Embodiments of this application disclose a communication method, a related device, and a system. The method includes: receiving, by a network device, a first preamble sequence that is sent by a first terminal in a time window; sending, by the network device, a response message to the first terminal based on the first preamble sequence; receiving, by the network device, a first message sent by the first terminal, where the first message includes information used to identify the first terminal; and sending, by the network device, a second message to a second terminal and the first terminal, where the second message is used to indicate that the first terminal and the second terminal belong to a same user equipment cooperative group. According to this application, efficiency of establishing a user equipment cooperative group can be improved.