OTFS 与 OFDM：在多用户低轨卫星通信中谁更优越
OTFS vs OFDM: Which is Superior in Multiuser LEO Satellite Communications
AI总结：
本文比较多用户 LEO 卫星通信中的 OTFS 与 OFDM，并提出功率及延迟-多普勒资源块联合分配算法，证明 OTFS 抗 CFO 且和速率更优。
摘要：
正交时频空间（OTFS）调制是一种延迟-多普勒（DD）域通信方案，对多普勒频移具有很强的鲁棒性，有潜力应用于低轨（LEO）卫星通信。然而，其与正交频分复用（OFDM）调制的性能比较，以及基于 OTFS 的多用户 LEO 卫星通信系统的资源分配方案，仍鲜有研究。本文在多种信道条件下对 OTFS 与 OFDM 调制进行性能比较，包括和速率与误比特率（BER）评估。此外，研究面向多用户下行基于 OTFS 的 LEO 卫星通信系统、以最大化和速率为目标的功率与延迟-多普勒资源块联合最优分配。不同于依赖时频（TF）域复杂输入-输出关系的传统调制，OTFS 调制同时利用时间和频率分集，即在一个 OTFS 帧内延迟和多普勒频移保持恒定，从而为研究提供了简单的 DD 域输入-输出关系。通过解耦条件约束，将所得非凸组合优化问题转化为等价的凸差分问题，并采用惩罚凸凹过程算法求解。仿真结果表明，OTFS 调制对 LEO 卫星高移动性导致的载波频偏（CFO）具有鲁棒性，性能优于 OFDM 调制。此外，数值结果表明，所提资源分配方案相比 OTFS 调制的现有方案（如延迟划分多址和多普勒划分多址）具有更高和速率，尤其在高信噪比（SNR）区域。
英文摘要：
Orthogonal time frequency space (OTFS) modulation, a delay-Doppler (DD) domain communication scheme exhibiting strong robustness against the Doppler shifts, has the potentials to be employed in LEO satellite communications. However, the performance comparison with the orthogonal frequency division multiplexing (OFDM) modulation and the resource allocation scheme for multiuser OTFS-based LEO satellite communication system have rarely been investigated. In this paper, we conduct a performance comparison under various channel conditions between the OTFS and OFDM modulations, encompassing evaluations of sum-rate and bit error ratio (BER). Additionally, we investigate the joint optimal allocation of power and delay-Doppler resource blocks aiming at maximizing sum-rate for multiuser downlink OTFS-based LEO satellite communication systems. Unlike the conventional modulations relaying on complex input-output relations within the Time-Frequency (TF) domain, the OTFS modulation exploits both time and frequency diversities, i.e., delay and Doppler shifts remain constant during a OTFS frame, which facilitates a DD domain input-output simple relation for our investigation. We transform the resulting non-convex and combinatorial optimization problem into an equivalent difference of convex problem by decoupling the conditional constraints, and solve the transformed problem via penalty convex-concave procedure algorithm. Simulation results demonstrate that the OTFS modulation is robust to carrier frequency offsets (CFO) caused by high-mobility of LEO satellites, and has superior performance to the OFDM modulation. Moreover, numerical results indicate that our proposed resource allocation scheme has higher sum-rate than existed schemes for the OTFS modulation, such as delay divided multiple access and Doppler divided multiple access, especially in the high signal-to-noise ratio (SNR) regime.
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