() to load from memory
at an unaligned memory address to avoid the segfault.
Discovered using clang; it is unclear why gcc did not encounter the same
segfault.
Add ulsch decoding measurements, which are reported by nr_ulsim. Start ulsch_decoding_stats measurement before
nr_ulsch_decoding is called and stop it after collection of all decoder tasks from Tpool. In the context of nr_ulsim,
ULSCH_id is allways == 0, testing is performed per one TB, therefore measurement is started and stopped only once per trial.
Reported ulsch decoding statistics show the mean ulsch decoding time over x trials (specified by -n command line option of nr_ulsim).
This measurement does not provide valid information in case of nr-softmodem, when the loop is done over multiple ULSCH IDs -
start of the measurement is done multiple times and stops only once in this case.
For unitary physical simulators, ULSCH processing loop is executed only once
- the max number of PUSCH is set to 1. This ensures exactly one start and stop
of the ULSCH decoding time measurement per processed TB.
Note: ulsch decoding statistics reports average time of segmentation, rate matching, interleaving and decoding of the TB
fixes the overflow issue in the PUCCH2 RX with 4+ RX antennas and 12+
bits (polar code format). The fix scales the polar decoding LLR
computation according to the number of RX antennas. The issue was clear
for 100 MHz 4 RX antennas. Even
nr_pucchsim -s -5 -q 8 -P 2 -b 12 -R 273 -z4 -n1000
doesn't converge to 0 BLER with increasing SNR. The issue didn't appear
in CI because of the bandwidth and antenna count limitations.
Sakthivel Velumani