Selective Combining for HARQ-Employed MIMO Systems with Spatial Correlations

In this paper, the selective combining scheme is proposed for hybrid automatic repeat request (HARQ)-employed multiple-input multiple-output (MIMO) systems with spatial correlations at the receiver. To reduce the computational complexity load during the reception procedure, through using only a part of the total receive antennas, the proposed scheme generates the subsets of receive antennas, and the receive antennas in each subset are utilized for selective combining. For a given number of selected receive antennas, each subset is generated to minimize the summation of the spatial correlations between the receive antennas in the subset. During the subset generation, the proposed scheme utilizes only spatial correlation information (i.e., the receiver correlation matrix) and does not require the instantaneous channel state information (CSI). Thus, the calculated subsets in the proposed scheme can be utilized for the selective combining as long as the receiver spatial correlation remains unchanged. Simulation results verify that the proposed scheme can outperform the norm-based selective combining scheme that requires an additional calculation for every new instantaneous CSI.