A method for performing a communication, the method executed by a user equipment, UE, supporting a carrier aggregation and a shortened processing time in a wireless communication system, the method being characterized by: reporting (S510), to a base station, BS, capability information based on the carrier aggregation configured for the UE, wherein the capability information comprises information indicating whether the UE supports the shortened processing time, information indicating a maximum number of carriers for which the shortened processing time is supported per band combination, and information indicating whether the UE supports a short transmission time interval, TTI, less than 1 msec; based on the UE supporting the short TTI, receiving, through a higher layer signal, configuration information indicating a length of a downlink short TTI and the length of an uplink short TTI; and performing (S530) uplink, UL, transmission to the BS according to the shortened processing time, wherein the processing time is - a time from a downlink, DL, data transmission to DL hybrid automatic repeat request, HARQ, feedback transmission or - a time from a UL grant transmission to UL data transmission, wherein the uplink transmission is the DL HARQ feedback transmission or the UL data transmission, wherein the length of the downlink short TTI and the length of the uplink short TTI are configured to be same for cells of a physical uplink control channel, PUCCH, cell group, and wherein the length of the downlink short TTI and the length of the uplink short TTI are configured to be same or different for cells of different PUCCH cell groups. reporting (S510), to a base station, BS, capability information based on the carrier aggregation configured for the UE, wherein the capability information comprises information indicating whether the UE supports the shortened processing time, information indicating a maximum number of carriers for which the shortened processing time is supported per band combination, and information indicating whether the UE supports a short transmission time interval, TTI, less than 1 msec; based on the UE supporting the short TTI, receiving, through a higher layer signal, configuration information indicating a length of a downlink short TTI and the length of an uplink short TTI; and performing (S530) uplink, UL, transmission to the BS according to the shortened processing time, wherein the processing time is - a time from a downlink, DL, data transmission to DL hybrid automatic repeat request, HARQ, feedback transmission or - a time from a UL grant transmission to UL data transmission, - a time from a downlink, DL, data transmission to DL hybrid automatic repeat request, HARQ, feedback transmission or - a time from a UL grant transmission to UL data transmission, wherein the uplink transmission is the DL HARQ feedback transmission or the UL data transmission, wherein the length of the downlink short TTI and the length of the uplink short TTI are configured to be same for cells of a physical uplink control channel, PUCCH, cell group, and wherein the length of the downlink short TTI and the length of the uplink short TTI are configured to be same or different for cells of different PUCCH cell groups. <EOS>