Estimation-based retransmission mode selection for reinforced HARQ operation in MIMO systems

In this paper, we introduce a new retransmission and combining scheme named estimation-based retransmission mode selection (E-RMS) that reinforces the error recovery capability of HARQ for MIMO systems in fast fading channels and present a framework for MIMO system equipped with HARQ capability. The E-RMS scheme is designed to select the more desirable retransmission mode between spatial multiplexing (SM) and space time code (STC) based on estimating the error recovery capability of the two retransmission modes. If the SM mode is selected, the E-RMS transmits all the erroneous streams using the SM mode and otherwise it transmits a part of the erroneous streams using the STC mode. For the E-RMS, we present a decision criterion that selects the more desirable retransmission mode using the channel realization of the previous transmission. Numerical results reveal that the proposed E-RMS achieves significant performance gain over the fixed SM or STC retransmission schemes, performing comparable to the optimal mode selection scheme.