Embodiments provide methods and devices for data transmission and assignment of uplink control channel resources in an uplink FDD carrier, for enabling a terminal device to provide HARQ feedback for data transmitted in the downlink using carrier aggregation of a downlink FDD carrier and at least one TDD carrier. A method includes associating each downlink subframe in the downlink FDD carrier with an uplink control channel subframe in the uplink FDD carrier, associating each downlink subframe and special subframe in the TDD carrier with an uplink control channel subframe in the uplink FDD carrier, assigning uplink control channel resources in the uplink FDD carrier to the terminal device according to the associations, and transmitting data on said downlink FDD carrier and/or TDD carrier, to be received by the terminal device.