Hello Experts,
What is the use of PCI in LTE?
Admin note: this post was updated with image below.
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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.
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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
- Frequency Synchronization
- Timing Synchronization
- 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.
Source:
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Frame structure of PCID 0 and PCID 6 are same…again for every multiple of 6 we have same frame structures
What is the difference between them?
If there is no difference then why do we have 503 PCI’s?
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Thanks bro for usefull information, so in a Site has 3 Sector and 1 sector give by 1 SSS value, so how does it affect to the synchronization signal in this site. Thanks
Why LTE support 504 unique cell ID, where as 5G have 1008 unique Cell id?
How is this number derived?
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.
The PCI value is created from two components – PSS and SSS Primary Synchronization Signal and Secondary Synschronization Signal.
After successful decode of PSS and SSS you UE will able to calculate its PCI using the below formula: PCI = (3 × SSS) + PSS.
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In 4G : PCI = (3 * 167) + 2 = 503.
- So PCI values will vary from 0 to 503 LTE supports 504 unique PCIs.
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In 5G : PCI = (3 * 335) + 2 = 1007.
- So PCI values will vary from 0 to 1007. 5GNR supports 1008 unique PCIs .
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Just a comment. The TechPlayon explanation is really good! It is accurate, which some online explanations are not. It is important to note that in my example below NID(1) = SSS = Range {0 -335}. NID(2) = PSS = Range {0 - 2}. I interpreted it logically (wrongly) at first thinking PSS is 1 and SSS is 2. No! Its the other way around. And it is easy once I got over that stupid mental stumbling block. Therefor the PCI in my example = 318
BTW, Great explanation!
I apologize if someone already shared this link, but I don’t see it. Here is a Link to Radio Calculator - Physical Cell Identity: Radio calculator
This is a really good tool to help you calculate the PCI from the PSS and SSS values. It works in reverse too.
Thank you all!
I believe the answer to your question is scale. Recall that new spectrum for 5G is mmWave, which is only effective with small cells (24 GHz and up). So, my take away was to insure no PCI signal overlaps. I could be wrong here, but that is what I interpreted it as. Note that the NID(2) range is only 3 (0, 1, 2). I put together a slide to show this better. I invite everyone interested in this topic to scrutinize my graphic and comment on it. Can you find anything wrong with it? Does it help show how cell splitting (e.g., 3 to 6) is accomplished with only three NID (2) values? Please let me know.
I am NOT a know it all! You have been so helpful. I simply want to contribute to these conversations, so here is my first try.
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The increase in the number of unique cell IDs in 5G compared to LTE allows for denser deployment of smaller cells, which in turn provides higher capacity and improved coverage.
Hi dear. Nobody here is. And that’s exactly what’s good.
Everyone try to help each other. So, thank you very much for the “explanations”, and please continue! 
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Thanks Mr. Mohammad_Saadat.
Please can you list the range of BCCH in 2G, PSC in 3G and PCI in 4G?
I mean for example if PCI=615 and I think it is not the correct PCI of this specific 4G physical Cell then to which number I need to change?
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
Got it, thanks RFGirl.