5G SSB Sweeping Overview (Article)
SSB Beam Sweeping
- Beam sweeping is a new concept newly introduced in 5G where g-NodeB can transmit a sequence of SSB beams in a different direction.
- Simply, gNB can transmit a sequence of SSB beams; beam sweeping is implemented by changing the direction of each SSB Transmission.
- All beams are simultaneously active, but each beam is allocated a separate SS/PBCH block within the SS/PBCH Burst, so each beam transmits its SS/PBCH Block with different timing.
- This allows the UE to see the transmissions from each beam and beam indices, which clearly can be identified based on the timing of the SS/PBCH block.
- The UE measures and reports all the transmitted SSB to the g-NB, and the best beam will be selected by the g-NB based on the RSRP.
What are the main advantages and disadvantages of Beam SSB Beam Sweeping?
- In general, transmitting SSB beams in a different direction is part of beamforming, which is expected to offer a gain in coverage and interference (SINR).
- However, More beams will introduce an extra Overhead for the resources occupied by SSB and for the resources occupied by CORESET(SIB1), as each SSB Beam will be associated with SIB1.
Time domain resource allocation
- According to 3GPP TS 38.213, the first symbol indexes for candidate SS/PBCH blocks are determined according to the SCS of SSB blocks, Frequency Band, and Duplex mode.
- The number of SSB beams supported in a cell will be indicated through a parameter called SSB-PositionInBurst.
- The Below figure will illustrate how the SSB resources will be allocated in the time domain for Case A to C:
- Five-time domain positions (Case A to Case E) are specified according to the protocol
- TDD 2.4 Band is currently using Case C
- All SSBs will be transmitted in total 5ms, usually in the first half of the frame
The below video simulate all the above contents
Sources:
- 5G NR in Bullets
- 3GPP TS 38.213
