Exact 3-D Channel Impulse Response for Spherical Receivers with Arbitrary Drift Directions

📅 2025-12-04
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🤖 AI Summary
Existing analytical channel models for three-dimensional molecular communication with spherical absorbing receivers are restricted to one-dimensional or planar flow configurations, lacking a general and accurate solution for arbitrary uniform drift directions. Method: This paper derives, for the first time, a closed-form analytical expression for the three-dimensional channel impulse response (CIR) of a spherical absorbing receiver under arbitrary drift directions. The core technique applies Girsanov’s theorem to perform a drift correction on the Brownian motion path measure, rigorously transforming the static absorption problem into an equivalent drifted-medium first-passage time problem. Contribution/Results: The proposed method overcomes geometric and directional constraints, enabling precise modeling of molecular propagation under arbitrary flow fields. It supports rapid analytical computation of key performance metrics—including peak time and amplitude—thereby significantly reducing reliance on computationally intensive Monte Carlo simulations and providing a solid theoretical foundation for system design and optimization.

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📝 Abstract
Accurate channel modeling for spherical absorbing receivers is fundamental to the design of realistic molecular multiple-input multiple-output (MIMO) systems. While advanced modulation schemes have been proposed to mitigate interference, determining the channel impulse response (CIR) under arbitrary flow directions remains a challenge; existing exact solutions are restricted to either 1-D/no-drift scenarios or planar receiver geometries. Addressing this gap, we derive the first exact analytical CIR for a spherical receiver in a 3-D molecular communication system with uniform drift in an arbitrary direction. Unlike prior approximations that ignore the angle between the drift and the transmission axis, our approach utilizes the Girsanov theorem to analytically transform the hitting-time distribution from a stationary medium to a drifted one. The proposed closed-form expression not only eliminates modeling errors inherent in previous approximations for off-axis receivers but also enables efficient parameter-space exploration of critical system metrics (e.g., peak time and amplitude), a task that would be computationally costly with pure simulation-based approaches.
Problem

Research questions and friction points this paper is trying to address.

Deriving exact 3D channel impulse response for spherical receivers with arbitrary drift directions
Overcoming limitations of existing models restricted to 1D/no-drift or planar geometries
Eliminating modeling errors in off-axis receivers to enable efficient system parameter exploration
Innovation

Methods, ideas, or system contributions that make the work stand out.

Exact 3-D CIR for spherical receivers with arbitrary drift
Uses Girsanov theorem to transform hitting-time distribution
Closed-form expression eliminates modeling errors and enables efficient exploration
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Yen-Chi Lee
Department of Mathematics, National Central University, Taoyuan, Taiwan
P
Ping-Cheng Yeh
Graduate Institute of Communication Engineering, National Taiwan University, Taipei, Taiwan
Chia-Han Lee
Chia-Han Lee
Professor, National Yang Ming Chiao Tung University
Wireless communications