On the Tail Transition of First Arrival Position Channels: From Cauchy to Exponential Decay
For molecular communication system designers, this work provides a physically grounded performance baseline and clarifies when drift regularization matters.
The paper characterizes how nonzero drift in first arrival position channels transitions the lateral displacement distribution from heavy-tailed Cauchy to exponential decay, identifying a characteristic propagation distance that separates diffusion- and drift-dominated regimes. Numerical experiments show that Gaussian approximations underestimate communication potential in low-drift environments, while the Cauchy law provides a robust baseline.
While the zero-drift first arrival position (FAP) channel exhibits a Cauchy-distributed lateral displacement, nonzero drift in practical systems introduces advective transport that regularizes this singular limit. This letter characterizes the drift-induced transition of FAP distribution from heavy-tailed algebraic regime to exponential regularization. By asymptotically examining the exact FAP density, we identify a characteristic propagation distance (CPD) that serves as the fundamental boundary separating diffusion-dominated and drift-dominated regimes. Numerical experiments demonstrate that in low-drift environments, variance-matched Gaussian approximations severely underestimate the true communication potential, whereas the zero-drift Cauchy law provides a robust, physically grounded performance baseline.