LEO Satellite Diversity in 6G Non-Terrestrial Networks: OFDM vs. OTFS

Non-terrestrial networks will play a crucial role in future wireless 6G systems to ensure ubiquitous connectivity and to complement terrestrial networks. With reference to a low Earth orbit (LEO) constellation, this letter performs a comparison in terms of pragmatic capacity between the orthogonal frequency division multiplexing (OFDM) and the orthogonal time frequency space (OTFS) modulation in a scenario where multi-satellite diversity is employed to ensure a more uniform throughput and to increase the system reliability against unforeseen blockages. The considered scenario is akin to a cell-free system, wherein each user may be jointly served by multiple satellites for better and more stable performance. Numerical results reveal that multi-satellite diversity is effective in increasing the link performance and that OTFS provides a better performance and is thus more robust to the impairments caused by the heavy Doppler shifts.