Through electro optic modulator, local oscillation signal in double sideband is generated at controller of base station. Through filtering by grating of optical fiber, base station end obtains local oscillation signal in single sideband restrained by carrier. Through electro optic modulator, base station end carries out full photomixing between radio-frequency signal and local oscillation signal in single sideband. Through up going optical fiber link, the mixed optical signal is transferred to the controller of base station. Through photo detector and intermediate frequency filter, the controller of base station obtains signal in intermediate frequency of passing through down-conversion. Base station does not need local laser and local oscillation source of microwave, which are centralized at controller of base station. Thus, cost of system is lowered greatly. The invention prevents influence on quality of signal from effect of optical fiber dispersion, and raises SNR of system. |