Multi-scale molecular communication (MC) employs the characteristics of information molecules for information exchange. The received signal in MC inevitably encounters severe inter-symbol interference and signal-dependent noise due to the stochastic diffusion mechanism. Focusing on the critical signal detection in MC, first this article reviews the commonly used model-based detectors, and exposes their limitations in practical implementation. Then, the emerging data-driven detectors that can make up for some deficiencies of the model-based detectors are presented. Despite the black-box nature of the data-driven detectors, the explainable artificial intelligence can be further investigated for the performance improvement of transparency and trust.
I. INTRODUCTION Molecular communication (MC) is an emerging multi-scale communication paradigm that conveys messages via the patterns of molecules [1]. MC has been regarded as an alternative for conventional communication techniques in virtue of its unique transmission mechanism.For the nano-scale and micro-scale channels in vivo, the implementation of the conventional communication techniques is hindered for the following reasons. The electromagnetic (EM) wave based wireless communication has its constraint in wave generation. As the wavelength in operation is proportional to the antenna size, nanomachine requires the Tera-hertz band for communications, which is, however, still in its research infancy, let alone the micro-scale implementation. Besides, optical communication is not an appropriate choice due to complex cell/tissue obstacles in the channel. Finally, acoustic communication has an energy issue on such an extremely tiny scale. In addition to the implementation restrictions, the bio-compatibility issue of the above schemes has not been verified in the open literature. As for the macro-scale channels, the EM wave based communication has the propagation problem in metal and aqueous environments. Inspired by the biological systems, MC can remedy the flaws in the existing communication systems. For micro-scale channels, MC via diffusion (MCvD) is an energy-efficient signal transmission mechanism that uses information molecules from the communication environments, and no extra energy is required for the