Scheduling-Based Transmit Signal Shaping in Energy-Constrained Molecular Communications

Diffusion-based molecular communications (DBMC) systems rely on diffusive propagation of molecules to convey information. In a DBMC system, as each emitted molecule experiences a stochastic delay, pulse shaping is crucial for a DBMC system’s reliability and overall performance. To this end, acknowledging the inherent resource-limited nature of a DBMC system, a novel framework to model and optimize a DBMC transmitter is introduced in this paper. Leveraging tools from wireless packet scheduling theory, the DBMC pulse shaping problem is formulated as an energy-constrained resource allocation problem. Through the developed framework, it is shown that the provably optimal pulse shape that minimizes the error probability is the delayed-spike pulse, where the incurred delay is a decreasing function of the available energy budget. The framework is then extended to both absorbing and passive/observing receiver structures, as well as systems where molecules can degrade in the transmitter body prior to release. Numerical results corroborate the developed analysis, and show that the delayed-spike outperforms conventional, non-zero-width pulse shapes in terms of error performance.