A communication device of handling at least one cyclic prefix, CP, comprising: a storage unit, for storing instructions; and a processing means, coupled to the storage unit, wherein the storage unit stores, and the processing means is configured to execute, all the following instructions of: performing a first communication operation with a base station, BS, according to at least one first CP which has at least one first format; performing a second communication operation with the BS according to a control signal, if receiving the control signal from the BS, the control signal indicating A) at least one second CP which has at least one second format, or B) no CP, wherein the second communication operation with the BS is performed using either A) or B), wherein the control signal, indicating the at least one second CP or no CP, is received according to the at least one first CP, and wherein the at least one first format is different from the at least one second format; and performing the second communication operation with the BS according to the at least one first CP, if the control signal is not received from the BS; and wherein the second communication operation with the BS comprises transmitting an uplink transmission using the at least one second CP if A) is indicated and using no CP if B) is indicated in the control signal. a storage unit, for storing instructions; and a processing means, coupled to the storage unit, wherein the storage unit stores, and the processing means is configured to execute, all the following instructions of: performing a first communication operation with a base station, BS, according to at least one first CP which has at least one first format; performing a second communication operation with the BS according to a control signal, if receiving the control signal from the BS, the control signal indicating A) at least one second CP which has at least one second format, or B) no CP, wherein the second communication operation with the BS is performed using either A) or B), wherein the control signal, indicating the at least one second CP or no CP, is received according to the at least one first CP, and wherein the at least one first format is different from the at least one second format; and performing the second communication operation with the BS according to the at least one first CP, if the control signal is not received from the BS; and wherein the second communication operation with the BS comprises transmitting an uplink transmission using the at least one second CP if A) is indicated and using no CP if B) is indicated in the control signal. performing a first communication operation with a base station, BS, according to at least one first CP which has at least one first format; performing a second communication operation with the BS according to a control signal, if receiving the control signal from the BS, the control signal indicating A) at least one second CP which has at least one second format, or B) no CP, wherein the second communication operation with the BS is performed using either A) or B), wherein the control signal, indicating the at least one second CP or no CP, is received according to the at least one first CP, and wherein the at least one first format is different from the at least one second format; and performing the second communication operation with the BS according to the at least one first CP, if the control signal is not received from the BS; and wherein the second communication operation with the BS comprises transmitting an uplink transmission using the at least one second CP if A) is indicated and using no CP if B) is indicated in the control signal.