Beam Sweeping is the concept of transmitting multiple SSBs in different locations to help determine the direction required for the transmission of the beam. The gNB will determine the SSB with the strongest signal, which provides the direction to focus the beamforming.

What is SSB for Beam Sweeping?

An Synchronization Signal Block (SSB) is used for establishing downlink synchronization. It consists of a primary and secondary sync signal and a Physical Broadcast Channel (PBCH). The transmission period is typically 20ms, but can be scheduled for 5, 10, 20, 40, 80, or 160ms.
What is an SSB – Synchronization Signal Block

The process is the following:

  1. Multiple SSBs are sent at the scheduled interval, each with a unique identifier (A SSB Index). Each SSB is transmitted in a different direction. The frequency helps determine the amount of SSBs that will be sent within a single transaction. For sub 6GHz it will either be 4 or 8 SSBs. For mmWave, it will be 64 SSBs.
  2. The User Equipment receives multiple SSBs, and determines the SSB with the strongest signal, identifying the index identifier.
  3. The User Equipment reports the index identifier back to the gNB via a process called SSB Index Reporting.

How does SSB Index Reporting work?

Once the UE determines the index identifier of the strongest SSB, it reports it back to the gNB via Index Reporting. This can be via a dedicated control channel or an uplink transmission.
How does SSB Index Reporting work?

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