Codebook design for MIMO retransmission system

This letter proposes a new retransmission structure with multiple retransmission codebooks for a linear precoding-based closed-loop multiple-input multiple-output (CL-MIMO) system. While conventional codebooks are defined only for the initial transmission in CL-MIMO systems, we propose a multiple codebook structure in which a different codebook is used for each retransmission, instead of a single identical codebook for every retransmission. Simulation results indicate that in slowly fading channels the proposed scheme achieves a larger gain over the conventional scheme using a single codebook, especially as the number of antennas increases.