A multi-access RF communication system in which a plurality of mobile user transceivers (MU) communicate with a central hub transceiver (MCU) through an earth orbiting satellite, and wherein groups of mobile user transceivers (MU1, MU2) in close proximity with each other share a common multi-access inbound (to hub) frequency F1 and a common outbound channel (from hub) frequency F0. Each said mobile user transceiver includes a continuously listening receiver for the outbound channel and a half-duplex transceiver on the inbound channel, determining the status of the common inbound frequency F0, and a device to indicate the status of the carrier outbound channel, which controls the ability to transmit on the inbound channel.
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