To advance research on maritime communications in sixth generation (6G) communication networks, a general three-dimensional (3D) non-stationary geometry-based stochastic model (GBSM) is proposed in this paper. The proposed model is applicable to a wide range of communication scenarios in maritime internet of things (IoT) communication networks, which involve diverse communication terminals including unmanned aerial vehicles (UAVs), unmanned surface vehicles (USVs)/ships, and shore-side base stations. It employs a comprehensive channel modeling framework to simulate space-time-frequency non-stationary properties in various maritime communication scenarios. Based on the sea spectrum, factors such as sea surface scattering, onboard array rotation, and line-of-sight (LoS) communication probability are jointly considered. Moreover, the proposed channel model incorporates distinct features of maritime channels, including UAV rotation, coastal building interference, and evaporation duct signal propagation, as observed in diverse scenarios. Utilizing the proposed channel model, we derive and simulate the channel statistical properties, such as space-time-frequency correlation function (STF-CF), angular power spectrum density (PSD), and root-mean-square (RMS) delay spread, as well as the channel capacity. We conduct an in-depth investigation to analyze effects of different channel parameters on statistical characteristics and channel capacity. Also, the good agreement between the measurement results and corresponding simulation results confirms the model’s applicability.

In this paper, a geometry-based stochastic model (GBSM) is proposed for multiple-input multiple-output (MIMO) maritime multi-user land-to-ship communication channels. The inter-link correlation between different users is modeled by spatial correlated large scale parameters (LSPs). In addition, the evaporation duct is modeled based on a twin-cluster model, and the signal propagation between two clusters is simulated by several-order reflections to obtain the delay and angle parameters of each ray. Simulations based on the proposed model focus on analyzing the statistical properties that reflect the spatial correlation between multiple users. Effects of the number of antennas, multipath components (MPCs), and different heights of evaporation duct on the correlation between users and the channel capacity are investigated and corresponding conclusions are drawn.

Inter-satellite links are significant to achieve complex space missions like high precision ranging and rendezvous navigation. However, the impact of spacecraft multipath on system performance cannot be ignored, especially for large spacecraft. To evaluate and optimize the satellite communication system, a geometry-based non-stationary inter-large-satellite wireless channel model is proposed. It includes three components, i.e., a line-of-sight component, solar-panel-bounce parts for multipath on solar panels, and body-bounce (BB) components resulting from spacecraft body scattering. The BB clusters’ time-variant azimuth angle of arrival and departure are derived because conventional angle distribution functions, like von Mises, are unsuitable for scatterers directionally located in a limited region in satellite scenarios. Channel evolution in the space-time-frequency (STF) domain is modeled with birth-death processes regarding self-rotation and solar panel rotation in addition to three-dimensional (3D) movement. Then, channel characteristics, e.g., STF correlation functions, Doppler power spectrum density, and stationary intervals, are derived and studied. Finally, the proposed channel model is validated to be accurate by ray-tracing simulation, satellite measurement and on-orbit observation.

Atmospheric ducts provide a potential way to establish beyond-line-of-sight (B-LoS) links for maritime communications. Based on the ray tracing (RT) method, long distance propagation in the maritime evaporation duct environment is studied in this paper. The variations of horizontal distance and height are calculated according to the refractivity distribution. Eigenrays between transmitter (Tx) and receiver (Rx) are determined by tracing the ray trajectories. Furthermore, the path loss, delay spread, and angles of arrival (AoAs) are estimated. Simulation results calculated by the RT method match theoretical results generated by parabolic equation (PE) methods in the short range. In the B-LoS range, the path loss estimated by RT is a bit higher than that estimated by PE. In the RT model, the increase in the number of rays calculated in the B-LoS range may lead to this case. Simulation results show that the RT method can well evaluate the anomalous propagation in the evaporation duct and estimate channel parameters effectively.

In this paper, we first propose a 3-dimensional (3-D) non-stationary geometry-based stochastic model (GBSM) for maritime massive multiple-input multiple-output (MIMO) communication systems with the uniform circular array (UCA) configuration. To reduce the model complexity and improve the mathematical tractability, a novel beam domain channel model (BDCM) is then proposed based on the transformation of the corresponding GBSM from the array domain to the beam domain for maritime communications. In the proposed BDCM, the beamforming matrices suitable for UCA structures are constructed and their invertibility is demonstrated to ensure the practicability of the BDCM. Two methods are used to characterize the array non-stationarity in maritime massive MIMO channels. First, the evolution of clusters over the large UCA is modeled by the visibility regions (VRs) attached to individual multipath components (MPCs). Second, the sphere wavefront (SWF) effect is captured by dividing the UCAs into several sub-arrays. Based on the proposed GBSM and BDCM, some important channel statistical properties are studied and compared, including channel power, power leakage, space-time-frequency correlation function (STF-CF), and root-mean-square (RMS) Doppler/beam spreads. Also, the importance of considering the array non-stationarity in maritime communication channels is revealed.

Due to the agile maneuverability, unmanned aerial vehicles (UAVs) have shown great promise for on-demand communications in the next-generation wireless networks. Considering the massive multiple-input multiple-output (MIMO) configuration, this paper proposes a novel three-dimensional (3D) beam domain channel model (BDCM) for UAV communications. Through dividing the large antenna array into several sub-arrays and classifying multipath components as near-field and far-field components, the proposed BDCM takes the spherical wave front (SWF) and array non-stationarity into account. Channel statistical properties including spatial-temporal-frequency correlation function (STF-CF), root-mean-squared (RMS) Doppler spread, beam spread, channel matrix collinearity (CMC), and stationary time interval are derived and simulated for the proposed BDCM. Influences of SFW and non-stationary properties on the statistical properties and system performance are analyzed. Simulation results show that, compared with the equivalent geometry-based stochastic model (GBSM), the proposed BDCM has better temporal correlation, while BDCM and GBSM are equivalent in the system performance evaluation. Furthermore, the performance of the proposed BDCM is evaluated in terms of accuracy, complexity, and pervasiveness. The results show that the proposed BDCM can represent massive MIMO channel properties accurately with low complexity and good compatibility.

In this paper, a novel 3-dimensional (3D) non-stationary geometry-based stochastic model (GBSM) is proposed to mimic the ship-to-ship multiple-input multiple-output (MIMO) communication channels. To reflect the realistic maritime propagation environment, the effects of rough sea surface scattering and evaporation duct propagation are investigated in the proposed channel model. The model considers the movements of transmitter (Tx), receiver (Rx), and scatterers, and is capable of capturing the channel characteristics, including non-stationary characteristics, spatial consistency, location-dependent property, etc. Through taking the array cluster evolution into account, the proposed channel model can describe massive MIMO channels and can easily switch to conventional MIMO channel model by adjusting corresponding parameters. Based on the proposed model, key statistical properties like delay/angular/Doppler power spectrum density (PSD), space-time correlation function (STCF), stationary interval, and root mean square (RMS) Doppler/delay spreads in multi-scenarios are derived. The usefulness and accuracy of the proposed model are demonstrated by comparing theoretical results, simulation results, and corresponding measurement results.

In the next-generation wireless networks, unmanned aerial vehicles (UAVs) equipped with aerial base stations (ABSs) can serve as the supplement of traditional terrestrial networks and provide high-speed access for ground users. In this paper, an extended multi-user massive multiple-input multiple output (MIMO) geometry-based stochastic channel model (GBSM) is proposed for UAV-aided communication systems. The proposed model is the extension of a non-stationary UAV channel model by taking the different antenna array layouts and spatial correlation between ground users into account. Based on the simulation, the effects of UAV height, user density, and antenna configuration on inter-user correlation and on channel capacity are thoroughly investigated. The extension of spatial correlation will enable UAV channel simulator to generate realistic spatial correlated channel impulse responses (CIRs) for multiple users that are relatively close to one another.

To achieve space-air-ground-sea integrated communication networks for future sixth generation (6G) communications, unmanned aerial vehicle (UAV) communications applying to maritime scenarios serving as mobile base stations have recently attracted more attentions. The UAV-to-ship channel modeling is the fundamental for the system design, testing, and performance evaluation of UAV communication systems in maritime scenarios. In this paper, a novel non-stationary multi-mobility UAV-to-ship channel model is proposed, consisting of three kinds of components, i.e., the line-of-sight (LoS) component, the single-bounce (SB) components resulting from the fluctuation of sea water, and multi-bounce (MB) components introduced by the waveguide effect over the sea surface. In the proposed model, the UAV as the transmitter (Tx), the ship as the receiver (Rx), and the clusters between the Tx and Rx, can be seen as moving with arbitrary velocities and arbitrary directions. Then, some typical statistical properties of the proposed UAV-to-ship channel model, including the temporal autocorrelation function (ACF), spatial cross-correlation function (CCF), Doppler power spectrum density (PSD), delay PSD, angular PSD, stationary interval, and root mean square (RMS) delay spread, are derived and investigated. Finally, by comparing with the available measurement data, the accuracy of proposed channel model is validated.