  Terahertz (THz) communications are envisioned as a promising technology for
sixth-generation (6G) and beyond systems, owing to its unprecedented
multi-gigahertz (GHz) bandwidth. In this paper, channel measurement campaigns
in indoor scenarios at 201-209~GHz are reported. Four different communication
scenarios including 90 transmitter-receiver pairs are measured in two channel
measurement campaigns of a meeting room and an office room, respectively. The
two measurement campaigns contains four scenarios, namely, a meeting room,
cubicle area, hallway and non-line-of-sight (NLoS) case. The propagation of
multi-path components (MPCs) in the four scenarios is characterized by the
power-delay-angular profiles. Based on them, the temporal and spatial
consistency for varying receiver locations in the complex hallway and NLoS
scenarios are verified. To characterize, the large-scale best-direction and
omni-directional path losses in indoor scenarios are separately analyzed and
modeled by the close-in (CI) model. Furthermore, the small-scale channel
parameters, e.g., the number of clusters, delay spread, angular spread, and
cluster time-of-arrival are analyzed and modeled by proper distributions. As a
general framework, a ray-tracing-statistical hybrid model is proposed for
wireless propagation at 201-209~GHz, although, admittedly, the measurement
results and analysis reveal that the channel characteristics in various indoor
scenarios exhibit noticeable differences that need tailored parameter settings.
