Adaptive Modulation and Coding for OTFS-Based LEO Satellite-Terrestrial Communications

In satellite-terrestrial links, the high-speed movement of low earth orbit (LEO) satellites induces significant doppler effects. By employing orthogonal time frequency space (OTFS) modulation technology, information symbols are effectively mapped into the delay-doppler domain, significantly mitigating the adverse impacts of doppler effects on transmissions. Furthermore, the short packet is introduced into satelliteterrestrial communications to meet diverse latency requirements. Due to the limited channel coding capacity of short packets, adjusting the channel coding rate and symbol modulation order according to the channel conditions is crucial in satellite communications. However, real-time channel state information feedback is precluded by the rapid variations in satellite-terrestrial channels, the large feedback latency, and the limited resources for frequent feedback. Therefore, implementing a feedback-free transmission approach is particularly essential. In this paper, we design a feedback-free OTFS-based adaptive modulation and coding (AMC) scheme to accommodate varying communication requirements and conditions. Extensive simulations with different orbital altitudes, carrier frequencies, and packet lengths have shown that the proposed approach can be effectively adapted to LEO satellite channels, enabling a feedback-free AMC in the LEO satellite-terrestrial communications.