Below are the description on possible handover scenarios in LTE network which will involve event A2, A3 and A4
1) Scenario #1
When UE is moving from Cell A to Cell B, there will be a handover. At this Handover Region, normally event A3 will be effective first. Handover from F1->F1, it is Intra-Freq HO and A3 will be effective. If we set A3= 3dB, A3 will compare the Serving RSRP and Neighbor RSRP. If the value differences is >=3db within the HO trigger time (640ms by default), it will trigger HO from Cell A (F1) to Cell B (F1).
When UE connected to Cell A (F2), then it move to Cell B (F1), cause Cell B (don't have F2), it will make use the event A2 and A4. A2 is threshold for serving cell, when UE is below this A2 threshold, UE will start Inter-Freq measurement. For example, we set A2 is =-102 dBm. Whenever UE serving RSRP <=-102 dBm it will start to measure the other frequency available. Event A4 is used to trigger Inter-Freq HO. A4 is threshold for neighbor cell, when UE is above this A4 threshold, UE will start Inter-Freq HO. For example, we set A4 is =-98dBm. Whenever UE neighbor RSRP >=-98 dBm within the HO trigger time (640ms by default), it will trigger HO from Cell A (F2) to Cell B (F1).
2) Scenario #2
When UE is moving from Cell A (F2) to Cell B(F2), there will be a handover. At this Handover Region, normally event A3 will be given priority. Handover from F2->F2 or F1->F1, it is Intra-Freq HO and A3 will be effective. If we set A3= 3dB, A3 will compare the Serving RSRP and Neighbor RSRP. If the value differences is >=3db within the HO trigger time (640ms by default), it will trigger HO from Cell A (F2) to Cell B (F2), or from Cell A (F1) to Cell B (F1).
When UE connected to Cell A (F2), then it move to Cell B and at the same time Cell B (F2) not available, it will start the Inter-Freq measurement whenever UE serving RSRP <=-102 dBm (A2). Event A4 is used to trigger Inter-Freq HO. A4 is threshold for neighbor cell, when UE is above this A4 threshold, UE will start Inter-Freq HO. For example, we set A4 is =-98dBm. Whenever UE neighbor RSRP >=-98 dBm within the HO trigger time (640ms by default), it will trigger HO from Cell A (F2) to Cell B (F1).
