Channel Selection HARQ Feedback in LTE-Advanced

LTE-Advanced supports carrier aggregation which implies that ACK/NACK information bits for multiple downlink carriers are fed back in the uplink. One method for HARQ feedback with multiple ACK/NACK bits is channel selection, wherein ACK/NACK information is encoded by the joint selection of a channel (transmit sequence) and a QPSK symbol. We give a signal design for mapping ACK/NACK information to the channels and modulation symbols, in order to minimize and equalize the ACK-to-NACK and NACK-to-ACK error probabilities. It is shown how the performance depends on the set of channels assigned to a given ACK/NACK bit.