MOBILE RADIO GROUP COMMUNICATIONS BY SATELLITE

Mobile radio group communications enable a closed group of users to co mmunicate among themselves using push-to-talk (PTT), half duplex trans missions, such that one's transmission is received by all. This paper presents new protocol designs which support group communications over mobile satellite systems. A new demand assignment multiple access (DAM A) protocol is necessitated by the inappropriateness of call-based cha nnel assignments. Channels are assigned to individual user-groups enga ged in active conversations. As members of a user-group contend for ac cess to the assigned channel, access control by the usual manual metho ds is ineffective due to the very long round trip delay. A novel signa ling protocol which automates access control is proposed. Carrier sens ing, signal capture, and collision detection are employed to minimize access contentions. The throughput and holding time of the assigned ch annel are analyzed. Numerical results show that the access control pro tocol improves the capacity of the assigned channel by up to 65%.