A method implemented in a first communication device of an OFDM-based communication system, the method comprising: generating a control frame having a bandwidth; causing the control frame to be transmitted via a first composite communication channel having the bandwidth of the control frame, wherein the first composite communication channel comprises a plurality of communication channels (62, 64, 66, 68); determining a bandwidth of a response frame received from a second communication device in response to transmitting the control frame, said bandwidth being determined by determining in which communication channels the response frame was received; determining a set of one or more communication channels of the plurality of communication channels (62, 64, 66, 68) as being idle, from a standpoint of the first and the second communication device (14, 25), on the basis of the communication channels in which the response frame was received; determining a second composite communication channel based on the set of communication channels determined as being idle, wherein the second composite communication channel comprises at least one communication channel from the plurality of communication channels (62, 64, 66, 68), and wherein the second composite communication channel is for transmitting in a transmit opportunity period, TXOP, of the first communication device; causing one or more data frames to be transmitted to the second communication device via the second composite communication channel during the TXOP; generating a subsequent control frame having a bandwidth different than the bandwidth of the second composite communication channel; causing the subsequent control frame to be transmitted during the TXOP via a third composite communication channel having the bandwidth of the subsequent control frame; determining a bandwidth of a subsequent response frame received in response to transmitting the subsequent control frame; determining a fourth composite communication channel based on the bandwidth of the subsequent response frame; and causing one or more subsequent data frames to be transmitted during the TXOP via the fourth composite communication channel. generating a control frame having a bandwidth; causing the control frame to be transmitted via a first composite communication channel having the bandwidth of the control frame, wherein the first composite communication channel comprises a plurality of communication channels (62, 64, 66, 68); determining a bandwidth of a response frame received from a second communication device in response to transmitting the control frame, said bandwidth being determined by determining in which communication channels the response frame was received; determining a set of one or more communication channels of the plurality of communication channels (62, 64, 66, 68) as being idle, from a standpoint of the first and the second communication device (14, 25), on the basis of the communication channels in which the response frame was received; determining a second composite communication channel based on the set of communication channels determined as being idle, wherein the second composite communication channel comprises at least one communication channel from the plurality of communication channels (62, 64, 66, 68), and wherein the second composite communication channel is for transmitting in a transmit opportunity period, TXOP, of the first communication device; causing one or more data frames to be transmitted to the second communication device via the second composite communication channel during the TXOP; generating a subsequent control frame having a bandwidth different than the bandwidth of the second composite communication channel; causing the subsequent control frame to be transmitted during the TXOP via a third composite communication channel having the bandwidth of the subsequent control frame; determining a bandwidth of a subsequent response frame received in response to transmitting the subsequent control frame; determining a fourth composite communication channel based on the bandwidth of the subsequent response frame; and causing one or more subsequent data frames to be transmitted during the TXOP via the fourth composite communication channel.