I have not very deep knowledge about it, but still I have something which I would like to share.

In lte, a physical cell can have max 3 sectors, each sector may have either one of the values {0,1,2}.

ZC-sequence is being used for PSS in lte. ZC-sequence has following properties:

1. A ZC sequence has constant amplitude.

2. ZC sequences of any length have ’ideal’ cyclic Auto-Correlation.

3. Two Sequences with M1 and M2 have constant cyclic

Cross-Correlation if M1 is relative prime to M2. Thisvalue achieves the minimum Cross-Correlation for any two sequences with ideal Auto-Correlation.

For PSS, ZC-Roots {29,34,25} are being used due to this 3 root index, PSS has three possible values which are nothing but 0, 1 or 2.

SSS tells about the group id of PCI. PCI = 3 * SSS + PSS.

SSS ranges from 0 to 167.

Please correct me if I am wrong.