5G • Spectrum
SSB
Synchronization Signal Block (SS/PBCH Block)
The fundamental radio broadcast block in 5G NR containing PSS, SSS, and PBCH for cell search, timing synchronization, and beam identification.
Technical Explanation
The SS/PBCH Block (SSB) consists of 4 OFDM symbols and 240 subcarriers (20 Resource Blocks). It encapsulates the Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), and the Physical Broadcast Channel (PBCH) carrying the Master Information Block (MIB). Multiple SSBs are transmitted in an SSB burst across different spatial beam directions (Beam Sweeping), allowing UEs to discover the cell, achieve frame synchronization, acquire basic system information, and select the optimal serving beam.
Key Functions
- Cell detection and Physical Cell ID (PCI = 3 × N_ID1 + N_ID2) discovery
- Downlink frame, subframe, and slot time synchronization
- Delivery of MIB containing SIB1 scheduling info and system frame number (SFN)
- Reference signal for beam measurement (SSB-RSRP) and beam selection
Specifications
3GPP TS 38.211, TS 38.213
Interfaces
Uu Air Interface (Physical Broadcast)
Related 5G Concepts
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