Unmanned aerial vehicle (UAV) assisted wireless communications have been expected to play a vital role in the next generation of wireless networks. UAVs can serve as either repeaters or data collectors within the communication link, thereby potentially augmenting the efficacy of communication systems. Despite their promise, the channel analysis and modeling specific to terahertz (THz) wireless channels leveraging UAVs remain under-explored. This work delves into a ground-to-UAV channel at 140 GHz, with a specific focus on the influence of UAV hovering behavior on channel performance. Employing experimental measurements through an unmodulated channel setup and a geometry-based stochastic model (GBSM) that integrates three-dimensional positional coordinates and beamwidth, this work evaluates the impact of UAV dynamic movements and antenna orientation on channel performance. Our findings highlight the minimal impact of UAV orientation adjustments on channel performance and underscore the diminishing necessity for precise alignment between UAVs and ground stations as beamwidth increases.

In the evolving domain of wireless communication, the investigation on terahertz (THz) frequency spectrum, spanning 0.1 to 10 THz, has become a critical focus for advancing ultra-high-speed data transmission technologies. The effective deployment of THz wireless communication techniques mandates a complete study of channel performance under various atmospheric conditions, such as rain, fog, cloud, haze, and notably, snow. These environmental elements significantly impact the design of the protocol stack, ranging from physical-layer signal processing to application design and strategic network planning. An in-depth understanding of channel propagation and fading characteristics in real-world environments, especially over ultra-wide bandwidths, is crucial. This work presents a comprehensive measurement-based and theoretical investigation of line-of-sight (LoS) THz channel performance in snowy conditions. It methodically examines both the empirical and predicted aspects of channel power and bit-error-ratio (BER). The effects of snowfall rate, carrier frequency, ambient temperature, and relative humidity on channel performance are analyzed and discussed. Our findings demonstrate that snowy conditions not only exert power loss but also induce rapid fluctuations in the power levels of the THz channel. Notably, our results reveal an absence of significant multipath effects in these scenarios. This insight highlights the need for further research into the dynamics of snowflake movement and their interaction with THz transmission paths.

Terahertz (THz) communications have emerged as a promising technology for 6G networks due to their potential for achieving terabit-per-second data rates. However, the impact of rainfall on THz channel characteristics remains incompletely understood, particularly regarding power attenuation mechanisms and bit error rate (BER) performance. This paper presents a systematic measurement-based and theoretical investigation of line-of-sight (LoS) THz channel behavior under rainfall conditions, methodically examining both power attenuation mechanisms and bit error rate (BER) performance. Our experimental campaign, conducted at frequencies of 220-230 GHz over a 54-meter outdoor channel, is complemented by analytical frameworks incorporating ITU-R and Mie scattering models. The study reveals that while rain induces significant power attenuation, multipath scattering effects remain minimal, with Rician K-factors maintaining high values. Notably, we observe substantial variations in power loss under constant rain rates attributed to dynamic changes in raindrop size distribution. Comparative analysis demonstrates superior BER performance of quadrature amplitude modulation (QAM) in rainfall conditions while revealing increased environmental sensitivity at higher frequencies. These findings underscore the necessity for adaptive modulation schemes and strategic frequency planning in future THz communication systems.

The terahertz (THz) band offers promising opportunities for high-capacity wireless communications but faces significant challenges from vegetation-induced channel impairments. This article presents a comprehensive investigation of THz channel propagation through vegetation, introducing a hybrid modeling approach that combines deterministic vegetation-dependent exponential decay (VED) modeling with statistical characterization of temporal variations. Through extensive laboratory measurements using Epipremnum aureum, we find that vegetation introduces angular-dependent power losses, with channel statistics following heavy-tailed Stable distributions rather than conventional Rician or Weibull models. Our outdoor measurements with dense and sparse lilac scenarios reveal pronounced foliage density variations in attenuation and height-dependent effects, while validating the VED model's ability to maintain excellent agreement with measured data and parameter stability across different heights without coefficient recalibration. Critical bit-error-rate (BER) analysis uncovers distinct SNR thresholds beyond which performance exhibits oscillatory behavior due to heavy-tailed fading, establishing fundamental capacity bounds with significant implications for modulation scheme selection and power control strategies in practical THz communication systems.

Non-line-of-sight (NLOS) data transmission through surface reflection is pivotal for enhancing the reach and efficiency of terahertz (THz) communication systems. However, this innovation also introduces significant eavesdropping risks, exacerbated by the complex bistatic scattering effects during adverse weather conditions like rain. This work delves into the assessment of the vulnerabilities of NLOS THz communication channels to eavesdropping under simulated rain conditions using metallic wavy surfaces (MWSs). The observation reveals the feasibility of successful signal interception under these conditions, highlighting a prevalent security concern for outdoor terahertz communication networks utilizing NLOS channels to broaden coverage. This insight underscores the critical need for addressing and mitigating potential eavesdropping threats to ensure secure and reliable terahertz communications in varied environmental conditions.

The propagation of millimeter-wave (mmW) and sub-terahertz (THz) waves through plasma sheaths is a critical concern for maintaining communication with hypersonic vehicles, yet the impact of complex plasma structures on these high-frequency channels remains insufficiently understood. In this work, we aim to characterize the transmission properties of mmW and sub-THz channels through plasma sheaths with various density profiles and ripple structures, addressing the gap in knowledge regarding the effects of plasma inhomogeneities on channel propagation. We employ an approach combining inductively coupled plasma (ICP) data with transfer matrix methods (TMMs) to model propagation through both flat and rippled plasma layers. Our findings reveal that ripple structures in plasma sheaths significantly affect the channel performance, with periodic ripples reducing the cutoff frequency and introducing frequency-selective behavior, while random ripples cause more unpredictable transmission characteristics. Our results explore the impact of the arrangement of plasma density layers and the parameters of ripple structures (period and amplitude) on channel transmission, group velocity dispersion (GVD), and angular dependence of wave propagation. These results provide crucial insights for the design and optimization of communication systems for hypersonic vehicles, potentially enabling the development of adaptive technologies capable of maintaining reliable communication in complex plasma environments.