Physical Cell ID (PCI) is one of the most important cell’s identifier in the wireless network of 4G and 5G system.It is PHY cell id which is required for DL synchronization.
PCI planning is one of the most important steps in 4G and 5G network planning and construction. To design PCI properly and efficiently will increase resource utilization and QoS of the 4G and 5G system for subscribers. Poor planning results in PCI collisions or conflicts which impact network performance.
The PCI value is created from two components – PSS and SSS Primary Synchronization Signal and Secondary Synchronization Signal
After successful decode of PSS and SSS you UE will able to calculate its PCI using the below formula:
PCI = (3 × SSS) + PSS
How 4G PCI is calculated ?
PSS has 3 values 0,1 and 2 and is created using Zad-off Chu sequence.
PSS helps to accomplish slot and symbol synchronization in the time domain.
SSS has 168 values 0 to 167 and is produced using concatenation of 2 m-sequences (max length sequence)
SSS aids to achieve radio frame synchronization
PCI = (3 * 167) + 2 = 503
So PCI values will vary from 0 to 503 LTE supports 504 unique PCIs
How 5G PCI is calculated ?
PSS has 3 values 0,1 and 2 and created using m-sequence
SSS has 336 values 0 to 335 and generated using product of 2 m-sequences
In 5G-NR, the basic structure of PSS is the same but the number of SSS are increased
PCI = (3 * 335) + 2 = 1007
So PCI values will vary from 0 to 1007. 5GNR supports 1008 unique PCIs .
5GNR has double of the PCI’s compared to LTE 4G