Is full duplex configuration better than MIMO spatial multiplexing?

By configuring the antennas as either transmit or receive antennas, the MIMO system can be configured into either a full duplex (FD) system or a half duplex (HD) spatial multiplexing (SM) system, which are considered as two important techniques to improve the spectral efficiency for MIMO systems. FD transmission suffers from the self interference, while the performance of a SM system is greatly affected by the spatial correlation. Therefore, there is an optimal tradeoff between FD and SM, depending on the system setting and channel conditions. In this paper, we analyze the exact and approximate average sum rates of the two systems. Based on the analytical results, the approximate threshold for selecting between FD and SM systems is derived to maximize the system sum rate. Finally, simulation results consolidate our analysis.