SS/PBCH Time domain Resource Allocation

SS/PBCH Time Domain Resource Allocation

SSB Burst set :

  • All SSBs are transmitted within 5 ms.
  • Maxmimum SSB in Cell is depend upon frequency.
  • Less than 3 GHz band  maximum SSB is 4
  • 3 GHz to 6 GHz maximum SSB is 8
  • greater than 6 GHz maximum SSB is 64.

SS Block Periodicity :

  • SSB periodicity for intial acquistion is fixed that is 20 ms.
  • Periodicity will vary from 5 ms to 160 ms.

You Can see for SSB 4, here UE is in connected mode, using 15 KHz scs with below 3GHz band, Maximum SSB supported is 4.

20 ms is required for initial access, 10 ms is for Idle and connected UEs with beam identical beam sweeping pattern.

Beam Management during Initial Access:
  • The gNB uses directional beams when transmitting and receiving from the cell.
  • The gNB transmits SS/PBCH blocks, with different SS/PBCH block index on different beams.
  • When a UE is powered on, it listens to the SS/PBCH blocks, scanning across its Rx beams, and identifies a SS/PBCH block index with
    power level that exceeds a threshold provided by higher layer parameter rsrp-ThresholdSSB.
  • This determines the beam-pair the gNB and the UE use to communicate with each other.
  • Let’s assume that the gNB and the UE have beam-correspondence, i.e. the beam used for reception determines the beam used for transmission, and vice versa.
  • The UE transmits the preamble based on the selected SS/PBCH block index on a beam determined by the Rx beam used to receive the SS/PBCH block.

complete topic I will update in Initial access procedure in coming days.

Check some other important article


  • Sonal kumar
    July 29, 2020

    Very nice explained.. Good work by cafetele team & Abhijeet!

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