A communication device for performing data transmission in bandwidth parts, BWPs, in a new radio, NR, system developed in 3 rd generation partnership project, 3GPP, the communication device comprising: a storage device; and a processing circuit, coupled to the storage device, wherein the storage device stores, and the processing circuit is configured to execute instructions of: receiving a first command from a base station, BS, in a first BWP, wherein the first command comprises a first Hybrid Automatic Repeat Request, HARQ, process number and a first uplink, UL, grant which assigns at least one first physical resource block, PRB; transmitting a first transmission to the BS on the at least one first PRB according to a first HARQ process of a first HARQ entity, wherein the communication device associates the first HARQ process to the first HARQ process number; receiving a second command from the BS in a second BWP, wherein the second command comprises a second HARQ process number and a second UL grant which assigns at least one second PRB; transmitting a second transmission to the BS on the at least second PRB according to a second HARQ process of the first HARQ entity, wherein the communication device associates the second HARQ process to the second HARQ process number; receiving a third command from the BS in a third BWP, wherein the third command comprises the first HARQ process number and a third UL grant which assigns at least one third PRB; associating a first HARQ process of a second HARQ entity to the first HARQ process number; and transmitting a third transmission to the BS on the at least one third PRB according to a first HARQ process of a second HARQ entity; wherein the first and second BWP belong to a first carrier or cell and the third BWP belongs to a second carrier or cell different from the first carrier or cell. a storage device; and a processing circuit, coupled to the storage device, wherein the storage device stores, and the processing circuit is configured to execute instructions of: receiving a first command from a base station, BS, in a first BWP, wherein the first command comprises a first Hybrid Automatic Repeat Request, HARQ, process number and a first uplink, UL, grant which assigns at least one first physical resource block, PRB; transmitting a first transmission to the BS on the at least one first PRB according to a first HARQ process of a first HARQ entity, wherein the communication device associates the first HARQ process to the first HARQ process number; receiving a second command from the BS in a second BWP, wherein the second command comprises a second HARQ process number and a second UL grant which assigns at least one second PRB; transmitting a second transmission to the BS on the at least second PRB according to a second HARQ process of the first HARQ entity, wherein the communication device associates the second HARQ process to the second HARQ process number; receiving a third command from the BS in a third BWP, wherein the third command comprises the first HARQ process number and a third UL grant which assigns at least one third PRB; associating a first HARQ process of a second HARQ entity to the first HARQ process number; and transmitting a third transmission to the BS on the at least one third PRB according to a first HARQ process of a second HARQ entity; receiving a first command from a base station, BS, in a first BWP, wherein the first command comprises a first Hybrid Automatic Repeat Request, HARQ, process number and a first uplink, UL, grant which assigns at least one first physical resource block, PRB; transmitting a first transmission to the BS on the at least one first PRB according to a first HARQ process of a first HARQ entity, wherein the communication device associates the first HARQ process to the first HARQ process number; receiving a second command from the BS in a second BWP, wherein the second command comprises a second HARQ process number and a second UL grant which assigns at least one second PRB; transmitting a second transmission to the BS on the at least second PRB according to a second HARQ process of the first HARQ entity, wherein the communication device associates the second HARQ process to the second HARQ process number; receiving a third command from the BS in a third BWP, wherein the third command comprises the first HARQ process number and a third UL grant which assigns at least one third PRB; associating a first HARQ process of a second HARQ entity to the first HARQ process number; and transmitting a third transmission to the BS on the at least one third PRB according to a first HARQ process of a second HARQ entity; wherein the first and second BWP belong to a first carrier or cell and the third BWP belongs to a second carrier or cell different from the first carrier or cell.