Deterministic Channel Modeling in Urban Multi-Factor Environments Based on a Hybrid Forward-Backward Ray Tube Tracing Approach.

Deterministic channel models are essential for high-frequency communication system design in complex urban environments, where multiple propagation mechanisms including reflection, diffraction, and vegetation scattering coexist. This paper proposes a hybrid forward-backward ray tube tracing (HFB-RTT-3D) approach that extends the established ray tracing fusion with multiple diffuse scattering (RT-MDS) framework from natural terrain to urban scenarios by introducing pyramid-shaped diffraction and vegetation scattering ray tubes. A vegetation scattering model based on a leaf-level bidirectional scattering distribution function (BSDF) is established, enabling computationally feasible representation of vegetation effects in deterministic channel prediction. The framework thereby covers buildings, vegetation, and terrain within a unified ray tube data structure. Simulation analyses quantify vegetation modulation of multipath structure and received power across frequencies from 5 to 15 GHz and different canopy sizes. Measurement validation in a campus tree-lined avenue scenario at 2.3 to 5.9 GHz demonstrates that incorporating vegetation scattering reduces the root mean square error (RMSE) of the prediction to 6.11 to 6.30 dB, an improvement of 0.57 to 1.67 dB over the case without vegetation, confirming the effectiveness of the proposed method.