Flexible FTN-OTFS for High-Mobility LEO Satellite-to-Ground Communication

TL;DR

This work tackles the challenge of high-mobility, power-constrained LEO satellite links by proposing a flexible FTN-OTFS framework (LEO-FFTN-OTFS) that adapts the time-domain compression factor $\alpha$ based on instantaneous SNR via a low-complexity LUT. It integrates a realistic LEO channel model using 3GPP TDL profiles, and provides a rigorous analysis of throughput, energy efficiency, and BER under FTN-OTFS with a linear MMSE detector. Theoretical expressions are complemented by extensive simulations showing that adaptive FFTN outperforms static FTN, achieving higher effective throughput while maintaining reliability across horizon-to-zenith channel variations. The approach offers a practical pathway for maximizing spectral efficiency and energy efficiency in next-generation non-terrestrial networks with tight latency and processing constraints.

Abstract

In this paper, a lightweight LEO satellite-assisted flexible faster-than-Nyquist (FTN)-orthogonal time frequency space (OTFS) (LEO-FFTN-OTFS) scheme is proposed to address the stringent constraints on onboard power consumption and the severe impact of fast time-varying channels in non-terrestrial networks. A rigorous system framework incorporating realistic 3GPP Tapped Delay Line (TDL) channel models is established to accurately capture high-mobility propagation characteristics. To counteract channel aging effects while maintaining low computational complexity, an SNR-aware flexible FTN strategy is introduced, wherein a low-complexity Look-Up Table (LUT) is utilized to adaptively optimize the time-domain compression factor based on instantaneous channel responses. Through this mechanism, the trade-off between rate acceleration and interference penalty is effectively resolved, ensuring that spectral efficiency is maximized while strict reliability constraints are satisfied with minimal processing overhead. Moreover, a comprehensive theoretical analysis is provided, in which analytical expressions for effective throughput, energy efficiency, and bit error rate are derived. Finally, it is demonstrated by extensive simulations that the proposed scheme significantly outperforms static FTN benchmarks, offering a superior balance of high throughput and robustness for next-generation LEO communications.

Figures (6)

• Figure 1: System model and signal processing.
• Figure 2: FTN showcase.
• Figure 3: Theoretical and simulation BER performance of LEO-FTN-OTFS scheme with $M=N=32$, TDL-A, and different $\alpha$.
• Figure 4: BER performance of various TDL models with FTN and FFTN applied in LEO-OTFS system with $M=N=16$ and $\alpha=0.9$.
• Figure 5: Effective throughput and $\alpha$ trend of LEO-FFTN-OTFS, LEO-OTFS with $\alpha=1$, and LEO-FTN-OTFS with $\alpha=0.9$ and $0.8$, as well as $M=32$, $N=16$, and $M_{\text{mod}}=4$.