6G BRAINS addresses current challenges in networks, beyond 5G (B5G), 6G, Terahertz (THz), Optical Wireless Communications (OWC), Artificial Intelligence (AI), Multi-agent Deep Reinforcement Learning, Highly Dynamic Ultra-Dense Device-to-Device (D2D) Cell-free Networks, Grant Free-Non-Orthogonal Multiple Access (GF-NOMA), End-to-End (E2E) Slicing, Integrated Access Backhaul (IAB), Industrial Virtual Assistant (IVA), Simultaneous Localization and Mapping (SLAM), Content Distribution Network (CDN), massive Machine Type Communication (mMTC) and Ultra-Reliable Low Latency Communication (URLLC). Ubiquitous smart wireless connectivity is critical for future large-scale industrial tasks, services, assets and devices. Very significantly improved connectivity needs to be unlocked through novel spectrum combinations and the fully autonomous management of the underlying network resources by applying online AI at multiple decision layers. 6G BRAINS aims to bring AI-driven multi-agent Deep Reinforcement learning (DRL) to perform resource allocation over and beyond massive machine-type communications with new spectrum links including THz and optical wireless communications (OWC) to enhance the performance with regard to capacity, reliability and latency for future industrial networks. We propose a novel comprehensive cross-layer DRL driven resource allocation solution to support the massive connections over device-to-device (D2D) assisted highly dynamic cell-free network enabled by Sub-6 GHz/mmWave/THz/OWC and high resolution 3D Simultaneous Localization and Mapping (SLAM) of up to 1 mm accuracy. The enabling technologies in 6G BRAINS focus on four major aspects including disruptive new spectral links, highly dynamic D2D cell-free network modelling, intelligent end-to-end network architecture integrating the multi-agent DRL scheme and AI-enhanced high-resolution 3D SLAM data fusion. The proposed solution will be validated by proof-of-concept trials. The primary and secondary appl
