Avoiding PCI conflict is the principle of network planning, and adjacent cells cannot use the same PCI; If adjacent cells use the same PCI, if the coverage area is crossed, only one cell can be synchronized in the initial (cell) search. This situation is called collision.
Using physically separated PCI can prevent UE from receiving multiple (same PCI) cell signals; PCI multiplex distance should be increased as much as possible.
PCI in 5G NR is:
1, the biggest difference is that there are 1008 pcis in 5G, and the set of all pcis is divided into 168 groups (corresponding to the protocol 38.21,ranging from 0 to 335), and each group contains 3 cell IDs.
2. Mode 3 interference: it affects the synchronization signal demodulation of PSS; Mode 4 interference: DMRS of PBCH on sub-carrier is calculated by mod 4, which may cause DMRS interference. Mode 30 interference: same as LTE.
The allocation of PCI in LTE is:
The starting position of the 1. reference symbol in the touch RB is also related to the cell-specific frequency offset. LTE defines six kinds of frequency offset, which are related to cell PCI, and the value is PCI mod 6. This frequency offset can avoid time-frequency resource conflicts between cell-specific reference signals of up to six neighboring cells.
2. Through the cell search process, the UE can obtain the PCI of the cell. And the cell-specific reference signal and its time-frequency position correspond to PCI one-to-one, so the UE also knows the cell-specific reference signal sequence and its time-frequency position after the cell search process.
3.LTE-* * defines 504 different PCI's (corresponding to the protocol 36.2 1 1, with values ranging from 0 to 503), and each PCI corresponds to a specific downlink reference signal sequence.
The set of all PCI's is divided into 168 groups (corresponding to the protocol 36.2 1 1, with a range of 0 ~ 167), and each group contains 3 unit ids (corresponding to the protocol 36.2 1 1, with a range of 0).