To realize a high-speed and high-capacity transmission link for fast mobile vehicles such as a bullet train, we propose a wavelength-division-multiplexing radio-on-radio-over-fiber (WDM-RoRoF) system with a linearly located distributed antenna system (DAS) on the 90-GHz band. All the conventional microwave (MW) radio signals such as mobile telecommunication and broadcast signals are encapsulated in a single millimeter-wave (MMW) carrier radio. Centralized control at a central office using the information of the position of a car can optimize and distribute the suitable RoRoF signal to each remote cell over optical fibers. An optical two-tone generator with an optical modulator can easily generate a 90-GHz RoRoF signal, and then, a high-speed photomixer directly converts from an RoRoF signal to an MMW RoR signal, which is composed of an MW signal with a 90-GHz carrier component, for irradiation over air. Heterodyne frequency down-conversion performs the direct frequency conversion from the MMW signal to an MW signal available to consumers.