The present disclosure describes methods and apparatuses for inter-radio access technology carrier (RAT) aggregation. In aspects, a user device (102) establishes a wireless link (106) for communicating with one or more base stations (104, 202) via a first component carrier (214) and a second component carrier (208, 220). The first component carrier uses a (RAT) having a first transmission time interval (TTI) and the second component carrier uses a second RAT having a second, different TTI. The user device receives user plane data via the second component carrier and analyzes the user plane data to determine whether data packets of the user plane data were successfully or unsuccessfully received by the user device (804, 806). The user device then transmits, via a next available uplink subframe or time slot of the first component carrier of the first RAT, a feedback communication based on which data packets were successfully received (808).