Exploiting transmit correlation and mutual coupling in MIMO transmitters

We explore the potential of advantageously utilizing transmit correlation and mutual coupling in large-scale multiple input multiple output (MIMO) transmitters using low complexity closed form precoding techniques. Towards this end, we investigate the effect of increasing the number of antenna elements in a fixed transmitter space. This gives rise to two contradicting phenomena: the reduction of spatial diversity due to reducing the separation between antennas and the increase in transmit diversity by increasing the number of elements. We explore a precoding technique that exploits the increasing transmit correlation and mutual coupling to improve the received signal power. We investigate densely deployed uniform linear antenna arrays modeled in the CST Microwave Studio. The simulations show the somewhat surprising result that, by reducing the separations between the antennas to significantly less than the transmit wavelength to fit more antennas, improved performance is obtained.¹