PCI Planning ( MOD3/6/30 rules??? )

[forumuser-2008]

Dear friends,

I have question regarding to PCI:

As I know PCI is like Scrambling Code in WCDMA to distinguish cells, if I am not wrong.
And it the combinations of SSS & PSS (PCI = 3*SSS+PSS).

My question: in some document I saw that we should not use PSS (exp "0") in the cell of the same site and in the neighbors due to MOD3 rule. I don't understand that how is it possible not to use, it is just three values in PSS (0,1,2).
Yesterday I saw in one book, the author mentioned that it is not advisable to use PCI 22 & PCI 28 in the neighbour cell, because their PSS is 1.
So in this case how can we make PCI planning between cells??? Same explanations also were mentioned in Harish Vadada PCI Planning Document.

If some of you have experience and detail (in simple way :)) explanation for PCI planning and the meaning of MOD3/MOD6/MOD30 rules, then can you share with us your skills?

Thanks in advance

[incoincov]

Hi Friend,

It's correct that PCI = 3*SSS+PSS . You have

SSS 168 groups
PSS 0,1,2 3cells/group

So in total 168x3=504
The main requirements is to avoid PCI collision and confusion. It’s recommended to avoid same PCIs or PCIs with the same frequency shift mod6 (1antenna) or mod 3(2,4 antennas) to nearby cells. Thus the problems in cell search and cell selection will be avoided


It gives an answer to your next question:

If we assume mod3 used for 2 or 4 Tx antenna case:

PCI=21 => RS frequency shift is 0 because 21mod3= 7
PCI=28 => RS frequency shift is 0 because 21mod3= 7

so not advisable to use PCI=21 and PCI=28 for neigh

BUT if Mod 6 is used in case of 1 Tx antenna:
PCI=21 => RS frequency shift 3 (21-18) because 21mod6=3
PCI=28 => RS frequency shift 4 (28-24) because 28mod6=4

it's possible to use PCI=21, PCI=28 for neighbours

Example 1 for PCI Planning: use same SSS and different PSS for the cells beloging to the same site and ovelappings cells.This strategy is inline with most vendor approach for PCi planning.
Example 2 for PCI Planning: Same PSS and different SSS for the cells belonging to the same site. It leads to Overlapping RS in different cells So same PSS means always same RS freq shift for mod 3-> PROBLEM!

Hope it helps.

regards!

[forumuser-2008]

Thanks friend,

I think you mean MIMO with mentioning the antennas (1,2, or 4), am I right?

In this case it seems to make the planning with tool is better than manual. I don't think that manual is possible to make PCI planning for 200-300 sites.

You mentioned that it is not possible to use: is it not possible or not advisable regarding to the cell search? What kind of issues might be if use the same PSS in the same site?

[incoincov]

Hi again,


Of course PCI planning is usually done with a tool. I've just meant to help you to get clearer view about PCI planning concept via the examples.
Ok, it's not advisable to use the same PSS for overlapping cells in order to avoid confusion and collisions. Having same PCI or RS freq shift in neighbour cells is similar to having same BCCH in GSM or same SC in UMTS. It would cause interference, unsuccessful HO, etc.

cheers!

[OKLATINGUY]

It's been a bit confusing. I think you mean:

PCI(22)-->3*7+1, PSS=1 or 22mod3=1
PCI(28)-->3*9+1, PSS=1 or 28mod3=1
Thus, same RS freq shift

Please let me know if I'm wrong.