This paper develops a tractable analytical channel model for first-hitting-time molecular communication 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 a closed-form 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 an explicit analytical expression for the Corrected-Inverse-Gaussian (C-IG) density, extending the classical IG model to strongly nonstationary drift conditions while preserving constant-complexity evaluation. High-precision Monte Carlo simulations under both smooth pulsatile and abrupt switching drift profiles confirm that the proposed model accurately captures complex transport phenomena, including phase modulation, multi-pulse dispersion, and transient backflow. The resulting framework provides a physics-informed, computationally efficient channel model suitable for system-level analysis and receiver design in dynamic biological and molecular communication environments.

翻译：本文针对时变漂移条件下的首达时分子通信系统，提出了一种可解析处理的信道模型。现有非平稳输运研究主要依赖于对流-扩散方程的数值解或参数化冲激响应拟合，但未能提供吸收边界处轨迹级到达动力学的闭式描述。通过采用测度变换公式，我们揭示了首达时密度可结构分解为累积漂移位移项与随机边界通量调制因子。由此推导出修正逆高斯密度的显式解析表达式，将经典IG模型扩展至强非平稳漂移条件，同时保持恒定计算复杂度。在平滑脉冲型与突变切换型漂移剖面下的高精度蒙特卡洛仿真证实，该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。所得框架构建了一个物理信息明确、计算高效的信道模型，适用于动态生物与分子通信环境中的系统级分析与接收机设计。