PCI Planning Tool
Check your 5G NR PCI list for PSS (mod-3), PBCH DMRS (mod-4) and uplink sequence-group (mod-30) collisions. Get safe-PCI suggestions for new cells.
In 5G NR, every cell has a Physical Cell ID (PCI) in the range 0–1007. PCI is derived from two sequences: N_ID(1) ∈ {0..335} from SSS, and N_ID(2) ∈ {0..2} from PSS, with PCI = 3·N_ID(1) + N_ID(2). When two neighbouring cells reuse the same PCI, the UE cannot distinguish them at all. But even when PCIs differ, two failure modes bite: mod-3 collisions reuse the same PSS sequence (degrading initial synchronisation and increasing interference at sector boundaries), mod-4 collisions put the PBCH DMRS on the same subcarriers (hurting PBCH demodulation), and mod-30 collisions reuse the same uplink reference-signal sequence group. A proper PCI plan avoids direct reuse, mod-3, mod-4 and mod-30 collisions across neighbours.
Collision Checker
Paste your PCIs (one per line or comma-separated). Format: 'Label, PCI' — the label is optional.
| Cell | PCI | mod 3 | mod 30 | Conflicts |
|---|---|---|---|---|
| Cell 2 | 100 | 1 | 10 | Cell 4 (mod-3), Cell 4 (mod-30), Cell 6 (mod-3), Cell 8 (mod-3), Cell 8 (mod-30), Cell 10 (mod-3), Cell 10 (mod-4), Cell 10 (mod-30) |
| Cell 4 | 130 | 1 | 10 | Cell 2 (mod-3), Cell 2 (mod-30), Cell 6 (mod-3), Cell 8 (mod-3), Cell 8 (mod-4), Cell 8 (mod-30), Cell 10 (mod-3), Cell 10 (mod-30) |
| Cell 6 | 103 | 1 | 13 | Cell 2 (mod-3), Cell 4 (mod-3), Cell 8 (mod-3), Cell 10 (mod-3) |
| Cell 8 | 250 | 1 | 10 | Cell 2 (mod-3), Cell 2 (mod-30), Cell 4 (mod-3), Cell 4 (mod-4), Cell 4 (mod-30), Cell 6 (mod-3), Cell 10 (mod-3), Cell 10 (mod-30) |
| Cell 10 | 280 | 1 | 10 | Cell 2 (mod-3), Cell 2 (mod-4), Cell 2 (mod-30), Cell 4 (mod-3), Cell 4 (mod-30), Cell 6 (mod-3), Cell 8 (mod-3), Cell 8 (mod-30) |
Suggest Next Safe PCI
Enter neighbour PCIs — we'll find the lowest PCI in [0, 1007] that avoids reuse, mod-3 and mod-30 collisions.
Parsed 5 neighbour PCIs.
How It Works
The tool performs three checks on every pair of PCIs in your list:
- Direct reuse — two cells with the identical PCI cannot coexist as neighbours.
- mod-3 collision — PCI mod 3 selects the PSS sequence. Two cells sharing the same value produce correlated PSS peaks, making cell search unreliable.
- mod-4 collision — PCI mod 4 sets the PBCH DMRS frequency shift (v). Two cells sharing it put their PBCH pilots on the same subcarriers.
- mod-30 collision — PCI mod 30 selects the uplink reference-signal sequence group (PUSCH DMRS, PUCCH, SRS). Collisions raise uplink interference between neighbours.
The suggester picks the lowest PCI in [0, 1007] that avoids all three of the above against your neighbour list. For dense urban clusters you typically want a reserved pool of at least 30 distinct mod-30 buckets.
3GPP References
- • TS 38.211 §7.4.2 — Synchronisation signals (PSS, SSS, PBCH-DMRS)
- • TS 38.211 §7.4.1.1.1 — PSS sequence generation (N_ID(2), 3 variants)
- • TS 38.211 §7.4.1.4.1 — DMRS for PBCH (v = PCI mod 4)
- • TS 38.211 §6.4.1.1.1 — UL RS sequence group (PCI mod 30)
- • TR 38.913 — Scenarios and requirements for NR
How to use the PCI Planning Tool
- Enter your PCIs. Paste your cells one per line or comma-separated, optionally as "Label, PCI" so the results are easy to read.
- Read the collision verdict. See at a glance how many cells have conflicts, with a clean/collision banner.
- Inspect the per-cell table. Check each cell’s PCI, its mod-3 and mod-30 values, and exactly which neighbours it clashes with and why (reuse, mod-3 or mod-30).
- List the neighbours. In the suggester, enter the PCIs already in use around a new site.
- Take the safe suggestion. Read the lowest PCI in 0–1007 that avoids reuse, mod-3 and mod-30 collisions against that neighbour set.
Frequently asked questions
- How many PCIs are there in 5G NR?
- There are 1008 physical cell IDs, numbered 0 to 1007. The number comes from PCI = 3 × N_ID_1 + N_ID_2, where N_ID_1 has 336 values and N_ID_2 has 3, giving 336 × 3 = 1008.
- Why do PCIs need mod-3 and mod-30 checks?
- PCI mod 3 equals N_ID_2, which selects the PSS sequence; two neighbouring cells sharing a mod-3 value interfere during cell search. PCI mod 4 sets the PBCH DMRS frequency shift (TS 38.211 §7.4.1.4.1), so a mod-4 clash puts two cells' PBCH pilots on the same subcarriers. PCI mod 30 selects the uplink reference-signal sequence group (PUSCH DMRS, PUCCH, SRS), so a mod-30 clash raises uplink interference. Good planning keeps both distinct among cells that can see each other, on top of avoiding outright PCI reuse.
- What is a PCI collision versus a PCI confusion?
- A collision is when two cells that are direct neighbours use the same PCI, so a UE on the boundary cannot tell them apart. A confusion is when one cell has two distinct neighbours sharing the same PCI, which breaks handover because the source cell cannot resolve which neighbour the report refers to. Both are avoided by keeping reuse distance large and checking the neighbour-of-neighbour relationships.
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