Handover process in the LTE system

What is handover? 

Handover is the process enables a call to proceed without interrupted when a user moves from a cell to another. It may degrade the performance of transmission control protocol (TCP) connections and real-time applications in wireless data networks. 

Figure: Handover process in LTE network

Handover can be divided into few steps; initiation, resources reservation, execution, and completion. The process flow as following:

1. the procedure starts with the UE measurement report configured by source eNB. 
2. If certain network configured conditions are satisfied,  UE will send measurement report according to the rules set by system specifications.
3. The source eNB will then make the decision to perform handover based on the measurement report where the measurement report indicates the which needed to be handed over.
4. Then, source eNB issues a handover request message to the target eNB.
5. The handover preparation involves exchange of signalling between serving and target eNB, and admission control of the UE is performed by  target  eNB. 
6. Upon successful handover preparation, the target eNB handover request acknowledgement to the source eNB. 
7. The handover decision is made and consequently the handover command will be sent to the UE. 
8. The UE responds with a  handover confirm message, which notifies the completion of the handover procedure at the radio access network part.

Upon successful synchronization at the target eNB, this last one transmits an uplink scheduling grant to the UE. It should be noted that the signalling messages described above belong to the radio resource control (RRC) protocol.