Scalable Long-Distance ISAC Signal Design for OFDM Systems With Theoretical Analysis and Practical Validation

The orthogonal frequency division multiplexing (OFDM) is a promising waveform for integrated sensing and communication (ISAC), but its sensing range is limited by the cyclic prefix (CP), making it unsuitable for long-distance requirements. Moreover, long-distance echoes spanning multiple OFDM symbols introduce inter-symbol ambiguity. To address this problem, we propose a novel scalable long-distance ISAC signal design and processing method, considering timing advance between uplink and downlink in practical base stations. First, cyclic shifts and inverse phase compensation with low implementation complexity are introduced to eliminate inter-symbol interference (ISI). Second, an efficient multi-symbol channel estimation and detection method is presented to resolve ambiguity caused by long-distance echoes. Theoretical analysis demonstrates improved signal to interference plus noise ratio (SINR) performance, while simulations confirm ISI-free sensing. Experimental validation on a millimeter-wave system successfully detects the distance and velocity of the unmanned aerial vehicle (UAV) beyond the CP limit, showcasing the practicality of the proposed approach.