Multidimensional Eigenwave Multiplexing Modulation for Non-Stationary Channels

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.