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With the challenge to form the networks of the Intelligent Transportation Systems (ITS), both technologies of vehicles and wireless communication are required to be connected tightly. In terms of wireless communication, the communication system in the terahertz (THz) frequency range with ultra-large bandwidth is a potential technology to support very high-data-rate wireless transmission at the age of beyond fifth-generation mobile communications (B5G). In this paper, the carrier frequency of 300 GHz with 8 GHz bandwidth vehicle-to-infrastructure (V2I) channel is characterized for the urban and highway scenario, respectively. The self-developed ray-tracing (RT) simulator is employed with the calibrated electromagnetic (EM) parameters. Since the wavelength of carrier frequency approaches the diameters of raindrops and snowflakes, the significant influence of the precipitation on the channel characterization is studied in our work as well. The large-scale parameters of the THz V2I channel, including path loss, Rician K -factor, root-mean-square (RMS) delay spread, and angular spreads are explored in the target scenarios under sunny, rainy, and snowy conditions, respectively. The channel characteristics studied in this paper can be used to support the link-level and system-level design for the future THz vehicular communications.INDEX TERMS Channel characteristics, ray-tracing simulation, terahertz communication, vehicle-toinfrastructure channel, wave propagation.

Terahertz (THz) communications are envisioned as a key technology for the sixth-generation wireless communication system (6G). However, it is not practical to perform large-scale channel measurements with high degrees of freedom at THz frequency band. This makes empirical or stochastic modeling approaches relying on measurements no longer stand. In order to break through the bottleneck of scarce fulldimensional channel sounding measurements, this paper presents a novel paradigm for THz channel modeling towards 6G. With the core of high-performance ray tracing (RT), the presented paradigm requires merely quite limited channel sounding to calibrate the geometry and material electromagnetic (EM) properties of the three-dimensional (3D) environment model in the target scenarios. Then, through extensive RT simulations, the parameters extracted from RT simulations can be fed into either ray-based novel stochastic channel models or cluster-based standard channel model families. Verified by RT simulations, these models can generate realistic channels that are valuable for the design and evaluation of THz systems. Representing two ends of 6G THz use cases from microscopy to macroscopy, case studies are made for close-proximity communications, wireless connections on a desktop, and smart rail mobility, respectively. Last but not least, new concerns on channel modeling resulting from distinguishing features of THz wave are discussed regarding propagation, antenna array, and device aspects, re-

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In the vision of intelligent transportation, vehicles are expected to feature with advanced applications, such as automatic road enforcement, dynamic traffic light sequence, and autonomous driving. Therefore, real-time and fast dynamic information exchanges are required, and vehicle-to-everything (V2X) communications are highly demanded. In this work, the channel characteristics of vehicular communication are analyzed in the millimeter-wave (mmWave) band at 22.1-23.1 GHz. Specifically, two types of links (the satellite link and the terrestrial link) are considered in urban and highway scenarios with different weather conditions. The ray-tracing simulator together with calibrated electromagnetic parameters is employed to practically generate wideband channels. The key channel parameters of each link including the received power, Rician K -factor, root-mean-square delay spread, and angular spreads are explored. The co-channel interferences between the two links are analyzed as well. The observations and conclusions of this work can be useful for the design of V2X communication technologies.