Next-generation LEO System Research Center (NeLS) has carried out the key technology development of global multimedia mobile satellite communications. In Phase I we studied the system definition and developed key technologies such as on-board active phased array antenna with digital beam forming, optical antenna, optical modem, wavelength division multiplexing for optical inter-satellite link system, satellite network, and variable rate modulation. In Phase 2, we plan to verify the developed technology in Phase 1 on space. In this paper, we introduce the results of development in Phase 1.