Coherent WDM-PON and free space optical (FSO) system for front-haul in next-generation cellular networks

The demand for optical networks that offer low latency and high capacity is increasing with the rise of next-generation cellular systems. Centralized Radio Access Network (C-RAN) architecture provides a cost-effective approach to mobile network deployment. To enhance flexibility and minimize fronthaul network implementation expenses, we propose a bidirectional fronthaul C-RAN configuration that combines coherent Wavelength Division Multiplexing (WDM), passive optical networks (PONs), and free-space optical (FSO) communication. This system utilizes an efficient wavelength reuse technique employing reflective semiconductor optical amplifiers (RSOAs), which helps reduce costs and boost capacity, resulting in a high-throughput network. The setup achieves a downstream data rate of 125 Gbps using 16-quadrature amplitude modulation (16-QAM) and an upstream data rate of 10 Gbps using on-off keying (OOK). An FSO link was modeled using a Gamma–Gamma channel for optical signal transmission. The bit error rate (BER) results suggest that the fronthaul based on WDM-FSO-PON can reach 4 Tbps over a 2.5 km free-space link.