Communicating between stations over a shared medium comprises: receiving a first waveform at a first station transmitted over the shared medium from a second station, the first waveform including a payload having multiple segments, and during reception of a first segment of the payload, initiating processing of one or more segments of the payload received before the first segment of the payload to generate acknowledgement information that specifies which of one or more segments of the payload including the one or more processed segments have been correctly decoded by the first station; transmitting a second waveform from the first station over the shared medium, the second waveform including the acknowledgement information; and transmitting a third waveform from the first station over the shared medium, after transmitting the second waveform, the third waveform including acknowledgement information that specifies which of one or more segments of the payload including the first segment of the payload have been correctly decoded by the first station.