What is SSS?
SSS (Secondary Synchronization Signal) is the second synchronization signal in the 5G NR SS/PBCH block, transmitted alongside the PSS and PBCH. While the PSS provides symbol timing and one of three N_ID_2 values, the SSS carries the remaining cell identity component N_ID_1 (one of 336 values), enabling the UE to determine the full Physical Cell Identity (PCI = 3×N_ID_1 + N_ID_2). The SSS also serves as the reference for SS-RSRP measurements.
How Does SSS Work?
The SSS is a length-127 Gold sequence transmitted on 127 subcarriers, with the specific sequence determined by N_ID_1. After detecting the PSS (which gives timing and N_ID_2), the UE correlates the received signal against all 336 possible SSS sequences to determine N_ID_1. The SSS occupies one OFDM symbol in the SS/PBCH block (symbol 2 in a 4-symbol SSB), positioned two symbols after the PSS (symbol 0). Because N_ID_1 has 336 possible values and N_ID_2 has 3, the total number of unique PCIs in 5G NR is 1,008 (same as LTE). The UE uses the detected PCI to descramble the PBCH and decode the Master Information Block (MIB) to obtain system information.
Use Cases
5G NR cell identity detection, physical cell identity (PCI) determination, SS-RSRP measurement reference, initial access and cell search, and cell reselection measurements.
3GPP / Standards Reference
3GPP TS 38.211 (NR physical channels — SSS sequence generation), 3GPP TS 38.213 (NR cell search procedures)
Related Terms
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