A method for an access point (100, 450) 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 (102, 106, 108) using orthogonal frequency division multiple access - OFDMA - and to communicate with a plurality of second wireless communication devices (104, 110) 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 (221, 222, 223), 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 (221, 222, 223), 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.