存在超扩展多普勒频移的OTFS系统的信道估计
Channel Estimation for OTFS Systems With Overspread Doppler Shifts
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中文总结 AI 辅助
针对非地面多卫星链路中OTFS系统超扩展多普勒频移导致的信道估计难题，本文提出含余弦导频的DD训练帧与两阶段配对方法，通过NMSE和BER验证了其性能。
中文摘要 AI 辅助
本文研究时变信道下存在超扩展多普勒频移的正交时频空间（OTFS）系统，这类场景常见于非地面多卫星链路中。超扩展多普勒频移的幅度大于子载波间隔的一半，由于OTFS的模运算，会在延迟-多普勒（DD）域产生混叠的多普勒频移，这使得信道估计极具挑战性，传统信道估计方法也随之失效。为解决该问题，本文提出一种DD训练帧和两阶段信道估计方法，训练帧包含余弦导频信号和导频符号。在信道估计的第一阶段，利用DD域的导频符号估计各传播路径的延迟、混叠多普勒频移和信道增益；第二阶段将接收时域信号转换至频域，通过余弦导频信号检测所有多普勒频移的峰值，再采用基于阈值的方法，将估计得到的实际多普勒频移与对应的延迟、信道增益配对。本文还讨论了所提信道估计方法的复杂度，最后在多种场景下，通过归一化均方误差（NMSE）和误码率（BER）验证了该方法的性能。
英文摘要
In this paper, we consider an orthogonal time frequency space (OTFS) system in time-varying channels with overspread Doppler shifts, typically found in non-terrestrial multi-satellite links. The overspread Doppler shifts with magnitude greater than half of the subcarrier spacing, result in aliased Doppler shifts in the delay-Doppler (DD) domain due to the OTFS modulo operation. This makes channel estimation very challenging and the traditional channel estimation methods become ineffective. To address this challenge, we propose a DD training frame and a two-stage channel estimation method. The training frame comprises a cosine pilot signal and a pilot symbol. In the first stage of the channel estimation, the pilot symbol in the DD domain is utilized to estimate the delays, aliased Doppler shifts, and channel gains of the propagation paths. In the second stage, the received time domain signal is converted into the frequency domain to detect the peaks of all the Doppler shifts using the cosine pilot signal. Then, we present a threshold-based method to pair the estimated actual Doppler shifts with their corresponding delays and channel gains. The complexity of the proposed channel estimation is also discussed. Finally, the performance of the proposed channel estimation is validated in terms of the normalized mean square error (NMSE) and bit error rate (BER) in various scenarios.
