Run-Length-Limited ISI-Mitigation (RLIM) Coding for Molecular Communication

Abstract: Inter-symbol interference (ISI) is a significant challenge in diffusion-based communication channels, where residual molecules from previous transmissions interfere with the current signal interval, leading to detection errors. We introduce a new infinite family of coding schemes, which we name RLIM, that require each 1-bit to be followed by at least i consecutive 0-bits, where i is any chosen positive integer. This enhances ISI mitigation and improves error correction capabilities compared to existing ISI-mitigating channel codes. Through extensive simulations, we demonstrate that the codebooks derived from the proposed RLIM scheme significantly reduce bit error rate compared to prominent coding methods. Simulation results also reveal that an important constraint in RLIM codes is redundant under zero-drift conditions, removal of which makes them equivalent to run-length-limited (RLL) codes. Notably, despite this equivalence, the proposed family of RLIM coding schemes retains a distinct power optimization constraint and employs a specialized error correction algorithm, preserving its unique character and advantages. Furthermore, in diffusion-based channels with time-varying drift, the previously redundant constraint becomes critical for ensuring robust detection, thus demonstrating the enhanced applicability of proposed RLIM codes for such channels as well.