What is the meaning of PCI mod30?
PCI mod30 is where the rest of the results after divided by 30.
In downlink every 30th PCI has the same pattern of uplink reference signals.
In uplink, the reference signals are present in the central symbol of the slot and their pattern or base sequence repeats for every 30th PCI.
Equal PCI values from multiple neighbors will lead to Accessibility and Retainability issues due to problems like collision & confusion.
If a cell and its neighbors all have the same PCI mod 3 values then you will have high interference on Reference Signals, the time taken for a UE to camp will be high.
There are 30 base sequences which are used by the UL RS. If two or more cells use the PCI values where the PCI mod 30 values are equal, the chance of having strong inter‐cell uplink interference is increased. The chance is higher when the neighbor cells are aligned in time frame and have high PRB utilization rate.
Assigning the same mod30 (PCI) to neighbor cells, will cause poor channel estimation of PUCCH DMRS if there is no group hopping and poor estimation of PUSCH DMRS if grpAssigPUSCH is the same.