Photonics-Aided THz Integrated Sensing and Communication System Based on a Time-Frequency Efficient SF-LFM-OFDM Waveform

Faced with the increasingly scarce spectrum resources in low-frequency bands, integrated sensing and communications (ISAC) technology is expanding into millimeter-wave (MMW) and terahertz (THz) frequencies to harness broader bandwidth. To achieve genuine high-performance integration of sensing and communication in these bands, we propose a photonics-aided THz ISAC system based on a step-frequency linear frequency-modulated orthogonal frequency-division multiplexing (SF-LFM-OFDM) waveform. The core idea of this waveform design is to map the sub-LFM pulses onto preallocated OFDM symbols, then perform the inverse fast Fourier transform (IFFT) and add the cyclic prefix (CP) to generate the ISAC signal. This novel scheme incurs minimal additional temporal or spectral cost over the OFDM signal, while fully retaining the inherent large time-bandwidth product (TBP) of the SF-LFM signal to enhance sensing robustness. Leveraging the high time-frequency efficiency of the designed waveform, our experiment demonstrates simultaneous 103.2-Gb/s data transmission and multiuser detection with 7-mm ranging resolution over a 3-m link at 313.2 GHz. Furthermore, this study investigates the impact of the sub-LFM pulse numbers and the power allocation on both the communication and sensing performance.