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：虽然由路径差异引起的时域干扰可通过OFDM调制缓解，但由速度差异导致的频域干扰可通过OTFS调制抑制。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），而现有文献中尚未存在缓解IDI的调制方法。文献中的两类方法均采用特定域载波在目标域实现正交性以抑制干扰。此外，这些调制无法直接融合空域，需要额外预编码技术来缓解MU-MIMO信道中的用户间干扰（IUI）。本文提出一种适用于任意多维信道的通用调制方法。近期提出的高阶Mercer定理（HOGMT）[1]可将多用户非平稳信道分解为独立衰落子信道（特征波）。基于HOGMT分解，我们开发了多维特征波复用（MEM）调制，该方法将从多维信道分解出的联合正交特征波作为子载波。通过这些特征波调制的数据符号可在每个自由度（如空间（用户/天线）、时频和时延-多普勒域）上实现正交性。因此，传输信号在高维信道上保持独立性，从而避免其他符号的干扰。