- the band is coming from the SI, therefore a function to get the band is not
necessary
- this solves also the limitations of the get_band algorithm with the NR bands
overlapping in the NR operating bands table (e.g. band 78 and band 48)
- adapted the get_band function: the algorithm is now taking into account
also the UL frequency in order to fetch the proper band (this was failing
before as some NR bands have the same DL band, e.g. band 65 and 66)
- added new bands to the NR table as per TS 38.101 V16.4.0 (2020)
- made the from_nrarfcn function compatible with UL FDD (this function,
used for both DL and UL was previously working with TDD only as it
did not compute properly the frequency for the UL FDD, throwing asserts)
- introduced common functions to get the NR table idx and the duplex mode,
removing repeated code in the process
- removed the unused function to get the uldl offset
- improved some logging
- other minor fixes to the relevant code
FEATURE STATEMENT:
- Introduce linear phase error noise model in Uplink at UE
- Perform common phase error (CPE) estimation and compensation at gNB
SOLUTION:
- A linear phase shift model is introduced in simulation.
- PTRS symbols are used to perform estimation of CPE from DMRS compensated signal
- The estimated values are interpolated in time domain and signal is compensated for the CPE.
- PTRS processing is done in Frequency Domain for each symbol in a slot and
LLR's are calculated for each symbol accordingly.
IMPLEMENTATION:
* sim.h/channle_sim.c
- Linear Phase Noise Generation model definition.
* nr_ul_channel_estimation.c/nr_ul_estimation.h
- CPE estimation from PTRS and DMRS compensated signal.
* nr_dmrs_rx.c/nr_refsig.h
- Regenerate PTRS symbols at gNB.
* nr_ulsch_demodulation.c
- Removed old PTRS processing code and move to a common PTRS processing function
* defs_gNB.h/init.c
- New PTRS variables definition and initialization
* nr_ulsch_ue.c
- Corrected PTRS parameter to get new PTRS symbols for each OFDM symbol
TESTING
* ulsim.c
- Added Phase noise, Enable PTRS signal and verified the output.
VERIFICATION
- The LLR are rotated back with estimated CPE and no error is observed in scrambling/decoding
- now the function gets more input arguments but can be used from both UE and gNB
- this change was needed because the prach fapi of UE differs from the gNB one
As adding PTRS leads to shortening of the coded data, redudandency is removed and the performance decreases on a pure AWGN channel.
So PTRS should only be enabled if phase noise is present.
Thomas Schlichter