In accordance with the exemplary embodiments of the invention there is at least a method, computer program, and apparatus for operating a receiver using at least four carriers to receive transport blocks from a transmitter, to compose a first codeword to acknowledge at least one of a reception and a lack of reception of individual transport blocks in a first part of the at least four carriers, to compose a second codeword to acknowledge at least one of a reception and a lack of reception of individual transport blocks in a second part of the at least four carriers, and to transmit the first codeword and the second codeword to the transmitter during one slot.