Revisiting the complex correlation in a MIMO system

It is commonly believed that a complex correlation of up to 0.5 in magnitude is negligible for multiple-input multiple-output (MIMO) performances and that the correlation affects the diversity gain or throughput only via its magnitude. In this work, we show that when the number of antenna ports is larger than two, the phase of the correlation coefficient affects the diversity gain and that even small correlation can severely degrade the throughput performance of MIMO systems with full spatial multiplexing and no diversity gain. We assume maximum ratio combining (MRC) to investigate the correlation effect on diversity gain and zero-forcing (ZF) equalizer to study the correlation effect on the MIMO throughput.