Extensive work has demonstrated the excellent performance of orthogonal time frequency space (OTFS) modulation in high-mobility scenarios. Time-variant wideband channel estimation serves as one of the key compositions of OTFS receivers since the data detection requires accurate channel state information (CSI). In practical wideband OTFS systems, the Doppler shift brought by the high mobility is frequency-dependent, which is referred to as the Doppler Squint Effect (DSE). Unfortunately, DSE was ignored in overall prior estimation schemes employed in OTFS systems, which leads to severe performance loss in channel estimation and the consequent data detection. In this paper, we investigate DSE of wideband time-variant channel in delay-Doppler domain and concentrate on the characterization of OTFS channel coefficients considering DSE. The formulation and evaluation of OTFS input-output relationship are provided for both ideal and rectangular waveforms considering DSE. The channel estimation is therefore formulated as a sparse signal recovery problem and an orthogonal matching pursuit (OMP)-based scheme is adopted to solve it. Simulation results confirm the significance of DSE and the performance superiority compared with traditional channel estimation approaches ignoring DSE.

翻译：已有大量研究证实正交时频空（OTFS）调制在高移动性场景中的优异性能。时变宽带信道估计是OTFS接收机的关键组成部分之一，因为数据检测需要精确的信道状态信息（CSI）。在实际宽带OTFS系统中，高移动性带来的多普勒频移具有频率依赖性，即多普勒斜视效应（DSE）。然而，现有OTFS系统中采用的几乎所有信道估计方案均忽略了DSE，导致信道估计及后续数据检测出现严重的性能损失。本文研究延迟-多普勒域中宽带时变信道的DSE，重点分析考虑DSE的OTFS信道系数表征。针对理想波形和矩形波形，给出了考虑DSE的OTFS输入输出关系的数学表述与评估。将信道估计建模为稀疏信号恢复问题，并采用基于正交匹配追踪（OMP）的方案进行求解。仿真结果验证了DSE的重要性，并表明所提方法相较于忽略DSE的传统信道估计方法具有显著的性能优势。