On capacity of two-way full-duplex and one-way MIMO with the same number of antennas

Two-way co-channel communication enabled by recent full-duplex (FD) transceiver designs offers the potential to double spectral efficiency. However, currently most of FD radios require additional antennas to facilitate the multi-stage self-interference cancellation (SIC). As increasing antenna number of transceiver certainly leads to higher theoretical link capacities, the real gain of FD systems over its half-duplex MIMO counterparts should be re-evaluated under a same antenna-number assumption. In this paper, we derive generic close-form expressions for two-way FD link capacity based on mainstream SIC approaches, analyze the impacts of Tx-EVM and transmitter channel information (CSIT) on FD link capacity, and thus illustrate the necessity of enabling close-loop FD to fully exploit spatial diversity. Numerical results show that, although the capacity gain of FD over MIMO is jointly determined by Tx power, SIC gain and Tx-EVM, the awareness of CSIT improves FD performance much more significantly than it does for MIMO. Moreover, for FD radios with Tx-noise, the SIC gain in RF-domain is the most important in determining the capacity of two-way FD communications.