  The multi-user Holographic Multiple-Input and Multiple-Output Surface
(MU-HMIMOS) paradigm, which is capable of realizing large continuous apertures
with minimal power consumption and of shaping radio wave propagation at will,
has been recently considered as an energy-efficient solution for future
wireless networks. The tractable channel modeling of MU-HMIMOS signal
propagation is one of the most critical challenges, mainly due to the coupling
effect induced by the excessively large number of closely spaced patch
antennas. In this paper, we focus on this challenge for downlink communications
and model the electromagnetic channel in the wavenumber domain using the
Fourier plane wave representation. Based on the proposed model, we devise a
Zero-Forcing (ZF) precoding scheme, capitalizing on the sampled channel
variance that depends on the number and spacing of the HMIMOS patch antennas,
and perform a spectral efficiency analysis. Our simulation results showcase
that the more patch antennas and the larger their spacing is, the performance
of the considered MU-HMIMOS system improves. In addition, it is demonstrated
that our theoretical performance expressions approximate sufficiently well the
simulated spectral efficiency, even for the highly correlated cases, thus
verifying the effectiveness and robustness of the presented analytical
framework.
