High-Resolution Ranging Scheme for Stepped-Frequency PMCW-based ISAC Systems

The phase-modulated continuous wave (PMCW)-based integrated sensing and communication (ISAC) system is gaining attention due to its suitability in automotive radar applications and its potential for next-generation vehicular communication systems. To enhance robustness in interference-prone environments, stepped-frequency (SF) modulation is introduced into PMCW-based ISAC systems. SF-modulation can also enable high target separability even when low sampling rates are used in the analog-to-digital converter. However, SF-modulation inherently reduces the instantaneous bandwidth of the systems, which, in turn, degrades the sensing performance by limiting the achievable range resolution. To address this limitation, we propose a ranging scheme for SF-PMCW-based ISAC systems that exploits the synthesized bandwidth, enabling high-resolution range estimation despite the reduced instantaneous bandwidth. With the proposed method, the range-velocity coupling caused by SF modulation can be effectively resolved, thereby enabling high-resolution range estimation. Through simulation, we demonstrated that the proposed method reduces the root mean square error in range estimation from 0.375 m to 0.025 m, outperforming conventional ranging schemes.