A method performed by a user equipment, UE, in a communication system supporting Carrier Aggregation, CA, of a primary cell and at least one secondary cell(s), the method comprising: receiving a downlink physical channel from a base station through one of the at least one secondary cell(s); and transmitting, to the base station, a Hybrid Automatic Repeat Request, HARQ, feedback corresponding to the downlink physical channel, characterised in that, when the UE is not configured to monitor a control channel in another cell for scheduling the one of the at least one secondary cell(s), and when the primary cell is configured as Time Divisional Duplex, TDD, and the one of the at least one secondary cell(s) is configured as Frequency Divisional Duplex, FDD: if a first subframe is either a downlink subframe or a special subframe in the primary cell, a timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the first subframe in the one of the at least one secondary cell(s) is identical with a TDD timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the first subframe in the primary cell; and if a second subframe is an uplink subframe in the primary cell, a timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the second subframe in the one of the at least one secondary cell(s) is identical with a TDD timing of transmitting a HARQ feedback corresponding to a downlink physical channel of either a downlink subframe or a special subframe of the primary cell which is closest to the second subframe. receiving a downlink physical channel from a base station through one of the at least one secondary cell(s); and transmitting, to the base station, a Hybrid Automatic Repeat Request, HARQ, feedback corresponding to the downlink physical channel, characterised in that, when the UE is not configured to monitor a control channel in another cell for scheduling the one of the at least one secondary cell(s), and when the primary cell is configured as Time Divisional Duplex, TDD, and the one of the at least one secondary cell(s) is configured as Frequency Divisional Duplex, FDD: if a first subframe is either a downlink subframe or a special subframe in the primary cell, a timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the first subframe in the one of the at least one secondary cell(s) is identical with a TDD timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the first subframe in the primary cell; and if a second subframe is an uplink subframe in the primary cell, a timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the second subframe in the one of the at least one secondary cell(s) is identical with a TDD timing of transmitting a HARQ feedback corresponding to a downlink physical channel of either a downlink subframe or a special subframe of the primary cell which is closest to the second subframe. if a first subframe is either a downlink subframe or a special subframe in the primary cell, a timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the first subframe in the one of the at least one secondary cell(s) is identical with a TDD timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the first subframe in the primary cell; and if a second subframe is an uplink subframe in the primary cell, a timing of transmitting a HARQ feedback corresponding to a downlink physical channel of the second subframe in the one of the at least one secondary cell(s) is identical with a TDD timing of transmitting a HARQ feedback corresponding to a downlink physical channel of either a downlink subframe or a special subframe of the primary cell which is closest to the second subframe.