Concentration and Position-Based Hybrid Modulation Scheme for Molecular Communications

Modulation design is a particularly interesting problem in the context of molecular communication via diffusion (MCvD), due to the heavy and signal dependent inter-symbol interference (ISI) imposed on the communication link. To tackle the modulation design issue in MCvD, a hybrid modulation family is proposed in this study. The proposed scheme operates by combining conventional concentration constellations with pulse position modulation symbols, and is able to encode more bits into a single joint symbol than traditional concentration or position-based schemes. Called molecular concentration-position modulation (MCPM), it is shown through theoretical and numerical results that the proposed scheme yields promising error performances, especially in the regime with high ISI and low transmission power. Furthermore, MCPM only utilizes a single type of molecule, which suggests an easier implementability for micro- or nano-scale machinery.