扩展的GFDM框架：OTFS和GFDM比较
Extended GFDM Framework: OTFS and GFDM Comparison
摘要：
正交时频空间调制（OTFS）最近已被提出来实现时间和频率分集，特别是在具有大多普勒频率的线性时变（LTV）信道中。该思想基于使用辛有限傅里叶变换（SFFT）对数据符号进行预编码，然后借助于正交频分复用（OFDM）波形来发送它们。因此，解调器和信道均衡可以耦合在一个处理步骤中。作为区别特征，解调的数据符号具有与信道选择性无关的大致相等的增益。另一方面，广义频分复用（GFDM）调制也采用使用循环滤波的时域和频域上的扩展。因此，以与在OTFS中应用SFFT类似的方式隐式地预编码数据符号。在本文中，我们提出了一个扩展的GFDM表示，它表明OTFS可以处理作为一个GFDM信号与简单的置换。然而，这种排列是OTFS在LTV信道中的出色性能背后的关键因素，如本工作所示。此外，OTFS在GFDM框架中的表示提供了一种高效的实现方式，该实现方式已经针对GFDM进行了深入的研究，并且有助于理解OTFS的不同特征。
英文摘要：
Orthogonal time frequency space modulation (OTFS) has been recently proposed to achieve time and frequency diversity, especially in linear time-variant (LTV) channels with large Doppler frequencies. The idea is based on the precoding of the data symbols using symplectic finite Fourier transform (SFFT) then transmitting them by mean of orthogonal frequency division multiplexing (OFDM) waveform. Consequently, the demodulator and channel equalization can be coupled in one processing step. As a distinguished feature, the demodulated data symbols have roughly equal gain independent of the channel selectivity. On the other hand, generalized frequency division multiplexing (GFDM) modulation also employs the spreading over the time and frequency domains using circular filtering. Accordingly, the data symbols are implicitly precoded in a similar way as applying SFFT in OTFS. In this paper, we present an extended representation of GFDM which shows that OTFS can be processed as a GFDM signal with simple permutation. Nevertheless, this permutation is the key factor behind the outstanding performance of OTFS in LTV channels, as demonstrated in this work. Furthermore, the representation of OTFS in the GFDM framework provides an efficient implementation, that has been intensively investigated for GFDM, and facilitates the understanding of the OTFS distinct features.
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