PROBLEM TO BE SOLVED: To provide a distributed radio communication base station system, a signal processing device, a radio device and a method for estimating signal distribution in an optical section, capable of accurately estimating channel quality in the optical section without once suspending the transmission/reception of a radio signal.SOLUTION: In regard to a downlink direction, channel quality estimation only in an optical section is performed using a reference signal of a radio signal (downlink) or the radio signal (downlink) itself transmitted through the optical section. In regard to an uplink direction, channel quality estimation only in an optical section is performed using a difference between a distortion, generated in the reference signal of the radio signal (downlink) or the radio signal (downlink) itself transmitted through the radio section, and a distortion generated in the reference signal of the radio signal (downlink) or the radio signal (downlink) itself transmitted through the optical
