Direct-Multicasting Satellite Communications System Using a new Multi-carrier and Multi-rate Modem

The Internet has become a global medium for communication, entertainment, and e-commerce. And there is increasing demand to deliver multimedia contents, such as audio and video data, from web sites to many customers simultaneously. The size of data to be delivered and the number of transmission points has been increasing recently. In this context satellite communication is thought to be effective network and communication infrastructure because it covers large area and easily provides high-speed service with great many reception points. A direct-multicasting satellite communications system was previously proposed to achieve a full mesh type satellite network economically and we developed the group modem, the efficient channel assignment control program, and the highly reliable multicasting program for it. This paper presents the architecture of the group modem that is used for direct-multicasting satellite communications system as a key technology of it.