A distributed antenna system (400, 500, 600, 700), comprising one or more access units (410-1 to 410-n, 601-1 to 601-n) configured to receive multiple downlink radio frequency signal sets from at least one base station, and the one or more access units (410-1 to 410-n, 601-1 to 601-n) further configured to convert the multiple downlink radio frequency signal sets into multiple downlink optical signal sets; a first wavelength division multiplexing unit (420, 520, 602), coupled to the one or more access units (410-1 to 410-n, 601-1 to 601-n), and configured to multiplex the multiple downlink optical signal sets to generate first wavelength division multiplexing optical signals; a first wavelength division demultiplexing unit (440, 540, 604) configured to demultiplex the first wavelength division multiplexing optical signals to obtain the multiple downlink optical signal sets; a first optical fiber (430, 530, 603), coupled between the first wavelength division multiplexing unit (420, 520, 602) and the first wavelength division demultiplexing unit (440, 540, 604), and configured to transmit the first wavelength division multiplexing optical signals; and one or more first remote units (450-1 to 450-n, 605-1 to 605-n), coupled to the first wavelength division demultiplexing unit (440, 540, 604), and configured to convert the multiple downlink optical signal sets into the multiple downlink radio frequency signal sets for transmission; wherein each of the multiple access units (410-1 to 410-n, 601-1 to 601-n) is configured to receive a corresponding downlink radio frequency signal set from the at least one base station, and the corresponding downlink radio frequency signal set includes a multi-channel downlink radio frequency signals for MIMO, and each access unit (410-1 to 410-n, 601-1 to 601-n) is further configured to convert the multi-channel downlink radio frequency signals into a downlink optical signal set, and the downlink optical signal set includes multiple downlink optical signals, and the number of multiple downlink optical signals is the same as the number of channel of the multi-channel downlink radio frequency signals; and each of the one or more first remote units (450-1 to 450-n, 605-1 to 605-n) is configured to convert multiple downlink optical signals in a corresponding downlink optical signal set into the downlink radio frequency signal set for transmission. one or more access units (410-1 to 410-n, 601-1 to 601-n) configured to receive multiple downlink radio frequency signal sets from at least one base station, and the one or more access units (410-1 to 410-n, 601-1 to 601-n) further configured to convert the multiple downlink radio frequency signal sets into multiple downlink optical signal sets; a first wavelength division multiplexing unit (420, 520, 602), coupled to the one or more access units (410-1 to 410-n, 601-1 to 601-n), and configured to multiplex the multiple downlink optical signal sets to generate first wavelength division multiplexing optical signals; a first wavelength division demultiplexing unit (440, 540, 604) configured to demultiplex the first wavelength division multiplexing optical signals to obtain the multiple downlink optical signal sets; a first optical fiber (430, 530, 603), coupled between the first wavelength division multiplexing unit (420, 520, 602) and the first wavelength division demultiplexing unit (440, 540, 604), and configured to transmit the first wavelength division multiplexing optical signals; and one or more first remote units (450-1 to 450-n, 605-1 to 605-n), coupled to the first wavelength division demultiplexing unit (440, 540, 604), and configured to convert the multiple downlink optical signal sets into the multiple downlink radio frequency signal sets for transmission; wherein each of the multiple access units (410-1 to 410-n, 601-1 to 601-n) is configured to receive a corresponding downlink radio frequency signal set from the at least one base station, and the corresponding downlink radio frequency signal set includes a multi-channel downlink radio frequency signals for MIMO, and each access unit (410-1 to 410-n, 601-1 to 601-n) is further configured to convert the multi-channel downlink radio frequency signals into a downlink optical signal set, and the downlink optical signal set includes multiple downlink optical signals, and the number of multiple downlink optical signals is the same as the number of channel of the multi-channel downlink radio frequency signals; and each of the one or more first remote units (450-1 to 450-n, 605-1 to 605-n) is configured to convert multiple downlink optical signals in a corresponding downlink optical signal set into the downlink radio frequency signal set for transmission.