UE in RRC_CONNECTED, it will measure multiple beams of the cell to determine cell quality.
Then it will report the measurements to network, based on that, network can inform UE to perform handover.
There are 2 types of measurement reporting:
1. Periodic reporting
2. Event reporting.
Event reporting refers to the situation that meets the conditions specified in the protocol.
The measurement events mentioned above, described in 38.331 Section 5.4, include
A1 – Serving cell measurement result is better threshold
Entering condition：Ms – Hys > Thresh
Leaving condition：Ms + Hys < Thresh
A2 – Serving cell measurement result is worse threshold
Entering condition：Ms + Hys < Thresh
Leaving condition：Ms – Hys > Thresh
A3 – The neighbor cell measurement result is higher than the serving cell measurement result + offset
Entering condition：Mn + Ofn + Ocn – Hys > Mp + Ofp + Ocp + Off
Leaving condition：Mn + Ofn + Ocn + Hys < Mp + Ofp + Ocp + Off
A4 – Neighbor measurement result is above threshold
Entering condition：Mn + Ofn + Ocn – Hys > Thresh
Leaving condition：Mn + Ofn + Ocn + Hys < Thresh
A5 – The serving cell measurement is below the threshold and the neighbor measurement is above the threshold
Entering condition 1：Mp + Hys < Thresh1
Entering condition 2：Mn + Ofn + Ocn – Hys > Thresh2
Leaving condition 1：Mp – Hys > Thresh1
Leaving condition 2：Mn + Ofn + Ocn + Hys < Thresh2
A6 – The measurement result of the neighbor cell is higher than the measurement result of the Scell + offset
Entering condition：Mn + Ocn – Hys > Ms + Ocs + Off
Leaving condition：Mn + Ocn + Hys < Ms + Ocs + Off
B1 – Inter-system cell measurement result is higher than the threshold
Entering condition：Mn + Ofn + Ocn – Hys > Thresh
Leaving condition：Mn + Ofn + Ocn + Hys < Thresh
B2 – Inter-system cell measurement result is higher than the threshold, SPcell measurement result is lower than the threshold
Entering condition 1：Mp + Hys < Thresh1
Entering condition 2：Mn + Ofn + Ocn – Hys > Thresh2
Leaving condition 1：Mp – Hys > Thresh1
Leaving condition 2：Mn + Ofn + Ocn + Hys < Thresh2
Source TS 38.331
