Simulation of Constant-Envelope THz Integrated Sensing and Communication System Based on Photonics with 2D Positioning

The terahertz (THz) band combined with microwave photonics (MWP) offers a promising solution for achieving ultra-high data rates and radar resolution in integrated sensing and communication (ISAC) systems. Inspired by the constant envelope orthogonal frequency division multiplexing (CE-OFDM), the ISAC signal is designed with two linear frequency modulation (LFM) bands and CE-OFDM in between. In particular, the two LFM sub-bands carry the DC-offset quadrature phase shift keying (QPSK) communication signal to increase the data rate. In this paper, we propose a novel THz MWP ISAC system and simulation is carried out to verify the two-dimensional (2D) positioning function. It possesses a 18.448 Gbit/s communication data rate and a 1.78 cm equivalent radar range resolution achieved by coherent fusion processing (CFP), characterized by a low peak-to-average power ratio (PAPR). In addition, CFP enables high spectral-efficiency. The performance shows two error-free 1.25 GHz QPSK signals and a 5 GHz 64-QAM CE-OFDM signal with a bit error rate (BER) of $\sim \mathbf{10}^{-\mathbf{4}}$. In addition, the 2D positioning function is successfully verified within 2 m distance by using the trilateration method, and the error is less than 5.81 cm. The low PAPR effectively mitigates nonlinear distortion in communication and enhances target detection in radar, demonstrating significant potential for future applications. To the best of our knowledge, this is the first demonstration of a THz ISAC system integrating 2D positioning and CFP.