Closed-Loop Molecular Communication with Local and Global Degradation: Modeling and ISI Analysis

TL;DR

This paper develops a physics-based model for closed-loop molecular communication systems, accounting for environmental effects and degradation mechanisms, and analyzes the resulting inter-symbol interference to improve understanding of signal propagation in biomedical applications.

Contribution

It introduces a comprehensive analytical model for closed-loop MC that includes local and global degradation, validated with simulations, and characterizes ISI effects unique to closed-loop systems.

Findings

Model accurately predicts SM propagation in closed-loop systems.

Both local and global degradation significantly affect ISI.

Model validated with 3-D particle-based simulations.

Abstract

This paper presents a novel physics-based model for signal propagation in closed-loop molecular communication (MC) systems, which are particularly relevant for many envisioned biomedical applications, such as health monitoring or drug delivery within the closed-loop human cardiovascular system (CVS). Compared to open-loop systems, which are mostly considered in MC, closed-loop systems exhibit different characteristic effects influencing signaling molecule (SM) propagation. One key phenomenon are the periodic SM arrivals at the receiver (RX), leading to various types of inter-symbol interference (ISI) inherent to closed-loop system. To capture these characteristic effects, we propose an analytical model for the SM propagation inside closed-loop systems. The model accounts for arbitrary spatio-temporal SM release patterns at the transmitter (TX), and incorporates several environmental effects such as fluid flow, SM diffusion, and SM degradation. Moreover, to capture a wide range of practically relevant degradation and clearance mechanisms, the model includes both local removal (e.g., due to SM absorption into organs) and global removal (e.g., due to chemical degradation) of SMs. The accuracy of the proposed model is validated with three-dimensional (3-D) particle-based simulations (PBSs). Moreover, we utilize the proposed model to develop a rigorous characterization of the various types of ISI encountered in closed-loop MC systems.