A method, comprising: determining, by a network entity, an uplink-downlink, UL/DL, configuration for a primary cell and at least one secondary cell, respectively; broadcasting the UL/DL configurations to a user equipment, wherein the user equipment is configured for carrier aggregation; enabling enhanced-interference-management-and-traffic-adaptation, eIMTA, for the primary cell and/or the at least one secondary cell for the user equipment; configuring via radio resource control signalling the user equipment with a DL hybrid-automatic-repeat-request, HARQ, reference UL/DL configuration for each cell for which elMTA is enabled; deriving DL HARQ acknowledgement, ACK, timing for the at least one secondary cell based on one or more of the at least one DL HARQ reference UL/DL configuration and at least one of the UL/DL configurations, wherein deriving the DL HARQ ACK timing comprises determining the DL HARQ ACK timing according to whether the DL HARQ reference UL/DL configurations for the primary cell and the at least one secondary cell are the same or not, or according to whether UL/DL configuration in one serving cell and the DL HARQ reference UL/DL configuration in another serving cell are the same or not such that: • if the DL HARQ reference UL/DL configurations are the same for the primary cell and the at least one secondary cell, or if the UL/DL configuration in one serving cell and the DL HARQ reference UL/DL configuration in another serving cell are the same, then the DL HARQ ACK timing for the at least one secondary cell is derived in accordance with Release 10 carrier aggregation rules, departing from the Release 10 carrier aggregation rules in that the DL HARQ reference UL/DL configuration of the corresponding secondary cell is used instead of the UL/DL configuration of the corresponding secondary cell to determine the DL HARQ ACK timing; and receiving HARQ ACK feedback in uplink according to the determined HARQ ACK timing. determining, by a network entity, an uplink-downlink, UL/DL, configuration for a primary cell and at least one secondary cell, respectively; broadcasting the UL/DL configurations to a user equipment, wherein the user equipment is configured for carrier aggregation; enabling enhanced-interference-management-and-traffic-adaptation, eIMTA, for the primary cell and/or the at least one secondary cell for the user equipment; configuring via radio resource control signalling the user equipment with a DL hybrid-automatic-repeat-request, HARQ, reference UL/DL configuration for each cell for which elMTA is enabled; deriving DL HARQ acknowledgement, ACK, timing for the at least one secondary cell based on one or more of the at least one DL HARQ reference UL/DL configuration and at least one of the UL/DL configurations, wherein deriving the DL HARQ ACK timing comprises determining the DL HARQ ACK timing according to whether the DL HARQ reference UL/DL configurations for the primary cell and the at least one secondary cell are the same or not, or according to whether UL/DL configuration in one serving cell and the DL HARQ reference UL/DL configuration in another serving cell are the same or not such that: • if the DL HARQ reference UL/DL configurations are the same for the primary cell and the at least one secondary cell, or if the UL/DL configuration in one serving cell and the DL HARQ reference UL/DL configuration in another serving cell are the same, then the DL HARQ ACK timing for the at least one secondary cell is derived in accordance with Release 10 carrier aggregation rules, departing from the Release 10 carrier aggregation rules in that the DL HARQ reference UL/DL configuration of the corresponding secondary cell is used instead of the UL/DL configuration of the corresponding secondary cell to determine the DL HARQ ACK timing; and • if the DL HARQ reference UL/DL configurations are the same for the primary cell and the at least one secondary cell, or if the UL/DL configuration in one serving cell and the DL HARQ reference UL/DL configuration in another serving cell are the same, then the DL HARQ ACK timing for the at least one secondary cell is derived in accordance with Release 10 carrier aggregation rules, departing from the Release 10 carrier aggregation rules in that the DL HARQ reference UL/DL configuration of the corresponding secondary cell is used instead of the UL/DL configuration of the corresponding secondary cell to determine the DL HARQ ACK timing; and receiving HARQ ACK feedback in uplink according to the determined HARQ ACK timing.