Degrees of Freedom of Holographic MIMO Channels
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This paper focuses on physically large spatially-continuous apertures, called holographic MIMO. Given the area limitation of the aperture, the limit on the available spatial degrees of freedom (DoF) is derived under isotropic propagation of electromagnetic waves. A linear-system theoretic interpretation of wave propagations reveals that the channel has a bandlimited spectrum. This is used in [1, 2] to approximate it with a Fourier plane-wave series representation that provides a simple and intuitive way to compute the DoF.
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