What is PSS?
PSS (Primary Synchronization Signal) is one of two synchronization signals (along with SSS) transmitted by 5G NR base stations as part of the SS/PBCH Block (SSB). The PSS enables initial time and frequency synchronization of the UE with the network, allowing the device to detect the presence of a cell and begin the cell search procedure. PSS carries partial cell identity information — specifically one of three possible values (N_ID_2), narrowing the Physical Cell Identity (PCI) to one of three groups.
How Does PSS Work?
The PSS is a length-127 m-sequence transmitted on 127 subcarriers around the DC subcarrier. Three possible PSS sequences exist (N_ID_2 = 0, 1, 2), each generated from a different cyclic shift of the same m-sequence. The UE performs PSS detection by correlating the received signal against all three possible sequences — the correlation peak reveals both the sequence index (N_ID_2) and the symbol timing. Because the PSS is a known sequence with excellent autocorrelation properties, it can be detected at very low SNR (-6 dB or below). After PSS detection, the UE knows the symbol timing and the N_ID_2 value, then proceeds to detect the SSS to determine the full PCI (= 3×N_ID_1 + N_ID_2, where N_ID_1 is encoded in the SSS).
Use Cases
5G NR initial cell search and detection, time and frequency synchronization, initial access procedure, cell reselection in idle mode, and handover measurement in connected mode.
3GPP / Standards Reference
3GPP TS 38.211 (NR physical channels — synchronization signals), 3GPP TS 38.213 (NR physical layer procedures — cell search)
Related Terms
SSS | NR | gNB | UE | Numerology
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
