Full-Duplex Transmissions in Heterogeneous Fiber-FSO-Wireless Converged Access Networks at Ka-Band

To overcome the challenges associated with increased demands for mobile capacity and network densification in the 5 G and beyond era, this paper experimentally demonstrates full-duplex heterogeneous fiber-FSO-wireless converged links between the central office-baseband unit (CO-BBU) and the remote radio head (RRH). The centralization of active optical sources for the downlink (DL) and uplink (UL) enables dynamic resource sharing and allocation, optimizing wavelength utilization and improving overall network efficiency. The DL uses a directly modulated laser (DML) with free-running laser-assisted mmWave signal generation and envelope detection for the downstream, transmitting a $100 \text{MHz} 16-\text{QAM}$ signal at 39 GHz. The UL reuses the DL wavelength for upstream transmission, employing intensity modulation and direct detection (IM-DD) of a 100 MHz QPSK signal at 36.5 GHz. The bidirectional heterogeneous network comprises a 10 km SSMF, a 1.8 m FSO link, and a 3 m wireless radio link, providing flexibility for future networks. The results show successful transmissions of 16-QAM and QPSK signals up to $200 \text{Mbit} / \mathrm{s}$ and $400 \text{Mbit} / \mathrm{s}$ for DL and UL, respectively, under the full-duplex transmissions. Additionally, using 5G NR OFDM signals, a maximum bit rate of $2.15 \text{Gbit} / \mathrm{s}$ and 1.07 Gbit/s is achieved for the DL and UL, respectively, demonstrating the cost-effectiveness of the proposed solution.