Hybrid Beamforming for Full-Duplex Enabled Cellular System in the Unlicensed mmWave Band

In this paper, we consider a full-duplex enabled cellular system operated in the unlicensed mmWave band. In particular, the full-duplex gNB is equipped with multiple antennas and applies hybrid beamforming for downlink transmissions, meanwhile mobile users send uplink traffic to the gNB with an omni-directional antenna. In the unlicensed bands, the cellular networks need to ensure a fair coexistence with other systems, such as WiGig. Therefore, a sum rate maximization problem is formulated to improve the throughput of the cellular system meanwhile suppressing its interference to the WiGig system. The formulated problem is non-convex and of high complexity. In order to efficiently address it, the sum rate maximization problem is first reformulated into a weighted mean square error minimization problem, and then the penalty dual decomposition method is applied to jointly optimize the uplink transmit power and downlink hybrid beamforming. Numerical results show that the performance of the proposed unlicensed full-duplex enabled cellular network degrades by nearly 29% in order to fairly coexist with the WiGig system. However, compared with half-duplex systems, applying full-duplex technology to our proposed network can improve the sum rate by nearly 56%.