Hybrid Amplify and Forward TV Whitespace Radio Over Free-Space Optics

While Radio-over-Free-Space-Optics (RoFSO) is a key xG enabler, most research focuses on high-complexity systems unsuitable for cost-sensitive rural deployments. This work presents and experimentally validates a low-complexity, sub-6 GHz RoFSO architecture designed for heterogeneous networks. We transport a 70 MHz intermediate frequency signal, carrying a spectrally-efficient TV Whitespace (TVWS) waveform, over an 800 m turbulent optical link using direct subcarrier intensity modulation. At the remote end, a mixer up-converts the signal back to the TVWS band for RF transmission, validating a cost-effective mix-amplify-and-forward remote antenna unit. We provide a detailed performance characterisation of the optical backhaul under real-world atmospheric conditions and demonstrate the end-to-end viability of the hybrid architecture. Our results establish a practical pathway for physically separating complex baseband processing from low-power and low-cost remote radio heads in challenging environments.