What is the PCI in LTE?

Hello Experts,

What is the use of PCI in LTE?

PCI stands for Physical Cell Identity, to make is as easy as possible, it is the identifier of LTE eutrancell, same like PSC in 3G or BCCH in 2G, it consists of 2 parts PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal), both used to give PCI, PCI=3xSSS+ PSS, they are used mainly to achieve radio frame, subframe, slot and symbol synchronization in the time domain and to Identify the center of the channel bandwidth in the frequency domain.

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In physical data processing flow we know scrambling step the scrambling uses PCI to be SC so if UE want to decode information from LTE Cell PCI need to be informed.

So, how is it informed? it carried by two synchronization signals (PSS&SSS) as PCI=3xSSS+ PSS after UE read these two signals UE can calculate current PCI configuration of the Cell.

PCI in LTE is physical layer Cell Identifier. Its range is from 0-503 total Identities as 504. It is consist of Primary Sync signal and Secondary Sync signal.
PSS possible values can be 0,1,2 and SSS value can be 0-167

PCI can be calculated as PSS+3x SSS
for an examples
SSS=5
PSS=1

PCI = 1+ 3*5=16
Here is an good read about PCI from techplayon.

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Physical Cell ID - LTE 4G vs 5GNR

Why is PCI required ?

PCI is used for Downlink Synchronization includes

  1. Frequency Synchronization
  2. Timing Synchronization
  3. Cell ID Detection

PCI includes two signals i.e., Primary Synchronization Signal and Secondary Synchronization Signal

After successful decode of SSS you will able to get PCI

PCI is calculated using the formula

PCI = (3 × SSS) + PSS

LTE 4G:

PSS has 3 values i.e., 0 to 2 and generated using Zad-off Chu sequence

SSS has 168 values i.e., 0 to 167 and generated using concatenation of 2 m-sequences

PCI = (3 * 167) + 2 = 503

So PCI values will vary from 0 to 503. LTE supports 504 unique PCIs

5GNR:

PSS has 3 values i.e., 0 to 2 and generated using m-sequence

SSS has 336 values i.e., 0 to 335 and generated using PN Gold sequence

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

Conclusion:

5G NR has double of the PCI’s compared to LTE 4G.

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