Fractional Fourier Transform for OFDM-LFM Integrated Sensing and Communication

Integrated Sensing and Communication (ISAC) is a cornerstone technology for 6G networks, yet the functional coupling poses significant challenges for signal processing. This letter proposes a novel Orthogonal Frequency Division Multiplexing Linear Frequency Modulation (OFDM-LFM) joint signal processing framework based on the Fractional Fourier Transform (FRFT), leveraging the time-frequency rotation properties of FRFT to decouple sensing and communication functionalities. Utilizing the additive property of FRFT orders, the mixing of the Inverse Fast Fourier Transform (IFFT) in OFDM and LFM for sensing is merged into a single-step operation that simplifies the ISAC signal synthesis in the transmitter. A Gbps-level transmission rate within a 300 MHz communication bandwidth is realized while maintaining a radar ranging error of 1.5 cm, and a velocity estimation error of 2 cm/s with a single radar echo. Compared to traditional 2D-FFT methods with a single echo, experimental results demonstrate that the proposed system significantly improves velocity resolution while maintaining a comparable bit error rate to pure OFDM systems, validating the efficient synergy of ISAC signals.