A Low-Complexity Standard-Compliant PAPR Reduction Scheme for OTFS Modulation

Abstract

Orthogonal Time Frequency Space (OTFS) modulation is widely recognized as a modulation scheme with advantageous properties for both radar and communication waveform designs. In OTFS, information symbols are mapped in the DelayDoppler (DD) domain leading to reliable communication in high Doppler channels. However, the presence of inverse-discrete Fourier Transform operation in OTFS architecture results in a high Peak-to-Average Power Ratio (PAPR) in the transmit OTFS frames. This paper introduces a novel metric-based symbol pre-distortion algorithm constrained by Error Vector Magnitude (EVM) limits to reduce the PAPR in OTFS modulation. The imposed constraint in the form of EVM limits establishes it as a pragmatic method that adds no side-channel information rather exploits the available EVM limit usually kept in wireless standards. The pre-distortion applied to each symbol/sample in an OTFS frame is determined by the proposed metrics, representing the contribution of each symbol to peak values in the output. The proposed method is simple, flexible, and does not require additional complexity for symbol detection on the receiver end. Our simulation results demonstrate a significant reduction in the PAPR of OTFS blocks for both QPSK and 16-QAM modulation schemes. Furthermore, our proposed Constrained Constellation Shaping scheme exhibits enhanced performance in PAPR reduction as the number of Doppler bins increases for an OTFS frame size.