Strategies for ARQ in 2x2 MIMO Systems

Packet retransmission strategies are presented for 2x2 MIMO spatial multiplexing systems. Antennas for retransmission are selected to maximize an approximation of the throughput of the system. A sign change or conjugate operation is allowed for retransmitted packets. The proposed scheme performs selection of retransmission antennas based on the CSI at the receiver: only 1 bit of feedback is additionally required, along with the acknowledgement bits. When 2 packets are decoded with errors, retransmission follows a space time block code structure, allowing a seamless switching between spatial multiplexing and space time block coding.