Each 5G NR cell corresponds to a Physical Cell ID (PCI) and it is used to distinguish cells on the radio side. The PCI planning for 5G NR is very much similar to PCI planning for LTE and scrambling code planning for 3G UMTS. Bad or wrong planning can affect the synchronization procedure , demodulation, and handover signalling and degrade the network performs. PCI Planning should be simpler for NR compare to LTE because there are double as many PCIs available for allocation.
每个5G(NR)小区都有一个物理小区ID(PCI)用于无线侧标识该小区；
5G(NR)中PCI规划与LTE网络PCI、3G UMTS中的扰码规划非常相同；
错、乱、差的规划将影响信号同步、解调和切换，降低网络性能；
与LTE相比NR的PCI规划将相对简单，这是由于5G(NR)比LTE多一倍；
In 5G New Radio, there are 1008 unique PCIs compare to LTE 504 PCIs and it is given by following formulation
5G(NR)中有1008个PCI，LTE有504个；计算公式如下：
N (1) ID = Secondary Synchronization Signal (SSS) and its range is from {0, 1….335}
辅同步信号(SSS)取值(0，1…..335)
N (2) ID = Primary Synchronization Signal (PSS) and its range is from {0, 1, 2}
主同步信号(PSS)取值(0,1,2)
图表与PSS,SSS
5G Network PCI Planning Principles
5G(NR)网络PCI规划原则
5G PCI planning should be done keeping following thing in mind
Avoiding PCI Collision: As part this principle of network planning, neighboring cells cannot be allocated the same PCI. If neighboring cells are allocated the same PCI, only one of the neighboring cells can be synchronized during the initial cell searching in the overlapping area. However, the cell may not be the most appropriate one. This phenomenon is called collision. So the physical separation between cell using the same PCI should be sufficient to ensure the UE never received the same PCI from more than one cell. This can be achieved by maximizing the re-use distance for PCI.
避免PCI碰撞做为网络规划原则，相邻小区之间不能使用相同PCI;如果邻区使用同一个PCI,越区覆盖区域，初始(小区)搜索中只有一个小区能够同步；这种情景叫做碰撞；
物理上间隔PCI使用可避免UE收到多个(相同PCI)小区信号；需尽量增大PCI复用距离；
PCI collision can result delay in DL synchronization in overlapping zone
PCI碰撞将延迟UE在重叠覆盖区域的下行同步；
High BLER and decoding failure of physical channels scrambled using PCI
引起高误块率、物理信道解码失败
Handover failures
切换失败
图表2.邻区和越区覆盖使用相同PCI
Avoiding PCI Confusion: Under this principle of network planning, two neighboring cells of one cell cannot be allocated with the same PCI. If they are allocated the same PCI, the base station will not know which is the target cell upon a handover request of a UE. This shall create a confusion situation. The approach while allocating PCI should be such that a cell should not have multiple neighbors using the same PCI and the physical separation between the cells using the same PCI should be sufficient large enough to avoid neighbor confusions.
避免PCI混淆 此原则是说两个相邻小区不能使用相同PCI;当PCI相同时，(准备)切入UE所在的基站将搞不清目标小区，混淆目标小区。
邻小区之间不能使用相同PCI。物理上避免这种情景出现方法就是尽量增大PCI复用层数；
图表3.邻区PCI相同和PCI利用距离
Minimizing Impact on network performance : Based on the design of different Physical layer signals (PSS, DMRS & SRS), channels (PUSCH, PUCCH) and time-frequency allocation, PCI planning must consider following Mod to reduce interference. As per this Mod Principle UE should not be able to simultaneously receive multiple PCI with following modes:
网络性能影响最小化基于不同物理层信号(PSS, DMRS & SRS)设计、(PUSCH, PUCCH) 信道和时域分配；PCI规划时须考虑以下模(MOD)的影响，减少相互干扰；在每种模下UE应尽量减少同时收到以下多个PCI模式的影响；
PCI Mod 3
PCI Mod 4
PCI Mod 30
Example of “Mod 3 PCI” the neighboring cell should be allocated PCI 25 and 28 because both has Mod 3 as value 1
例：PCI模三， 邻区中存在PCI=25和28,它们的MOD3值都为1
Why Mode 3 : PCI Mod 3 rule is based on relationship between PCI and sequence generated by PSS. There are 3 PSS (0,1,2) which are reused across the network . The cells having same ‘PCI Mode 3’ result will use the same PSS and simulation results has shown that if UE receive same PSS from multiple cell result in delay in cell acquisition and misleading channel estimation. Over all it will impact on synchronization delay and user experience.
PCI模3原则，这是由于PCI是由PSS生成的；网络中只有3个PSS(0，1，2)循环利用；小区的“PCI模3”相等，其PSS也相等。这将影响UE对小区的识别和信道估计错误，其将影响同步和用户感知；
Why Mode 4: PCI Mod 4 rule is based on subs-carrier positions of DMRS for PBCH. The subcarriers are allocated to DMRS using ‘Mod 4’ computation. If neighboring cell use PCI having same Mod 4 value, shall result in DMRS to DMRS interference.
PCI模4原则，这是由于在PBCH信道子载波位置上的DMRS原因；承载DMRS的子载波位置遵循“除4”原则；如果邻区间PCI除4结果相同，其DMRS之间将相互干扰(SSB上位置相同—相互干扰)。
Why Mode 30: DMRS for PUCCH/PUSCH and SRS based on the ZC sequence, 30 groups of roots. The roots are associated with the PCI, hence the neighbor cell should not have PCIs having same Mod 30 value to ensure the uplink inter cell interference.
模30.PUCCH/PUSCH上的DMRS和SRS都是根据ZC序列生成，每个根有30组；它们的根都与PCI相关；因此邻区之间不能有相同的“PCI除30”，否则小区间将产生上行干扰；
原文来自/5g-nr-physical-cell-id-pci-planning/