Energy-Saving UAV-Assisted Multiuser Communications With Massive MIMO Hybrid Beamforming

In this letter, we consider hybrid beamforming for unmanned aerial vehicle (UAV)-assisted communications with massive multiple-input multiple-output (MIMO). Using a hybrid beamforming design, we derive an approximate closed-form expression of rate and provide a power allocation design under the line-of-sight (LoS) channels. It is revealed that the total transmit power should be inversely proportional to the number of antennas of UAV in order to satisfy the rate requirement of each user. Furthermore, we propose the optimal location design of the UAV. For the special case the pathloss exponent is 2, the optimal location is the weighted average location of all users where the weights are signal to interference plus noise ratio (SINR) requirements of all users. It is shown that the weighted average location could be an approximate method to design the UAV location with little performance gap to the optimal location even when path loss exponent is not 2