Acknowledgment of uplink orthogonal frequency division multiple access transmission

An apparatus, comprising:

• a network interface device associated with a first communication device, the network interface device having one or more integrated circuits configured to:
• receive an uplink orthogonal frequency multiple access (OFDMA) transmission, wherein the uplink OFDMA transmission includes respective transmissions from multiple second communication devices, wherein the respective transmissions from the multiple second communication devices include indications of respective acknowledgment policies corresponding to the respective transmissions from the multiple second communication devices,
• generate one or more acknowledgment physical layer (PHY) data units to acknowledge at least a portion of the uplink OFDMA transmission, and
• cause the first communication device to transmit the one or more acknowledgment PHY data units to acknowledge at least the portion of the uplink OFDMA transmission;
• wherein the one or more integrated circuits are further configured to:
• when one of the acknowledgment policies specifies that one of the transmissions in the uplink OFDMA transmission from one of the second communication devices is to be acknowledged beginning at a predetermined time period after an end of the uplink OFDMA transmission, transmitting another PHY data unit, following the reception of the uplink OFDMA transmission, that does not acknowledge the uplink OFDMA transmission prior to transmitting the one or more acknowledgment PHY data units.