Irregular-shaped Geometry-based Channel Modeling for UAV-to-ground at Port Bulk Cargo Terminal

To enhance the reliability of unmanned aerial vehicle (UAV) communication systems in low-altitude complex industrial environments and to support the development of low-altitude intelligent connectivity technologies and smart port construction, an intelligent channel model for UAV inspection scenarios at port bulk cargo terminals is presented. The operating environment of port bulk cargo terminals is characterized by dynamically operating large-scale loading and unloading machinery, random blockage caused by irregular cargo stacking, and continuously varying UAV flight altitudes. The dynamic machinery operations, irregular cargo stacking, and UAV mobility jointly lead to severe multipath propagation, rapid time variation, and pronounced non-stationarity in UAV-to-ground communication channels. Therefore, accurate characterization of channel properties in such complex port environments is required to ensure reliable communication links and stable cooperative operation of UAV swarms./t/nA high-precision ray-tracing (RT) technique is employed to construct a UAV-to-ground communication dataset for a port bulk cargo terminal scenario. Two representative yard utilization conditions, i.e., 40% and 70% utilization, are considered to reflect different operational intensities and obstruction densities. Dynamic posture variations of large machinery, including lifting and translational movements, are incorporated into the simulation environment. Communication frequency bands of 5.9 GHz and 28 GHz, together with UAV flight altitudes of 80 m and 120 m, are investigated. The constructed dataset captures key propagation mechanisms in port environments, including shadowing, scattering, and multipath effects induced by large metallic structures and irregular cargo piles./t/nBased on the RT simulation data, key statistical characteristics of the UAV-to-ground channel are systematically analyzed, including the time autocorrelation function (TACF), singular value spread (SVS), and Doppler power spectral density (DPSD). The TACF is evaluated under different flight altitudes, communication frequency bands, and yard utilization conditions. The analysis indicates that, compared with the 5.9 GHz band, the TACF in the 28 GHz band exhibits a faster decay rate due to shorter wavelength and higher sensitivity to environmental blockage. A faster TACF decay is also observed at a flight altitude of 120 m compared with 80 m, which is attributed to increased propagation distance and enhanced scattering effects. Furthermore, under high yard utilization conditions, dense cargo stacks generate a large number of scattering clusters, resulting in accelerated TACF decay and stronger channel time variation. In addition, SVS and its cumulative distribution function are derived through singular value decomposition of the channel matrices. The SVS distribution in the 28 GHz band is observed to shift toward larger values, reflecting increased channel sparsity and reduced spatial degrees of freedom. At higher UAV flight altitudes, steeper SVS curves are obtained due to the dominance of the line-of-sight (LoS) component, whereas broader SVS distributions are observed at lower altitudes as a result of frequent blockage and shadowing. Moreover, high yard utilization significantly increases the SVS magnitude, indicating severe degradation of spatial multiplexing capability in dense port environments. DPSD analysis further reveals stronger Doppler frequency shifts at lower flight altitudes, higher frequencies, and higher yard utilization levels, confirming intensified channel non-stationarity./t/nTo accurately describe the observed channel behaviors, a geometric-based stochastic model (GBSM) is proposed for UAV-to-ground communication channels in port bulk cargo terminal scenarios. The proposed GBSM explicitly incorporates dynamic scattering and blockage effects caused by large machinery operations and irregular cargo piles. The capability of the proposed GBSM to characterize channel non-stationarity and statistical consistency is validated through comparison with ray-tracing simulation results. The validation results demonstrate that the proposed GBSM achieves high accuracy in representing realistic port communication environments, thereby providing a reliable foundation for the design and optimization of UAV communication systems in smart ports and other complex industrial scenarios.