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Terahertz (THz) wireless data centers can provide low-latency networks and dynamic scalability that are vital for the next-generation cloud computing infrastructure. The knowledge of THz propagation characteristics in a data center environment is essential to the development of novel THz communication systems. However, a comprehensive characterization and modeling of THz propagation channels, which includes various obstructions in a data center is not available. This paper presents results from a THz channel measurement campaign conducted in a data center environment. Various propagation scenarios such as lineof-sight (LoS) link, non-LoS (NLoS) link using existing materials in a data center to redirect the beam, and obstructed-LoS (OLoS),-NLoS (ONLoS) links with common objects in data centers (cables and server racks' mesh doors) serving as obstruction were investigated. Propagation channel parameters such as pathloss and root-mean-squared (RMS) delay spread were analyzed in the aforementioned scenarios while cluster-based modeling was implemented for some scenarios. The proposed model for THz propagation in a data center environment was validated with the measured data. The average inter-arrival time of clusters (1/) and rays (1/λ) are estimated as 4.4 ns and 0.24 ns, respectively. We find that local scattering objects such as server-rack frames/pillars can be used to assist the NLoS type of link, and that cooling airflow in the data center has a negligible impact on THz propagation. Power cables and mesh doors of the server racks can cause additional attenuation of about 20 dB and 6 dB, respectively. Cluster model and other characterization results provided in this work are pertinent to THz wireless system design for data center environments. INDEX TERMS Channel measurements, channel modeling, statistical channel model, terahertz (THz) communications, wireless data centers.

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The time-variant vehicle-to-vehicle radio propagation channel in the frequency band from 59.75 to 60.25 GHz has been measured in an urban street in the city center of Vienna, Austria. We have measured a set of 30 vehicle-to-vehicle channel realizations to capture the effect of an overtaking vehicle. Our experiment was designed for characterizing the large-scale fading and the small-scale fading depending on the overtaking vehicle's position. We demonstrate that large overtaking vehicles boost the mean receive power by up to 10 dB. The analysis of the small-scale fading reveals that the two-wave with diffuse power (TWDP) fading model is adequate. By means of the model selection, we demonstrate the regions where the TWDP model is more favorable than the customarily used the Rician fading model. Furthermore, we analyze the time selectivity of our vehicular channel. To precisely define the Doppler and delay resolutions, a multitaper spectral estimator with discrete prolate spheroidal windows is used. The delay and Doppler profiles are inferred from the estimated local scattering function. Spatial filtering by the transmitting horn antenna decreases the delay and Doppler spread values. We observe that the RMS Doppler spread is below one-tenth of the maximum Doppler shift 2f v/c. For example, at 60 GHz, a relative speed of 30 km/h yields a maximum Doppler shift of approximately 3300 Hz. The maximum RMS Doppler spread of all observed vehicles is 450 Hz; the largest observed RMS delay spread is 4 ns.INDEX TERMS 5G mobile communication, automotive engineering, communication channels, fading channels, intelligent vehicles, millimeter wave propagation, millimeter wave measurement, multipath channels, RMS delay spread, RMS Doppler spread, parameter extraction, time-varying channels, two-wave with diffuse power fading, wireless communication.

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