Iterative PAPR Reduction Scheme With Optimized Phase Pre-Distortion Sequence for OTFS Systems

To achieve the expected peak-to-average power ratio (PAPR) reduction of orthogonal time frequency space (OTFS) signals and thus improve the energy efficiency of the power amplifier in practical systems, we propose an iterative PAPR reduction scheme with phase pre-distortion sequences for the embedded-pilot OTFS system. In the proposed scheme, each large peak in the time domain is searched and its corresponding symbols in the delay-Doppler (DD) domain (i.e., a vector in the Doppler domain) are multiplied with the phase pre-distortion sequence and the pre-distortion sequence is optimized to minimize the introduced linear distortions (only phase distortions without amplitude distortions) with the expected PAPR constraint. The optimized phase pre-distortion sequence is determined by exhaustive search or pre-trained Random Forest from the available pre-distortion sequence set. If the pilot is distorted by the phase sequence, its position in the DD domain is used to transmit the information about its phase distortion and can be detected by the variance of the amplitude in all available embedded-pilot regions at the receiver. Simulation results demonstrate that the gain of PAPR reduction in our scheme is about 3.6dB over the conventional OTFS signals when complementary cumulative distribution function (CCDF) is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-4}$ </tex-math></inline-formula> with negligible bit error rate (BER) degradation, which is much superior to the modified Iterative Clipping Filtering (m-ICF) scheme.