The disclosure relates to selection of acknowledgment timing in wireless communications. Disclosed is a user equipment device configured to select a suitable acknowledgement timing configuration in atime division duplex-frequency division duplex (TDD-FDD) carrier aggregation (CA) enabled wireless network, comprising establishing, by a user equipment (UE), a connection to a primary serving cell (PCell) and a secondary serving cell (SCell) of a base station, the PCell having a first TDD or first FDD configuration, the SCell having a second FDD or second TDD configuration, receiving, by the UE,downlink data through the PCell and SCell, categorizing a type of downlink data subframe in use by the SCell, selecting, by the UE, a hybrid automatic repeat request (HARQ) timing configuration basedon the type of downlink data subframe for use by the SCell, and transmitting acknowledgement information associated with the downlink data according to the selected hybrid automatic repeat request (HARQ) timing configuration on PCell. Other embodiments may be described and claimed.