In wireless communications, an access point may send a trigger frame to multiple stations. The trigger frame's payload may include a first content and a second content, where the first content is associated with a legacy signal field of an uplink frame, and the second content is associated with a non-legacy signal field of the uplink frame. In response to the trigger frame, one or more stations may generate the uplink frame(s) based on the trigger frame and transmit the uplink frame(s) to the access point. The uplink frame(s) may include a legacy signal field and a non-legacy signal field. The legacy field may include a length of the uplink frame(s) that is based on the first content. The non-legacy signal field may include a remaining transmission opportunity (TXOP) duration that is generated based on the second content. Other methods, apparatus, and computer-readable media are also disclosed.