A communications device, wherein the communications device comprises a baseband unit BBU and a remote radio unit RRU that has n physical antenna or physical antennas; the BBU and the RRU are connected by using an optical fiber; the n is 1 or 2; the BBU is configured to: acquire four channels of signals; generate a baseband digital signal based on at least two channels of signals in the four channels of signals; transmit the baseband digital signal to the RRU through the optical fiber, wherein the four channels of signals are in a one-to-one correspondence with four logical ports of the BBU; and the RRU is configured to convert the baseband digital signal into a radio-frequency signal, and transmit the radio-frequency signal by using the n physical antenna or physical antennas; and a) wherein the n is 1, and that the BBU is configured to generate a baseband digital signal based on at least two channels of signals in the four channels of signals comprises: that the BBU is configured to generate the baseband digital signal by adding up m channels of signals in the four channels of signals, wherein the m is 2, or 3, or 4; or b) wherein the n is 2 and the baseband digital signal comprises a first baseband digital signal and a second baseband digital signal, and that the BBU is configured to generate a baseband digital signal based on at least two channels of signals in the four channels of signals comprises: that the BBU is configured to generate the first baseband digital signal by adding up two channels of signals of the four channels of signals, and generate the second baseband digital signal by adding up the other two channels of signals of the four channels of signals; or that the BBU is configured to use one channel of signal of the four channels of signals as the first baseband digital signal, and use another channel of signal of the four channels of signals as the second baseband digital signal. a) wherein the n is 1, and that the BBU is configured to generate a baseband digital signal based on at least two channels of signals in the four channels of signals comprises: that the BBU is configured to generate the baseband digital signal by adding up m channels of signals in the four channels of signals, wherein the m is 2, or 3, or 4; or b) wherein the n is 2 and the baseband digital signal comprises a first baseband digital signal and a second baseband digital signal, and that the BBU is configured to generate a baseband digital signal based on at least two channels of signals in the four channels of signals comprises: that the BBU is configured to generate the first baseband digital signal by adding up two channels of signals of the four channels of signals, and generate the second baseband digital signal by adding up the other two channels of signals of the four channels of signals; or that the BBU is configured to use one channel of signal of the four channels of signals as the first baseband digital signal, and use another channel of signal of the four channels of signals as the second baseband digital signal. that the BBU is configured to generate the first baseband digital signal by adding up two channels of signals of the four channels of signals, and generate the second baseband digital signal by adding up the other two channels of signals of the four channels of signals; or that the BBU is configured to use one channel of signal of the four channels of signals as the first baseband digital signal, and use another channel of signal of the four channels of signals as the second baseband digital signal.