Aspects of the disclosure provide an apparatus that includes a transceiver circuit and a processing circuit. The transceiver circuit is configured to receive a trigger signal this is transmitted by another apparatus. The trigger signal triggers transmissions by a first group of apparatuses including the apparatus, and defers transmissions by a second group of apparatuses that interfere the transmissions by the first group of apparatuses. The processing circuit is configured to, in response to the trigger signal, generate a frame with a first preamble structure that is different from a second preamble structure that is used by the second group of apparatuses, and provide the generated frame to the transceiver circuit for transmission.