A method for transmitting Acknowledgement/Negative Acknowledgement, ACK/NACK, bits for Long Term Evolution, LTE, or Long Term Evolution-Advanced, LTE-A, carrier aggregation between a first cell (602, 604) and a second cell (604, 602) by a User Equipment, UE,, wherein the first cell and the second cell are of a different uplink-downlink, UL-DL, configuration, the method comprising: for a sub-frame, comparing a first number of ACK/NACK bits for the first cell with a second number of ACK/NACK bits for the second cell, wherein the second number is greater than the first number; and setting an average number being an average of the first number of ACK/NACK bits for the first cell and the second number of ACK/NACK bits for the second cell, while rounding up if necessary, if the second number minus the first number is equal to one, append an extra bit position to the ACK/NACK bits of the first cell, if the second number minus the first number is greater than one, adjusting the ACK/NACK bits between the first cell and the second cell, whereby after adjusting: the number of ACK/NACK bits for the second cell is equal to the average number, the number of ACK/NACK bits for the first cell is the first number plus an extra number of ACK/NACK bits, wherein the extra number is equal to the second number minus the average number, if the number of the adjusted ACK/NACK bits for the first cell is smaller than the average number, append a DTX bit to the adjusted ACK/NACK bits for the first cell, transmitting one or more ACK/NACK bits for the second cell using the extra number of an ACK/NACK bit position from the first cell, in the same order as they were ordered in the second number of ACK/NACK bits for the second cell, the one or more bits starting immediately after the first number of the ACK/NACK bits from the first cell. for a sub-frame, comparing a first number of ACK/NACK bits for the first cell with a second number of ACK/NACK bits for the second cell, wherein the second number is greater than the first number; and setting an average number being an average of the first number of ACK/NACK bits for the first cell and the second number of ACK/NACK bits for the second cell, while rounding up if necessary, if the second number minus the first number is equal to one, append an extra bit position to the ACK/NACK bits of the first cell, if the second number minus the first number is greater than one, adjusting the ACK/NACK bits between the first cell and the second cell, whereby after adjusting: the number of ACK/NACK bits for the second cell is equal to the average number, the number of ACK/NACK bits for the first cell is the first number plus an extra number of ACK/NACK bits, wherein the extra number is equal to the second number minus the average number, if the number of the adjusted ACK/NACK bits for the first cell is smaller than the average number, append a DTX bit to the adjusted ACK/NACK bits for the first cell, transmitting one or more ACK/NACK bits for the second cell using the extra number of an ACK/NACK bit position from the first cell, in the same order as they were ordered in the second number of ACK/NACK bits for the second cell, the one or more bits starting immediately after the first number of the ACK/NACK bits from the first cell. the number of ACK/NACK bits for the second cell is equal to the average number, the number of ACK/NACK bits for the first cell is the first number plus an extra number of ACK/NACK bits, wherein the extra number is equal to the second number minus the average number, if the number of the adjusted ACK/NACK bits for the first cell is smaller than the average number, append a DTX bit to the adjusted ACK/NACK bits for the first cell, transmitting one or more ACK/NACK bits for the second cell using the extra number of an ACK/NACK bit position from the first cell, in the same order as they were ordered in the second number of ACK/NACK bits for the second cell, the one or more bits starting immediately after the first number of the ACK/NACK bits from the first cell.