This paper develops a tractable analytical channel model for first-hitting-time molecular communication (MC) systems under time-varying drift. While existing studies of nonstationary transport rely primarily on numerical solutions of advection-diffusion equations or parametric impulse-response fitting, they do not provide an explicit analytical description of trajectory-level arrival dynamics at absorbing boundaries. By adopting a change-of-measure formulation, we reveal a structural decomposition of the first-hitting-time density into a cumulative-drift displacement term and a stochastic boundary-flux modulation factor. This leads to a closed-form Corrected-Inverse-Gaussian (C-IG) density that generalizes the classical IG model to nonstationary drift while preserving O(1) evaluation complexity. Monte Carlo simulations under both smooth pulsatile and abrupt switching drift profiles confirm that the proposed C-IG model accurately captures complex transport phenomena, including phase modulation, multi-pulse dispersion, and transient backflow -- effects that traditionally complicate symbol synchronization and induce severe inter-symbol interference. The resulting framework provides a physics-informed, computationally efficient channel model suitable for system-level analysis and advanced receiver design, such as real-time maximum likelihood detection, in dynamic biological and MC environments.

翻译：本文针对时变漂移条件下首次命中时间分子通信（MC）系统，建立了一种易处理的解析信道模型。现有非平稳输运研究主要依赖平流扩散方程的数值解或参数化脉冲响应拟合，但未能提供吸收边界处轨迹级到达动力学的显式解析描述。通过采用测度变换公式，我们揭示了首次命中时间密度的结构分解，将其分解为累积漂移位移项与随机边界通量调制因子。由此推导出封闭形式的修正逆高斯（C-IG）密度函数，该函数在保持O(1)计算复杂度的前提下，将经典IG模型推广至非平稳漂移场景。针对平滑脉动与突变切换两种漂移轮廓的蒙特卡洛仿真表明，所提C-IG模型能精确捕捉复杂输运现象，包括相位调制、多脉冲色散及瞬态回流——这些效应传统上会复杂化符号同步并引发严重码间干扰。最终框架形成的物理约束型高效计算信道模型，适用于动态生物及MC环境中的系统级分析与先进接收机设计（如实时最大似然检测）。