The rotation compensating the shifted OFDM position _before_ the channel estimation makes the CIR peak move back to 0.
We have to take this into account on gNB side when calculating the timing advance command, and on UE side in the time adjustment.
Currently we cute the PUSCH and PDSCH OFDM symbols starting within the last 1/8th of the CP to avoid ISI.
This time shift leads to a rotation in frequency domain.
The current PRB based channel estimation does not compensate for the rotation _within_ a PRB, leading to bad performance.
This commit should _not_ make it into develop branch, it is just for testing!
Instead, we should do some compensating rotation before channel estimation.
- new function has been introduced for the computation of UL SNR
- minor bugfix to noise power computation
- FAPI data type for referenceSignalPower has been updated to reflect the
range of values for the SSB power
- removed commented out code
- improved logging in UL channel estimation
- minor fixes according to OAI coding guidelines
- moving fetching TDD configuration parameters in nr-ue.c only in TDD case
- CDM groups used, multiple DMRS locations tested
- REMOVED compiler define NR_SC_FDMA
- enabled -Z option in ulsim for testing NR SC-FDMA
- Gnb UL Processing of LLRS even if last symbol allocated has no data
- transform precoding Enumerations used
- Most DL code is reused for Ul also to reduce code duplication
- Common CPE calculation function is used for error estimation
- Common slot processing function is used for inter/extrapolation
- Removed old implementation dedicated to UL
- updated return function value to -1
- removed static variable for dmrs symbol selection for channel
- Updated sin cos quadrant check conditions
- removed casting from PTRS slope and related calculations
- To enable PTRS use -T flag followed by 3 integers
- Example: ./nr_ulsim -T 2 0 2
- 1st Value is the list of arguments -> e.g. 2
- 2nd Value is for L_PTRS{0,1,2} -> e.g. 0
- 3rd Value is for K_PTRS{2,4} -> e.g. 2
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
Raymond Knopp