Spread Spectrum Peak-to-Average Power Ratio Suppression for OTFS System

‍ ‍Orthogonal Time Frequency Space （OTFS） modulation technology is increasingly being applied in high-dynamic scenarios due to its adaptability to Doppler shifts and delay conditions. Although OTFS as a multicarrier modulation scheme demonstrates strong performance in high-mobility communication， it faces a significant challenge with its high Peak-to-Average Power Ratio （PAPR）. High PAPR can lead to nonlinear distortion in OTFS signals， degrading signal quality and adversely affecting the overall performance of communication systems. To effectively reduce the PAPR of OTFS system waveforms and enhance transmission performance， this study proposes a PAPR suppression scheme based on spreading techniques. Specifically， by employing soft spreading and direct sequence spreading in the delay-Doppler domain， OTFS information symbols are extended using the favorable autocorrelation and constant modulus properties of Zadoff-Chu （ZC） sequences， along with the strong autocorrelation of m-sequences. This approach significantly suppresses signal PAPR， reduces nonlinear distortion， and enhances system capacity. Through theoretical derivation， this study further demonstrates that under Phase Shift Keying （PSK） modulation， the transmitted signal waveform exhibits higher PAPR when the number of OTFS symbols exceeds the spreading factor and is an integer power of two of the spreading factors. Simulation results show that， compared to the original OTFS system， the proposed spreading-based OTFS system offers substantial improvements in PAPR performance. In particular， the soft-spreading OTFS system based on Zadoff-Chu （ZC） sequences displays constant modulus characteristics in its transmitted signal， significantly reducing the linearity requirements for power amplifiers. Additionally， the direct sequence spreading scheme based on m-sequences achieves approximately an 8.5 dB improvement in the PAPR of the transmitted signal. The simulation results validate the accuracy of the theoretical analysis and indicate that the proposed spreading-based OTFS system enhances transmission performance.