The upcoming 5G and beyond wireless systems aim to support billions of devices and handle data traffic 1000 times greater than current 4G systems. Researchers are focusing on two main directions for achieving 6G goals: (1) targeting higher frequency bands to develop new, efficient physical layer techniques, and (2) deploying more active nodes (e.g., antennas, reflecting surfaces) in a given area. Physical layer advancements include shifting from millimeter waves to sub-Terahertz frequencies, utilizing ultra-massive MIMO beamforming for multiple parallel users, and designing new multi-carrier waveforms for better spectral efficiency and reliable wireless links. This thesis concentrates on the first direction, particularly channel modeling, beamforming, and parameter estimation for outdoor sub-THz mobile communication systems, addressing the ultra-reliable, high-mobility communication and high data traffic needs of beyond 5G networks.