It is provided a method, comprising instructing a first cell to transmit a first packet data unit to a terminal on a first active bandwidth part of a first carrier of the first cell in a first frame and to instruct a second cell to transmit a second packet data unit to the terminal on a second active bandwidth part of a second carrier of the second cell in a second frame; wherein the first and second bandwidth parts have first and second bandwidth part identifiers, respectively; if the first cell is the same as the second cell: the first and second bandwidth part identifiers are different from each other, and the first and second system frame numbers are the same; and if the first cell is different from the second cell: a frequency range of the first carrier is the same as the frequency range of the second carrier.