Design of Robust LoS-MIMO Transmission in HAPS Feeder Link

In line of sight multiple input multiple output (LoS-MIMO) transmission in a feeder link, which involves communication between a ground station and a high altitude platform station (HAPS), the design of antenna arrays that ensure a stable and high channel capacity is a challenge because of the degradation of the channel capacity caused by changes in the distance and angle owing to the movement of the HAPS. In this study, we first evaluate the channel capacity characteristics of a basic uniform linear array (ULA) for LoS-MIMO transmission during movement. To compensate for this drawback, we propose a uniform cross array (UXA) configuration with two crossed ULAs as the antenna array and show that the LoS-MIMO transmission with the UXA configuration is robust against HAPS movement. The method in this paper is applicable to HAPS as well as LoS-MIMO transmission between two stations with changing positions. LoS-MIMO transmission using UXA exhibits excellent performance with the channel capacity approaching the theoretical upper bound.