PAPR Reduction for OFDM-ISAC Signals via Frequency-Domain Multiple Degree-of-Freedom Waveform Enhancement

Abstract

This paper studies peak-to-average power ratio (PAPR) reduction for orthogonal frequency division multiplexing (OFDM) integrated sensing and communication (ISAC) signals. We propose active constellation extension with constant-modulus tone reservation (ACE-CMTR), which constrains the reserved tones to have constant modulus and applies bounded outward ACE only to eligible outer quadrature amplitude modulation (QAM) data symbols. The resulting alternating projection exploits both reserved-tone phase rotation and bounded datasymbol perturbation while fixing the reserved-tone amplitudes and limiting the ACE-induced distortion. Simulations show that ACE-CMTR achieves the lowest tail PAPR among the tested schemes, maintains bit error rate (BER) performance under additive white Gaussian noise (AWGN) and ITU Vehicular-A fading, preserves the after-PA far-delay sidelobe behavior of the aperiodic autocorrelation function (ACF), does not increase the adjacent channel leakage ratio (ACLR) after the power amplifier (PA), maintains a comparable zero-delay velocity profile, and improves zero-velocity weak target detection relative to OFDM and Clipping-TR.