Ratio Shift Keying Modulation for Time-Varying Molecular Communication Channels

TL;DR

This paper introduces Ratio Shift Keying (RSK), a novel molecular communication modulation scheme that encodes information in concentration ratios, demonstrating its advantages over traditional methods in dynamic, time-varying channels through theoretical and practical analysis.

Contribution

The paper provides the first information-theoretical analysis of RSK modulation and evaluates its performance in mobile molecular communication scenarios, showing its superiority over CSK.

Findings

RSK can significantly outperform CSK in dynamic MC scenarios.

RSK's capacity depends on ligand similarity and receptor number.

Numerical results confirm RSK's robustness in time-varying channels.

Abstract

Molecular Communications (MC) is a bio-inspired communication technique that uses molecules to encode and transfer information. Many efforts have been devoted to developing novel modulation techniques for MC based on various distinguishable characteristics of molecules, such as their concentrations or types. In this paper, we investigate a particular modulation scheme called Ratio Shift Keying (RSK), where the information is encoded in the concentration ratio of two different types of molecules. RSK modulation is hypothesized to enable accurate information transfer in dynamic MC scenarios where the time-varying channel characteristics affect both types of molecules equally. To validate this hypothesis, we first conduct an information-theoretical analysis of RSK modulation and derive the capacity of the end-to-end MC channel where the receiver estimates concentration ratio based on ligand-receptor binding statistics in an optimal or suboptimal manner. We then analyze the error performance of RSK modulation in a practical time-varying MC scenario, that is mobile MC, in which both the transmitter and the receiver undergo diffusion-based propagation. Our numerical and analytical results, obtained for varying levels of similarity between the ligand types used for ratio-encoding, and varying number of receptors, show that RSK can significantly outperform the most commonly considered MC modulation technique, concentration shift keying (CSK), in dynamic MC scenarios.