Orthogonal time frequency and space (OTFS) modulation is a promising technology that satisfies high Doppler requirements for future mobile systems. OTFS modulation encodes information symbols and pilot symbols into the two-dimensional (2D) delay-Doppler (DD) domain. The received symbols suffer from inter-Doppler interference (IDI) in the fading channels with fractional Doppler shifts that are sampled at noninteger indices in the DD domain. IDI has been treated as an unavoidable effect because the fractional Doppler shifts cannot be obtained directly from the received pilot symbols. In this paper, we provide a solution to channel estimation for fractional Doppler channels. The proposed estimation provides new insight into the OTFS input-output relation in the DD domain as a 2D circular convolution with a small approximation. According to the input-output relation, we also provide a low-complexity channel equalization method using the estimated channel information. We demonstrate the error performance of the proposed channel estimation and equalization in several channels by simulations. The simulation results show that in high-mobility environments, the total system utilizing the proposed methods outperforms orthogonal frequency division multiplexing (OFDM) with ideal channel estimation and a conventional channel estimation method using a pseudo sequence.

翻译：交替时间频率和空间调制( OTFS) 是符合未来移动系统高多普勒高要求的有前景的技术。 调制 OTFS 将信息符号和试点符号编码为二维( 2D) 延迟- 多普勒( DD) 域。 收到的符号在分形多普勒变换的淡化渠道中受到多普勒干扰( IDI), 分形多普勒变换在DD 域的非内位指数中抽样。 IDI 被视为一种不可避免的效果, 因为分数多普勒变换无法直接从收到的试点符号中获得。 在本文中, 我们为分数的多普勒变换换换分数路径提供了一种解决方案。 拟议的估算结果显示,在高流动性环境中, 将OTFS 的输入- 输出关系作为2D 循环相近的循环变换法, 对DDD域域中的OFS 输入- putut the complical chare roupal ass ass imation imational droupal roup orations roupal oration roupdiction ( orma) ortigraduction a ormaphal ormaphal drold progs) 。