Patent ID: 7715422

Claim:
A half-duplex radio communication method comprising: accepting an application from a sender terminal for multicasting data to a multicast group formed from each terminal of first radio communication terminals belonging to a first cellular network and second radio communication terminals belonging to a second cellular network whose present state meets a designated condition; automatically registering the present state of each terminal of the first radio communication terminals of the first cellular network and the second radio communication terminals of the second cellular network; and multicasting data from the sender terminal to the multicast group formed from each terminal of the first radio communication terminals of the first cellular network and the second radio communication terminals of the second cellular network when the present state of the respective terminal meets the designated condition, wherein the present state is a positional condition of each respective radio communication terminal, wherein the second cellular network is different from the first cellular network, and wherein forming the multicast group from each terminal of first radio communication terminals belonging to a first cellular network and second radio communication terminals belonging to a second cellular network whose present state meets a designated condition is based only on the positional condition of each respective radio communication terminal meeting the designated condition.