This application discloses a signal transmission method, related devices, and a system. The method includes: sending, by a terminal, link reconfiguration request information to a network device at a moment n, where the link reconfiguration request information is used to initiate link reconfiguration; and detecting, by the terminal based on first information, a physical downlink control channel (PDCCH) during a first time period after the moment n. The first information includes QCL information of a first reference signal and a second reference signal. The first reference signal is used to demodulate the PDCCH. The second reference signal is a reference signal meeting a first threshold.