In this paper, we investigate the impacts of transmitter and receiver windows on the performance of orthogonal time-frequency space (OTFS) modulation and propose window designs to improve the OTFS channel estimation and data detection performance. In particular, assuming ideal pulse shaping filters at the transceiver, we derive the impacts of windowing on the effective channel and its estimation performance in the delay-Doppler (DD) domain, the total average transmit power, and the effective noise covariance matrix. When the channel state information (CSI) is available at the transceiver, we analyze the minimum squared error (MSE) of data detection and propose an optimal transmitter window to minimize the detection MSE. The proposed optimal transmitter window can be interpreted as a mercury/water-filling power allocation scheme, where the mercury is firstly filled before pouring water to pre-equalize the time-frequency (TF) domain channels. When the CSI is not available at the transmitter but can be estimated at the receiver, we propose to apply a Dolph-Chebyshev (DC) window at either the transmitter or the receiver, which can effectively enhance the sparsity of the effective channel in the DD domain. Thanks to the enhanced DD domain channel sparsity, the channel spread due to the fractional Doppler is significantly reduced, which leads to a lower error floor in both channel estimation and data detection compared with that of rectangular window. Simulation results verify the accuracy of the obtained analytical results and confirm the superiority of the proposed window designs in improving the channel estimation and data detection performance over the conventional rectangular window design.

中文翻译：

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正交时频空间调制的发射器和接收器窗口设计

在本文中，我们研究了发射器和接收器窗口对正交时频空间（OTFS）调制性能的影响，并提出了一些窗口设计来改善OTFS信道估计和数据检测性能。特别是，假设收发器处有理想的脉冲整形滤波器，我们可以得出加窗对有效信道的影响及其在延迟多普勒（DD）域，总平均发射功率和有效噪声协方差矩阵中的估计性能。当收发器处有信道状态信息（CSI）时，我们将分析数据检测的最小平方误差（MSE），并提出一个最佳发送器窗口以最小化检测MSE。提议的最佳发射器窗口可以解释为汞/充水功率分配方案，在先注满汞后再倒水以预先均衡时频（TF）域通道的位置。当CSI在发送器上不可用但可以在接收器上估计时，我们建议在发送器或接收器上应用Dolph-Chebyshev（DC）窗口，这可以有效地增强DD中有效信道的稀疏性领域。由于增强的DD域信道稀疏性，分数多普勒引起的信道扩展大大减少，与矩形窗口相比，这导致信道估计和数据检测的错误基底更低。