Fundamental investigation of extending 4G-LTE signal over MMF/SMF-FSO under controlled turbulence conditions

In this paper, we propose a hybrid radio over multi-mode/single-mode fibre and free space optics (RoMMF/SMF-FSO) system to enhance the 4th generation-long term evolution (4G-LTE) signal performance when used in local area access networks. A single mode fibre pigtailed gradient index lens is used to minimise the modal effect of the optical link at different turbulence strengths. The proposed system is characterised in terms of the system transfer function, error vector magnitude (EVM), and optical launch power (OLP). Results demonstrate the robustness of the proposed scheme in terms of increased available passband bandwidth by 2 GHz and improving the transmission shape by reducing the system transfer function ripple by more than 5 dB. Successful transmission of the 4G-LTE signal is achieved over a MMF/SMF-FSO channel with a 1.5 dB power penalty under the higher turbulence level (i.e., Rytov variance of 0.1).