  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.
