Hybrid Beamforming Optimization for UAV-Enabled mmWave Beamspace MIMO System

The combination of unmanned aerial vehicles (UAVs) and millimeter wave (mmWave) multiple-input multiple-out (MIMO) systems is considered as a key enabling technology for 5G networks, as it provides high data rate aerial links. However, establishing UAV-enabled mmWave MIMO communication is challenging duo to the high hardware cost in terms of radio frequency (RF) chains. As explored in this work, the joint optimization of the UAV's altitude and hybrid beamspace precoding is proposed for the UAV-enabled multiuser MIMO system, in which the discrete lens arrays (DLA) is exploited to decrease the amount of the RF chain. In the proposed scheme, the optimization problem is formulated as a minimum weighted mean squared error (MWMSE) method. Then an efficient algorithm with the penalty dual decomposition is proposed to optimize the altitude of UAV, selection of the beam and the method of digital precoding jointly. Simulation results confirm the superior performance of the explored scheme and perform close to full-digital beamforming in terms of achievable spectral efficiency.