Tradeoff Between the Number of Transmitted Molecules and the BER Performance in Molecular Communication Between Bionanosensors
Recent advancements in nanotechnology, biotechnology, and synthetic biology have led to the development of bionanosensors—nanomachines capable of performing fundamental functions such as sensing, computation, and actuation. By enabling communication among these nanomachines, it becomes possible to create complex nanonetworks of interconnected nanoscale devices, thereby enhancing their overall functionality.
Molecular Communication (MC) is an emerging communication paradigm inspired by biological systems. It allows nanoscale devices, such as bionanomachines or biosensors, to exchange information using signaling molecules, including DNA, calcium ions, or neurotransmitters. Information can be encoded through various molecular features, such as concentration, type, and timing of release. These signals typically propagate via diffusion, modeled as Brownian motion, and do not require an external energy source.
Despite its potential, MC systems face significant limitations stemming from the finite molecular resources available at the transmitter. The small size of the transmitter restricts the storage of molecules, and slow production rates—due to chemical kinetics—necessitate frequent replenishment. Additionally, communication efficiency may decline if the number of released molecules surpasses the receiver's capacity. To tackle these challenges, recent research has focused on optimizing molecule release strategies to minimize the average bit error rate (BER) in MC systems.
This study examines a three-dimensional diffusion-based MC system, which consists of a point transmitter and a spherical passive receiver. The study analyzes the relationship between BER and the number of transmitted molecules. Increasing the number of molecules improves the signal-to-noise ratio (SNR) and reduces BER; however, it also increases energy consumption and puts additional strain on the transmitter’s molecular reservoir. A critical challenge is intersymbol interference (ISI), caused by residual molecules from previous transmissions. While ISI generally diminishes after a short time window, it can still distort subsequent signals.
Signal detection at the receiver is performed using a threshold-based binary detection mechanism that monitors molecular concentration. This method is highly sensitive to both the number of molecules and the channel conditions, requiring precise calibration to maintain reliable performance.
To optimize system efficiency, this study introduces a balance function that simultaneously considers BER and molecular resource consumption. A Gradient Descent Algorithm is applied to this function to identify the optimal number of transmitted molecules for reliable and efficient communication. The optimization framework reflects a trade-off between communication reliability and resource usage, incorporating both normalized BER and the molecule count into the balance function. The algorithm iteratively updates these variables using partial derivatives to converge on an efficient configuration.
Analysis reveals diminishing returns in BER reduction beyond a certain number of transmitted molecules. Moreover, SNR decreases with increasing distance between the transmitter and receiver due to a reduced arrival of molecules. Simulation results validate the necessity for efficient resource allocation to support sustainable MC system operation.
This study emphasizes the importance of molecular resource management in maintaining MC systems. It presents a tunable optimization framework that can be adapted to prioritize either communication quality or resource conservation, depending on application requirements.