Molecular Communication Transmitter Design in Limited-Capacity Storage Regime.

The limited storage capacity at the transmitters of a molecular communication (MC) system can affect the system's performance. One of the reasons for this limitation is the size restriction of the transmitter, which the storage must be replenished so that the transmitter has enough molecules for future transmission. This paper proposes a biologically inspired transmitter model based on neurons for MC whose storage charging and discharging follow differential equations. The proposed transmitter opens its outlet for a specific time in each time frame to exponentially release a portion of stored molecules to code bit-1 and remains silent to code bit-0. We analyze our model based on different transmission parameters. These parameters are the symbol duration, the release time duration, the storage capacity, and the release and replenishment rate of the storage. We find that the storage outlet must be open for a certain period within the time slot duration in order to improve the performance of the proposed system. Additionally, we demonstrate that determining the effect of storage capacity size can be important for practical MC due to the significant differences between the ideal transmitter and the proposed one, which have a limited size. We show that increases in the transmitter storage size can improve the system performance. As a result, taking a closer look at these practical transmitters is essential to solving the problems and challenges of molecular communication systems.

Performance Evaluation and Optimal Detection of Relay-Assisted Diffusion-Based Molecular Communication With Drift.

In this paper, we consider a decode-and-forward (DF) relay-assisted diffusion-based molecular communication system inside one of the blood vessels of a human body with positive drift from transmitter to receiver. We use the normal approximation to the distribution of the number of received molecules and derive a closed-form expression for the end-to-end bit error probability of the system. We then propose an optimization problem that aims at minimizing the bit error probability of the system and solve it at the receiver nanomachine by an algorithm based on the bisection method to determine the optimal detection threshold. Furthermore, we study the impact of the system parameters, such as drift velocity, position of the relay node and number of allocated molecules on the performance of the system. The numerical results show that with a constant molecular budget, DF relying strategy can considerably improve the system performance.