PCI Planning Tool
Check your 5G NR PCI list for PSS (mod-3) and DMRS (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), and mod-30 collisions reuse the same DMRS sequence for the PBCH (hurting demodulation and throughput). A proper PCI plan avoids direct reuse, mod-3 collisions, 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-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-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-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-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-30 collision — PCI mod 30 maps to the PBCH DMRS sequence. Collisions here degrade PBCH demodulation margin.
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 (mod-30 dependency)
- • TR 38.913 — Scenarios and requirements for NR
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