Continuous OFDM Signal for ISAC in 6G

Abstract

For orthogonal frequency division multiplexing (OFDM)-based integrated sensing and communication (ISAC), the maximum sensing round-trip time (RTT) delay is limited by the cyclic prefix (CP) duration. Communication-dimensioned CP durations may be insufficient for long sensing ranges, thereto symbols within the pulse repetition interval (PRI) can employ variable CP durations in 6G. To enable larger RTT delays, we propose a precoder that enforces phase and amplitude continuity across symbol boundaries for arbitrary CP durations. We prove that this precoder constitutes a special case of $N$ -continuous OFDM. Beyond ensuring continuity, the proposed signal enhances energy accumulation at the receiver’s correlator. Furthermore, we derive the closed-form periodic ambiguity function (PAF) of the precoded continuous OFDM signal. Evaluations demonstrate that the proposed signal significantly suppresses PAF sidelobes and improves the integrated sidelobe level ratio (ISLR) compared to conventional OFDM.