Localization With Joint Diffusion-Based Molecular Communication and Sensing Systems: Fundamental Limits and Tradeoffs

This paper introduces and examines a novel joint communication and sensing system based on molecular diffusion. Using a configuration of at least four fully absorbing spherical receivers, the proposed system achieves precise 3D-localization of a pointwise transmitter by counting the same molecules emitted for communication purposes. We develop an analytical framework to explore the fundamental limits of communication and localization within this context. Exact closed-form expressions for the bit error probability and the Cramér-Rao bound on localization error are derived, considering both Poisson concentration and timing transmitter models, with and without accounting for molecule degradation. For the first time, theoretical trade-offs between communication and localization performance are established, taking inter-symbol interference and molecule degradation into account. In scenarios without molecule degradation, inter-symbol interference detrimentally affects communication but enhances localization. Conversely, the introduction of degradation improves communication performance but partially compromises localization effectiveness. These trade-offs are navigated by adjusting number of transmitted symbols or degradation rate, respectively. Furthermore, we compare communication and localization ranges, alongside the associated costs measured in terms of average emitted molecules required to meet performance requirements.