Codebook Design and Beam Training for Conformal Array-Enabled UAV mmWave Communications With the Airframe Shadowing

Millimeter-wave (mmWave) communications exhibits considerable potential for high-data-rate UAV transmission, where the full-spatial 3D Beam Training (BT) is usually performed to establish mmWave link. However, the narrow BT in full space is challenging, especially in the scenario with the airframe shadowing (AS). Aiming to address these difficulties, the cylindrical conformal array (CCA) is integrated with the surface of UAV for full-spatial coverage and high spectrum efficiency (SE) in highly dynamic UAV mmWave communications. In this letter, the CCA codebook design and the BT algorithm with the AS are investigated. More specifically, we first propose the activated subarray optimization problem based on the AS model and obtain the corresponding optimal solution. Next, a hierarchical codebook for CCA based on the optimal maximum subarray size, and the corresponding BT algorithm are developed. Simulation results show that the proposed CCA codebook and BT outperform those for single and double uniform planar arrays (UPA) in terms of spectrum efficiency (SE).