On Medium Chemical Reaction in Diffusion-Based Molecular Communication: a Two-Way Relaying Example

TL;DR

This paper explores the use of chemical reactions within the medium of molecular communication to perform computation, reduce noise, implement network coding, and mitigate inter-symbol interference, demonstrated through a two-way relaying example.

Contribution

It introduces a novel molecular physical-layer network coding scheme that performs XOR operations in the medium, outperforming traditional relay-based XOR methods especially under inter-symbol interference.

Findings

PNC scheme reduces signal-dependent noise and ISI.

PNC outperforms traditional SNC scheme in simulations.

Chemical reactions enable in-medium computation for molecular communication.

Abstract

Chemical reactions are a prominent feature of molecular communication (MC) systems, with no direct parallels in wireless communications. While chemical reactions may be used inside the transmitter nodes, receiver nodes or the communication medium, we focus on its utility in the medium in this paper. Such chemical reactions can be used to perform computation over the medium as molecules diffuse and react with each other (physical-layer computation). We propose the use of chemical reactions for the following purposes: (i) to reduce signal-dependent observation noise of receivers by reducing the signal density, (ii) to realize molecular physical-layer network coding (molecular PNC) by performing the natural XOR operation inside the medium, and (iii) to reduce the inter-symbol interference (ISI) of other transmitters by canceling out the remaining molecules from previous transmissions. To make the ideas formal, we consider an explicit two-way relaying example with a transparent receiver (which has a signal-dependent noise). The proposed ideas are used to define a modulation scheme (which we call the PNC scheme). We compare the PNC with a previously proposed scheme for this problem where the XOR operation is performed at the relay node (using a molecular logic gate). We call the latter, the straightforward network coding (SNC). It is observed that in addition to the simplicity of the proposed PNC scheme, it outperforms the SNC scheme especially when we consider ISI.