A Low-Complexity Hybrid DCT and Companding-Based PAPR Reduction Technique for AFDM Systems

Abstract

The recently proposed multi-chirp-based physical layer waveform, affine frequency division multiplexing (AFDM), has attracted significant attention for enabling efficient and reliable communication over doubly dispersive (DD) channels while maintaining robustness against Doppler effects. However, the high peak-to-average power ratio (PAPR) of AFDM remains a major challenge for practical deployment, as it limits the efficiency of the high-power amplifier (HPA) used at the transmitter. Although discrete cosine transform (DCT) precoding reduces PAPR through energy compaction, the achieved PAPR reduction remains moderate, and its bit error rate (BER) performance in the high signal-to-noise ratio (SNR) region degrades in the presence of HPA nonlinearity, especially for higher-order modulation schemes. To address this issue, a low-complexity hybrid scheme integrating DCT precoding with normalized $\mu $ -law/A-law companding is proposed for AFDM systems. Furthermore, analytical expressions for PAPR, transform gain, complementary cumulative distribution function (CCDF) of PAPR and attenuation factor are derived for the proposed schemes, and the companding parameter selection criteria are investigated. The performance of proposed schemes is evaluated in terms of power levels, CCDF of PAPR, spectral efficiency, BER and computational complexity. Simulation results indicate that the proposed schemes achieve significant PAPR reduction compared with existing techniques while providing lower BER degradation than conventional DCT-AFDM systems under HPA nonlinearity.