Evaluation of 6G Candidate Waveforms Under RF Impairments

Sub-Terahertz (sub-THz) communication is a potential technology to enable 6 G wireless communication with extreme experience due to its rich spectrum resources. Working on sub-THz frequency, radio frequency (RF) impairments including phase noise (PN) and non-linear power amplifier (PA) become more severe and will heavily degrade communication performance. Considering the new characteristics in such high frequency, various waveform schemes have been proposed to achieve better performance under RF impairments, among which the enhanced waveforms based on discrete Fourier transform spreading orthogonal frequency diversion (DFT-s-OFDM) are highly regarded for the low peak to average power ratio (PAPR) characteristic. This paper focuses on 6 G candidate waveforms of orthogonal frequency division multiplexing with cyclic prefix (CP-OFDM), DFT-s-OFDM and enhanced DFT-s-OFDM including unified non-orthogonal waveform (uNOW), DFT-s-OFDM with frequency-domain spectral shaping (DFT-sOFDM with FDSS), and DFT-s-OFDM with FDSS and spectral extension (DFT-s-OFDM with FDSS and SE). In this paper, 6G candidate waveforms are evaluated for different sub-carrier spacing (SCS) considering PN and non-linear PA in sub-THz. Specially, waveforms are compared and analyzed from various aspects including PN robustness without compensation, PN compensation performance based on phase tracking reference signal (PT-RS), and output power back-off (OBO). In addition, under non-linear PA, this work has in-depth discussions on the changing trend of each RF requirement as OBO increases for different 6 G candidate waveforms. The results indicate that uNOW outperforms other waveforms for BLER performance considering both PN compensation and OBO, making it the promising 6 G candidate waveform.