An Improved OCDM-FMCW ISAC Waveform With a Cyclically Shifted Dedicated Sensing Subcarrier Index

The integrated orthogonal chirp division multiplexing (OCDM) and frequency-modulated continuous-wave (FMCW) waveform is a promising low-cost solution for integrated sensing and communication (ISAC) in sixth-generation (6G) wireless networks. However, conventional designs with a cyclic prefix (CP) and a fixed dedicated sensing subcarrier (DSS) index suffer from inter-symbol frequency discontinuity, resulting in severe structural sensing interference. This letter derives the closed-form signal-to-interference ratio (SIR) expression characterizing this degradation. To address this, we propose a cyclically shifted DSS index (CSDSSI) scheme that cyclically shifts the index by one CP-length per symbol to restore frequency continuity. Additionally, an asymmetric subcarrier guard band configuration is designed to extend the maximum sensing range without increasing spectral overhead. Furthermore, a data-aided sidelobe interference cancellation (DASIC) algorithm is developed to suppress communication leakage within the sensing passband. Simulation results demonstrate that the proposed scheme significantly improves sensing accuracy and robustness in high-mobility scenarios without compromising communication reliability.