Affine frequency division multiplexing (AFDM) has recently emerged as a promising multicarrier waveform for high-mobility and doubly selective channels. However, similar to orthogonal frequency division multiplexing (OFDM), AFDM signals suffer from a high peak-to-average power ratio (PAPR), which limits the efficiency of radio frequency (RF) power amplifiers. To address this issue, we propose a chirp parameter selected mapping (CSM) scheme that exploits the tunable chirp parameter of AFDM to generate multiple candidate signals and selects the one with the lowest PAPR for transmission, thereby achieving low-PAPR signal generation without introducing waveform extensions. A theoretical lower bound on the complementary cumulative distribution function (CCDF) of CSM is established under the independence assumption, which exhibits an exponential tail decay with the selection order. Accordingly, both a candidate design criterion and a practical guideline are developed to minimize the cross-correlation between signals. Simulation results show that the proposed CSM scheme approaches the theoretical bound and achieves significant PAPR reduction over existing baselines, while maintaining error-rate performance in doubly selective channels.
