Photonic-aided Doppler-robust ISAC system based on index modulation and chirp multiplexing

Integrated sensing and communication (ISAC) is considered to be a pivotal trend in the development of the low-Earth-orbit (LEO) satellite networks. The previous demonstrations have faced challenges in accommodating significant Doppler frequency shifts of high-mobility environments. Therefore, in this work, a photonic-aided Doppler robust ISAC system is proposed and demonstrated. A chirp-multiplexed and index modulated linearly frequency modulated (IM-LFM) waveform is designed and generated by a dual polarization up-converter, which consists of a dual-wavelength laser, a circulator, a fiber Bragg grating (FBG), a dual parallel quadrature phase shift keying modulator (DP-QPSKM), a polarization beam splitter, and two high-speed photodetectors. A photonic dual polarization radar receiver is designed for dual channel de-chirp processing, while the communication reception and demodulation are implemented through down conversion and FFT operation. A 16.3-17.826 GHz IM-LFM waveform is experimentally generated and demonstrated for ISAC purposes. The sensing range resolution is better than 0.146 meters with a probability larger than 86%, and a 29.99-Mbps rate communication is achieved with a 500 kHz Doppler frequency shift. This scheme is particularly suitable for high-mobility ISAC applications.