A method of a User Equipment, UE, in a mobile communication system, the method comprising: determining whether the UE transmits a physical uplink shared channel, PUSCH, and a physical uplink control channel, PUCCH on a primary cell; determining a first maximum uplink transmission power for a Type 1 power headroom, PH, and a second maximum uplink transmission power for a Type 2 PH with respect to the primary cell based on at least one of cell specific maximum allowed transmission power and UE specific maximum allowed transmission power, wherein the first maximum uplink transmission power and the second maximum uplink transmission power are a real maximum uplink transmission power if the UE transmits the PUSCH with the PUCCH or if the UE transmits the PUSCH without the PUCCH, wherein the first maximum uplink transmission power and the second maximum uplink transmission power are a reference maximum uplink transmission power with back-off parameters being zero if the UE does not transmit the PUSCH and the PUCCH, and wherein the first maximum uplink transmission power is the reference maximum uplink transmission power and the second maximum uplink transmission power is the real maximum uplink transmission power if the UE transmits the PUCCH without the PUSCH; calculating the Type 1 PH based on the first maximum uplink transmission power and the Type 2 PH based on the second maximum uplink transmission power with respect to the primary cell; and transmitting a power headroom report, PHR, for at least one cell to a base station, the PHR including the type 1 PH and the type 2 PH with respect to the primary cell among the at least one cell, wherein the back-off parameters include Maximum Power Reduction, MPR, Additional-MPR, A-MPR, and an operating band edge transmission relaxation value. determining whether the UE transmits a physical uplink shared channel, PUSCH, and a physical uplink control channel, PUCCH on a primary cell; determining a first maximum uplink transmission power for a Type 1 power headroom, PH, and a second maximum uplink transmission power for a Type 2 PH with respect to the primary cell based on at least one of cell specific maximum allowed transmission power and UE specific maximum allowed transmission power, wherein the first maximum uplink transmission power and the second maximum uplink transmission power are a real maximum uplink transmission power if the UE transmits the PUSCH with the PUCCH or if the UE transmits the PUSCH without the PUCCH, wherein the first maximum uplink transmission power and the second maximum uplink transmission power are a reference maximum uplink transmission power with back-off parameters being zero if the UE does not transmit the PUSCH and the PUCCH, and wherein the first maximum uplink transmission power is the reference maximum uplink transmission power and the second maximum uplink transmission power is the real maximum uplink transmission power if the UE transmits the PUCCH without the PUSCH; wherein the first maximum uplink transmission power and the second maximum uplink transmission power are a real maximum uplink transmission power if the UE transmits the PUSCH with the PUCCH or if the UE transmits the PUSCH without the PUCCH, wherein the first maximum uplink transmission power and the second maximum uplink transmission power are a reference maximum uplink transmission power with back-off parameters being zero if the UE does not transmit the PUSCH and the PUCCH, and wherein the first maximum uplink transmission power is the reference maximum uplink transmission power and the second maximum uplink transmission power is the real maximum uplink transmission power if the UE transmits the PUCCH without the PUSCH; calculating the Type 1 PH based on the first maximum uplink transmission power and the Type 2 PH based on the second maximum uplink transmission power with respect to the primary cell; and transmitting a power headroom report, PHR, for at least one cell to a base station, the PHR including the type 1 PH and the type 2 PH with respect to the primary cell among the at least one cell, wherein the back-off parameters include Maximum Power Reduction, MPR, Additional-MPR, A-MPR, and an operating band edge transmission relaxation value.