LoS+NLoS Holographic MIMO: Analysis and Application of Wavenumber-Division Multiplexing

Abstract: 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 develop a unified LoS+NLoS channel representation for holographic lines that integrates spatial-sampling-based and expansion-based formulations. Building on this model, we extend the wavenumber-division multiplexing (WDM) framework, originally introduced for purely LoS channels, to the LoS+NLoS scenario. 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.