The presentation focuses on the measurement-based investigations to accurately characterize and model the ultra-massive multiple-input-multiple-output (UM-MIMO) channel at mm-wave frequency bands in different scenarios, which are necessary for evaluating system performance and designing communication systems.

In this thesis, measurement campaigns were conducted using vector network analyzer (VNA)-based channel sounders to investigate device-to-device (D2D) and base station-to-device (B2D) wireless communication at mm-wave frequency bands. A high-resolution parameter estimation (HRPE) algorithm was applied to estimate the propagation parameters of the multipath components (MPCs) under the spherical wavefront assumption. A dynamic channel model was constituted for the channel obtained from an indoor hall to a corridor within the 28-30 GHz frequency band. Furthermore, a geometry-based stochastic channel model (GSCM) was constituted for the channel characteristics obtained in an outdoor scenario at the frequency band of 28-30 GHz, with the assistance of 3-D Ray Tracing simulations. In addition, to constitute a GSCM for the UM-MIMO channel, a novel scatterer localization algorithm was proposed. The thesis makes a significant contribution to the field of joint communication and sensing for 6G applications. Furthermore, it serves as a valuable point of reference for the continuous advancements in 3GPP standardization.