Achievable Information Rate Analysis in Diffusive Channels with Memory and Markov Source

TL;DR

This paper analyzes the achievable information rate in diffusive molecular communication channels with memory, considering ISI effects, source correlation, and optimizing detection thresholds to enhance channel capacity.

Contribution

It introduces a comprehensive analysis of AIR in diffusive channels with memory, incorporating source correlation and threshold optimization for the first time.

Findings

Correlated sources yield higher capacity.

Maximum AIR is achieved with non-uniform input distributions.

Strong ISI reduces the effectiveness of equiprobable signaling.

Abstract

This paper explores the Achievable Information Rate (AIR) of a diffusive Molecular Communication (MC) channel featuring a fully absorbing receiver that counts the absorbed particles during symbol time intervals (STIs) and resets the counter at the start of each interval. The MC channel, influenced by memory effect, experiences inter-symbol interference (ISI) arising from the molecules' delayed arrival. The channel's memory is quantified as an integer multiple of the STI and a single-sample memoryless detector is employed to mitigate complexity in computing the mutual information (MI). To maximize MI, the detector threshold is optimized under Gaussian approximation of its input. The channel's MI is calculated, considering the influence of ISI, in the context of binary concentration shift keying modulation. Two distinct scenarios were considered; independent and correlated source-generated symbols, the latter modeled as a first-order Markov process. For each communication scenario, two degrees of knowledge: ISI-Aware and ISI-Unaware were considered. Remarkably, it is demonstrated that employing a correlated source enables the attainment of higher capacity. The results indicate that the capacity-achieving input distribution is not necessarily uniform. Notably, when the STI is small, corresponding to the case of strong ISI, the maximum AIR is not achieved through equiprobable symbol transmission.