Spreading the Wave: Low-Complexity PAPR Reduction for AFDM and OCDM in 6G Networks

The high Peak-to-average-power ratio (PAPR) is still a common issue in multicarrier signal modulation systems such as Orthogonal Chirp Division Multiplexing (OCDM) and Affine Frequency Division Multiplexing (AFDM), which are expected to play a central role in 6G networks. This paper presents a novel unified premodulation data spreading framework that repurposes four well-established transforms—Walsh-Hadamard Transform (WHT), Discrete Cosine Transform (DCT), Zadoff-Chu (ZC) sequences, and Interleaved Discrete Fourier Transform (IDFT)—to achieve up to 4 dB PAPR reduction with lower complexity and zero side information. Conventional PAPR reduction frameworks such as Partial transmission Sequence (PTS) or Selected Mapping (SLM) have a high complexity drawback, as they require extensive search and signaling overhead. In contrast, our framework leverages fast transforms and the inherent chirp structure to redistribute energy before modulation without additional overhead, delivering not only superior PAPR performance but also enhanced phase selectivity and interference resilience. Extensive simulations and analytical derivations confirm its energy efficiency and scalability in large-scale IoT deployments.