A method for an access point of a wireless communication network, wherein the access point is adapted to use a communication channel resource to communicate with a plurality of first wireless communication devices using orthogonal frequency division multiple access - OFDMA - and to communicate with a plurality of second wireless communication devices using carrier sense multiple access with collision avoidance - CSMA/CA, wherein the communication channel resource comprises a bandwidth of frequencies, the bandwidth of frequencies being dividable into a plurality of sub-carriers for OFDMA and a part of the bandwidth of frequencies forming a primary channel for CSMA/CA, the method comprising: transmitting a downlink packet over all frequencies of the bandwidth for triggering one or more of the first wireless communication devices to perform OFDMA based uplink transmission , wherein the downlink packet comprises an indication of an allocation of one or more sub-carriers to each of the triggered first wireless communication devices for the OFDMA based uplink transmission, the allocated sub-carriers for OFDMA and the primary channel for CSMA/CA being non-overlapping; receiving the OFDMA based uplink transmission from the triggered first wireless communication devices; and receiving a CSMA/CA based uplink transmission from one of the second wireless communication devices, wherein the CSMA/CA based uplink transmission and the OFDMA based uplink transmission at least partly overlap in time; characterized by, if an end of the CSMA/CA based uplink transmission is later than an end of the OFDMA based uplink transmission; delaying transmission of an acknowledgement message associated with the OFDMA based uplink transmission until after the end of the CSMA/CA based uplink transmission provided that a time interval between the end of the OFDMA based uplink transmission and the end of the CSMA/CA based uplink transmission is smaller than a maximum time interval. transmitting a downlink packet over all frequencies of the bandwidth for triggering one or more of the first wireless communication devices to perform OFDMA based uplink transmission , wherein the downlink packet comprises an indication of an allocation of one or more sub-carriers to each of the triggered first wireless communication devices for the OFDMA based uplink transmission, the allocated sub-carriers for OFDMA and the primary channel for CSMA/CA being non-overlapping; receiving the OFDMA based uplink transmission from the triggered first wireless communication devices; and receiving a CSMA/CA based uplink transmission from one of the second wireless communication devices, wherein the CSMA/CA based uplink transmission and the OFDMA based uplink transmission at least partly overlap in time; characterized by, if an end of the CSMA/CA based uplink transmission is later than an end of the OFDMA based uplink transmission; delaying transmission of an acknowledgement message associated with the OFDMA based uplink transmission until after the end of the CSMA/CA based uplink transmission provided that a time interval between the end of the OFDMA based uplink transmission and the end of the CSMA/CA based uplink transmission is smaller than a maximum time interval. <EOS>