Method (500) in a radio network node (110), a radio network node (110), method (700) in a recipient (120) and a recipient (120), for data transmission and assignment of uplink control channel resources (310) in an uplink FDD carrier (300), for enabling a recipient (120) to provide HARQ feedback for data transmitted in the downlink using carrier aggregation of a downlink FDD carrier (350) and at least one TDD carrier (200). The method (500) comprises associating (501) each downlink subframe (360) in the downlink FDD carrier (350) with an uplink control channel subframe (310) in the uplink FDD carrier (300). Further, the method (500) comprises associating (502) each downlink subframe (210) and special subframe (220) in the TDD carrier (200) with an uplink control channel subframe (310) in the uplink FDD carrier (300). The method (500) also comprises assigning (503) uplink control channel resources (310) in the uplink FDD carrier (300) to the recipient (120), according to the made associations (501, 502). In addition, the method also comprises transmitting (504) data on said downlink FDD carrier (350) and/ or TDD carrier (200), to be received by the recipient (120).