About 5G initial cell search

When a UE powers on or loses coverage, it performs initial cell search to acquire timing, frequency, the Physical Cell ID (PCI) and the Master Information Block. 5G NR packages these signals into a Synchronization Signal Block (SSB) — 4 OFDM symbols wide and 240 subcarriers (20 PRBs) tall, broadcast periodically (typically every 20 ms) and optionally beam-swept with up to L = 4 / 8 / 64 beams in FR1 / FR2.

The UE first correlates against the 3 possible PSS sequences (m-sequences with cyclic shifts 0, 43 and 86). That yields N_ID_2 and OFDM symbol timing. It then correlates against the 336 possible SSS Gold-like sequences to resolve N_ID_1, giving PCI = 3·N_ID_1 + N_ID_2 . PBCH is decoded next (its DMRS v-shift is PCI mod 4) to extract the 24-bit MIB, which tells the UE where Type0-PDCCH common search space lives so it can go fetch SIB1.

Who uses this visualizer?

RAN developers use it to teach PHY layer bring-up. Field engineers use PSS (mod 3), DMRS (mod 4 / 30) planning insights when debugging interference. Students use it to anchor the abstract TS 38.211 equations to a concrete frame picture.

Related tools

• PCI Planning Tool
• SSB Beam Planner
• Random Access Simulator