A radiomap, representing the spatial distribution of wireless signal strength within a specific region, is fundamentally determined by the local propagation channel and finds extensive applications in network planning and optimization. The channel model is inherently linked to electromagnetic (EM) wave propagation, and the advent of high-frequency communications presents a new picture - microscopic (and thus negligible) scatterers in lower frequency bands become mesoscopic, rendering non-negligible EM effects. In this paper, we establish a channel model for multiple scatterers based on a spherical wave mode expansion. The source radiation, single scatterer response and multiple scatterer interactions are formed in the superposition of spherical-wave modes, capturing the multi-path effect in wave perspective. Iterative methods are used to handle the massive coupling between scatterers. This forward model is converted to an inverse optimization problem, where the scattering responses and the scatterer locations are jointly learned from sparse field measurements. A simplified approximate model is then introduced, employing fewer and simpler low-order modes while still allowing a larger number of more densely placed scatterers. Simulation results demonstrate that the proposed model accurately reconstructs and extrapolates radiomaps in both the spatial domain and the beam domain. Overall, the proposed framework offers a physically interpretable approach to localized propagation modeling.

翻译：无线电地图描述了特定区域内无线信号强度的空间分布，其本质由局部传播信道决定，在网络规划与优化中具有广泛应用。信道模型与电磁波传播具有内在关联，高频通信的出现带来了新的图景——低频段中微观（因而可忽略）的散射体在中高频段演变为介观尺度，从而产生不可忽视的电磁效应。本文基于球面波模态展开建立了多散射体的信道模型。将源辐射、单散射体响应及多散射体相互作用均表示为球面波模态的叠加，从波动角度捕捉多径效应。采用迭代方法处理散射体间的强耦合效应。将该正向模型转化为逆向优化问题，通过稀疏场测量数据联合学习散射响应与散射体位置。随后引入简化近似模型，在减少使用低阶模态数量的同时，允许容纳更多且更密集分布的散射体。仿真结果表明，所提模型能在空间域与波束域中精确重建并外推无线电地图。总体而言，该框架为局部传播建模提供了具有物理可解释性的方法。