FIG. 1 is a schematic diagram of an application scenario according to an embodiment of this application. The communication system may include a core network device, a network device, and at least one terminal device. For example, as shown in FIG. 1, A plurality of terminal devices share one paging subframe (Paging Occasion, PO) and a WUS before the PO. Therefore, provided that any terminal device belonging to the PO needs to be paged, another terminal device that is not paged also detects the WUS before the PO. To prevent a terminal device that is not paged from also detecting the WUS before the PO, a network device configures a plurality of wake up signals, where a configuration of the plurality of wake up signals includes a mapping relationship between group information and a wake up signal, and sends the configuration of the plurality of wake up signals to a terminal device, so that the terminal device may calculate, based on an identifier of the terminal device, a group to which the terminal device belongs, and then determine, based on the group and the mapping relationship, a wake up signal that needs to be monitored, so as to monitor the wake up signal, without a need to monitor a wake up signal corresponding to another group. In this way, when a terminal in a group needs to be paged, only a terminal device in the group detects the WUS before the PO, and a terminal device in another group does not detect the WUS before the PO, and therefore is not woken up. However, in this manner, only theoretically a quantity of woken-up terminal devices is decreased and a false alarm probability of paging is reduced, but another factor that affects wake-up of a terminal device is not considered.