Low-PAPR OFDM-ISAC Waveform Design Based on Frequency-Domain Phase Differences
Kaimin Li, Jiahuan Wang, Haixia Cui, Bingpeng Zhou, Pingzhi Fan
TL;DR
This work tackles the high PAPR challenge in OFDM-ISAC by introducing a frequency-domain phase-difference (PD) as a new design DoF, enabling full-spectrum usage for both communications and sensing. The PD-based waveform structure enforces unimodular frequency-domain signals and PD constraints, linking them to a time-domain low-PAPR objective via the time-frequency relationship $\mathbf{s}=\mathbf{A}\mathbf{x}$. An ADMM-based algorithm (ADMM-PLPOI) decouples $\mathbf{x}$ and $\mathbf{s}$, providing closed-form updates and FFT-based efficiency, with rigorous projection steps to satisfy the PD and unimodular constraints. Simulations show substantial PAPR reductions (4–5 dB) and improved BER under AWGN and Rayleigh fading, while sensing performance remains high-resolution with excellent range-Doppler discrimination, validating the practicality of the proposed ISAC waveform for 6G-like systems.
Abstract
Low peak-to-average power ratio (PAPR) orthogonal frequency division multiplexing (OFDM) waveform design is a crucial issue in integrated sensing and communications (ISAC). This paper introduces an OFDM-ISAC waveform design that utilizes the entire spectrum simultaneously for both communication and sensing by leveraging a novel degree of freedom (DoF): the frequency-domain phase difference (PD). Based on this concept, we develop a novel PD-based OFDM-ISAC waveform structure and utilize it to design a PD-based Low-PAPR OFDM-ISAC (PLPOI) waveform. The design is formulated as an optimization problem incorporating four key constraints: the time-frequency relationship equation, frequency-domain unimodular constraints, PD constraints, and time-domain low PAPR requirements. To solve this challenging non-convex problem, we develop an efficient algorithm, ADMM-PLPOI, based on the alternating direction method of multipliers (ADMM) framework. Extensive simulation results demonstrate that the proposed PLPOI waveform achieves significant improvements in both PAPR and bit error rate (BER) performance compared to conventional OFDM-ISAC waveforms.