Experimental Investigation and Modeling of the Throughput of a 2 $\times$ 2 Closed-Loop MIMO System in a Reverberation Chamber

Throughputs of 2 × 2 long term evolution (LTE) multiple-input multiple-output (MIMO) systems in both open- and closed-loop configurations have been studied previously. However, in the previous work, the study of the closed-loop MIMO system is limited to receive semi-correlation (i.e., correlations exist only at the receive side only), resulting in inaccurate modeling of the closed-loop throughput with large transmit antenna correlations and incomplete conclusion about the effectiveness of codebook based precoding based on 2-bit feedback. In this work, the effect of the transmit antenna correlation on the closed-loop throughput is examined. Unlike in the previous work, an inversely weighted mean square error (MSE) matrix is proposed as the precoding selection criterion, resulting in good agreements between the simulations and the RC measurements of a closed-loop LTE system with various correlations. It is found that the closed-loop MIMO system is superior to its open-loop counterpart in the presence of large transmit antenna correlation in the low and medium signal-to-noise (SNR) regimes.