Retransmission Strategies for Spatially Multiplexed 2×2 MIMO Systems

Packet retransmission strategies are presented for 2x2 MIMO spatial multiplexing systems where adaptive modulation and coding (AMC) is implemented based on outdated CSI at the transmitter. Antennas for retransmission are selected to maximize the throughput of the system. A sign change or conjugate operation is allowed for retransmitted packets. The proposed schemes perform antenna selection based on the CSI at the receiver and feed back relevant information to the transmitter. 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.