Physical cell id for new cells/eNB

Hi Experts,

When we add a new eNB to a cell in LTE how the physical cell id for that eNB is decided?
And who decides the cell id?

Auto PCI is a SON feature which decides initial PCI.

Thanks @sadanandk2, but can you please eleborate it a little more?

Or manual on planning tools like Atoll.

There is a feature in Ericsson called “Automated Rach Root Sequence Allocation”.
It can helpful in your case.

Hi @Tammam.Hajj, thanks.
I checked the feature and it says the RACH PREAMBLE is allocated based on the cell ID.
But what I am more interested in is how the Cell id is configured when a new eNB is installed.

Do you mean to say ‘add cell to eNB’?
1 eNB has many cells (upto 9 or 16 depending on Basebands).
From what I remember, Physical cell id used to come from RF planning team and than manually added when Cell or eNB is deployed.

There is also difference in Physical Cell ID and PCI.
PCI is planned based on PCI planning (as you might be aware).
Physical Cell ID is combination of eNB ID, cell ID, etc.

If I am not wrong, sorry it was 5 years ago… :wink:

Actually it’s Eutra cell id.
It’s like lnbtsid*256+ lcrid

I think you are referring to it…

I guess your are referring to local cell Id, which is used for ECGI.

Something like this:

Cell ID should be planned already.

Great. And how is the (best) way to do it?

Planning team should be responsible for that.
There are many online documents that can be helpful as well (PCI should be mod3, mod 30…).

Cellid has no special meaning.
It is just a number.
Usually there are rules (defined by MNO) per carrier and per sector.
But nothing special.

For PCI Planning:

Range is 0 to 503.
We can do it manually like :

  1. If there is any PCI available between 0 to 503? If not then you can use it far away Site PCI?
  2. Make sure no mod3 clash with neighboring cell.

Usually with MIMO we use MOD3, without MIMO MOD6.

The RS position varies for PCI MOD3 (2/4 antenna) and PCI MOD 6 (single antenna). The following table lists a PCI plan, in which PCI MOD 3 determines the pilot position. The following figure shows the RS position distribution. Different colors indicate the positions of different RSs. Because the plan uses 2-path antennas, the pilot position takes three values.

More details here (The MOD3 principle):

This helps to understand the reason why PCI planning is needed.

LTE Resource Grid:

Almost all channels are allocated based on PCI, not only CRS.
On UL, RSI planning is also needed.

How much impact on LTE performance if we plan PCImod3=0 in collocated cells?

It’s impact on LTE performance in terms of KPI (CQI,DCR,SNIR,TPUT) Majorly.