A signal transmission method, wherein the method comprises: determining, by a base station, a first carrier signal that is to be sent in a first cell on a first carrier and a second carrier signal that is to be sent in a second cell on a second carrier; mapping, by the base station, the first carrier signal and the second carrier signal to N physical ports of a remote radio unit, RRU, so that within a same orthogonal frequency division multiplexing, OFDM symbol, a type B symbol that is used to transmit a pilot in the first carrier signal and a type B symbol that is used to transmit a pilot in the second carrier signal are mapped to different physical ports, wherein the type B symbol represents a symbol that has a pilot position, and a total power of signals sent on each of N physical channels is not greater than a rated power of the RRU; and sending, by the base station, the first carrier signal and the second carrier signal through the N physical ports, wherein the first carrier signal corresponds to N antenna ports, and the second carrier signal corresponds to N antenna ports; and the mapping, by the base station, the first carrier signal and the second carrier signal to N physical ports of a remote radio unit, RRU comprises: mapping, by the base station, the N antenna ports corresponding to the first carrier signal and the N antenna ports corresponding to the second carrier signal to the N physical ports, so that within the same OFDM symbol, an antenna port for sending the type B symbol that is used to transmit a pilot in the first carrier signal and an antenna port for sending a type B symbol that is not used to transmit a pilot in the second carrier signal are mapped to a same physical port, wherein the type B symbol that is used to transmit a pilot has a higher power than the type B symbol that is not used to transmit a pilot. determining, by a base station, a first carrier signal that is to be sent in a first cell on a first carrier and a second carrier signal that is to be sent in a second cell on a second carrier; mapping, by the base station, the first carrier signal and the second carrier signal to N physical ports of a remote radio unit, RRU, so that within a same orthogonal frequency division multiplexing, OFDM symbol, a type B symbol that is used to transmit a pilot in the first carrier signal and a type B symbol that is used to transmit a pilot in the second carrier signal are mapped to different physical ports, wherein the type B symbol represents a symbol that has a pilot position, and a total power of signals sent on each of N physical channels is not greater than a rated power of the RRU; and sending, by the base station, the first carrier signal and the second carrier signal through the N physical ports, wherein the first carrier signal corresponds to N antenna ports, and the second carrier signal corresponds to N antenna ports; and the mapping, by the base station, the first carrier signal and the second carrier signal to N physical ports of a remote radio unit, RRU comprises: mapping, by the base station, the N antenna ports corresponding to the first carrier signal and the N antenna ports corresponding to the second carrier signal to the N physical ports, so that within the same OFDM symbol, an antenna port for sending the type B symbol that is used to transmit a pilot in the first carrier signal and an antenna port for sending a type B symbol that is not used to transmit a pilot in the second carrier signal are mapped to a same physical port, wherein the type B symbol that is used to transmit a pilot has a higher power than the type B symbol that is not used to transmit a pilot.