Among the several emerging use case families in 5G, high-mobility use case family is a technologically challenging one. It is expected that there will be a growing demand for mobile services in vehicles, high-speed trains, and even aircraft. The degree of mobility support required (i.e., speed) will depend upon the specific use case (e.g., 500 km/h in bullet trains and 1000 km/h in airplanes). Mobility-on-demand, ranging from very high mobility to low or no mobility, need to be supported. The currently used waveforms fail to perform well in high-mobility scenarios where the Doppler shifts witnessed are quite high (e.g., several kHz of Doppler). Orthogonal time–frequency space (OTFS) is a recently proposed radio access technology waveform suited very well for high-mobility environments. It is a two-dimensional modulation scheme in which information symbols are multiplexed in the delay–Doppler domain. We present an overview of delay–Doppler representation of wireless channels and introduce OTFS modulation along with OTFS basis functions. We illustrate the slow variability and sparse nature of the delay–Doppler channel using an urban multi-lane scenario. Focusing on MIMO-OTFS systems, we present signal detection and channel estimation schemes and their performance. MIMO-OTFS is shown to achieve significantly better performance compared to MIMO-OFDM in high-Doppler environments operating in 4 GHz and 28 GHz frequency bands.

中文翻译：

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OTFS：用于高移动性用例的新调制方案

在 5G 的几个新兴用例系列中，高移动性用例系列在技术上具有挑战性。预计车辆、高速列车甚至飞机对移动服务的需求将不断增长。所需的移动支持程度（即速度）将取决于特定用例（例如，子弹头列车为 500 公里/小时，飞机为 1000 公里/小时）。需要支持从非常高的移动性到低移动性或无移动性的按需移动性。当前使用的波形在多普勒频移非常高（例如，几 kHz 的多普勒）的高移动性场景中表现不佳。正交时频空间 (OTFS) 是最近提出的无线电接入技术波形，非常适合高移动性环境。它是一种二维调制方案，其中信息符号在延迟多普勒域中复用。我们概述了无线信道的延迟多普勒表示，并介绍了 OTFS 调制和 OTFS 基函数。我们使用城市多车道场景来说明延迟多普勒信道的缓慢变化和稀疏特性。专注于 MIMO-OTFS 系统，我们介绍了信号检测和信道估计方案及其性能。与 MIMO-OFDM 相比，在 4 GHz 和 28 GHz 频段的高多普勒环境中，MIMO-OTFS 表现出明显更好的性能。我们使用城市多车道场景来说明延迟多普勒信道的缓慢变化和稀疏特性。专注于 MIMO-OTFS 系统，我们介绍了信号检测和信道估计方案及其性能。与 MIMO-OFDM 相比，在 4 GHz 和 28 GHz 频段的高多普勒环境中，MIMO-OTFS 表现出明显更好的性能。我们使用城市多车道场景来说明延迟多普勒信道的缓慢变化和稀疏特性。专注于 MIMO-OTFS 系统，我们介绍了信号检测和信道估计方案及其性能。与 MIMO-OFDM 相比，在 4 GHz 和 28 GHz 频段的高多普勒环境中，MIMO-OTFS 表现出明显更好的性能。