Method for configuring a harq rtt timer in a carrier aggregation system and a device therefor

A method for a user equipment operating in a wireless communication system, the method comprising:

• receiving data in a subframe n via a SCell (Secondary Cell) being a FDD (Frequency Division Duplex) serving cell;
• and
• monitoring re-transmission of the data starting from a subframe n+k+4 via the SCell, if the PCell (Primary Cell) is a TDD (Time Division Duplex) serving cell,
• wherein k is an interval between downlink data transmission on the SCell and a transmission of HARQ (Hybrid-ARQ) feedback associated with the downlink data transmission on the PCell.

A base station (BS) operating in a wireless communication system, the BS comprising:

• a RF (Radio Frequency) unit;
• and
• a processor configured to control the RF unit,
• wherein the processor is configured to configure a plurality of cells including at least one FDD (Frequency Division Duplex) serving cell and at least one TDD (Time Division Duplex) serving cell, to transmit data in subframe n via a SCell (Secondary Cell) being a FDD serving cell of the plurality of cells, and to re-transmit the data in subframe m via the SCell, if a PCell (Primary Cell) is a TDD serving cell of the plurality of cells, wherein m is equal to or greater than n+k+4, wherein k is an interval between downlink transmission and transmission of associated HARQ (Hybrid-ARQ) feedback.

A user equipment (UE) operating in a wireless communication system, the UE comprising:

• a RF (Radio Frequency) unit;
• and
• a processor configured to control the RF unit,
• wherein the processor is configured to receive data in subframe n via a SCell (Secondary Cell) being a FDD (Frequency Division Duplex) serving cell, and to monitor re-transmission of the data starting from a subframe n+k+4 via the SCell, if the PCell (Primary Cell) is a TDD serving cell, wherein k is an interval between downlink data transmission on the SCell and a transmission of HARQ (Hybrid-ARQ) feedback associated with the downlink data transmission on the PCell.