1st thing is that to get measurement report eNB has to configure, so it means that eNB configured the measurement configuration
To configure for getting inter RAT frequency measurement eNb need to configure following thing in measConfig in rrc reconfiguration,
1> Measurement object ---- measObjectToAddModList : Add Frequency related to Inter RAT(utra, gsm, cdma) using this structure
2> Report config- You need to configure reportConfigInterRAT ReportConfigInterRAT to tell UE that i need report based on these INTER RAT event.
3> Measurement id - Based on meas object and report config ....
So when eNB received report based on meas id eNb can know i had configured this meas for INTER-RAt frequencies ... if measurement result is good then go for INTER-RAT ho ...
Hope it will help you.