## 1 Introduction  
In communication networks, ground base stations are vulnerable to destruction by natural disasters such as earthquakes, tsunamis and flash floods. As a result, the communication infrastructure in the disaster area is damaged, and communication services cannot be provided. This further hampers rescue operations. UAVs combined with cellular networks can support UAV communication at low cost and high mobility, and also provide the possibility of establishing new private ground networks [1; 2; 3]. In areas with dense urban traffic hotspots, the coverage of traditional cellular base stations cannot meet the demand. UAVs are highly flexible and easy to deploy. They can quickly provide coverage and service classification for hotspots, with a wide range of application scenarios. Air base stations (ABS) are more resilient to environmental changes than ground base stations [4]. Therefore, UAVs can also be deployed in areas without infrastructure coverage to provide emergency communication connections. To improve the transmission performance of UAV communication, Relay-Assisted Free-Space Optical-Radio Frequency (RA-FSO-RF) was introduced into the communication system [5; 6]. The Low Density Parity Coding Multiple-Input Multiple-Output/Free-Space Optical (LDPC-MIMO/FSO) method was used to evaluate the performance of Malaga distributed MIMO/FSO links with m-QAM and pointing error (PE) based on power series [7]. In the previous work, our team proposed a Dynamic Hybrid Precoding (DHP) double-hop hybrid FSO-RF system inspired by Manifold Learning (ML) based on antenna zoning algorithm [8]. MIMO technology can be used to eliminate the effects of atmospheric disturbance (AT) and pointing error (PE) on link performance in FSO systems [9]. Under the joint action of AT and PE, the bit error rate (BER) and channel capacity of MIMO systems using the optical space scheme are studied in the reference [10]. The communication environment of UAVs is greatly affected by AT. This is mainly because AT has a great influence on the performance of laser communication. The factors affecting the communication performance of UAVs mainly include visual axis error and jitter error. Scholars have studied the performance of hybrid free-space optical and radio frequency (FSO-RF) relay systems in the presence of AT and PE [11]. These studies on FSO-RF systems have addressed the issue of FSO link or trunk selection [12; 13; 14; 15]. However, there have been few reports of PE and beam misalignment studies of millimeter-wave massive MIMO/FSO in UAV RF communication links. The effective coverage of UAV base stations is affected by problems such as dynamic movement of UAVs and obstacles, beam shift and Doppler frequency shift caused by obstacle interference and wind speed [16; 17]. Beamforming of UAV antenna arrays helps to overcome the problems of beam misalignment and Doppler shift to improve UAV communication performance. Beamforming designs can also be used for drone communication. The 3D location of UAV base stations with a certain number of indoor users and obstacles was determined [18]. UAV base stations can sense the location of users and obstacles for maximum coverage. A Zero Forcing Hybrid Beam Forming (ZF-HBF) method for downlink multi-user orthogonal frequency-division multiplexing systems is explored in [19; 20; 21]. This method was used to achieve beamforming according to the Spectral Efficiency (SE) of the system up to the maximum upper bound. In order to achieve fast beamforming training and tracking, the hierarchical structure of the beam codebook and the hierarchical codebook with different beam widths based on the subarray technology were studied in [22]. By studying the Doppler effect caused by UAV motion, it was found that the Doppler effect can be catastrophic when using low-gain beamforming. An millimeter-wave massive MIMO hybrid beamforming with channel estimation was proposed in [23; 24; 25].