A signal transmission method performed by a first device, the method comprising: • mapping a first reference signal, the first reference signal being a phase tracking reference signal, PT-RS, to a first symbol according to a time-domain density of the first reference signal and according to a time-domain mapping rule of the first reference signal, the time-domain mapping rule being predefined by a protocol, ∘ wherein the time-domain density is determined based on at least one of a cyclic prefix, CP, type of the first reference signal, a subcarrier spacing of the first reference signal, and a modulation and coding scheme, MCS, of the first reference signal, ▪ wherein different CP types correspond to different time-domain densities of the first reference signal, ▪ wherein different subcarrier spacings correspond to different time-domain densities of the first reference signal, and ▪ wherein different MCSs correspond to different time-domain densities of the first reference signal, ∘ wherein the first symbol is a symbol that carries a physical downlink shared channel, PDSCH, and a physical downlink control channel, PDCCH, and that precedes, in the time-domain, a second symbol, and the second symbol is, in the time-domain, a starting symbol carrying a demodulation reference signal, DMRS, ∘ wherein the first reference signal, the PDSCH and the PDCCH are arranged in a manner of frequency-division multiplexing in the first symbol, and, in the frequency-domain, the first reference signal is mapped to a resource other than a resource for the PDCCH in the first symbol; • sending (S 102) the first reference signal to a second device on the first symbol. • mapping a first reference signal, the first reference signal being a phase tracking reference signal, PT-RS, to a first symbol according to a time-domain density of the first reference signal and according to a time-domain mapping rule of the first reference signal, the time-domain mapping rule being predefined by a protocol, ∘ wherein the time-domain density is determined based on at least one of a cyclic prefix, CP, type of the first reference signal, a subcarrier spacing of the first reference signal, and a modulation and coding scheme, MCS, of the first reference signal, ▪ wherein different CP types correspond to different time-domain densities of the first reference signal, ▪ wherein different subcarrier spacings correspond to different time-domain densities of the first reference signal, and ▪ wherein different MCSs correspond to different time-domain densities of the first reference signal, ∘ wherein the first symbol is a symbol that carries a physical downlink shared channel, PDSCH, and a physical downlink control channel, PDCCH, and that precedes, in the time-domain, a second symbol, and the second symbol is, in the time-domain, a starting symbol carrying a demodulation reference signal, DMRS, ∘ wherein the first reference signal, the PDSCH and the PDCCH are arranged in a manner of frequency-division multiplexing in the first symbol, and, in the frequency-domain, the first reference signal is mapped to a resource other than a resource for the PDCCH in the first symbol; ∘ wherein the time-domain density is determined based on at least one of a cyclic prefix, CP, type of the first reference signal, a subcarrier spacing of the first reference signal, and a modulation and coding scheme, MCS, of the first reference signal, ▪ wherein different CP types correspond to different time-domain densities of the first reference signal, ▪ wherein different subcarrier spacings correspond to different time-domain densities of the first reference signal, and ▪ wherein different MCSs correspond to different time-domain densities of the first reference signal, ▪ wherein different CP types correspond to different time-domain densities of the first reference signal, ▪ wherein different subcarrier spacings correspond to different time-domain densities of the first reference signal, and ▪ wherein different MCSs correspond to different time-domain densities of the first reference signal, ∘ wherein the first symbol is a symbol that carries a physical downlink shared channel, PDSCH, and a physical downlink control channel, PDCCH, and that precedes, in the time-domain, a second symbol, and the second symbol is, in the time-domain, a starting symbol carrying a demodulation reference signal, DMRS, ∘ wherein the first reference signal, the PDSCH and the PDCCH are arranged in a manner of frequency-division multiplexing in the first symbol, and, in the frequency-domain, the first reference signal is mapped to a resource other than a resource for the PDCCH in the first symbol; • sending (S 102) the first reference signal to a second device on the first symbol.