Constant-Envelope Multicarrier Modulations vs. Multicarrier Modulations in Non-Terrestrial Network Scenarios

Some recent work highlighted the potential advantages of constant-envelope (CE) multicarrier modulations (CE-OFDM and CE-SC-OFDM) in various wireless scenarios. The strengths of CEmulticarrier modulations have been recognized in terms of nonlinear distortion immunity and improved multipath resilience owing to the augmented diversity against frequency selectivity. As far as the trade-offs are concerned, they should point out: i) the increased bandwidth occupation of the RF signal (at least twice than that of the conventional multicarrier signals), ii) the increased computational complexity due to oversampling, iii) the nonlinear effects involved by arctangent demodulation of the received phase-modulated signal, and, finally, iv) the possibility of exploiting orthogonal multicarrier multiple access only in the downlink. During the activities of the Integrated Terrestrial-Non-Terrestrial Network (ITA-NTN) project, funded by the EU in the framework of NextGenerationEU workprogramme, a wide range of waveforms have been considered for NTN scenarios, including CE multicarrier ones. This paper aims to analyze in detail this typology of waveforms and to contextualize them in NTN application scenarios of technical interest. The performance of CE-multicarrier waveforms will be carefully assessed across different NTN channels (with and without LOS), revealing the influence of parameterization (modulation index and oversampling) on the link performance of these nonconventional PHY-layer formats. The comparison will be conducted with conventional multicarrier modulations (OFDM, SC-OFDM) in a realistic NTN transmission scenario, characterized by nonlinear amplification and phase noise. Some guidelines about the employment of CE multicarrier waveforms in future NTN applications will conclude the paper.