While interference in time domain (caused by path difference) is mitigated by OFDM modulation, interference in frequency domain (due to velocity difference), can be mitigated by OTFS modulation. However, in non-stationary channels, the relative difference in acceleration will cause Inter-Doppler Interference (IDI) and a modulation method for mitigating IDI does not exist in the literature. Both methods in the literature use carriers in a specific domain which achieve orthogonality in the target domain to mitigate interference. Moreover, those modulation cannot directly incorporate space domain, which requires additional precoding technique to mitigate inter-user interference (IUI) for MU-MIMO channels. This work presents a generalized modulation for any multidimensional channel. Recently, Higher Order Mercer's Theorem (HOGMT) [1] has been proposed to decompose multi-user non-stationary channels into independent fading subchannels (Eigenwaves). Based on HOGMT decomposition, we develop Multidimensional Eigenwaves Multiplexing (MEM) modulation which uses jointly orthogonal eigenwaves, decomposed from the multidimensional channel as subcarriers. Data symbols modulated by these eigenwaves can achieve orthogonality across each degree of freedom(\eg space (users/antennas), time-frequency and delay-Doppler). Consequently, the transmitted remain independent over the high dimensional channel, thereby avoiding interference from other symbols.

翻译：尽管由路径差异引起的时域干扰可通过OFDM调制得以缓解，但由速度差异引起的频域干扰则可借助OTFS调制处理。然而在非平稳信道中，加速度的相对差异将引发多普勒间干扰（IDI），而现有文献中尚不存在能缓解IDI的调制方法。现有文献中的两类方法均采用特定域载波实现目标域正交性以消除干扰，且这类调制无法直接融合空间域——在多用户MIMO信道中需额外采用预编码技术消除用户间干扰（IUI）。本文提出面向任意多维信道的广义调制方案。基于近期提出的高阶Mercer定理（HOGMT）[1]对多用户非平稳信道的分解能力，我们发展了多维本征波复用（MEM）调制技术。该技术将多维信道分解出的联合正交本征波作为子载波，经这些本征波调制的数据符号可在各自由度（如空间域（用户/天线）、时频域、延迟-多普勒域）实现正交性。由此，发射信号在高维信道中保持独立，从而避免符号间干扰。