LTE Measurement Reporting Events (A1,A2,A3,A4,A5,B1,B2)

Event A1

The LTE Event A1 is triggered when the serving cell becomes better than a threshold. The event is triggered when the following condition is true: 

MEAsserv - Hyst > Threshold 

Triggering of the event is subsequently cancelled when the following condition is true: 

MEAsserv + Hyst < Threshold

The hysteresis can be configured with a value between 0 and 30 dB.

Event A2

The LTE Event A2 is triggered when the serving cell becomes worse than a threshold. The event is triggered when the following condition is true: 

MEAsserv + Hyst < Threshold 

Triggering of the event is subsequently cancelled when the following condition is true. 

MEAsserv - Hyst > Threshold 

The hysteresis can be configured with a value between 0 and 30 dB.

Q. What is difference between event A3 and A4 in LTE from handover purpose.

What is role of A3 in handover

Answer:

A3 event - UE measures both serving and neighbor cell.

A3: Yes, UE measure both Serving and neighbor cell but with the following condition:
The LTE Event A3 is triggered when a neighboring cell becomes better than the serving cell by an offset. The offset can be either positive or negative. The event is triggered when the following condition is true:

MEASneigh + Oneigh,freq + Oneigh,cell - Hyst > MEASserv + Oserv,freq + Oserv,cell + Offset
MEASneigh + Oneigh,freq + Oneigh,cell + Hyst < MEASserv + Oserv,freq + Oserv,cell + Offset

A3 event is used to trigger intra or inter freq HO.

A4 event - UE measures only neighboring cell.

A4: yes, UE measures only neighboring cell but with the below condition.
When  a neighboring cell becomes better than a threshold.

MEASneigh + Oneigh,freq + Oneigh,cell - Hyst > Threshold 

Triggering of the event is subsequently cancelled when the following condition is true:

MEASneigh + Oneigh,freq + Oneigh,cell + Hyst <Threshold

is there any specific events in LTE that support only interfrequency and intrafrequency HO?

Ans:
I can be possible that only one event can support both inter and intra frequency HO. This depends on eNodeB software implements.  Suppose an UE wants to perform inter frequency HO but is does not support a5 event measurement and support a3 event measurement then eNodeB can configure a3 event for inter frequency HO with intra frequency HO.

Event A5

LTE Event A5 is triggered when the serving cell becomes worse than threshold-1 while a neighboring cell becomes better than threshold-2.

The event is triggered when both of the following conditions are true:
MEASserv + Hyst < Threshold-1
MEASneigh + Oneigh,freq + Oneigh,cell - Hyst >Threshold-2

Event B1

The LTE Event B1 is triggered when a neighboring inter-system cell becomes better than a threshold. The event is triggered when the following condition is true: 

MEASneigh + Oneigh,freq - Hyst > Threshold 

Triggering of the event is subsequently cancelled when the following condition is true:

MEASneigh + Oneigh,freq + Hyst < Threshold

Event A6

Neighbor becomes offset better than Scell

As per my understanding, Any of the event a3 or a5 can be used for inter frequency HO. eNodeB configures these event for an UE on the basis of UE capability. I think if UEs does not support a5 event,

in that case a3 event can be configured for both intra as well as inter frequency HO. If both the events can be supported by UE, in that case we have option which event should be better option.

Triggering criteria of the LTE event are as below.

A1 - Serving becomes better than threshold
A2 - Serving becomes worse than threshold
A3 - Neighbour becomes offset better than PCell
A4 - Neighbour becomes better than threshold
A5 - PCell becomes worse than threshold1 and neighbour becomes better than threshold2
A6 - Neighbour becomes offset better than SCell
B1 - Inter RAT neighbour becomes better than threshold
B2 - PCell becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2

http://niviuk.free.fr/lte_event.php