Information Rates of ASK-Based Molecular Communication in Fluid Media

TL;DR

This paper investigates the capacity of ASK-based molecular communication in fluid media, analyzing both ISI-free and ISI-affected scenarios, and provides bounds and optimal input distributions for these channels.

Contribution

It introduces capacity analysis for molecular channels with amplitude shift keying, including the effects of ISI and practical constraints, with new bounds and input distribution strategies.

Findings

Capacity bounds are close over various parameters.

Optimal input distribution shifts from binary to uniform with increasing time-slot.

ISI significantly impacts channel capacity and output correlations.

Abstract

This paper studies the capacity of molecular communications in fluid media, where the information is encoded in the number of transmitted molecules in a time-slot (amplitude shift keying). The propagation of molecules is governed by random Brownian motion and the communication is in general subject to inter-symbol interference (ISI). We first consider the case where ISI is negligible and analyze the capacity and the capacity per unit cost of the resulting discrete memoryless molecular channel and the effect of possible practical constraints, such as limitations on peak and/or average number of transmitted molecules per transmission. In the case with a constrained peak molecular emission, we show that as the time-slot duration increases, the input distribution achieving the capacity per channel use transitions from binary inputs to a discrete uniform distribution. In this paper, we also analyze the impact of ISI. Crucially, we account for the correlation that ISI induces between channel output symbols. We derive an upper bound and two lower bounds on the capacity in this setting. Using the input distribution obtained by an extended Blahut-Arimoto algorithm, we maximize the lower bounds. Our results show that, over a wide range of parameter values, the bounds are close.