In this paper, we propose an aerial reconfigurable intelligent surface (ARIS)-enhanced unmanned aerial vehicle (UAV)-to-vehicle channel model that considers a three-dimensional (3D) continuously arbitrary trajectory. The model uses an ARIS mounted on a UAV to reflect signals to the terrestrial vehicle, which facilitates and enhances signal propagation. A generalized 3D random mobility model (RMM) with smooth turns is developed to characterize ARIS kinematics, where state differential equations and Euler approximation are employed for low-complexity real-time trajectory updates. Moreover, we model both the ARIS translational jitter and attitude jitter caused by wind or air turbulence as zero-mean Gaussian random variables, investigating the sensitivity of channel characteristics to assess the system robustness under non-ideal control conditions. The resulting trajectory and jitter models capture the unique channel properties in realistic scenarios. Furthermore, key statistical properties of the proposed channel model are derived, including spatial-temporal (ST) cross-correlation functions (CCFs), temporal auto-correlation functions (ACFs), and frequency correlation functions (FCFs). We analyze the impact of ARIS trajectory and physical parameters on these statistical properties, such as velocity magnitude, phase shifts design, unit numbers, and rotation angles. Numerical simulation results demonstrate the superiority of ARIS-enhanced UAV communications using the proposed generalized 3D smooth-turn RMM with both translational jitter and attitude jitter, highlighting the significant role of ARIS in UAV communications.

The integration of movable antenna (MA) technique into unmanned aerial vehicle (UAV) communications offers a promising solution to reliable and energy-efficient non-terrestrial networking for low-altitude economy. To characterize multi-MA-assisted UAV-to-UAV wideband fading channels, we propose a three-dimensional arbitrary-elevation two-concentric-cylinders reference model. Based on this model, we derive the space-time-frequency correlation function (STF-CF) in closed form. From the STF-CF, we also obtain the space-Doppler power spectral density (SD-PSD) and the power space-delay spectrum (PSDS). The excellent agreement between the theoretical PSDS and some previously reported measurement data demonstrates the utility of the reference model. We then establish corresponding simulation models, which produce consistent results with the derived expressions. By leveraging the closed-form correlation function, the gradient of the log-determinant of spatial correlation matrix with respect to the MA positions can be conveniently obtained, which may serve as a method to maximize the ergodic capacity of the multi-MA assisted wideband UAV-to-UAV channels.

An arbitrary-elevation two-sphere reference model is utilized to mimic the unmanned aerial vehicle (UAV) air-to-air fading channels. The model considers the line-of-sight (LoS), the single-bounced transmit (SBT), the single-bounced receive (SBR), and the double-bounced (DB) rays. Based on this model, the closed-form expression of the space-time correlation function (ST-CF) is obtained for the first time under the widely-used assumption of von Mises-Fisher (vMF) distributed scatterers. To further improve the model’s adaptability to realistic scattering environments, the distribution of the scatterers is generalized from a single unimodal vMF density into a mixture that can possess multimodality. Using the single-vMF ST-CF, the ST-CF under the mixture is also written in closed-form. Corresponding to the reference channel model, both the deterministic and the stochastic simulation models are provided, which yield consistent results with the respective derived expressions. This validates the correctness of the suggested closed-form ST-CFs. Moreover, a detailed analysis of the outage probability and the outage capacity is reported, which offers revealing insights into the behaviors of the system performance with respect to change of some key model parameters under multimodal distributions of the scatterers.

A 3-D arbitrary-elevation two-cylinder reference model is proposed for multiple-input-multiple-output (MIMO) air-to-air communications in unmanned aerial vehicle (UAV) channels. This model accounts for not only the Line-of-Sight (LoS) but also the single-bounced at the transmitter (SBT) and the single-bounced at the receiver (SBR), as well as the double-bounced (DB) rays. Therefore, it is endowed with a high adaptability to various UAV-to-UAV communication scenarios. From the reference model, a closed-form expression of the space-time correlation function (ST-CF) is derived. This expression is shown to be the generalizations of many existing correlation functions from the 2-D one-ring, the 3-D low-elevation one-cylinder, the 2-D two-ring, and the 3-D low-elevation two-cylinder model. Corresponding deterministic and stochastic simulation models are also developed in addition to the reference model. The well agreements between the channel capacities obtained from the simulation models and those from the derived ST-CF not only display the usefulness of the simulators but also confirm the correctness of the derivations. Based on the derived closed-form ST-CF, the effects of some model parameters on the capacity are evaluated in a computationally efficient manner.

Fine-scale 3-D morphological features of rocks on the Martian surface provide important clues to Mars exploration missions and scientific discoveries. To obtain such information, an automatic approach for high-precision measurement of 3-D morphological features of Martian rocks is proposed in this letter. The approach directly detects 3-D rocks from dense point cloud that is generated by interpolating triangulated irregular network (TIN) model, through a coarse-to-fine process combining cloth simulation filtering (CSF) and connected-component labeling algorithms. Multiple 3-D morphological features are then precisely extracted by modeling rock points and fitting local ground plane. Experimental results demonstrate that the proposed approach provides an effective way for the extraction of complete 3-D rocks and comprehensive morphological features with over 90% accuracy.

A three-dimensional (3D) theoretical model for unmanned aerial vehicle (UAV) communications is proposed in this paper. From the theoretical model, the envelope level crossing rate (LCR) and average fade duration (AFD) are derived under a 3D propagation environment. Based on the derived expressions, we for the first time investigate the LCR and AFD for UAV channels with different UAV- related parameters. The close agreement between the theoretical results and measured data demonstrates the utility of the proposed model.

Unmanned Aerial Vehicles (UAVs) have been a promising platform in realizing high-speed wireless networks. As an emerging scenario, the UAV communication is distinct from widely used cellular systems or vehicular networks, requiring the development of practical yet easy-to-use channel models. In this paper, for the first time we introduce the geometry-based stochastic model (GBSM) to UAV channel modeling, and propose a new three- dimensional (3D) GBSM for UAV Multi-Input Multi- Output (UAV-MIMO) channels. Based on the proposed model, we derive and investigate the space-time correlation function (STCF) under a 3D moving and scattering environment. The usefulness of this model is verified by the comparison between the theoretical results and some measurement data.