LoS+NLoS Holographic MIMO: Analysis and Application of Wavenumber-Division Multiplexing
Holographic multiple-input multiple-output (MIMO) enables electrically large continuous apertures, overcoming the physical scaling limits of conventional MIMO architectures with half-wavelength spacing. Their near-field operating regime requires channel models that jointly capture line-of-sight (LoS) and non-line-of-sight (NLoS) components in a physically consistent manner. Existing studies typically treat these components separately or rely on environment-specific multipath models. In this work, we present a comprehensive analysis of the wavenumber-division multiplexing (WDM) framework, originally proposed for purely LoS channels, applied to a unified electromagnetic (EM)-based LoS+NLoS channel model. We first formulate the EM-based channel model for holographic lines and then apply WDM to this model, enabling a comparison between the corresponding spatial-sampling-based and expansion-based formulations. Applying WDM to the NLoS component yields its angular-domain representation, enabling direct characterization through the power spectral factor and power spectral density. We further derive closed-form characterizations for isotropic and non-isotropic scattering, with the former recovering Jakes' isotropic model. Lastly, we evaluate the resulting degrees of freedom and ergodic capacity, showing that incorporating the NLoS component substantially improves the performance relative to the purely LoS case.