problem with offsetToPointA and kSSB computation
from the mailing list (https://lists.eurecom.fr/sympa/arc/openair5g-user/2023-12/msg00000.html):
Hello everyone:
when I use gNB band1 absoluteFrequencySSB= 431550(2157.75MHz),dl_absoluteFrequencyPointA=431064(2155.32MHz),ul_absoluteFrequencyPointA=393064(1965.32MHz).By calculation,ssb_OffsetPointA(offsetToPointA)=3, sb_SubcarrierOffset(Kssb)=6.
But there is an erro:
Assertion (cfg->ssb_table.ssb_subcarrier_offset.value < 16) failed!
In config_common() /home/long/openairinterface5g/openair2/LAYER2/NR_MAC_gNB/config.c:335
cannot handle ssb_subcarrier_offset 18 resulting from Point A 431064 SSB 431550: please increase dl_absoluteFrequencyPointA in the config by 16.
The difference between SSB center frequency (absolute frequency SSB) and PointA (absolute frequency PointA)：
2157.75MHz-2155.32MHz=2423 KHz.
The difference between PointA of SSB and RB # 0 of the 0th subcarrier:
2423 KHz - 10(10 RBs at the bottom of SSB)*12(One RB contains 12 consecutive subcarriers)*15KHz(subcarrierSpacing) = 630 KHz.
Calculate number of RB= 630 KHz/12(One RB contains 12 consecutive subcarriers)*15khz(subcarrierSpacing)=630/180=3.5.
offsetToPointA = 3.
Kssb=（630 –3*12*15）/15 KHz=6 subcarriers.I see the same problem.
Units used in functions get_ssb_subcarrier_offset() and get_ssb_offset_to_pointA() are not clear, I cannot fix (I could switch to using unit Hz, maybe things would then be simpler to understand).
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Edited by Cédric Roux