When an LTE user attaches to the LTE core network and its connectivity with the LTE network is maintained while moving within the LTE network coverage is known as Intra-LTE mobility. In short , "No change in the radio access technology".
There are two variants of Intra-LTE mobility.
Intra-Frequency Mobility: When UE performs handover from one eNodeB to another eNodeB running on the same frequency used at source eNodeB.
Inter-Frequency Mobility : When UE moves to the target eNodeB running on the different frequency.
Example for 1 : When source cell has poor coverage or user is moving away from source cell. Source eNodeB triggers handover to another eNodeB which has better coverage on the same frequency. The level of coverage is detected based on the threshold values for RSRP.
Example for 2: When source cell is overloaded and but UE is observing good signal strength. Despite of, source cell ask for inter-frequency measurement report from UE and triggers the handover to a cell having different frequency.
There can be possible scenarios in which Intra-Frequency or Inter-Frequency handover is used. I just coverage one scenario for each.
