Nonlinear PAPR suppression in OTSM systems using a reduced candidate strategy for energy-efficient 6G networks

Abstract

Orthogonal Time Sequence Multiplexing (OTSM) is a promising waveform for beyond-5G and 6G systems due to its flexible time–sequence structure and robustness to doubly dispersive channels. However, like other multicarrier techniques, it suffers from a high peak-to-average power ratio (PAPR) that forces high-power amplifiers (HPAs) to operate with large input back-off and degrades bit error rate (BER) performance. This paper proposes a low-complexity hybrid PAPR mitigation framework that combines DFT-spreading with an energy–entropy-aware Chaos-SLM scheme using a minimal candidate size ($U=2$) and no per-frame side information. Simulations across 64-, 256-, and 512-subcarrier OTSM systems with a Rapp HPA show PAPR reductions of up to 9 dB over OFDM and 8 dB over baseline OTSM at the $10^{-3}$ CCDF level, accompanied by 10–13 dB SNR gains at a target BER of $10^{-3}$, lower error vector magnitude (EVM), and reduced out-of-band emissions. The reduced PAPR translates into a smaller HPA back-off requirement, which improves the achievable PA operating efficiency; direct measurement of hardware power consumption is left for future work.