This disclosure describes methods, apparatuses, and systems for signal transmission based on DCI. An example method includes: receiving DCI from a base station, the DCI includes a precoding matrix index, the precoding matrix index belongs to a first index set, wherein the precoding matrix index is used to determine a precoding matrix for transmitting data by the terminal device, each index in the first index set corresponds to a precoding matrix in a first precoding matrix set, a second precoding matrix set comprises a codebook, the first precoding matrix set is a proper subset of the second precoding matrix set, and each precoding matrix index in the first index set has a value that is less than or equal to a quantity of precoding matrices comprised in the first precoding matrix set; and transmitting, by the terminal device, the data according to the precoding matrix index.