Orthogonal time frequency space (OTFS) has shown to be a promising modulation technology that achieves the robust wireless transmission in high-mobility environments. The high mobility incurred Doppler effect in OTFS system, is represented as a continuous and relatively large band in the Doppler frequency. It yields the equivalent channel responses (ECRs) in the system change significantly within one symbol block, posing a challenge to channel estimation (CE) or tracking. In order to tackle this issue, in this paper, a set of transform-domain basis functions is designed to span a low-dimensional subspace for modeling the OTFS channel. Then, the CE can be performed by estimating a few projection coefficients of ECRs in the developed subspace, with training pilots. According to the individual transmission characteristic of OTFS signal, we propose a corner-inserted pilot pattern, which targets the low pilot overhead and satisfactory CE performance. Moreover, an OTFS signal detector, leveraging the time-domain channel equalization, linear-complexity interference cancellation and delay-Doppler domain maximal ratio combining detection, is developed to retrieve the transmitted data symbols. The simulations show the precisely estimated ECRs enable the detector to ideally demodulate 256-ary quadrature amplitude modulation signaling, under a velocity of 550 km/h at 5.9 GHz carrier frequency.

中文翻译：

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OTFS系统中连续多普勒扩展信道的低维子空间估计


正交时频空间（OTFS）已被证明是一种有前途的调制技术，可以在高移动性环境中实现稳健的无线传输。 OTFS系统中高移动性引起的多普勒效应，表现为多普勒频率中连续且相对较大的频带。它产生系统中的等效信道响应（ECR）在一个符号块内显着变化，这对信道估计（CE）或跟踪提出了挑战。为了解决这个问题，本文设计了一组变换域基函数来跨越低维子空间来对 OTFS 通道进行建模。然后，可以通过估计开发子空间中 ECR 的一些投影系数来执行 CE，并训练飞行员。根据OTFS信号的单独传输特性，我们提出了一种角插入导频模式，其目标是低导频开销和令人满意的CE性能。此外，还开发了一种OTFS信号检测器，利用时域信道均衡、线性复杂度干扰消除和延迟多普勒域最大比组合检测来检索传输的数据符号。仿真显示，精确估计的 ECR 使探测器能够在 5.9 GHz 载波频率、550 km/h 的速度下理想地解调 256 进制正交调幅信号。