Beam Alignment Methods for 5G mmWave UDNs and their Applicability in Indoor Environments

Millimeter-wave (mmWave) communications, using multiple-input multiple-output (MIMO) transmission, is a key technology for expanding the capacity of fifth-generation (5G) networks. While it offers benefits such as increased bandwidth and spatial diversity, it also faces challenges such as line-of-sight obstruction and significant propagation loss. To overcome these challenges, dense deployment of base stations (BSs) has emerged as a promising approach. However, this often leads to severe and complex interference problems due to the large number of mm Wave beams. In this paper, we review existing research on beam alignment issues, with a particular focus on downlinks in outdoor mmWave ultra-dense network (UDN) environments, and investigate the challenges that need to be addressed to extend these solutions to indoor mmWave UDN environments.