5G NR SSB Positioning - Time & Frequency Resources

Home > Technical Articles > 5G NR SSB Positioning - Time & Frequency Resources

Introduction

In 5G NR, Each SSB (Synchronization Signal Block) spans across 4 OFDM symbols in the time domain. An SSB is periodically transmitted with a periodicity of 5ms, 10ms, 20ms, 40ms, 80ms, or 160ms. Longer SSB periodicities enhance network energy performance, the shorter periodicities facilitate faster cell search for UE’s. It refers to the Synchronization Signal block because the Synchronization signal and PBCH channel are packed as a single block that always moves together. SSB includes PSS (Primary Synchronization Signal), SSS (Secondary synchronization signal), and PBCH (Physical broadcast channel). In 5G, the SSB location on the Bandwidth part is not fixed and can be located anywhere across the carrier bandwidth. 

SSB Time-domain resources

• SS block consists of 4 Consecutive OFDM symbols
• The 1st symbol position is determined by the combination of the carrier bandwidth (CBW) + sub-carrier spacing (SCS). 

SSB Frequency domain resources

• SSB in frequency domain consists of 240 consecutive subcarriers numbered in increasing order from 0 to 239 is equal to 20 PRB’s. 
• If SSB-Subcarrier offset is not provided, SSB is derived from the frequency difference between the SS/PBCH block and point A.
• In NSA mode operation the location of the SSB is determined by information provided by the higher layer in the RRC Reconfiguration message. 

FD Resource Allocation & Positioning of SSB on CBW

• SSB in 5G NR consist of 240 consecutive Sub carriers = 20 PRB’s 
• The location of the SSB on the CBW is determined by information provided by a higher layer in the RRC Reconfig message.