Designing molecular circuits for approximate maximum a posteriori demodulation of concentration modulated signals

TL;DR

This paper designs molecular circuits for demodulating concentration-modulated signals, deriving an approximate filter analytically, implementing it biologically, and validating its performance through simulations and yeast circuit experiments.

Contribution

It introduces a method to approximate and implement demodulation filters for molecular communication using biochemical circuits, bridging theory and biological realization.

Findings

The derived molecular circuit approximates the log-posteriori probability.

Simulation results show the circuit's output closely matches the theoretical filter.

A yeast biochemical circuit exhibits similar behavior to the designed demodulation filter.

Abstract

Motivated by the fact that living cells use molecular circuits (i.e. a set of chemical reactions) for information processing, this paper investigates the problem of designing molecular circuits for demodulation. In our earlier work, we use a Markovian approach to derive a demodulator for diffusion-based molecular communication. The demodulation filters take the form of an ordinary differential equation which computes the log-posteriori probability of a transmission symbol being sent. This work considers the realisation of these demodulation filters using molecular circuits assuming the transmission symbols are rectangular pulses of the same duration but different amplitudes, i.e. concentration modulation. This paper makes a number of contributions. First, we use time-scale separation and renewal theory to analytically derive an approximation of the demodulation filter from our earlier work. Second, we present a method to turn this approximation into a molecular circuit. By using simulation, we show that the output of the derived molecular circuit is approximately equal to the log-posteriori probability calculated by the exact demodulation filter if the log-posteriori probability is positive. Third, we demonstrate that a biochemical circuit in yeast behaves similarly to the derived molecular demodulation filter and is therefore a candidate for implementing the derived filter.