Millimeter-Wave Full-Duplex MIMO Systems with Hybrid Beamforming

In this paper, we investigate a millimeter-wave full-duplex (FD) multiple-input multiple-output system, where an FD base station is capable of concurrently receiving data from a half-duplex (HD) uplink user and transmitting data to an HD downlink user via hybrid beamforming. To effectively mitigate the self-interference and co-channel interference, the sum rate of the uplink and downlink transmissions is maximized by jointly designing hybrid beamforming at the base station and digital beamforming at the two users. The design problem is non-convex due to the multiplication among beamforming matrices, and it is converted to an equivalent weighted sum minimum mean square error (WMMSE) problem for mathematical tractability. An iterative WMMSE hybrid beamforming algorithm is first proposed based on alternative optimization. By adding semi-unitary structures to digital beamforming, a low-complexity semi-unitary hybrid beamforming algorithm is developed without requiring iterations. Computer simulations are used to demonstrate the effectiveness of the proposed systems, as compared with conventional HD systems.