A method includes: receiving, by a first terminal device, a first downlink control channel on a third time-frequency resource; and based on the first downlink control channel and on a first time-frequency resource, sending, by the first terminal device, a first uplink message or receiving a first downlink message, where transmission directions of the first uplink message and a second downlink message are different, and the second downlink message is a message that the network device schedules a second terminal device to receive on a second time-frequency resource; transmission directions of the first downlink message and a second uplink message are different, and the second uplink message is a message that the network device schedules the second terminal device to send on the second time-frequency resource; and the first time-frequency resource and the second time-frequency resource include a same time domain resource and a same frequency domain resource.