Integrated ultra-large dynamic vibration sensing with fronthaul analog radio-over-fiber transmission

The utilization of optical fiber in fronthaul transmission within radio access networks (RANs) offers significant advantages in terms of high quality, stability, and long-reach capabilities. Simultaneously, distributed acoustic sensing (DAS) enables network surveillance and human activity detection through environmental monitoring. However, the implementation of large-scale strain measurement remains a challenge. In this paper, we propose a novel linear frequency modulated (LFM) pilot-aided radio OFDM fronthaul waveform specifically designed for integrated sensing and communication over fiber (ISACoF). The continuous LFM pilots facilitate the demodulation process at the communication side and serve as sensing probes to detect vibrations along the fiber using pulse compression techniques. Furthermore, by leveraging the large bandwidth of OFDM radio signals, the frequency-demodulated DAS enabled by multiple LFM pilots overcomes the limitations of traditional phase-demodulated DAS in scenarios involving large dynamic vibrations. We experimentally demonstrate the transmission of OFDM radio signals through a 10-km fiber and a 4-m free-space channel, assisted by 128 LFM pilots. By utilizing millimeter-wave (MMW) radio signals operating within a frequency range of 27.2 GHz to 29 GHz and a bandwidth of 1.8 GHz, dynamic vibration measurements of up to 6 με are achieved. Additionally, by optimizing the power ratio between OFDM payloads and LFM pilots, we achieve a sensing sensitivity of 0.81 nε∕^{p‣‣‣‣‣‣} Hz and a demodulated signal-to-noise ratio of over 20 dB for 64-QAM-OFDM. Various modulation formats and vibration waveforms are validated via experiments, thereby confirming the feasibility of implementing the proposed ISACoF system in practical RAN design.