5G STEP FWD proposes a new architecture that uses UDWDM PONs as the backhaul of mmWave networks in order to achieve high capacity and low latency backhauling. The proposed architecture takes full advantage of the ultra-narrow wavelength spacing of the UDWDM technology, in order to provide connectivity to a dense small-cell population. At the physical layer domain, 5G STEP FWD aims at providing a comprehensive framework based on a disruptive device- or user-centric cellular concept, which will allow smart overlaid peer-to-peer communications, while it will also optimally allocate small cells where the fiber goes. At the network layer domain, we envision the modelling and optimization of the 5G STEP FWD network resource usage through the incorporation of a Software-Defined-Network (SDN) framework, which integrates multiple wireless and backhaul resources into a single pool, and could play a key role in supporting multi-tenancy and enabling the network operation management and optimization. Moreover, the mission of 5G STEP FWD is to create a vibrant EU-based training and research environment for young European and international researchers, aiming at designing architectures, systems and algorithms for building the 5G cellular network of tomorrow.