Orthogonal time frequency space (OTFS) modulation has been confirmed to provide significant performance advantages against Doppler in high-mobility scenarios. The core feature of OTFS is that the time-variant channel is converted into a non-fading 2D channel in the delay-Doppler (DD) domain so that all symbols experience the same channel gain. In now available literature, the channel is assumed to be quasi-static over an OTFS frame. As for more practical channels, the input-output relation will be time-variant as the environment or medium changes. In this paper, we analyze the characterizations of OTFS modulation over a more general multipath channel, where the signal of each path has experienced a unique rapid fading. First, we derive the explicit input-output relationship of OTFS in the DD domain for the case of ideal pulse and rectangular pulse. It is shown that the rapid fading will produce extra Doppler dispersion without impacting on delay domain. We next demonstrate that OTFS can be interpreted as an efficient time diversity technology that combines space-time encoding and interleaving. Simulation results reveal that OTFS is insensitive to rapid fading and still outperforms orthogonal frequency-division multiplexing (OFDM) in these types of channels.

翻译：OTFS 的核心特征是将时间变异频道转换成一个非淡化的 2D 频道, 使所有符号都体验到同一频道的增益。 在现有的文献中, 频道被假定为在 OTFS 框架上是准静态的。 至于更实际的渠道, 输入输出关系将随着环境或介质的变化而具有时间变量。 在本文中, 我们分析了 OTFS 的调制在更普通的多路径频道上的特性, 在每个路径的信号都经历了独特的快速淡化。 首先, 我们得出在 DTFS 域中OTFS 在理想脉冲和矩形脉冲情况下的明显输入输出关系。 显示快速淡化将产生额外的多普勒分散, 而不会影响延迟域 。 我们接下来显示 OTFS 可以被解释为一个高效的时间多样性技术, 将这些对空间- 时间变异的频率的轨迹显示为快速变异式的 O- developtional- developtional- developtional- developtional- divations