OFDM modulation and OTFS modulation have demonstrated their efficacy in mitigating interference in the time and frequency domains, respectively, caused by path delay and Doppler shifts. However, no established modulation technique exists to address inter-Doppler interference (IDI) resulting from time-varying Doppler shifts. Additionally, both OFDM and OTFS require supplementary precoding techniques to mitigate inter-user interference (IUI) in MU-MIMO channels. To address these limitations, we present a generalized modulation method for any multidimensional channel, based on Higher Order Mercer's Theorem (HOGMT)[1][2] which has been proposed recently to decompose multi-user non-stationary channels into independent fading subchannels (Eigenwaves). The proposed method, called multidimensional Eigenwaves Multiplexing (MEM) modulation, uses jointly orthogonal eigenwaves decomposed from the multidimensional channel as subcarriers, thereby avoiding interference from other symbols transmitted over multidimensional channels. We show that MEM modulation achieves diversity gain in eigenspace, which in turn achieves the total diversity gain across each degree of freedom(e.g., space (users/antennas), time-frequency and delay-Doppler). The accuracy and generality of MEM modulation are validated through simulation studies on three non-stationary channels.

翻译：OFDM调制与OTFS调制已分别在时域和频域上证明了其在抑制由路径延迟和多普勒频移引起的干扰方面的有效性。然而，目前尚无成熟的调制技术能够处理由时变多普勒频移导致的跨多普勒干扰（IDI）。此外，OFDM和OTFS均需借助额外的预编码技术来减轻MU-MIMO信道中的用户间干扰（IUI）。为解决上述局限，我们基于近期提出的高阶梅塞定理（HOGMT）[1][2]（该定理用于将多用户非平稳信道分解为独立衰落子信道，即特征波），提出了一种适用于任意多维信道的广义调制方法。所提方法名为多维特征波复用（MEM）调制，它将从多维信道中分解得到的联合正交特征波作为子载波，从而避免多维信道上其他符号传输带来的干扰。研究表明，MEM调制能够在特征空间中实现分集增益，进而在每个自由度（如空间（用户/天线）、时频域及延迟-多普勒域）上达到总分集增益。通过三类非平稳信道的仿真研究，验证了MEM调制的准确性与通用性。