US Patent 7420950 Multiplex communication with slotted retransmission on demand

A method for communication in a sequence of frames includes assigning a respective time slot to each of a plurality of mobile units, while reserving an unassigned time slot. During a first frame, one of the mobile units transmits an uplink signal in the respective time slot, carrying first uplink data over the air to a base station. The base station transmits a downlink signal to the mobile unit indicating that retransmission of the first uplink data is required. Responsively to the downlink signal, during a second frame subsequent to the first frame, the mobile unit transmits the uplink signal both in the respective time slot and in the reserved time slot so as to carry the first uplink data and second uplink data over the air to the base station. A similar method may be used for downlink retransmission.