Low Complexity Waveform PAPR Reduction in Uplink ISAC System

Waveform design is expected as the core of uplink integrated sensing and communication (ISAC) to provide distributed sensing capability in the 6th generation (6G) mobile communication. The widely used orthogonal frequency division multiplexing (OFDM) waveform in communication systems suffers from a high peak-to-average power ratio (PAPR), while conventional PAPR reduction methods overlook the performance trade-offs between PAPR reduction and dual functionalities of sensing and communication. In this letter, we propose a low-PAPR waveform design method based on joint optimization of time-frequency domain statistical characteristics for uplink ISAC system, where the phase and amplitude are jointly optimized to enhance the PAPR performance without compromising sensing performance. Specifically, a low-complexity particle swarm optimization (PSO) method is derived for phase optimization, demonstrating the same sensing capability as OFDM. An exponential transformation is further applied to optimize the amplitude characteristics, achieving about 4 dB PAPR reduction compared to discrete Fourier transform spread OFDM (DFT-s-OFDM), with minimal impact on the communication bit error rate (BER). Simulation results validate the effectiveness of PAPR reduction and analyze the periodic autocorrelation function (ACF) and BER performance for dual-functionality evaluation.