Field experiment results using 2×2 and 4×4 MIMO precoding in E-UTRA downlink

We present field experiment results on multiple input multiple output (MIMO) precoding using orthogonal frequency division multiple access (OFDMA) in the E-UTRA downlink. We measured the throughput performance of 4×4 MIMO precoding with 1- to 4-stream transmission. Time variation characteristics of throughput, SINR, and antenna correlations are compared to evaluate the selection criteria for the number of streams. The throughput performance of 2×2 MIMO precoding are also evaluated and compared with the results of the 4×4 MIMO case. Based on the evaluation of the field experiment results, we verify that the throughput is maximized using 3- or 4-stream transmission. Furthermore, we verify that 2-stream transmission is also effective for 4×4 MIMO in an actual propagation environment, since high antenna correlation sometimes happens on which the throughput performance of 3- or 4-stream transmission is severely degraded. Evaluation results also show that the estimated gain of rank adaptation is about 11.6% for 4×4 MIMO and about 6% for 2×2 MIMO.