Measurement Events In LTE

In LTE system, RRC connection reconfiguration message is used to configure UE measurement reporting. It replaces the measurement control message used in the UMTS system. The stands defines 5 intra-system and 2 inter-system measurement reporting events as described below.

LTE Events A1, A2, A3, A4 and A5 are based upon either RSRP or RSRQ messages. 

Inter-system LTE events B1 and B2 are based upon CPICH RSCP or CPICH Ec/Io for UMTS system,

The criteria for triggering and subsequently cancelling each event are evaluated after layer-3 filtering has been applied. The criteria for each event must be satisfied during at least the time to trigger. The time to trigger can be configured independently fpr each reporting event. The values are as follows: 
{0,40,64,80,100,128,160,256,320,480,512,640,1024,1280}

1. S-Measure

Serving cell RSRP threshold controlling whether or not the UE is required to perform measurements of intra-frequency, inter-frequency and inter-RAT neighbouring cells.

2. Event-A1

The serving cell becomes better than certain threshold

3. Event-A2
Serving cell becomes worse than certain threshold

4. Event A3

Neighbour cell becomes better than serving cell

5. Event A4

The neighbour cell becomes better than certain threshold

6. Event A5

Serving cell becomes worse than specific threshold and the neighbour cell becomes better than another threshold.                                  

7. Event B1

InterRAT Neighbour cell becomes better than certain threshold

8. Event B2

The serving cell becomes worse than threshold1 and inter RAT neighbour cell becomes better than threshold2

Reference:
3GPP TS 36.331