OFDM-Based Waveforms in 6G NTN: A Comparative Analysis

Kurzfassung

5G NR has supported Non-Terrestrial Networks (NTN) to extend coverage to underserved regions through minimal and necessary adaptations to the NR protocol stack. Looking ahead, 6G is envisioned to integrate terrestrial networks (TNs) and NTNs from day one, establishing a resilient, unified wireless infrastructure. However, this convergence introduces challenges, particularly in the domain of radio access technologies (RATs), such as the identification of an NTN compatible waveform inherently more resilient to the challenges of satellite communication systems. To this end, this paper compares four different waveforms, namely cyclic prefix orthogonal frequency division multiplexing (CP-OFDM), discrete Fourier transform-spread OFDM (DFT-s-OFDM), block-filtered OFDM (BF-OFDM), and orthogonal time frequency space (OTFS), based on properties that support NTN link characteristics. Thus, this work considers: i) NTN-specific impairments, particularly delay and Doppler shift impairments typical of non-geostationary constellations, and ii) the nonlinear distortions induced by high-power amplifiers. We assess the impact of the mentioned impairments on the waveforms through bit error rate (BER) loss, power spectral density (PSD), adjacent channel leakage ratio (ACLR), and total degradation (TD) in a single-user single-beam scenario. Furthermore, we consider a fifth waveform that combines filtering and DFT spreading, namely BF-DFT-s-OFDM. Finally, we evaluate the peak-to-average power ratio (PAPR) of DFT-s-OFDM and CP-OFDM in a multi-user multi-beam scenario considering both frequency and space division multiplexing techniques.