Patent ID: 6999519

Claim:
A multicast radio system comprising a master station and a plurality of slave stations, the master station comprising means to transmit data to the plurality of slave stations simultaneously, each slave station comprising means to receive the data and means for determining whether it requires retransmission of the data, wherein at least one slave station is in a first state and the other one or more slave station are in a second state, wherein the at least one slave station in the first state, if retransmission is not required, transmits a positive acknowledgement in a predetermined time slot which is substantially non-overlapping with any positive acknowledgement transmitted by any other slave station in the first state, wherein the other one or more each slave stations in the second state do not transmit a positive acknowledgement if retransmission is not required and transmits a negative acknowledgement if retransmission is required, wherein at least one negative acknowledgement transmitted by at least one slave station in the second state is transmitted at least partially concurrently with at least one said predetermined time slot, and wherein the master station retransmits the data if it does not receive the positive acknowledgement from the other one or more of the slave stations in the first state or if the master station receives at least one negative acknowledgement, and if the validity of the data has not expired, wherein at least one of the plurality of slave stations is commanded into one of the first and second states by the master station, wherein the master station has means for assessing the quality of radio communication with each of the plurality of slave stations, and the at least one slave station in the first state has respectively lower quality radio communication with the master station than the other one or more slave stations in the second state.