The technology of this application relates to communications systems. In one example, a network device sends a first message to a terminal device, where the first message includes configuration information of a reference signal resource. The network device sends a second message to the terminal device, where the second message includes a first bit field and/or a second bit field, the first bit field is used to indicate an availability status of the reference signal resource, and the second bit field is used to indicate that the terminal device uses a synchronization signal/physical broadcast channel resource block signal resource and/or the reference signal resource.