A Cross-domain PAPR Reduction Method for OTFS Modulation

In this work, a cross-domain PAPR reduction scheme is proposed, which is a combination of the phase rotation in the Delay-Doppler (DD) domain and the iterative clipping filtering (ICF) in the time domain. The former technique is distortion-less to the signals while incurring additional signaling overhead between the transceivers. The latter technique is more effective for PAPR reduction, but it can cause increased signal detection errors. Therefore, by leveraging the advantages of the two techniques, the proposed scheme can achieve improved PAPR reduction, given a trade-off between the signaling overhead and the bit error rate (BER). Specifically, the phase-rotation vectors optimization problem in the DD domain is formulated, and an iterative algorithm based on successive convex approximation (SCA) method and penalty convex-concave procedure (PCCP) is employed to solve this non-convex problem. Considering the phase quantization and signaling overhead in practical systems, a low-overhead group randomization algorithm is proposed to select the phase mapping in the grouped phase rotation stage, while the linear filtering is applied in the ICF stage, which can flexibly adjust the signaling overhead and the BER. Compared to the existing methods, numerical simulations justify the advantages of the proposed scheme, which further reduces 1-3 dB PAPR, while causing a lower BER.

I. Introduction

A wide range of communication scenarios will be supported in the beyond 5G and 6G wireless communication networks, including diversified communication devices such as self-driving cars [1], unmanned aerial vehicles, low Earth orbit satellites [2], [3] and high-speed trains. One of the key challenges imposed in these scenarios is to provide reliable communication service in a high-mobility environment. The orthogonal frequency division multiplexing (OFDM), being the mainstream modulation technique in the current communication systems, suffers severe performance degradation due to Doppler effect. Orthogonal time frequency space (OTFS) is a recently proposed two-dimensional (2D) multi-carrier modulation technique [4], which is a promising candidate for high-mobility communications [5]. OTFS modulates the information in the Delay-Doppler (DD) domain and each symbol is mapped to the entire time frequency (TF) domain by 2D transformation, which takes advantage of the full TF diversity of the channel [6]. Additionally, it converts the complex time-varying channel in the time domain into a sparse channel in the DD domain [7]. Therefore, OTFS can obtain better performance in high-mobility channels.