Assessment of Beamforming Algorithms with Subarrayed Planar Arrays for B5G/6G LEO Non-Terrestrial Networks

Non-Terrestrial Networks (NTNs) in Beyond 5G (B5G) and 6G ecosystems are expected to play a crucial role in providing the requests of connections anywhere and anytime by offering wide-area coverage and ensuring service availability, continuity, and scalability. Full Frequency Reuse (FFR) schemes, which are able in cooperation with digital beamforming algorithms to cope with the substantial co-channel interference, are considered to be an efficient solution to meet the growing demand of high data rates in B5G/6G systems. In this paper, we propose a Limited Field Of View (LFOV) planar array architecture composed of smaller planar subarrays in order to increase the directivity of an on-board Low Earth Orbit (LEO) satellite antenna array and mitigate the interference. We evaluate the performance of feed-space beamforming schemes, including both full digital schemes based on Channel State Information (CSI) at the transmitter, such as Minimum Mean Square Error (MMSE), and full analog schemes that only require the users' locations, such as Conventional Beamforming (CBF). The numerical results of the system performance, presented by means of spectral efficiency, demonstrate a remarkable improvement in the proposed beamforming design with subarraying w.r.t. the one with no subarrayed configuration; in particular, we show that an analog beamforming scheme with subarraying can outperform a full digital beamforming scheme with no subarraying.