Spatial Characterization of Holographic MIMO Channels
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Imagine beings surrounded by continuous apertures that can emit and receive electromagnetic waves. A system of this sort, having an uncountably infinite number of antennas in a compact space, is called Holographic MIMO. Given the solid results for Massive MIMO, one might expect a holographic system to realize extreme spatial resolution, incredible energy efficiency, and unprecedented spectral efficiency. At present, however, the fundamental advantages of continuous apertures over conventional discrete spaced antenna arrays have not been conclusively established. A major challenge for the analysis and understanding of such a paradigm shift is the lack of mathematically tractable and numerically reproducible spatially-continuous channel models that retain some semblance of the physical reality. Physical models are too complex for tractable analysis. This paper aims to take a closer look at this challenge through the conventional tools of linear systems theory and Fourier transform. Notably, this leads to a rather simple Fourier plane-wave spectral representation of a three-dimensional spatially-continuous channel from which a computationally efficient way to generate samples over compact continuous apertures can be developed.
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