Modulation Schemes for Functionalized Vesicle-based MC Transmitters

TL;DR

The paper addresses TX-induced memory in functionalized vesicle-based MC transmitters by developing a realistic release model that includes delay, buffering, and leakage. It introduces two TX-tailored modulation schemes, Memory-Aware Modulation (MAM) and Memory-Erasing Modulation (MEM), to mitigate memory effects directly at the transmitter, enabling simple, low-complexity receivers. Through detailed modeling with Hill kinetics, buffering factors, and leakage, and via numerical simulations, the authors demonstrate that MAM and MEM outperform conventional schemes like OOK and OOK-GI under realistic biochemical constraints, especially in buffered scenarios. This work advances physically realizable MC systems by reducing TX-induced memory and improving reliability without compromising data rate, paving the way for practical bio-inspired MC implementations.

Abstract

Molecular communication (MC) enables information exchange through the transmission of signaling molecules (SMs) and holds promise for many innovative applications. However, most existing works in MC rely on simplified transmitter (TX) models that do not account for the physical and biochemical limitations of realistic biological hardware and environments. This work extends previous efforts toward developing models for practical MC systems by proposing a more realistic TX model that incorporates the delay in SM release and TX noise introduced by biological components. Building on this more realistic, functionalized vesicle-based TX model, we propose two novel modulation schemes specifically designed for this TX to mitigate TX-induced memory effects that arise from delayed and imperfectly controllable SM release. The proposed modulation schemes enable low-complexity receiver designs by mitigating memory effects directly at the TX. Numerical evaluations demonstrate that the proposed schemes improve communication reliability under realistic biochemical constraints, offering an important step toward physically realizable MC systems.

Figures (8)

• Figure 1: Schematic illustration of the considered end-to-end MC system featuring a binary LED as the modulator, the realizable TX, a diffusive channel, and a FAR (from left to right, not drawn to scale). Created with BioRender.com.
• Figure 2: Hill curve for $n \in \{1, 2, 3, 4, \infty\}$. The curve for $n \rightarrow \infty$ (hard threshold) is highlighted in red and the activity threshold $C^{\mathrm{H^{+}}}_{\xi}$ for $n = 3$ (see \ref{['sec:mam']}) is indicated by a green dotted line. $C^{\mathrm{H^{+}}}_{\mathrm{in, 0}}$ and $C^{\mathrm{H^{+}}}_{\mathrm{in,eq}}$ are indicated by gray dashed lines and the gray-shaded area indicates the operation interval of the TX. The parameter values in \ref{['tab:params']} were used.
• Figure 3: Flux attenuation factor $\vartheta_{\mathrm{buf}}(t)$ vs. intravesicular $\mathrm{H^{+}}$ concentration for the system parameters in \ref{['tab:params']} and buffer molarity $C_{0} = 5\mol \per \cubic m$. The green dotted line corresponds to $C^{\mathrm{H^{+}}}_{\mathrm{in}, \xi}$. $C^{\mathrm{H^{+}}}_{\mathrm{in, 0}}$ and $C^{\mathrm{H^{+}}}_{\mathrm{in,eq}}$ are indicated by gray dashed lines. The gray-shaded area indicates the operation interval of the TX. Created in part with BioRender.com.
• Figure 4: $C^{\mathrm{H^{+}}}_{\mathrm{in}}(t)$ for the considered modulation schemes and an exemplary bit sequence. Gray-shaded areas indicate bit "1" intervals. (a) OOK, (b) OOK-GI, (c) MAM, (d) MEM. Colored bars indicate times during which the LED is switched on for the different modulation schemes and the horizontal black dashed line indicates $C^{\mathrm{H^{+}}}_{\mathrm{in}, \xi}$. Vertical dotted colored lines indicate the times at which $C^{\mathrm{H^{+}}}_{\mathrm{in}, \xi}$ is crossed.
• Figure 5: (a) Derivation of upper bounds for $T_\mathrm{l}$ and $T_\mathrm{d}$, i.e., $T_\mathrm{l}^\mathrm{max}$ and $T_\mathrm{d}^\mathrm{max}$. (b) Derivation of lower bounds for $T_\mathrm{l}$ and $T_\mathrm{d}$, i.e., $T_\mathrm{l}^\mathrm{min}$ and $T_\mathrm{d}^\mathrm{min}$.