Inter RAT handovers can be following:-
• Intra LTE inter cells HO (LTE HO within eNB)
• Intra LTE inter eNB HO (LTE HO between eNB)
• Inter LTE HO (HO between LTE and other access technologies)
– Between E-UTRAN and UTRAN (3G)
– Between E-UTRAN and GSM
– Between E-UTRAN and non 3GPP Access
And for every handover there is separate algorithm and measurements.
The steps used:-
• Setting up measurements
• Evaluating measurement reports
• Handover Preparation
• Handover Execution
• Handover Completion
• Data forwarding
• If inter-RAT is to GSM, NACC(Network assisted Cell Change) is used and no resources are prepared in the target system. UE enter GSM system in RRC_Idle mode and start the RRC Connection Setup Procedure.
The below algorithm diagram is just for reference to a inter RAT handover: -
