Joint millimeter-wave communication and optical multipath interference localization for RoF mobile fronthaul.

Millimeter-wave (mm-wave) radio-over-fiber (RoF) technology is a promising solution for next-generation mobile networks. However, its practical implementation faces two critical challenges: the high cost and bandwidth requirements of optoelectronic components for mm-wave signal generation, and vulnerability to optical multipath interference (MPI) caused by reflections at dirty fiber connectors in large-scale mobile fronthaul networks. To address these challenges, we propose and demonstrate a joint mm-wave communication and MPI localization scheme for high-capacity mm-wave RoF links based on a novel linear frequency modulation single sideband (LFM-SSB) waveform, which is generated by combining a virtual-carrier-aided SSB signal with a digital LFM carrier. In the LFM-SSB waveform, the virtual-carrier-aided SSB signal enables photonic-aided mm-wave up-conversion, while the LFM carrier achieves MPI localization. The LFM carrier in the LFM-SSB waveform is eliminated after self-heterodyne detection in the absence of MPI, resulting in a negligible impact on transmission performance. Simulation results demonstrate that the proposed scheme achieves sub-decimeter (5 cm) MPI localization accuracy while maintaining robustness against large linewidth lasers. With lasers having linewidths below 2 MHz, both high-precision MPI localization and robust communication performance are achieved. It indicates that the proposed scheme offers the advantage of low-cost, large-linewidth lasers without compromising on high accuracy and large capacity. Experimental validation demonstrates the transmission of a 2 Gbaud 16QAM mm-wave signal at 30 GHz, with successful localization of a single MPI reflection path at 107.46 m. Additionally, an MPI localization resolution of 9.78 cm is achieved at a chirp rate of 200 THz/s. The experimental system supports a maximum of 6 Gbaud 16QAM mm-wave signals and successfully locates two MPI reflection paths.